TITLE:
  Non-LTE radiative mesospheric study for Mars Pathfinder Entry

AUTHORS:
  Lopez-Valverde, M. A., R. M. Haberle and M. Lopez-Puertas 

REFERENCE:
  Icarus, in press, 2000


ABSTRACT:

Detailed calculations of thermal cooling and solar heating rates under
non-local 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 1994a,b 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(nu2) by O(3P). 
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 downwards as the optical thickness at 15-mu 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).