Extension of atmospheric dust loading to high altitudes during the 2001 Mars dust storm: MGS TES limb observations

Abstract

Mars Global Surveyor (MGS) visible (solarband bolometer) and thermal infrared (IR) spectral limb observations from the Thermal Emission Spectrometer (TES) support quantitative profile retrievals for dust opacity and particle sizes during the 2001 global dust event on Mars. The current analysis considers the behavior of dust lifted to altitudes above 30 km during the course of this storm; in terms of dust vertical mixing, particle sizes, and global distribution. TES global maps of visible (solarband) limb brightness at 60 km altitude indicate a global-scale, seasonally evolving (over 190–240° solar longitudes, L S ) longitudinal corridor of vertically extended dust loading (which may be associated with a retrograde propagating, wavenumber 1 Rossby wave). Spherical radiative transfer analysis of selected limb profiles for TES visible and thermal IR radiances provide quantitative vertical profiles of dust opacity, indicating regional conditions of altitude-increasing dust mixing ratios. Observed infrared spectral ( λ = 5 – 40 μ m ) dependences and visible-to-infrared opacity ratios of dust scattering over 30–60 km altitudes indicate particle sizes characteristic of lower altitudes (cross-section weighted effective radius, r eff = 1.5 – 2.0 μ m ), during conditions of significant dust transport to these altitudes. Conditions of reduced dust loading at 30–60 km altitudes present smaller dust particle sizes ( r eff ∼ 0.5 – 1.0 μ m ) . These observations suggest rapid meridional transport at 30–80 km altitudes, with substantial longitudinal variation, of dust lifted to these altitudes over southern hemisphere atmospheric regions characterized by extraordinary (m/s) vertical advection velocities. By L S = 230 ° dust loading above 50 km altitudes decreased markedly at southern latitudes, with a high altitude (60–80 km) haze of fine (likely) water ice particles appearing over 10°S–40°N latitudes.