even in the driest atmospheres. This also explains why moisture in the mid-levels of the troposphere, roughly at the 500 hPa level, is normally a requirement for development. However, when dry air is found at the same height, temperatures at 500 hPa need to be even colder as dry atmospheres require a greater lapse rate for instability than moist atmospheres. At heights near the tropopause, the 30-year average temperature (as measured in the period encompassing 1961 through 1990) was −77 °C (−132 °F). A recent example of a tropical cyclone that maintained itself over cooler waters was Epsilon of the 2005 Atlantic hurricane season. See also Global surface temperature The Blob (Pacific Ocean) Sea level rise Halocline refers to a salinity difference often altered by temperature-dependent factors Loop Current, with plots of sea temperature in the Gulf of Mexico Pacific decadal oscillation (PDO) Salinity Ghrsst-pp the Group for High Resolution SST Satellite temperature measurements Instrumental temperature record References External links Global map of current sea surface temperatures Global map of current sea surface temperature anomalies SQUAM, SST Quality Monitor (A near real-time Global QC Tool for monitoring time-series stability & cross-platform consistency of satellite SST) iQuam, in situ SST Quality Monitor (A near real-time quality control & monitoring system for in situ SST measured by ships and buoys) MICROS, Monitoring of IR Clear-sky Radiances over Oceans for SST Aquatic ecology Meteorological phenomena Marine meteorology Oceanography Thermodynamic cycles Articles containing video clips