High Altitude Dust Global Distribution , Vertical Mixing , and Particle Sizes during the 2001 Planet - Encircling Dust

Introduction: Dust aerosols are observed to extend to high altitudes during planetary-scale dust storms [1-4]. Most recent GCM modeling of vertically extensive dust loading over the course of such storms indicates that dust particles with radii of 1-2 µm may be lifted to altitudes above 40 km, and their vertical distributions strongly affected by vigorous meridional transport which is intensified by the resulting dust absorption of solar flux [5]. Here we present a multiple scattering, spherical radiative transfer (RT-[6]) analysis of Mars Global Surveyor (MGS) TES (Thermal Emission Spectrometer [7]) solarband bolometer and thermal infrared spectral limb observations, taken during the 2001 planet-encircling dust storm (starting around Mars solar longitude, L s , 185° [8, 9]). The latitude longitude distribution of TES solarband limb brightness at 60 km tangent altitudes is displayed versus L s to illustrate the evolving global pattern of high altitude dust loading in the context of lower atmos-phertic dust lifting/dust columns. Retrievals for dust mixing ratio and particle size vertical profiles are performed for selected locations and periods. TES Solarband and Thermal IR Limb Observations: TES limb observations provide vertical profiles of solar bolometric (0.3-3.0 µm, µ≈0.7 µm) and thermal IR spectral (6-50 mµ) radiance profiles with 10-15 km vertical resolution [7]. TES limb observations were obtained daily with coarse global mapping coverage (10-20° latitude, 30° longitude), and so characterize the three dimensional distribution of dust aerosol loading in the global Mars atmosphere versus time [8]. The combined visible/IR spectral coverage of TES limb observations further supports retrievals of dust and ice aerosol extinction opacity and particle size profiles [10]. Dust particle size constraints are limited for altitudes above 30 km (e.g., [11]), where variations associated with rapid gravitational settling rates are expected to be most important. Measurements of visible-to-IR dust opacity ratios, which have provided quatita-tive particle sizes for lower atmospheric dust columns [12-13], are essential for determinations of dust particle size profiles from TES limb observations. Spherical RT analysis of TES Limb Observations: Combined RT analysis of TES solarband and thermal IR limb observations requires self-consistent spherical, multiple scattering treatment of atmospheric scattering and emission by dust aerosols. In concert