An inversion is a departure from the usual decrease or increase with altitude of the value of an atmospheric property. Most of the time in meteorology, an inversion refers to an increase in temperature with height. Temperature inversions occur when the air above a certain level is warmer than the air below.
2 Main Types
• Subsidence Inversions - An increase in temperature with height that develops aloft as a result of air gradually sinking over a wide area and being warmed by adiabatic compression. This inversion is enhanced by vertical mixing in the air layer below the inversion. They typically form in regions of large scale sinking motion.
Figure 7.This sounding is an example of a subsidence inversion.
• Radiation Inversions – Form when the lowest levels of the atmosphere are cooled by contact with the earth’s surface, which cools by emitting radiation.
Some factors which help a radiation inversion to form include:
- calm winds
- dry air
- clear skies
- long nights
- surface wetness
- surface type
Figure 8. This sounding is an example of a radiation inversion.
Figure 9. This diagram shows the set-up of a radiation inversion (red line) during a clear, cold night. The blue dotted line shows the location of the temperature curve during the daytime hours.
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“Factors Promoting Radiation Inversion Formation.” Department of Atmospheric Sciences – Lyndon State College. 2006. http://apollo.lsc.vsc.edu/classes/met130/notes/chapter3/rad_invers2.html
American Meteorological Society. Glossary of Meteorology Online. Allen Press. 2005. http://amsglossary.allenpress.com/glossary
Skew-T Analysis Cards -- Inversions. Airmap Wx Toolbox. 2003. http://www.ccrc.sr.unh.edu/~stm/AS/Weather_Toolbox/Skew_T.html#Inversions