Where do aurorae australis begin and in which direction do they move?

Auroras start at a distance of 80-200 km above the Earth's surface.

The color of the aurora will be blue/purple if the air molecules in the area below 120 km are excited.

If the air molecules in the area from 120-180 km are the ones that gets excited the colour will be yellow/green.

Above 180 km gives the red light in the aurora.

The most powerful aurora will in general be 180 degree from the Sun's position and it will move from east to west at the opposite side to where the Sun is.

During powerful auroras the aurora arch can easily cover 270 degrees or more if close to the magnetic poles, if the aurora covers the area away from the magnetic poles the aurora arch will get smaller.

When the charged particles from the Sun interact with Earth's magnetic field a powerful ground current will be induced, this can induce DC power in power lines and severely damage the AC power transformers. Should an event like the one that happened on September the first, 1859 (the Carrington event) hit us today we would have major problems with power supply and satellite communication.

You can read more about all of this here, Aurora and please take a look in the sources there too.


Have the landmasses of North and South America ever been part of the same continent?

Apart from today, yes.

Back in the Cambrian (~500 million years ago), there was a continent in the southern hemisphere called Gondwana. It was a combination of several modern day continents: South America, Australia, Antarctica and Africa. A small piece of North America that corresponds mostly to modern day northern Canada existed in the northern hemisphere, called Laurentia. Curiously, some parts of northwestern Europe were part of that as well (Scotland, Norway).

Between the Devonian (~370 million years ago) and the Triassic (~200 million years ago) almost every continent on the Earth was amalgamated into one super continent called Pangaea, including Gondwana and Laurentia. During the Jurassic and Cretaceous (~150 million years ago) the entire thing separated due to the opening of the Atlantic Ocean, sending North America north west and South America south west. Since then the two continents were separated, until very recently (geologically speaking) that a land bridge formed between the two.

A very good website with reconstructions of paleogeographical maps is this one:

http://scotese.com/

Note that these are all interpretations and they are open for debate. But the general idea is correct.


The cause is partly geometry and partly process. Subduction zones generally take oceanic crust and upper mantle down into the deeper mantle, but the angle of the subduction zone varies greatly. For example, the Tonga Trench is very steep, giving rise to a 'tight' earthquake zone. At its shallowest, the two plate boundary isn't even a subduction zone at all, but becomes obduction, overthrusting oceanic crust/mantle over the plate, as happened with the Oman ophiolite. Then there are ocean-continent collisions, such as western South Americas. Because the continental crust is much less dense than oceanic crust, it is more buoyant, so you get a broader subduction zone than you would with a back arc overlying ocean-ocean collision. Finally, there are continent-continent collisions, typified by India-Tibet, where none of the crust can sink very deep, so you get a stack of imbricate over-thrusts, as in most of Tibet and the Himalayas, all linked to earthquakes over hundreds of kilometres width, as in the Nepalese quake of last year.

Also consider the tectonics involved. Where two tectonic plates slide against each other there may be little or no subduction, but stress release in the transcurrent fault can still create major earthquakes - think the San Andreas Fault, or New Zealand. Kim points out the thickness of earthquake zones such as those north of Australia. It isn't just in southeast Asia. We can see similar complexities in the Eastern Mediterranean, the Caribbean and elsewhere, where there are many micro-plates jostling in a complex pattern. They only seem like one seismic zone because of the scale of your diagram. There is yet a different story in the Rift Valley of Africa.

The above are just some sketchy simplifications of a revolution in geological understanding that started in the late 1960s, and which are still continuing. It's not possible to give a detailed explanation in this forum, but there are many excellent and fascinating textbooks. Warning - you can get hooked. Then it becomes a lifetime study.


The oceans have a huge effect on the climate and temperature of the various regions of the world. Climates fall into two categories: marine and continental. In Britain we have a marine climate, which protects us from the extremes of the European continental climate. Our winters are milder, our summers cooler, because of the proximity of the Atlantic and the warm Gulf Stream coming up from the Gulf of Mexico. It also gives us a damper climate, with more mist and rain. This moderating effect and increased dampness and humidity is characteristic of marine climates. In the S.Pacific they have El Nino, a strange subtropical current which reverses every ten years or so, causing droughts and other adverse effects for the countries of the region.

The Galapagos archipelago is another example of a marine climate, in this case cooled by the Humboldt Current coming up the coast of Chile from the Southern Ocean. The Galapagos Islands are on the equator, yet the climate is only subtropical and the waters are cool enough for penguins to thrive. These cold currents, like the Benguela current coming up the west coast of S.Africa, are rich in nutrients and in fish. The Benguela Current has strange effects on the climate of Namibia.


For a tree over its entire existence, does it actually have a net negative effect on atmospheric CO2?

A brief review of recent non-paywalled available literature indicates that such an effect likely exists but that it is difficult to quantify based on currently available data.
Some amount of carbon from trees can be sequestered in the soil for periods time significantly longer than the typical above-ground decomposition time of organic matter, potentially for millennia. This clearly lengthens the carbon cycle time, but it is not clear to me whether this represents carbon storage, as there does not seem to be a well established minimum cut-off time for this. The primary source for soil-sequestered carbon are tree roots, with leaf litter constituting a secondary source.
The following paper (preprint online) addresses the question in the specific context of agroforestry, i.e. cropland interspersed with trees. The paper notes multiple times that the processes involved in soil sequestration are not well understood and that quantitative measurements and estimates vary widely, as one would expect based on differences in climatic and soil condition. Note on units: A Mg corresponds to a metric ton.
Klaus Lorenz and Rattan Lala, "Soil organic carbon sequestration in agroforestry systems. A review." Agronomy for Sustainable Development, Vol. 34, No. 2, April 2014, pp. 443-454.

The soil organic carbon (SOC) pool, in particular, is the only terrestrial pool storing some carbon (C) for millennia which can be deliberately enhanced by agroforestry practices. [...] The SOC storage in agroforestry systems is also uncertain and may amount up to 300 Mg C ha−1 to 1 m depth.
[...] Further, between 30 and 300 Mg C ha−1 may be stored in agroforestry soils up to 1-m depth [...] The SOC sequestration depends primarily on the soil C input and soil stabilization processes. Plant root and rhizosphere inputs, in particular, make a large contribution to SOC [...] Litter fall and in turn SOC sequestration may be affected by stand-density management as, for example, higher stocking levels of trees enhance the vegetation C pool.

Another paper that deals specifically with urban trees mentions in passing that the soil accounts for a significant part of the carbon sequestered in non-urban forests (presumably both naturally growing and human-managed):
David J. Nowak and Daniel E. Crane, "Carbon storage and sequestration by urban trees in the USA". Environmental Pollution 116 (2002) 381–389

Another area of the urban forest carbon cycle that this paper does not analyze is urban soils. Sixty-one percent of the total carbon in non-urban forest ecosystems
in the USA is stored in the soil environment (Birdsey and Heath, 1995). The amount of carbon from trees that is retained in urban soils, its residence time, and the amount of carbon currently stored in these soils remains to be investigated. It is likely, however, that urban soils contain less carbon per hectare than forest soils due to lower carbon inputs and increased soil decomposition rates due to warmer air and soil temperatures (e.g. Pouyat et al., 1997).


Is there value in using a model that fails at validation against measurements?

The late George Box famously said:

  All models are wrong. Some models are useful

All models are wrong.

That's important.

All models are wrong.

In any real-world system that we're interested in, the only accurate model of the system, is the system itself. Anything else, any simplification, gives wrong answers.

Some models are useful.

That's important, too.

Some models help us structure our discussions of the uncertainties (H/T Prof Neil Strachan)

Some models allow us to test "what if" scenarios, and look at what the relative changes might be. Now, in the real world, exogenous influences that the model can't account for, would mean that the actual outcomes would be different: but if the model gives a near-enough account of the scale of relative changes, we can still make informed judgements on the basis of the models. Even when it involves pesky things such as turbulence.

Some models give us insights into emergent properties of systems: a lot of the really interesting problems are emergent properties that aren't necessarily obvious from just looking at the basic rules of the system, and any insights we can gain are valuable.

Some models allow us to do experiments on systems that we couldn't possibly experiment on. And although we know the models are wrong, they can at least give us an indication of the range of possible outcomes.

That's not to defend the use of bad models to do bad work. There's far too much of that in my field, and I do not like it. As Simon W says, it is possible to test models to see if they are suitable for a particular purpose. To continue using a model for a purpose where it is known to be inapplicable, is charlatanry, not academia.


Are there areas of desert sands which experience blizzards?

It really depends on what you consider "desert sands".  For instance, Sand Mountain in Nevada https://en.wikipedia.org/wiki/Sand_Mountain_(Nevada) is an area of sand dunes in a desert, and occasionally experiences snowstorms that reach blizzard conditions.

Although most of the lower elevations are sagebrush steppe, there are other areas of sand (and dry lake beds &c) in the Great Basin, and the area experiences winter cold, occasional snow, and high winds.  I'd expect similar conditions in the Gobi Desert, though I have no first-hand experience: https://en.wikipedia.org/wiki/Gobi_Desert


Did you use the right Vtable? That error message is saying that the soil temperature variable is missing/couldn't be read.


It may take a few minutes of work this way...

But did find digging through NCDC's climate data inventory, the climatological rankings pages should help find what you're looking for if you're looking for their full state averages.

However, I think can help you a step further with addresses to go through: if you replace STATENUMBER in the address of:

  Temperature: https://www.ncdc.noaa.gov/cag/statewide/time-series/STATENUMBER/tavg/1/4/1895-2018?base_prd=true&begbaseyear=1901&endbaseyear=2000

Instead with each of the numbers 1 through 48, you can get the state data for each of the US contiguous states.  And Alaska is 50.  Likewise with precip:

  Precipitation: https://www.ncdc.noaa.gov/cag/statewide/time-series/STATENUMBER/pcp/1/4/1895-2018?base_prd=true&firstbaseyear=1901&lastbaseyear=2000

However, it looks like disappointingly Hawaii (and territories) doesn't get the same data produced, or at least available anywhere I can find on that site.  If you really want to seek that out, you might consider using Honolulu and Juan climate reports for a reasonable proxy, or the answer to the question Current Global Climate Dataset? on GSE may offer a rough avenue towards fair gridded information.

Not the easiest avenue, would love to see something better (and hopeful if you do go through this tedious method, perhaps post it to a Github repo or such so that more data may be easily available in the future to others facing the same problem.


mountain database of elevation and distance from saddle (as a proxy for gradient)


What is this strange feature on Mars in Valles Marineris

Looking at the 2nd image in your question, namely of the vertical profile, the feature inhabits what appears to be an erosion channel to the valley floor (a very rough estimate of the erosion channel is shown below).

(Please excuse the rough-MS Paint style arrow)

The feature has the appearance of being an example of a small slope failure, a similar, but much smaller example of other much larger landslides have been observed in the Valles Marineris according to the article Long-runout landslides and the long-lasting effects of early water activity on Mars (Watkins et al. 2014).

According to research based on observations of similar larger scale features, the article Mechanisms of slope failure in Valles Marineris, Mars (Neuffer and Schultz, 2006) slope failures on Mars have been found to occur due to gravitational, fluid or seismic (i.e. 'marsquakes') influences.

The other influence as to why these landslides occur in the area is explained by Watkins et al. (2014) from observations and models based on spectral imaging and satellite image analyses, a significant amount of hydrated silicate clays contained within the stratigraphy of the Valles Marineris facilitate geomorphic processes, including landslides - the process is aptly used as the title of the Red Planet Report web-article Clays greased long landslides in Valles Marineris.


Can small-scale backyard gardening produce more food per acre than broadscale [grain] farming?

Efficacy of food production per square foot/acre differs from soil quality and rate of regeneration. It's also a case of if you can produce year round. Some permaculture specialists, monitored one case in an article of "Green America" A 500 sq foot garden producing 300 lbs of produce per year. Among other's. Soil nutrient recycling is a key aspect of producing food year round, along with temperature (Green houses).

Composting
Soil/air temp
Growth rate of produce involved
So the answer is "Yes" if dedication is involved.


Deep sea pumps that work on wind power, can they control the weather?

In theory your idea is not bad,But it needs to be placed as far from land as possible this is to avoid the soil on land from being contaminated by saltwater.

So spraying saltwater into the air is not usefull for creating rain over land,But it can be used to cool the ocean and the planet.

Salt water spraying into the air can possibly help creating condensation nucleus,And help clouds to form and these clouds can shade the ocean and limit the heat absorption.

But this is not as simple as it sounds,Clouds tend to form more in the evening and night when the temparature drops and not as easy in the daytime when they are needed.

Clouds can limit the heating in the daytime,But they will trap or reflect heat in the night time,And then the positive effect is limited.

I think it is best to use the hotter water from the surface of the ocean as it will evaporate faster and probably create clouds faster.


Your question is

  How does quartz form in calcite veins?

But maybe a more appropriate question will be

  How does quartz not form in calcite veins?

Quartz is one of the most common vein material in Earth's crust, and for a reason. SiO2 is not a particularly soluble compound at the surface, but once you get deeper it becomes extremely soluble (source):

The solubility of SiO2 is almost 0 at at 1 bar and 25 °C, but increases strongly with pressure and temperature. For example, at 200 °C and 2000 bar (2 kbar, 0.2 GPa, about 5–6 km depth), conditions that are reasonable for an unmetamorphosed but deeply buried limestone, you can fit about 500 mg of SiO2 in 1 kg of H2O. At atmospheric pressure that's one litre of water, but it's much less voluminous at depth. That is a lot of SiO2! Once the fluid goes up towards the surface, it depressurises and cools, causing precipitation of quartz.

There is no shortage of sources for SiO2. It is the most common chemical component in the crust. Even in seemingly pure limestone there are more than enough impurities of silicates to provide a source for SiO2.

The fact that quartz and calcite occur together in a vein is no problem at all. You might expect them to react, but they actually do not. Here's a diagram to show it (source):

Calcite and quartz can peacefully coexist, unless it's extremely hot and then they react to form wollastonite (a Ca-silicate). This is the kind of stuff you find in high grade metamorphosed marbles, for example.

As an aside, another question that may be asked is why only calcite and quartz? If hot dense water are so good in dissolving stuff? Where's the rest of the periodic table? Well, most of the elements are readily soluble in acidic fluids. In this case, the abundant calcite buffers the pH of the water to rather basic conditions, which are not that great in dissolving stuff.


Are there four-times daily sea surface temperature (SST) data product for Tropical Cyclone research?

The issue with satellite SST is that in most cases it is captured via infrared radiometers. Those sensors can't see through clouds. Daily products are used to try to remove the cloud effects. Alternatively, passive microwave radiation can be used (e.g., TMI, AMSR2, AMSR-E). It is not affected by cloud cover, but has lower horizontal resolution (~25km, vs 1-5km from IR).  You can try to get the individual passes of each satellite and deal with gaps: For instance


USGS conducts regular survey in over 20000 wells across the United States. The frequency of data collection depends on the site with around 7000 providing daily data. For some of those wells (currently, 3777 groundwater sites) daily statistics are provided. An increasing number of wells are providing real time (updated every 15 or 30 min) data.

Source: USGS

You can visualize the daily changes using this animation.

Go to https://waterdata.usgs.gov/nwis/gw for  information as well as the ability to get the data directly from the source.


Why a stratus cloud does not always reach all the way to the ground?

I'd postulate that this is purely temperature-driven.

If the dew point temperature of your 'empty' layer is not reached then the water vapour will not condense to form fog.

Do you observe the clouds there during the day? Thin clouds such as stratus primarily transmit incoming solar radiation whilst trapping some of the outgoing long-wave radiation, thus insulating the air between the ground and the base of the cloud layer and preventing dew point temperature being reached.


The rock that gives birth to quartz sand

In only one minute of presentation there isn't time for detailed discussion, so one has to make broad generalizations which, on closer inspection, aren't quite true. It is true that most sand is made of quartz, and that most of this quartz arises from weathered granitic rocks, of which the main minerals are quartz, orthoclase and plagioclase, usually with some mica, quite rarely some amphibole and almost never olivine. In the magma olivine and quartz react to make either amphiboles (if it is a very hydrous melt) or pyroxenes.

It is possible to find a sedimentary rock made of weathered out quartz and feldspar grains. Depending upon the original chemistry the feldspar could be potassium-rich (orthoclase) or sodium-calcium-rich (plagioclase). The resulting sedimentary rock is known as an arkose. Arkose is common in dry areas of eroding granite, such as the dryer parts of sub Saharan Africa. However, it is much more common for the weathering to involve wet erosion - thousands of cycles of rain and sun, hot and cold, in which case the feldspars mostly decompose to clay (many varieties and sub-species).

Olivine is much more characteristic of basic volcanic rocks, especially basalts, which do not weather to yield quartz grains. Another rock type in which olivine is a major component is peridotite. This weathers to yield goethite (a kind of ironstone) and serpentine. Occasionally, if the pyroxene to olivine ratio is sufficiently high, the weathering can yield quartz as a secondary by-product.

Another feature of quartz: Over long periods and especially at high temperatures and/or high pressures, it is very slightly soluble. Not that you would notice. The sand isn't going to dissolve beneath your feet, but every litre of surface water contains a few milligrams of dissolved quartz as silicic acid, which takes part in a whole catalogue of geological processes. In addition, there are many other rocks besides granite which yield quartz grains, including quartzite, weathered pre-existing sandstone, schist, gneiss, and some intermediate rocks (complex chemistry between granite and basalt. Even limestone - rocks that are generally thought of as 'pure' calcium carbonate, generally have a percent or two of insoluble residue, of which quartz is the dominant component.


How can I estimate a 2 m temperature from / in an atmospheric model?

Your premise is incorrect.
Numerical models normally have:

A full temperature profile
A specific field for the 2 metre temperature
A specific field for the skin temperature

For example, see ERA-40 daily fields, which both 2 metre temperature and Skin temperature, or CFS reanalysis 6-hour fields, which has Air temperature, Skin temperature, and Surface air temperature, (I think surface air temperature means 2-metre temperature, but check their full documentation to be sure).
It is not accurate to take the lowest temperature level in the temperature profile for either of the two, nor to interchange skin temperature with 2-m temperature.  But, in some cases, the data distribution may be such that either or both of these are actually attached to the temperature profile.  For example, the CFS hourly timeseries has the question:

Where is Sea Surface Temperature (SST) in CFSR? Where is Skin Temperature?

CFSR does not label SST and skin temperature grids differently than temperature grids on other levels. Select the parameter 'Temperature' and the level 'Ground or water surface' to obtain the SST/skin temperature grids, and then use the land/sea mask to determine whether a gridpoint is over water (SST) or land (skin temperature).

(I had the opposite problem, needing skin temperature, and being tempted to use 2 metre temperature instead, until I realised where the data were).
If you encounter a model that really only has the full temperature profile, then I would contact the authors to inquire.  Maybe it is a model that really only does well in the free atmosphere, and is not suitable for the extraction of (near-) surface temperatures.  The boundary layer can be a hard thing to model!


Are trends in crossplots of compositional data from different analyses valid?

The question is not exactly clear. Are you asking about the different methods used to analyse the rock, or are you asking about using closed (aka compositional) data in a bivariate plot?

Using different methods

This is just fine, as long as both methods are accurate. For instance, you can analyse a mineral for major elements (e.g. TiO2) using an electron probe, and then use LA-ICP-MS for trace elements (e.g. Nb). If both methods are properly standardised and all possible interferences are taken care of there is no reason why the analyses should not be used together. If the analysis was not performed properly, I wouldn't trust even as single one, regardless of whether it is used in a database together with data acquired using a different method.

Closed data

Closed data means that it has to sum to 1 or 100%, and this can cause correlations that don't necessarily mean anything. A simple example is an MgO vs FeO plot in olivine. Of course there would be a negative correlation! This type of plot would be obvious and wouldn't tell us a thing. However, in more complicated cases, this becomes less and more of a problem. It mostly depends on a case by case basis. Note that if you're comparing a major element (TiO2) with a trace element (Nb), there is less of a problem. The trace element is not one of the components that hardly has any implications for the close problem. Whether you have 10, 20 or 100 ppm Nb will not change anything for the 5% of TiO2 you got in your rock.

Classic statistics done on compositional data is almost always wrong. In the past 20 years or so, a new statistical field called "compositional data analysis" has emerged to solve some of the problems arising from the closure problem. In short, it means that you have to transform all of your data to log-ratio form, do your stats, and transform it back. This can't solve all of the problems, however.

Now, the question is - do we care that it's wrong? In the vast majority of papers, there is hardly any statistics done of compositional data, and many correlations and trends are eyeballed and drawn by hand. Often, the hassle of doing statistics the correct way does not actually contribute everything. I've heard senior petrologists claim more than once that "if it looks like a line, it is a line. If it doesn't, then it is not a line. I don't need the R2 and p-values for that".


Why is at high altitude more light from oxygen in the auroras while it is heavier than nitrogen?

The visible emissions from atomic oxygen take place between the fine structure levels of the ground state, and transitions between these states are not quantum-mechanically allowed by electric-dipole radiation. These "forbidden" transitions take much more time to occur, proceeding by magnetic dipole or electric-quadripole radiation. As a result the atom spends a long time in the excited state (~1sec for the 557.7 nm transition, and ~200 s for the 630 nm transition), during which time the atom can make collisions and deactivate without radiating. However, the emissions from molecular nitrogen take place between dipole-allowed transitions, and spend only ns to micro-seconds in the excited state before radiating. Thus, they survive to radiate even in high collision conditions (i.e. low altitudes).

The frequency of collisions an atom or molecule makes increases with decreasing altitude. In addition, the higher the energy of the auroral electrons (2 keV to 20 keV), the lower in the atmosphere they deposit the energy (150 km to 90 km). If there are low energy electrons in the aurora, the emission occurs at very high altitude and both the excited atomic oxygen and the molecular nitrogen make few collisions. Thus they both radiate, but at these altitudes there is more atomic oxygen than molecular nitrogen and the reds and greens of atomic oxygen dominate.

As the auroral energies increase and the electrons deposit their energy at lower altitudes, collisions are much more frequent and the atomic oxygen excited states do not live long enough to radiate. This kills off the green and red emissions at low altitudes. However, the molecular nitrogen, with its short excited state lifetimes, continues to radiate and the lower border of the aurora turns pinkish-purple with the nitrogen emissions.


This is the classic description of a porphyry copper-molybdenum deposit.
What happens is that there is a magmatic intrusion (the porphyry), which then solidifies. When it solidifies, it expels acidic hydrothermal fluids which carry metals in them - most often copper (represented by chalcopyrite) but also sometimes molybdenum (represented by molybdenite).
Once the fluids hit solid rocks, they react with it, and become neutralised. The carrying capacity of the fluids diminish, and they deposit the metals into the minerals you observe. The solid rocks can be pretty much anything. It can be the porphyry itself, another porphyry that happened to be around, sedimentary rocks, or whatever.


A simple formulation to calculate the sequence and rate of salt precipitation in a brine?

Here is a link to a hydrochemical consultant, Dr. C.A.J. Appelo, and the public-domain software FREEQC.

It can be downloaded from here

This link leads to an example of salt precipitation rates when evaporating sea water.

The formulation used is detailed in a second manual


What temperature do small meteorites have on impact

Love & Brownlee (1991) put together numerical models for the experiences of micrometeorites entering the atmosphere. They say:

  The peak temperatures experienced by submillimeter micrometeoroids rarely exceed 1700°C. Maximum temperature and mass loss rate generally occur at altitudes between 85 and 90 km during ∼1 sec of peak heating. A typical melted particle spends ∼2 sec at temperatures above the melting point.

Flynn (1989) discusses interplanetary dust, with figures for peak temperatures given in the abstract.

But I think that what you really want is Sears (1975), Temperature gradients in meteorites produced by atmospheric passage:

  Temperatures in the order of 200°C have usually penetrated no further than 5-10mm, which is consistent with a luminous flight time of the order of 10s.

Using the geologists' rule of thumb for timescales of cooling (I believe $\tau^2 = \ell/\kappa$, where $\tau$ is the timescale, $\ell$ is the thickness of the cooling body, and $\kappa$ is the thermal conductivity - though it's a while since I've had to do this so I may be misremembering...), the information above about the height above the surface at which peak temperature is commonly reached, and an estimate of particle velocity, you can probably back-of-envelope a temperature for a meteorite on impact!


Why does lightning strike from the ground-up?

Does lightning strike from the sky down, or the ground up?

  The answer is both. Cloud-to-ground lightning comes from the sky down,
  but the part you see comes from the ground up. A typical
  cloud-to-ground flash lowers a path of negative electricity (that we
  cannot see) towards the ground in a series of spurts. Objects on the
  ground generally have a positive charge. Since opposites attract, an
  upward streamer is sent out from the object about to be struck. When
  these two paths meet, a return stroke zips back up to the sky. It is
  the return stroke that produces the visible flash, but it all happens
  so fast - in about one-millionth of a second - so the human eye
  doesn't see the actual formation of the stroke.

  Source: National Severe Storms Laboratory

The reason is that when cloud-to-ground strike approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field and the "downward leader" strike creates bridge for the "return stroke"; this per the wiki page for Lightning.

Cloud to cloud and Intra-Cloud Lightning

Might be worth also noting that cloud-to-ground is not as common as Cloud to cloud (CC) and Intra-Cloud (IC):

  Lightning discharges may occur between areas of cloud without
  contacting the ground. When it occurs between two separate clouds it
  is known as inter-cloud lightning, and when it occurs between areas of
  differing electric potential within a single cloud it is known as
  intra-cloud lightning. Intra-cloud lightning is the most frequently
  occurring type.

Ground-to-Cloud

Appears that ground-to-cloud is possible, though normally only a result of a man-made object creating "unnatural" electric potential, and is the least common type of lightning.


Scientific GPS and SLR have been used for some time now, and the measurements are rather accurate. Not only do we measure horizontal movements of tectonic plates, but also uplift as e.g. in the Tibetan and Colorado plateaus.

Before the GPS was introduced, paleomagnetism were used in some studies to estimate the velocities; The age of oceanic crust are estimated by various methods and the travel distance is estimated from the width of the magnetic polarized bands in the ocean floor. To understand paleogeography and make good models we need to incorporate all branches of geology. E.g. fossil records, paleomagnetism, radiometric age estimation of rocks.

Some active faults (E.g. San Andreas) can also be directly measured with laser ranging or, in some cases, with a measurement tape to measure deformation of trenches or railway tracks.

Still, scientists are trying to understand the exact driving forces behind plate tectonics. Modelling of mantel dynamics is an interesting field of research and many questions remains.


Percentage of power plants with carbon capture and sequestration (CCS) technology?

If you accept GE's estimate of the number of global fossil fuel power plants ( 17,500 ) and compare it to the number of CCS projects out there ( 22 ), you get roughly 0.1 %.

The Global CCS Institute released its 2014 annual report;

  The world’s first large-scale carbon capture and storage (CCS) project in the power
  sector commenced operation in October 2014 at the Boundary Dam power station
  in Saskatchewan, Canada. Two additional large-scale CCS projects in the power
  sector – at the Kemper County Energy Facility in Mississippi and the Petra Nova
  Carbon Capture Project in Texas – are planned to come into operation in 2015 and
  2016 respectively. Construction is also underway on the world’s first large-scale CCS
  project in the iron and steel sector, the Abu Dhabi CCS Project in the United Arab
  Emirates (UAE). These four projects are among the 22 large-scale CCS projects in
  operation or construction around the world – double the number at the beginning of
  the decade.


Running WRF with ECMWF GRIB2 model levels

I finally solved this problem with the following steps:

Download the ECMWF data separately for model level variables (Q,T,U,V and geopotential) and surface variables. In this way, you will get 'pure' GRIB1 and 'pure' GRIB2 files rather than the hybrid type.
Run ungrib twice: for the model levels files, use this Vtable. For the surface file, use the 'old' Vtable.ECMWF_sigma. Between the two ungrib runs, change the ungrib prefix in the namelist.wps (e.g. I used prefix = 'FILE_ML' and prefix = 'FILE_SFC').
Run util/calc_ecmwf_p.exe. This only works if the program can read both files. To achieve this, make sure that in the metgrid part of the namelist.wps, both input names are given (fg_name = 'FILE_ML','FILE_SFC','PRES',). Not sure whether 'PRES' makes a difference here, but since it will be used for metgrid I already put it there and it worked for me. 'PRES' are the files created by calc_ecmwf_p.exe. Note that you'll also need an 'ecmwf_coeffs' file for this step.
Run metgrid, real and wrf as usual.


How different can microclimates be than their surrounding areas?

Elevation is often responsible for the biggest differences; you can have snow and glaciers on the top of mountains in warm climates. South America can show you how extreme the differences in precipitation can be: rain forest on one side of the Andes Mountains, world's driest (non-polar) desert on the other. So really it depends on how high and complete your mountain ring is.
Here is a decent book on the subject.


What would it take to confirm or refute the Snowball Earth Hypothesis?

In order to confirm the snowball earth hypothesis, we'd need at least:

A paleogeographic model which extends to greater than 650ma and has been shown be be conclusively accurate throughout that entire period. (i.e. one we can trust)
Sedimentation structures/patterns (or other paleoclimate proxy data), consistent with a glaciation event, tied into the same time period, from the north pole to the south pole


How long does a magnetic pole reversal take to complete?

The entire process appears to take 3,000-4,000 years, according to Valet and Fournier's May 2016 review article "Deciphering records of geomagnetic reversals," which was published in AGU's Reviews of Geophysics.

  The complex dynamical structure of reversals is supported by
  sedimentary and volcanic records. Provided that resolution is
  adequate, the reversal process seems to incorporate one precursor and
  one rebound prior to and after the transition. However, the three
  phases are rarely observed in a single record. This is likely to be
  caused both by field geometry and recording limitations. The duration
  of each phase does not exceed 3–4 kyr. Therefore, precursors and
  rebounds can be seen as part of the whole process, and the expression
  of a continuum of behavior between secular variation, excursions, and
  reversals. Another possibility is that the dipole collapse is not
  large enough or that the nondipole/dipole ratio varies.

Better resolution of the process and the time involved will require at least a 10-fold improvement in paleomagnetic sampling resolution, the authors contend. And one of the challenges is finding suitable lava flows or sediment layers that were created during the transition(s) in question.

As for whether current fluctuations indicate the earth is about to have a reversal: We can't tell, because the recent paleomagnetic record includes similar changes (sometimes regional rather than global) that did not result in reversals, Valet and Fournier write.

  The present evolution falls within the normal range of field
  variability that prevailed for the past 2 Ma.


What would happen if the same soil received waste water contaminants for a long time?

Like many things in Earth Science, the answer is, "It depends."

In this case it depends on the composition of the soil and the contaminant you are talking about. Climate, particularly the amount of precipitation, can also have an effect.

Septic systems are primarily designed to promote aerobic conditions and aerobic bacteria to degrade organic compounds and pathogens. In a well designed and maintained system, that will be effective for a long time. One of the important considerations is to be sure the soil will allow enough infiltration that it doesn't become waterlogged. Some places need a sand mound because the natural soil isn't suitable.

Some contaminants aren't treated by the septic system. Some are transported down in the infiltrating water with little or no interaction with the soil. These can quite easily contaminate the groundwater if concentrations are too high. Salt,  (NaCl), for example, is transported with practically no retardation. Many positively charged cations with charges of 2+ or more will be adsorbed onto the surface of (mainly) clay minerals or in between layers in the clay crystals. They do that because the surface favours them more than the cations that are already present so the new cations replace the old. But the minerals only have a finite ability to exchange the new ions for old. With time the new ions will flow deeper into the unsaturated soils (the vadose zone) until they breakthrough to the groundwater. How fast this happens depends on the soil properties, the concentration and properties of ions in the waste, and the amount of infiltration.

Negatively charged anions are interesting. They are generally poorly adsorbed by mineral surfaces so they are quite mobile in the subsurface compared to cations. Compounds of oxygen and other elements can form important anions like nitrate (NO3-) and sulfate (SO42-). My favourite is pertechnetate (TcO4-), which makes this man-made radioactive element quite mobile under oxidizing conditions. Since many elements have several valence states, changing the oxidation-reduction conditions can change their mobility.

You mention acidic and basic wastes. These can do several things. First, they can exchange for adsorbed ions on the sediments and compete with others ions, increasing the mobility of the others, Secondly, they can affect the chemical form of the ions in solution. Thirdly, they can react with the minerals and alter them to ones with different properties. Finally, they can affect the microbiology in the sediments and change the ability to degrade contaminants.

It is important to inspect and maintain household septic systems by pumping out the tank and checking the leach field for problems. Some places require that you define the location for a replacement leach field before building in case it is needed. Be careful not to put contaminants down your system - especially things like pesticides and herbicides.


Why are titanium oxides lumped in with magnetite for the purposes of analyzing water bubble nucleation?

In iron oxides, titanium commonly substitutes for iron in the crystal structure. Two solid solution series are important: the ulvöspinel-magnetite and ilmenite-hematite series.

The composition of a solution changes continuously, without any change in crystal habit. Your reference indicates its the size of crystals than matter for being efficient nucleation sites. Composition is not expected to be important.


Why does vertical diffusivity increase with depth in the ocean?

I think you are confusing eddy diffusivity with molecular diffusivity. Whereas the latter increases with temperature, for the former there is no such relationship. Eddy diffusivity describes momentum transport due to eddies. The strength of the eddy diffusivity increases with decreasing buoyancy frequency, which is the case, when moving from the bottom of the mixed layer further downwards in the ocean.


Earth's Spin

Earth rotating clockwise is the result of a chain reaction that started when Earth's star formed as the result gas clouds collapsing. During the collapse of the gas, one direction was shorter and a disc formed. Due to the law of conservation of angular momentum, the disc gained an overall spin, which was passed to all the objects of notable mass within its solar system; these objects are commonly known as planets. As a result, all planets within a given solar system have the same spin as the star in it to start. That said, the axis of a planet may do a 180-degree flip on its axis at some point, and if this happens, like Venus, it would spin counter to its native spin; in fact, in the case of Earth, it appears given there appears to be evidence that it's has flipped in the past, that the Earth's axis has already flipped at least twice, since it's current back in sync with the Sun's spin.

Might be worth noting that all rotating bodies that rotate clockwise when viewed from the southern hemisphere rotate and counter-clockwise when viewed from the northern hemisphere. Also, since the Sun is not solid on the surface, it does not rotate as a solid body; meaning it rotates faster at its equator and slower at its poles.

Earth's Axis

As for the reasoning behind, the axis of the rotation, as pointed out in other answers, this is the result of Earth's past impacts with objects of enough mass to produce the shift from a zero offset from the stars axis, to the current axis of the rotation. Future impacts would be able to change the rotation.

Will the Earth's axis flip?

  Scientists have found evidence that the Earth might have flipped over
  in the past, completely shifting the orientation of its poles. The
  theory has been around for years; that a large mountain range or
  supervolcano might unbalance the spinning Earth. Over the course of
  millions of years, the Earth would change the orientation of its axis
  until the object was balanced at the equator again.

Current Axis of the Planets in Earth's solar system


The effect of atmospheric pressure on sea level is described as "inverted barometer" effect. The basic equation governing the effect (Wunsch & Stammer, 1997) is: $\delta_{IB}  = -{\Delta P_{atm} \over  \rho_{water}*g}$, where $\delta_{IB}$ is the change in sea level, $\Delta P_{atm}$ is the change in atmospheric pressure, and $\rho_{water}$ is the density of water.

A good example of the effect was observed by Close (1918)
 From Wunsch & Stammer, 1997.

In reality, while atmospheric pressure can vary between 870 and 1070 mb, the problem is that it might result in a change of 2m over a distance between high and low pressures that could be many hundreds of km. By comparison, the sea level gradient across the Gulf Stream is on the order of 1m/100km. The other problem is that the ocean adjusts dynamically to the differences in air pressure and the resulting sea level gradient might be smaller.

To convert pressure to force (acceleration), you can use $P=\rho g h$. The biggest differences in $g$ at the surface of Earth are around 50 mgal (50 $\mu m/s^2$) and caused by differences in latitude, altitude, and local topography and geology. The differences in gravity cause by the extra meter of water will be way smaller and can be considered negligible.

Wunsch, C., and D. Stammer (1997), Atmospheric loading and the oceanic “inverted barometer” effect, Rev. Geophys., 35(1), 79–107, doi:10.1029/96RG03037.

Close, C. (1918), The Fluctuations of Mean Sea-Level with Special Reference to Those Caused by Variations in Barometric Pressure. The Geographical Journal 52, no. 1, 51-58.


I'm still confused about what "probability of precipitation" means

I agree that the PoP = C x A that we see on a lot of websites leaves something to be desired.  It gets across the loose idea that the definition involves the area affected as well as the probability of occurrence, which is fine for most casual readers but can be frustrating for more inquisitive minds.  How much are the confidence and the area estimated from ensemble forecasts versus expert judgement?  How was it done before ensemble NWP started in the 1990s?

Anyway, there’s an interesting survey by Stewart et al (2016) that gives a broader overview of how different meteorologists use the phrase “probability of precipitation”.  They categorise the PoP = C x A usage as following the NWS Operations Manual (1984), which is nicely summarized in a comment by Schaefer and Livingstone (1990).  In short, your interpretation in terms of expectations is correct and, as you mention, they describe it in terms of a sum over a hypothetical network of points rather than a continuous integral:

$\textrm{PoP} = \frac{1}{N} \sum_{i=1}^N E[R_i]$,

where $R_i$ equals 1 if it rains at station $i$ and 0 if it doesn't.  In your Pluieville example, this could be approximated as a town with one rain gauge in the north and one in the south, giving PoP = (1.0 + 0.5)/2 = 0.75.

I don't know for sure, but it wouldn't surprise me if these things are still calculated by subsampling gridded NWP models at actual rain gauge network locations, which would allow for comparable long-term verification of the probabilistic forecasts.

Stewart, A.E., C.A. Williams, M.D. Phan, A.L. Horst, E.D. Knox, and J.A. Knox, 2016: Through the Eyes of the Experts: Meteorologists’ Perceptions of the Probability of Precipitation. Wea. Forecasting, 31, 5–17, doi:10.1175/WAF-D-15-0058.1

National Weather Service, 1984: Zone and local forecasts. NWS Operations Manual W/OM15.

Schaefer, J.T. and R.L. Livingston, 1990: Operational Implications of the “Probability of Precipitation”. Wea. Forecasting, 5, 354–356, doi:10.1175/1520-0434(1990)005<0354:OIOTOP>2.0.CO;2


What are the applications of hydrostatic solvers vs non-hydrostatic solvers in numerical weather prediction?

The hydrostatic approximation begins with the full 3-D momentum equation (Navier-Stokes) and through scale analysis the vertical momentum equation reduces to:

$$\dfrac{\partial p}{\partial z} = -\rho g$$

This is a balance between the vertical pressure gradient force and gravity with no net acceleration.  This tends to hold for atmospheric phenomena that are much wider than they are tall.  On the synoptic scale where vertical motions are on the order of 1 cm s$^{-1}$ this holds, but in a thunderstorm where updrafts can attain speeds of 100 m s$^{-1}$ this approximation doesn't work.

A hydrostatic model uses the hydrostatic approximation in place of an equation for $w$, while a non-hydrostatic model uses the momentum equation for $w$.  As the ECMWF  page you link to suggests, models with low grid resolution can get by with the hydrostatic approximation.  A model with dx=dy=10 km means the grid volume is 100 km$^{2}$ times whatever the vertical grid spacing is.  The $w$ value for that grid box needs to be representative of the entire volume and you aren't going to explicitly resolve convection at this resolution (convection will be parameterized and in general a model can only resolve features that are about 4x bigger than the grid spacing).

As you reduce grid spacing (increase resolution) and start to resolve non-hydrostatic features (thunderstorm updrafts, downdrafts, etc), then you need to make sure you are using a non-hydrostatic solver.  For high resolution operational regional modeling and research modeling in the mesoscale using WRF-NMM, WRF-ARW, CM1, ARPS you'll find non-hydrostatic solvers.

The non-hydrostatic solver is more computationally expensive than a hydrostatic solver, and is often found in higher resolution models which themselves are more computationally expensive than coarse grids.


hydrologic vs. hydrodynamic modelling of surface runoff

The word "hydrological" is meant to indicate that the model only includes a sort of bulk description of the water: where it is, how much is there, and where it flows. It generally only includes length and time scales of interest to the system in question. So, for ground water models, this may be tens of meters and longer in horizontal direction, and hours and longer in time.

On the other hand, "hydrodynamic" is generally understood to resolve the governing equations for water flow, i.e., the Navier-Stokes equations (possibly posed in a porous medium). This must then deal with the length and time scales of eddies, which are substantially smaller and shorter than the ones above, and consequently requires a lot more computational power.


Were there any plans or proposals for "unilateral geoengineering deployments" before this paper was publsihed?

I think the introduction of the paper itself covers this adequately:

… a growing number of studies have investigated regional SG application scenarios, which could prove preferential to a global application by restricting the geospatial magnitude of the climate response or by being used to target specific climate changes8,9,10,11.

The cited references are:

Robock, A., Oman, L. & Stenchikov, G. L. Regional climate responses to geoengineering with Tropical and Arctic SO2 injections. J. Geophys. Res. 113, D16101 (2008).

MacCracken, M. C. On the possible use of geoengineering to moderate specific climate change impacts. Environ. Res. Lett. 4, 045107,  https://doi.org/10.1088/1748-9326/4/4/045107   (2009).

MacMartin, D. G., Keith, D. W., Kravitz, B. & Caldeira, K. Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing. Nat. Clim. Change 3, 365–368 (2013).

Haywood, J. M., Jones, A., Bellouin, N. & Stephenson, D. Asymmetric forcing from stratospheric aerosol impacts Sahelian rainfall. Nat. Clim. Change 3, 660–665 (2013).

Of those, [9] seems the most obviously relevant, although it covers more techniques than just SAI. One particularly relevant passage from [9] reads:

… materials lofted this high and staying
in the atmosphere for extended periods tend to spread out to
cover the globe. As a result, both their climatic influences
and any unintended side effects (e.g., increased scattering
of incoming solar radiation that diminishes the efficiency of
direct-beam solar energy technologies) tend to be global in
extent.

Since [9] is focused on discussing regionally-targeted geoengineering techniques, the presumed global spread of SAI is here being mentioned mainly as a potential disadvantage.
I think Jones et al. are actually raising two concerns with their work:

Unilaterally deployed SIA targeted at a particular region could have negative side-effects. This is the topic most relevant to your question. As the references show, there were indeed plans for this, at least in the sense that it had been discussed in the literature for some years. I don't know of any state drawing up concrete plans for SIA stations yet, but it's probably a good idea to raise these concerns before the policy train gets rolling.

SIA might be deployed at a single site as a globally targeted SG technique, with the assumption (as seen in [9]) that it doesn't matter where you do it because the aerosols will spread evenly over the globe in any case. Jones et al. show that this will not necessarily happen.


How closely related is surface air temperature to pressure?

You have opened a very large can of worms.  You will need a larger can to get them all together again.

The problem is time lag.

Let's do some thought experiments:

It's dawn in the desert.  Right now the bottom of the atmosphere is cool.

Sun heats the dirt, and the dirt heats the air.  Air expands some.  But the air above it is lazy about getting out of the way.  So the air pressure goes up some.  Air finally shoves that air above up, and then whether the pressure goes up or down depends on how fast it can get out of the way.  Small area -- parking lot, the air spills in all directions.  adjusts quickly.  Gobi desert air starts to push out sideways, Coriolis rears up, and you have a temporary high pressure.  At night the reverse happens.  Ground cools, air shrinks, but the air around it doesn't fill in right away.

Lets look at longer term features.  Consider the Alaska low.  The north pacific is warm, at least by ocean standards, and so the air above it is warm.  Warmer air is less dense, and since the low stays more or less put for months at a time, the entire air column is warmish.  Warm air is less dense than the cooler air around it. It has a lower effective surface pressure than cooler air around it. The cooler air from around it tries to rush in, but... Coriolis again. Friction restricts how much of that air can enter the low area. Low pressure warm air is pushed out by moving upward as a series of cloud and rainy weather.

We think of the atmosphere in our heads as this thick blanket covering the earth.  But most of the interesting stuff is in the bottom 3/4 of the atmosphere (by mass) which is about 36,000 feet. Call it 5 miles. It's a thin apple skin.

One of the messy bits is the scale problem:  There is very little change in energy moving a parcel horizontally.  But moving it vertically gets messy.  Pressure changes.  Temperature changes.  Water condenses/evaporates adding/removing sensible heat.

One of the eye openers for me was realizing that in a lot of physics, you can analyze and quickly conclude that certain forces have small effects and can be ignored.  In atmospheric dynamics I find myself unable to figure out what can be ignored, or left with a first level approximation.  Everything affects everything else.

Anyway to answer your question:  Warming temperatures will initially increase pressure, but later decrease pressure.  Cooling temperatures the opposite.

Looking at Edmonton, AB's forecast for the next 10 days, we are getting daily temp fluctuations of about 11 C, and daily pressure variations of about 4 hPa.

From the gas laws this is an 11 K compared to about 300 K so the pressure should change by about 11/300 of it's absolute pressure.  This would be about 37 hPa.  Why doesn't it?

Because it's not the whole air column that's changing temp.  Typically only about the bottom 3000 feet changes on a daily basis -- daytime mixing depth, with some mixing higher up.  3000 feet has about 1/10 of the atmosphere in it so the variation is only about a tenth.  Ok, that gives 3.7 hpa.  Closer to 4, but still off.  Remember you ignore factors at your peril in atmospheric.


How does the synthesis of Kaolinite (and it's by products) influence porosity in granodiorite?

Kaolinite "grains", for want of any better term, are swollen with chemically bonded water compared to the crystals they weather out of so porosity is decreased by particle expansion while at the same time overall density drops. Kaolin also has very strong particle-particle adhesion so any mechanical deformation of the material tends to compress it leading to further reductions in bulk porosity. The influence of Calcium and Potassium on the ongoing weathering of the rock and it's overall porosity depends greatly on the weathering regime; for example if weathering is continuously under wet conditions then Calcium and Potassium will be mobilised in ground water and removed. On the other hand in a wetting-drying cycle Calcium and Potassium liberated from the parent rock become oxides when the material dries out, those subsequently react strongly with water in the next wetting cycle acidifying the environment and accelerating rock decomposition.


The Basic ENVISAT Atmospheric Toolbox (BEAT) contains a component called the Common Data Access toolbox (CODA; also available on github).  BEAT and CODA are written in C and have bindings for Python (as well as Matlab, IDL, and a few other languages).  Among the long list of supported products is IASI L1C.  Apparently, BEAT is going to be replaced by HARP (github page), but HARP reportedly does not yet support IASI L1C.  BEAT, CODA, and HARP are all available under the GPL.

Although the BEAT website reports Python bindings are only available for Python 2.7, I have successfully used CODA with Python 3.5 (I did not try BEAT as I do not currently need the higher-level functionality it offers).


What are the most similar Earth analogues to Mars' seasonally recurring slope linea?

Analogues to Mars Recurring Slope Linea (RSL) is a current study topic in  Antarctica (Dry Valleys). On Earth, analogues are known as water tracks, which are linear zones of higher moisture along slopes in polar regions where water transit during snowmelt. This figure from Ward Hunt Island (NU, Canada) show well developed and typical water tracks.

Source:  Water tracks in the High Arctic: a hydrological network dominated by rapid subsurface flow through patterned ground Michel Paquette et al. Arctic Science, 2017, 3:334-353, https://doi.org/10.1139/as-2016-0014

On Earth, as shown on this picture from Ward Hunt Island, water tracks are from snowmelt and thus not from brine, unlike in Antarctica where brine water as runoff is common.

  Water tracks share many morphological and seasonal characteristics with RSL, including downslope propagation of linear or branching patterns of surface darkening, growth during spring/summer seasons, and fading during winter

and

  Saline fluids associated with water track flow are sourced by snowmelt, shallow ground ice melt, and the direct conversion of atmospheric water vapor into brines through high-elevation salt deliquescence

from Joseph Levy, Hydrological characteristics of recurrent slope lineae on Mars: Evidence for liquid flow through regolith and comparisons with Antarctic terrestrial analogs, Icarus, Volume 219, Issue 1, 2012, Pages 1-4

This mean that this Antarctica analogue to Mars RSL have several sources of water (meltwater, shallow ground ice and atmospheric water vapor deliquescence).

Comparatively, on Mars, source for the RSL have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow groundwater. And more recently, from deep aquifers  through fractures (impact, tectonic) such as shown in this study at Palikir Crater inside Newton Crater Basin and Triolet Crater.

Nevertheless, there is entire sessions at the Lunar and Planetary Science Conference dedicated at Martian Brines (MARTIAN BRINES:  OLD SALTS AND NEW VIEWS) and RSL or actual slope processes (THING FALL DOWN GO BOOM:  MARS DOWNSLOPE MOTION). While models are getting better and more elaborated, there is still opposing views and this dynamic field of study is moving very rapidly.

Finally, life found in brine on earth are halophiles, a type of extremophiles - but this is a whole topic in itself.


Are there any metal anomalies other than iridium in the K-Pg boundary?

According to the conference article Can Siderophile Element Abundances and Ratios across the K-Pg Boundary be used Discriminate between Possible Types of Projectiles?, (Belza et al. 2013) state that the enrichment is not only in Iridium, but also in the other Platinum Group Elements and siderophile elements.

From the article Platinum-group elements (PGE) and rhenium in marine sediments across the Cretaceous–
Tertiary boundary: Constraints on Re-PGE transport in the marine environment (Lee et al. 2003) elaborates that from

  A traverse
  across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of
  which is approximately symmetrically distributed over a distance of 1.8 m across the KTB.

(KTB is a reference to Cretaceous-Tertiary Boundary from the article).

In a re-evaluation of geochemical data in Reevaluation of siderophile element abundances and ratios
across the Cretaceous–Paleogene (K–Pg) boundary:
Implications for the nature of the projectile (Goderis et al. 2013), took into account several more studies (published and unpublished), find that cobalt, chromium and nickel display in some places, an elevated concentration; however, the Co/Cr, Ni/Co, Ni/Cr, Co/Ir, Ni/Ir and Cr/Ir ratio are considerably higher than that of the average continental crust, which the authors suggest is consistent with chondrites.


Average Aragonite:Calcite ratio in biogenic CaCO3 in the oceans

After some more research, the conclusion is that aragonite is somewhere between 10 and 50% of total CaCO3 production:

Aragonite, calcite-Mg and calcite are the 3 main species of marine CaCO3. Aragonite is unlikely to be a major component of the total CaCO3 flux (Berelson, 2007), though the exact contribution is uncertain and falls in the range of 10-50% of global CaCO3 production (Gangstø, 2008). Minimum values of 12% (Berner and Honjo, 1981) and 13% (Fabry and Deuser, 1992) have been reported based on sediment traps. Calcite-Mg contributes ~8% (Fabry and Deuser, 1992) to 24% (Morse, 2006) to CaCO3 production. The sediment trap-based contribution of aragonite of ~12% is thought to be lower than the actual contribution of aragonite to CaCO3 production because aragonite is about 1.5 times more soluble than calcite and therefore more depleted than calcite in the sediment trap records.

An educated guess of me would therefore be ~20% aragonite, ~10% calcite-Mg and ~70% calcite globally on average.


Why are there no subduction trenches on continental land?

Continental crust is thick and relatively buoyant.  Ocean crust is much thinner, and relatively dense.
Hence ocean crust "goes down" more easily, and the density can even help pull the ocean slab due to metamorphism.
In contrast, the continents are almost like floating scum which won't go down! When they collide, you get faulting and folding, and the building up of very thick continental crust. Tibet is the best example today. Yes the Tibetan Plateau is high, but the crust is over 100km thick! (think of an iceberg, most of it is below)


How to distinguish between Altocumulus, Stratocumulus and Cumulus clouds?

You are not alone. Allmost everyone has difficulty differentiating Ac from Sc because, apart from the obvious low clouds, you can't accurately discern a cloud's height purely from looking at it. For that you need a 'ceilometer', which is a vertical beam of light reflected off the cloud-base. Not many met sites have this.


What is the Carbon Footprint of not changing car oil?

This is an interesting question, and a life cycle emissions analysis can give a pretty good answer.  Obviously there are a lot of variables, so some basic assumptions have to be made.

We start with the CO2 equivalent emissions from building and driving a car over its lifetime.  There are various analyses out there, but here is one that I found which gives the following values for a typical gasoline powered automobile over a "typical" lifetime of 150,000 km (93,000 miles): 24,000 kg of CO2e emissions total, of which 5600 kg is from the fabrication of the car.

For the oil, I found this, which gives a range of 2.5 to 13 kg CO2e per gallon of motor oil.  The lower value assumes the new oil is made from recycled oil, and the waste oil is sent to a recycler.  The higher value assumes the new oil is not from a recycled source, and the waste oil is not recycled.  For the most extreme case, we can assume virgin oil, and assume the oil is changed every 3000 miles, and that the car holds 4 quarts (1 gallon).  That makes 31 oil changes in the car's lifetime, which gives 403 kg of CO2e from oil changes.  Another perfectly reasonable value might be to assume recycling and assume an oil change every 7000 miles which results in 33 kg CO2e emissions.

So the oil changes are contributing something in the 30 to 400 kg range over the life of the car, compared with 24,000 kg from building and driving the car.  Skipping all oil changes in the most extreme case results in less than 2% reduction in total CO2e emissions.  You can get almost exactly the same result by changing the oil every 7000 miles instead of every 3000, and by using recycled oil and making sure that your used oil is recycled.

Even though you're not asking about it, I have to add that I think you have been exceptionally lucky if you drove 400,000 miles without changing the oil.  I don't think you should expect that result again.  And note that the emissions associated with building a car are 5600 kg - 10 to 100 times greater than the emissions contributed by changing the oil.  If you don't change the oil in any car again for your entire life, and end up ruining just one car as a result, you will cause far more emissions than you saved.


Equation for predicting contrail formation

Schmidt-Appleman criterion (SAC) is used to model contrail formation. I advise reading in full Ulrich Schumann's article "A contrail cirrus prediction model" (http://www.geosci-model-dev.net/5/543/2012/gmd-5-543-2012.pdf) to get all the relevant formulae and literature references.

While it is possible to transcribe the formulae here, the reference cited does a better job of presenting state of the art (2012).


With humans out of the equation, what could cause forest fire?

Wildfires are mainly caused by humans (or their technology) and lightning. Lightning is the most prolific natural source.  There really aren't many other sources in most areas, unless there is volcanic activity or a meteor strike as you mention.  There are also occasional cases of wildfire when peat dries out.
During a hot-dry summer, it can take several days of rain to moisten vegetation enough so that the fire danger is curtailed.  If there is a little rain accompanied by lightning, it is probably much less than what is needed to lower the fire potential (dryness of vegetation).

Furthermore, lightning strikes are not "usually accompanied by rain".  In the Pacific Northwest, for example, there are several lightning-caused wildfires every summer in areas where summer rain is quite scarce.  This is discussed a little in Wikipedia:

  The term dry lightning is used in Australia, Canada and the United States for lightning that occurs with no precipitation at the surface. This type of lightning is the most common natural cause of wildfires. Pyrocumulus clouds produce lightning for the same reason that it is produced by cumulonimbus clouds.


Was the filling of the Three Gorges Dam's impact on the Earth's rotation rate detectable?

The .06 microseconds figure doesn't sound accurate

The moment of inertia for a solid sphere is $$I = \frac{2mr^2}{5},$$ where $m$ is the mass of the sphere and $r$ is its radius. Applied to the Earth, this gives us $$I = \frac{2\cdot5.972\times10^{24} \text{ kg} (6371000 \text{ m})^2}{5} = 9.70\times10^{37} \text{ km-m}^2.$$

A simplified estimate of moment of inertia for the water in the three gorges dam is $mr^2$. The change in moment of inertia from raising that water by 175m can be calculated by $$\begin{align}\Delta I &= m_{water}\left[(r_{earth}+175)^2-r_{earth}^2\right] \\ &= 39\times10^{12}\left(6371175^2-6371000^2\right) \\&= 8.69\times10^{22} \text{ km-m}^2.\end{align}$$

Assuming that the angular momentum ($L$) of the Earth stays constant, then since $L=I\omega$, $$I_{before}\omega_{before} = I_{after}\omega_{after},$$ or $$\omega_{after}=\omega_{before}\frac{I_{before}}{I_{after}}.$$ The angular velocity, $\omega$, of the Earth (before) is $7.292\times10^{-5} \text{ radians/s}$. The discrepancy between the before and after moment of inertia is so insignificant that I would be wary of floating point error on this calculation, but using Python2 I calculate the delta in rotational speed to be $6.776\times10^{-20} \text{radians/s}$. For a rotation of the Earth this means the rotation will take about 80 picoseconds longer, or 0.00008 milliseconds.

Conclusion

The statements made by VSauce don't match up with Physics 101. I am not inclined to believe this claim unless there is some other explanation or compelling evidence. Given that the magnitude of the change in rotational speed is three orders of magnitude less than he claims, and that 80 picoseconds is about 1/4 of the time it would take your computer to add 2 integers, I think it is safe to say that this is not measurable.


How can a storm drop 40 inches (1 metre) of rain?

You were right to question whether the atmosphere really held that much water.  It comes nowhere close!  We use precipitable water to track this, which is the measure of all moisture in the entire column of air in the troposphere.  We can get good widespread estimates from remote observations.  This animation shows current amounts of precipitable water levels across the US from satellite.  Here is a still from this afternoon (Sunday, August 27) during the Harvey event:

75 mm is less than 3 inches.

We also get in-situ exact measurements worldwide from twice daily radiosonde balloon launches.  Unfortunately none are located right near the locations receiving excess rainfall.  But you can check US sites of current precipitable water measurements any time by going to SPC's sounding page and looking for the PW value in the left side of the bottom table.  SPC also maintains a climatology page for precipitable water and other values.  You can see there that 3 inches (76 mm) of moisture in the sounding is extremely rare, and no US site has ever had 4 inches (102 mm) of precipitable water.

However, the answer is also not truly found in evaporation rates.  The conditions in strong hurricanes do greatly enhance evaporation rates due to the high wind speeds and warmer waters.  Measurements are actually a bit difficult to come by in such extreme conditions, with challenges in isolating evaporation effects from spray as well as in getting the instruments positioned into such environments (new field campaign: who wants to take the research ship out into the category 5 hurricane!?!).  As this 2007 study by Trenberth et al. noted:

  We are unaware of reliable estimates of evaporation in hurricanes, and published measurements do not exist in winds above about 20 m s−1 although some progress has been made in the Coupled Boundary Layer Air-Sea Transfer Experiment (CBLAST)

However, in that study model analyses suggested that evaporation rates in the core of hurricanes are likely no more than 1-2 inches (25–50 mm) per day.

How is that possible?

It's quite important to notice that heavy rainfall - well over 5 inches (125 mm) - can actually fall in as little as a couple hours almost anywhere, such as in this 2015 flood event in Nebraska.  How can that be?

The secret lies in the nature of even the weakest storm: even as a storm is just beginning to form, it begins to draw in air from surrounding areas.  This is NOAA's diagram of a typical developing thunderstorm cell:

You can see the curve at the arrows near the bottom, indicating inflow of surrounding air into the storm.  This inflow turns a thunderstorm into more of an engine, processing a continuing stream of incoming air, removing its moisture.  In a single cell thunderstorms in an environment without background winds, the "waste" air will eventually pile up and choke off the influx.  But even in such circumstances, a few inches of rain may fall.  That isn't by using up all of the moisture from the cloud's environment, but instead by using just a portion of the moisture from the reservoir in and around the cloud.

If some upper level winds exist to help exhaust the "spent" air, storm systems can persist for even longer periods of time.  For example, the Midwestern United States commonly sees long-duration late summer heavy rainfall initiated along stationary boundaries in which inflow lacks direct access to significant warm water bodies.

Larger systems that dump huge amount of precipitation over greater areas must pull in a more consistent, stronger inflow of warm, moist air from greater distance.  Examples of this happening include the Pineapple Express for rainfall in California/the southwest US, the low-level jet for spring and summer squall lines in the Plains, onshore winds during the Indian monsoon, and air from off the Gulf Stream in Nor'easters.

In all these regional large precipitation events moist air gathered from a great surface area flows into a smaller region.  As the air approaches, it is lifted by the low pressure and its associated features, condenses, and finally falls as rain (or snow).  This process is often termed "moisture convergence".  The Storm Prediction Center also offers plots of localized deep moisture convergence [choose a region, then look under the upper air menu].  The convergence contours, shown in red, really show the piling up of humidity that is causing the heavy rainfall in Harvey:

But perhaps to visualize the scale involved in creating a catastrophic largescale flood such as Harvey, this plot, created from a base image from pivotalweather.com, best shows the conditions around the storm (from the GFS model):

Basically the atmosphere of the entire Gulf (and beyond) is being pumped into the southeast Texas area.  So although the air can only hold a couple inches (some 50 mm) of water, and evaporation rates are typically only a fraction of an inch (several mm) per day... bringing that together from such a large source region, and focusing it down into one small area... can lead to these awful extreme deluges.

Addendum: It should also be highlighted that the NHC adds in their report on Harvey that rising motion was also enhanced by a front which had stalled in the area.  Air being advected in by Harvey's flow would naturally rise over that layer of cooler air when moving inland (a process called isentropic lift), which proves particularly efficient in condensing out the (abundant) moisture en masse into rainfall.  Most substantial regional floods require similar existence of a significant broad lifting mechanisms overlaid with such a relentless inflow of warm, moist air.


Did the Neolithic Revolution have an effect on the earth's climate?

Raising herd animals would likely contribute more than mere farms.  Many farms simply produce feed for animals anyway, and this can lead to an inflated population which can wreck havoc when released in the wild to graze.  That said, with the exception of Egypt and a few rare cases, every agricultural society eventually failed because they could either could not keep up with the deposits of silt clogging their water works, or they could not contend with the the rising salinity of soil, caused by prolonged irrigation.  The evaporation of water leaves behind an excess of mineral salts, and eventually a field's production drops and the desert takes over.  The usual method people employ to contend with these issues is to build more canals and irrigate more land elsewhere.  So for a few thousand years agriculture societies have been converting land to desert and this no doubt this would have effected the climate.  But probably only a scant iota when compared to the last 100 years of agriculture . . .


There are currently two ways to extract geothermal energy: one mainstream, one still at the experimental / demonstration level.
Pollack et al (2010) estimate the global geoethermal heat loss at 44 TW (by comparison, civilisation's rate of energy use is about 20 TW).
As the USA Department of Energy notes, all methods rely on the combination of three factors:

heat underground,
fluid to carry the heat to the surface, and
permeability to allow the fluid to flow.

The mainstream geothermal method
This happens close to tectonic plate boundaries. Reservoirs of hot liquid are tapped, to bring the hot fluids to the surface. Typically the temperature of the fluids is well over 100 &degC;, and can be used for electricity generation, as well as for heating.
The experimental method is Hot Dry Rock
aka Enhanced Geothermal System or EGS.
As Pavel V. commented, this is being piloted in the Czech Republic, amongst other places, and allows geothermal heat extraction from places that are not close to tectonic plate boundaries. From that link:

the projected depth of the ... borehole was between 2100 and 2500 m. The drilling diameter ranges from 393,7 mm for the starting upper section to 152 mm at the borehole bottom

One tube is placed inside another, inside the borehole. Water can be injected down the inner tube, and returned up through the gap between tubes, or the other way around.
That paper reproduces the following chart from Šafanda, J., Dědeček, P., Krešl, M., Čermák, V. [2007] Report from geothermal research for PVGT-LT1 (in Czech):

As you can see, these temperatures are much lower, so are unsuitable for electricity generation, because one must accept very low efficiencies (Carnot's Law). They are used for space- and water-heating.


I think that your question is not really answerable.  But perhaps the reasons it's not answerable are themselves interesting.  There are two parts to this answer:

why do we think abiogenisis is likely?
is Earth, today, hospitable for organisms which originate through abiogenesis, if it is likely?

My answer to the first part is, I think, more well-founded than my answer to the second (I'm a physicist not a biologist!).

Is abiogenesis likely?

Well, we have exactly one example of a planet we can study closely with life on it (indeed there is only one example of a planet that we know has life at all at present), and life has been there for such a long time and has modified the environment of that planet so extensively that I think speculation about how life originated on that planet is, well, speculation.  That doesn't mean it's not interesting or that there might not be plausible and attractive hypotheses.

As an example it's tempting to argue that, because life originated on Earth almost as soon as it could, and disregarding panspermia, that abiogenesis must therefore be very common.  That argument is wrong.  There are a huge number of potentially-earthlike planets: this paper (arXiv version) claims that around 10% of stars may have a planet that is about the same size as Earth and gets around the same amount of sunlight as Earth.  There may be around $10^{24}$ stars in the observable universe: based on this paper (arXiv) there may be around $2\times 10^{12}$ galaxies and assuming each galaxy has $10^{12}$ stars we get $2\times 10^{23}$ stars.  So this means perhaps $2\times 10^{22}$ potentially-earthlike-planets.  All we know is that life originated on one of those planets, somehow (and abiogenesis is only one of at least two options), and it did so rather early.  What does that tell us?  Well, statisticians can play games and those games are probably reasonable, but it doesn't tell us, for sure, that the chance of that happening is higher than $1/10^{22}$.

This argument is related to the anthropic principle which I find rather unappealing in terms of explanatory power: I find the idea that the fine-structure constant must be what it is because otherwise we would not be here to measure it unappealing for instance.  But the anthropic principle is nevertheless not an idea that can be ruled out in general: we know life evolved on Earth because we're here to observe it, but this doesn't, yet, tell us anything about the probability of life evolving elsewhere: the universe could have just thrown a $10^{22}$-sided dice $10^{22}$ times and come up with the side that says 'life' once.

This doesn't mean that abiogenisis can't be really common, or even that it not likely that it is, it just means that we don't know that it is.  With luck this will change in the relatively near future, as we begin to be able to observe expolanets which convincingly have life.  Then we'll be able to use statistics in a more useful way.

How hospitable is Earth, today?

Well, let's assume abiogenisis is common, what can we say about Earth's hospitability to new life generated that way?  Well, we know that organisms on Earth are continually under attack by other organisms and things which may be organisms (I'm not a biologist, I'm not sure if viruses count as organisms or not).  And we know that these attacks can be pretty successful: for instance when Cortés invaded what is now Mexico the population was around 25-30 million, 50 years later it was around 3 million, and most of this decline happened due to disease (Wikipedia).

So life on Earth exists in this continual arms-race: things try to attack organisms and organisms develop hugely sophisticated immune systems to deal with those attacks.  We're living, right now, through an example of what happens when an agent attacks us for which our immune system is not yet prepared: fortunately it's not going to kill that many of us.

So let's propose that abiogenesis happens on Earth, now.  There are really two options.

Whatever appears is, say, RNA-based, and as such is recognisable by the existing warring factions.  It has no defences and gets promptly attacked and eaten.
Whatever appears is based on some significantly different chemistry.  But whatever it is, it's harvesting energy from somewhere and making it into itself.  As soon as it starts harvesting enough energy it becomes interesting to existing organisms who would be quite interested in getting that energy for themselves, who pretty quickly evolve to being able to do so and eat it.

The third option is that whatever it is turns out to be so efficient in some way that it wins the fight with the existing stuff.  I suspect, without any kind of proof, that this option is absurdly unlikely to happen.

I think what is more likely to happen is that, any time some new way of chemically stashing energy happens, it becomes attractive to existing organisms, who evolve to be able to harvest that energy and do so, long before whatever thing has happened could be described as 'alive'.

In summary: Earth is almost certainly not currently hospitable to newly-generated life, at all, because the existing life will eat it, one way or the other.


Why was there a negative temperature anomaly between 1950 to 1980?

This phenomenon is known as global dimming.

It was due to the particles and aerosols mostly released by combustion of fossil fuels such as diesel. Those particles block the radiation from the sun, so they have a cooling effect. For some decades this effect counterbalanced the warming effect of greenhouse gases, although it is no longer the case at a global scale (see for instance Wild et al. 2007). Particles emission has been reduced thanks to better engines and new regulations, which stopped their masking effect on global warming. Which is a good thing since those particles have a serious impact on health.


Can we see the circulation cells in wind maps?

Yes, the wind cells are just a toy model, where we can suppose that the homogenity of the Earth and other things. But there are other things and Earth isn't same on the all points, so the instantaneous winds don't follow their cells. Of course, it is possible (by pure statistics) that sometimes in the Earth history, the majority of the winds was aligned with their cells. But the cells are just averaged over the period of more decades and centuries.


How are chenier ridges and strand plains formed at wave dominated coastlines?

The following sources helped me understand these landforms - hopefully they can help you too :)

From the Miranda Shorebird Centre: The Miranda-Kaiaua cheniers are first formed as sand and cockle-shell bars on the foreshore or intertidal flats. The bars are then moved landward by wave action. Eventually the bars attain sufficient height to withstand such wave action.

From NASA's Earth Observatory: Strandplains are built by successive additions of beach sand, usually from some nearby source. Each ridge shows the position of a prior shoreline.


Try:

Federal Contaminated Sites Inventory

as well as

Crown Contaminated Sites Database (British Columbia)

Orphaned/Abandoned Mine Site Rehabilitation (Manitoba)

Abandoned Mines Information System-AMIS (Ontario)


Calculate the maximum power angle of a solar panel (photovoltaics)

This question can be answered in many different ways that take into account, or ignore, the many factors that affect the total output of a fix solar panel over a year.

In general, all answers will agree that the solar panel will have to face the north in the southern hemisphere, and the south in the northern hemisphere. This is because that is the direction where the Sun will be when it reaches the maximum elevation during the day. Or if you are within the tropics ($\pm$23.5° of latitude), that's the direction where the Sun will be most of the days when it reaches the maximum elevation.

The tricky part is the inclination angle, because the solar elevation changes trough the day, and the maximum elevation changes trough the year. In general, the mean elevation at solar noon (that usually do not match the clocks noon due to standardized time zones), is given by:

$\overline{h_{max}}=90^o-\text{Latitude}$

And through the year it will vary $\pm$23.5°.

So in a first zero-order approach you can just use that mean value. Now, to find the optimum value you have to model the Sun's position trough the year and run a complex calculation to find the angle that maximizes output. Thankfully some people have done that, and they have reduced the output to simple empirical formulas. For example, in solarpaneltilt.com they provide the following formulas:

$\text{Optimim angle}=\left\{ \begin{array}{rcl} \text{Latitude} \times 0.87 & \mbox{if} & \text{Latitude}<25^o \\ \text{Latitude} \times 0.76 + 3.1 & \mbox{if} & 25^o<\text{Latitude}<50^o\end{array}\right.$

And if you don't want to put the fingers in a calculator they provide a table with some values for different latitudes:

However, this approach pinpoints to an angle with great accuracy, while neglecting what can be one of the main factors affecting the output of your solar panels: weather. Therefore, the above approach would be very accurate if you live in a desert, but misleading if you are in an area with clear weather in winter and rainy weather in summer.

To tackle this problem you can download weather statistics for your location and find the optimum angle yourself. Ideally you would do this by calculating solar output on each day, but I'll first show you also a simpler approach month by month that you can reproduce with very little computer skills and the results will be very similar.

The general workflow is as follows:

Find the typical solar radiation reaching the surface at your location each month/day of the year. Let's call this parameter $S$.
Find the typical solar elevation over the horizon at solar noon at your location each month/day of the year. Let's call this parameter $h$,
Find the maximum solar power that a solar panel could receive if directly facing the Sun, let's call this $S_{max}$ and it will be given by

$\hspace{12em} S_{max}=\frac{S}{\sin(h)}$

Find the effective power hitting a solar panel at a set angle $\theta$. Let's call this $S_{eff}$ and it will be given by

$\hspace{12em} S_{eff}=S_{max} \cos(90^o-h-\theta)$

Adding $S_{eff}$ for each month/day of the year. Let's call this $S_{total}$.
Put all these calculations in a spreadsheet and then play with different values of $\theta$ until you find the one that produces the maximum $S_{total}$.

Now, to get the typical $S$ values for each month you can go to the KNMI Climate Explorer, click the option "ERA-interim 1979-now", then select the variable "surface net solar/longwave radiation", and click "Select Filed" on the top.
Then, you will see a bunch of options, but only focus on the first box:

Fill, the coordinates, add half a degree around your location (this model resolution is ~ 80 km, so don't get picky with accurate locations), select the "max" option (mean would work too), and hit "make time series".

You will get a time series of solar radiation in your area, and the average per month from 1979 to 2019, it will look like this:

Now, you click the "raw data" link above the plot and you will get the numbers for $S$ to feed into your spread sheet, they are in the first data column:

For daily values you start from Daily fields, and select ERA-interim 1979-now rsds field. From there is the same as before. And the plot will look like this:

Now, to get the solar elevation for each month you can use this Solar elevation angle (for a year) Calculator and just take the day closer to the center of the month to feed it into your spredsheet. For getting angles for each day, you can use this Rise/Set/Transit Times for Major Solar System Bodies calculator, this is how I filled the form for my area of interest:

Note that I choose a leap year so it matches the number of days in the output from the KNMI Climate Explorer.

Whith all this, the formulas above and a bit of spreadsheet skils you can find the optimal angle for your location.

My monthly spreadsheet looks like this:

And the daily one like this:

As you can see, for my area of interest the angles differ only by 1° between the monthly and daily calculation. And about 4° with the formulas from solarpaneltilt.com. However, in other climates the differences could be much larger.

This method can be adjusted also if you want to maximize power during the winter months, that are usually the most challenging ones for a solar power supply.
If you area have large temperature variations and want to get fancy, you can also incorporate the effect of temperature in solar panels' efficiency.


What "g" would be needed to keep helium on Earth?

Atmospheric escape is the loss of planetary atmospheric gases to outer space. You'd never be able to contain ALL of any gas forever by gravity. Ultimately you end up in the rarefied atmosphere where there is some probability that a molecule of gas will reach escape velocity. The probability distribution is given by the Maxwell-Boltzmann distribution and the thermal escape mechanism is known as the Jeans escape.

On earth the problem is compounded by the fact that helium is lighter that the other gases. So (1) helium migrates to the upper atmosphere because of its density and (2) helium atoms on average have the same kinetic energy as oxygen and nitrogen molecules which means that helium atoms are on average traveling much faster than oxygen or nitrogen molecules.

All of this is made more complicated by needing a temperature profile of the atmosphere as a function of the height.

It doesn't help to assume temperature of background radiation because even at that temperature you can calculate the probability of a helium atom having 80% of light speed. This sort of like being able to calculate the probability of throwing $n$ heads in a row regardless of how big $n$ is.


Wind is caused by pressure differences.  Think of a balloon full of air; poke a hole in it and the air comes out.  Why?  Because the pressure in the balloon is higher than outside, and so to regain equal pressure, mass moves and that is the wind.

There is a bit more to this in the atmosphere as the Earth rotates and near the surface friction also plays a role.  The equation of motion is the Navier-Stokes and in vector form in Cartesian space is:

$$\dfrac{\partial\mathbf u}{\partial t} = - \mathbf u \cdot \nabla \mathbf u  -\dfrac{1}{\rho}\nabla p-2 \mathbf \Omega \times \mathbf u + \mathbf g + \mathbf F$$

In this equation, $\mathbf u$ is the vector wind, $(\mathbf u \cdot \nabla)$ is the advection operator, $\rho$ is density, $\mathbf \Omega$ is the vector rotation of the Earth, $\mathbf g$ is effective gravity and $\mathbf F$ is friction.

The LHS is the time rate of change of the wind at a point in space (as opposed to following the parcel).  The RHS represent a number of factors that produce a change in the wind.  From left to right:

Advection of momentum (non-linear)
Pressure gradient force (this is wind blowing from high to low pressure)
Coriolis force (this turns wind to the right in the NH and left in the SH and causes the wind to flow parallel to isobars)
gravity (provides hydrostatic balance with the PGF in the vertical)
Friction (in the boundary layer you may see this as $\nu\nabla^2\mathbf u$)

For large scale synoptic flow above the surface, this is often simplified as a balanced flow called geostrophic balance.  This a steady flow with a balance between the PGF and Coriolis force in the horizontal and hydrostatic balance in the vertical.

$$ \dfrac{1}{\rho}\nabla p = 2 \mathbf \Omega \times \mathbf u $$

Which can also be written as

$$u_g = -\dfrac{1}{\rho f}\dfrac{\partial p}{\partial y}$$
$$v_g =  \dfrac{1}{\rho f}\dfrac{\partial p}{\partial x}$$
$$\dfrac{\partial p}{\partial z} = -\rho g$$

In these equations, $u_g$ is the geostrophic wind in the east/west direction and $v_g$ is the geostrophic wind in the north/south direction and $f$ is the Coriolis parameter ($f = 2\Omega\sin\phi$, where $\phi$ is lattitude).

For this idealized geostrophic and hydrostatic balance, there is no vertical motion and all horizontal flow is parallel to isobars, flowing clockwise (counter-clockwise) around high pressure in the NH (SH) and flowing counter-clockwise (clockwise) around low pressure in the NH (SH).

For curved flow, we can consider another balance, the gradient wind balance that allows acceleration of the flow though centrifugal forces.  This can be written as (where $n$ is in the cross-wind direction):

$$ \dfrac{V^2}{R_t} = -fV - \dfrac{1}{\rho}\dfrac{\partial p}{\partial n} $$

Where $R_t$ is the radius of curvature in the flow. In the limit of $R_t \rightarrow \infty$ the acceleration term vanishes and this becomes geostrophic flow.  The consequence of this balance is that wind will flow slower than geostrophic balance around a low pressure center, this is said to be subgeostrophic.  Around a high pressure center we have supergeostrophic flow, or faster than geostrophic.

You may have noticed the wind balances above are non-divergent and lack vertical flow.  This makes for boring weather, and does not hold near the ground or where vertical motion is large.

We term the deviation from geostrophic flow the ageostrophic wind and this accounts for friction.  This results in wind converging toward low pressure and diverging from high pressure.

Another flow is the isallobaric wind, and this is wind that blows from pressure rises toward pressure falls.  A place you will normally see this wind is just as a cold front passes and the pressure rises behind the front and falls in front of it.  This enhances the cross frontal wind and helps produce the often strong, gusty winds after a cold front passes.


Is the Cameroon Line still an active rift zone?

The actual cause of the Cameroon Line is described by many authors (including the 2 included in this answer as being source of controversy and uncertainty - but it seems that it is not an active rift system, certainly not like the east Africa Rift.  According to the article A lithospheric instability origin for the Cameroon Volcanic Line (Milelli et al. 2012) describe the Cameroon Volcanic Line (CVL) as being

  an enigmatic structure that defies common dynamic models of
  melt generation and volcanic activity on Earth.

The enigma is due to the CVL having no spatial age progression in the rift system, despite having continual magma intrusion over 70 million years along the 1600 onshore-offshore line.

The authors also suggest that

  The chain is nearly perpendicular to the coastline and
  terminates in a Y-shaped structure that has not been affected by absolute plate motions, implying that
  the mantle upwelling that feeds magmatic activity is attached to the continent.

The authors model that rather than a developing rift system, the CVL is likely to be an example of where the lithosphere becomes unstable due to cooling from the crust above.

It should be noted that the CVL lies in between 2 cratons, shown as white in the seismic tomography image below from Macquarie Universty - what also should be noted, is the colour of the active East African Rift.

Further, according to the article Formation of the Cameroon Volcanic Line by lithospheric basal erosion:
Insight from mantle seismic anisotropy (Elsheikh et al. 2014), modelled the sub-crust dynamics that

  involves a channel flow at the bottom of the lithosphere originated from the
  NE-ward movement of the asthenosphere relative to the African plate.

from this, the authors hypothesise that

  progressive
  thinning of the lithosphere through basal erosion by the flow leads to decompression melting and is
  responsible for the formation of the CVL. The model is consistent with the lack of age progression of
  the volcanoes in the CVL, can explain the formation of both the continental and oceanic sections of the
  CVL, and is supported by previous geophysical observations and geodynamic modeling results.

A key conclusion the authors made regarding the flood basalts and volcanism in the CVL is that observations do not support mantle convection or mantle plume causes, rather, they assert that basal lithospheric erosion due to

  concentration of mantle flow associated with the
  sharp change in the orientation of the continental margin of western
  Africa.