CHEMICAL HEATING ABOVE THE POLAR MESOPAUSE IN WINTER

Abstract

Earlier predictions that the upper atmosphere at high latitudes is warmer in winter than in summer in the region between about 70 and 100 km have been verified during the IGY by direct temperature measurements with rockets. However, calculations based on radiative balance alone indicate that there should be a net loss of heat in the middle of this region of about 10?4 watts per g of air, or a rate of decrease of temperature of about 10 deg per day. It is suggested that this heat loss can be compensated by a release of the energy of recombination of atomic oxygen, which may be carried downward from higher altitudes by large-scale subsidence. (The downward transport by some sort of eddy diffusion is not ruled out.) The required release of energy can be achieved by a rate of descent of as little as 42 m per day, under optimum conditions, and is considerably more effective than adiabatic heating everywhere above 85 km. The explanation of these high winter temperatures in terms of heating by aurora1 particles is ruled out on the grounds that such a process is not a seasonal one and that aurora1 particles are generally stopped at somewhat higher altitudes.