Non-LTE radiative mesospheric study for Mars Pathfinder entry

Detailed calculations of thermal cooling and solar heating rates under nonlocal thermodynamic equilibrium (non-LTE) situations have been conducted in order to analyze the atmospheric structure measured by the ASI/MET instrument during the Mars Pathfinder entry into the martian atmosphere. A time-marching version of the non-LTE model of Lopez-Valverde and Lopez-Puertas (1994, J. Geophys. Res. 99, 13,093-13,115) has been developed and used to evaluate the diurnal forcing by the CO2 near-IR bands. Allowance is made for uncertainties in the abundance of atomic oxygen and the rate coefficient of collisional deactivation of CO2(nu(2)) by O(P-3). The results indicate that a mesosphere (60-120 km) in radiative equilibrium should experience a large daily temperature variation, with a maximum change over 30 K between 90 and 110 km, Radiative lifetimes and instantaneous damping rates of simulated disturbances produced by atmospheric waves are also computed throughout that region. These depend on the thermal structure and, therefore, follow a similar daily cycle in response to the solar heating of the martian mesosphere. Values of a couple of hours and less than an hour are typical between 80 and 105 km during nighttime and daytime, respectively, increasing downward as the optical thickness at 15 mu m increases. Above 90 km, radiative relaxation times do not decrease with height, in clear contrast to the LTE approximation. On the basis of these calculations we conclude that the different temperatures between Viking and Pathfinder could be explained by a radiatively driven martian mesosphere, especially in the upper part of this region (90-120 km). (C) 2000 Academic Press.