when these magnetic field lines reconnect. Velocity and density Near the Earth's orbit at 1 Astronomical Unit (AU) the plasma flows at speeds ranging from 250–750 km/s (155–404 mi/s) with a density ranging between 3–10 particles per cubic centimeter and temperature ranging from 104 to 106 Kelvin. On average, the plasma density decreases with the square of the distance from the Sun while the velocity is nearly constant, see Figure 4.2. Pressure At , the wind exerts a pressure typically in the range of (), although it can readily vary outside that range. The ram pressure is a function of wind speed and density. The formula is where mp is the proton mass, pressure P is in Pa (pascals), n is the density in particles/cm3 and V is the speed in km/s of the solar wind. Coronal mass ejection Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called coronal mass ejections, or CMEs. CMEs are caused by a release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. CMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME. When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. CME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora. CMEs are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Fast-moving streams tend to overtake slower streams that originate westward of them on the Sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles,