RADIATIVE ENERGY-BALANCE OF CO2 NON-LTE INFRARED EMISSIONS IN THE MARTIAN ATMOSPHERE

A new non-LTE radiative transfer model has been applied to study the r adiative cooling and heating rates induced by the infrared emissions i n the martian atmosphere. The cooling rate produced by the CO2 15-mu m bands, for the revised COSPAR mean reference temperature and recent v alues for CO2-O(P-3) collisions, is very large in the upper mesosphere and thermosphere, reaching values about 300 K/day between 115 and 145 km. The greater part of the cooling rate above about 120 km is due to the 15-mu m fundamental band. In the upper mesosphere and part of the lower thermosphere (70-100 km), vibrational-vibrational collisions ma ke the isotopic and hot bands produce much larger contributions than t he fundamental band. The solar heating rate has been calculated, and a detailed analysis of the radiative and collisional paths followed by the solar energy from its initial absorption until its final thermaliz ation is presented. It is found to be negligible above about 140 km an d reaches a maximum value of 190 K/day in the upper mesosphere (65-95 km) at the subsolar point. The absorption in the 2.7-mu m bands is the most important source of solar infrared heating above 50 km. The sola r radiation in the weak near-infrared (lambda less than or equal to 2 pm) bands plays a relevant role in the heating of lower layers of the middle atmosphere (45-65 km). Absorption in the 4.3-mu m bands is impo rtant only below 50 km. A sensitivity study of the cooling rates at 15 mu m shows that thermal collisions of CO2(nu(2)) with CO2 and O(P-3) are of most importance. The solar heating rates are mainly influenced by the deactivation rate of CO2(nu(2)) by O(P-3) and the vibrational r elaxation of the high-energetic combinational levels. Direct effects o f kinetic temperature are very large on the cooling rate of the upper mesosphere and lower thermosphere (70-120 km), and of small significan ce for the solar heating rates. The atmospheric density changes produc ed by kinetic temperature variations give rise to very important effec ts on the cooling and heating rates. A global mean radiative equilibri um temperature profile for the mesosphere and lower thermosphere is al so presented and discussed. (C) 1995 Academic Press, Inc.