Stratospheric Cooling

Neutrino - thanks for the correction on the lapse rate. Do I get part credit for the average lapse rate being between the wet and dry adiabatic lapse rates?

Stratospheric cooling is a complicated subject, but the dauntless Captain Imperio will attempt to oversimplify it. Think of this as a tale where our hero (the stratosphere) maintains a radiative quasi-equilibrium with three heat reservoirs: the Sun (hot), the Earth below (a little warmer than our protagonist), and space (damn cold). The ozone in the stratosphere absorbs heat from the Sun, mainly in the form of ultraviolet radiation, but infrared and visible play a role as well. It radiates heat to space, almost entirely in the form of infrared, and it receives some infrared from the Earth. Stratospheric temperature is determined by the balance of those processes.

While UV absorption is done by ozone (O3), infrared absorption and emission is the province of the greenhouse gases, especially CO2. If stratospheric ozone is depleted (as it has been over the past decades), it absorbs less solar UV, and that cools it. An increase in CO2 makes the stratosphere both a more effective radiator and absorber of infrared radiation, but since it radiates more IR than it absorbs, on balance it cools the stratosphere. The effects vary quantitatively with height, so it is possible to separate out how much each effect contributes to stratospheric cooling. A more detailed discussion is here: http://www.atmosphere.mpg.de/enid/20c.html.

Extended contemplation of figure 3 is recommended to those who would seek the higher enlightenment. When you understand why each part of the figure is the color it is, you have attained qualitative stratospheric cooling Zen. (Make sure that you grok 1050 cm^-1) Playing around with Dave Archer’s MODTRAN pony (http://geosci.uchicago.edu/~archer/cgimodels/radiation.html) also helps.

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