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 radiative cooling and heating rates induced by the infrared emissions in the martian atmosphere. The cooling rate produced by the CO2 15-mu m bands, for the revised COSPAR mean reference temperature and recent values 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 make the isotopic and hot bands produce much larger contributions than the 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 thermalization is presented. It is found to be negligible above about 140 km and 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 solar 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 important 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 relaxation of the high-energetic combinational levels. Direct effects of kinetic temperature are very large on the cooling rate of the upper mesosphere and lower thermosphere (70-120 km), and of small significance for the solar heating rates. The atmospheric density changes produced by kinetic temperature variations give rise to very important effects on the cooling and heating rates. A global mean radiative equilibrium temperature profile for the mesosphere and lower thermosphere is also presented and discussed. (C) 1995 Academic Press, Inc.