Global characterization of the Martian global dust optical depth with 2.7 μm observations by OMEGA/MEx - INSU - Institut national des sciences de l'Univers
Communication Dans Un Congrès Année : 2024

Global characterization of the Martian global dust optical depth with 2.7 μm observations by OMEGA/MEx

Résumé

Dust is a key parameter of the Martian atmosphere, controlling its heating through direct absorption of solar radiation. The quality of dust is not constant in time and space, and dust storms explain part of this variability. Local dust storms, occurring at scales below 1.6 × 10 6 km 2 , have been suggested to develop into vertical dust transport movements that reach high altitudes, such as rocket dust storms [1,2]. Local dust storms can also coalesce and develop into regional dust storms [3,4,5,6]. Dust storms, notably regional dust storms larger than 1.6×10 6 km 2 have been frequently investigated by visible observations from orbiters [6,7]. However, spectroscopic observations of dust storms, notably local dust storms, are more limited, and no statistical studies have been conducted on such datasets yet. We successfully retrieved dust optical depth and statistically detected local dust storms using observation data from the Mars Express during Martian years (MY) 27-29, which was equipped with the high-resolution Near-Infrared Spectrometer OMEGA. We then conducted a statistical analysis of local dust storms over three Martian years, including MY28 when a global dust storm occurred, investigating their occurrence locations and frequencies.

Method: In this analysis, we developed a new method to retrieve the dust optical depth using the atmospheric 2.77 μm CO2 absorption band. Typically, this band saturates during nadir observations when surface pressures is greater than approximately 400 Pa in the Martian environments, resulting in almost zero observed radiance under low dust conditions. However, when the aerosols are lifted into the atmosphere, reflected sunlight by aerosols can be detected in nadirobservations. We utilized this technique to retrieve dust optical depth in the atmosphere using the L-channel of OMEGA at 2.77 μm used here. For the retrievals of the dust optical depth, we employed a Look-up-table method [8,9] that calculates many synthetic spectra at 2.77 μm in advance for tabulated grid values of physical parameters (such as dust opacity, observing geometry, atmospheric temperature, etc) by DISORT radiative transfer module [10] implemented in the ARS code [11]. With this method, an instantaneous retrieval of dust optical depth is possible by comparing them with observed spectra.

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Dates et versions

insu-04682905 , version 1 (31-08-2024)

Identifiants

Citer

A Kazama, S Aoki, Yann Leseigneur, M Vincendon, Thomas Gautier, et al.. Global characterization of the Martian global dust optical depth with 2.7 μm observations by OMEGA/MEx. Tenth International Conference on Mars, Jul 2024, Pasadena, United States. pp.LPI Contribution No. 3007, 2024, id.3103. ⟨insu-04682905⟩
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