Radiative Transfer Modeling of the Martian Atmosphere

Introduction: Studies of the past and current climate and weather on Mars depend on accurate calculations of the radiative properties of the Martian atmosphere. Atmospheric and Environmental Research, Inc. (AER) is the source of the state-of-the-science radia-tive transfer codes for terrestrial applications [1] and these models are continuously updated and validated [2]. Recently, they have been modified to extend their applicability to conditions other than found on current-day Earth, such as those relevant to paleo-Earth and current and ancient Mars. This presentation will describe these developments, in the hope that they will contribute to achieving broad Mars research and exploration goals via modeling and remote sensing. LBLRTM: In our radiative transfer work, AER's well-known LBLRTM model [1, 2] serves as the foun-dational line-by-line reference. LBLRTM participates in ongoing radiative closure studies [3, 4] enabling it to be quickly and rigorously updated as our knowledge of the fundamental spectroscopic parameters improves. A recent example involves the implementation of new P and R branch line coupling coefficients for CO 2 [5, 6]. The inclusion of this work in the EOS-Aura Tropo-spheric Emission Spectrometer forward model (for which AER has primary responsibility [7]) has led to improvements in the atmospheric temperature retrievals in the most recent data version release. Of particular relevance to the proposed work is our ongoing NASA-funded work that has enhanced the capabilities of LBLRTM specifically for the development of GCM-suitable radiation codes for studies of the climate of paleo-Earth,-Mars, and other terrestrial planets. This development has involved a number of upgrades to the model. First, newly calculated CO 2-broadened line parameters (half-widths, line shifts, and temperature dependence of widths) of water vapor lines [8, 9] have been incorporated. Since these calculations did not cover numerous water vapor lines of interest (e.g. near-infrared bands, weaker lines, most isotopologues), a scheme was developed to estimate the CO 2-broadened line parameters of these lines. Second, the water vapor continuum model, MT_CKD [1] has been adjusted to account for the difference between air-and CO 2-broadening of water vapor lines and their relative efficiency in generating collision-induced absorption. Finally, the CO 2 collision-induced absorption parameterization presented in [10] has been added to the MT_CKD continuum model. In our presentation , we will provide details of these modifications and their effect on the relevant radiative transfer calculations. For example, preliminary results indicate a change of 10-20% in the retrieved column water vapor