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Diurnal Thermal Structure of the Martian Atmosphere from MAVEN/IUVS Stellar Occultations

Loïc Verdier
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  • PersonId : 1050626
Ashwin Braude
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  • PersonId : 1059982
Franck Montmessin
Majd Mayyasi
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  • PersonId : 1032335

Abstract

Recent Mars missions have provided a wealth of observations to study the red planet and its relationship to Earth. However, only few observations of Martian upper mesosphere/lower thermosphere (~80 – 160 km) are available, a region that includes the mesopause and homopause, and is closely coupled to the atmospheric layers above and below. The existing datasets in this altitude range provide only limited temporal and spatial coverage. Stellar occultations by the Imaging Ultraviolet Spectrograph (IUVS) aboard the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission are being designed and executed in dedicated bimonthly campaigns for the last seven years to fill this observation gap. However, only the nightside observations are useable as the current data-reduction pipeline rejects any dayside occultation with stray light contamination. We have devised an improved stray light removal algorithm to process the daytime observations as well. Of the 3003 observations from March 2015 to January 2022, the reprocessed data includes 1145 dayside and 1259 nightside events, thereby resulting in the first Martian dataset that consistently measures both the dayside and the nightside mesosphere. We present the results of the study of diurnal thermal structure in ~80 – 160 km altitude range (10-6 to 10-2 Pa). The dayside is observed to be warmer than the nightside at all pressure levels, with the diurnal variations of ~30 K in the lower thermosphere, ~20 K near the mesopause, and little day/night differences at low altitudes. This is found to be consistent with short radiative time constant of the order of 1 sol, suggesting strong tidal damping. The data also shows that the regions at pressures less than 2x10-3 Pa are under strong solar control with no prominent migrating tidal signatures. Whereas, on Earth, the temperature variations due to tides are quite large near the mesopause, with radiative time constant of ~10 Earth days. The Mars Climate Database shows an opposite diurnal trend in the mesosphere, with the dayside mesopause cooler than the nightside, along with signatures of a vertically propagating tide. The IUVS dataset provides an unprecedented constraint on the structure of the Martian mesosphere. The inconsistencies with the data imply that we do not really understand the dynamics and structure of this important region.
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Dates and versions

insu-03919073 , version 1 (02-01-2023)

Identifiers

  • HAL Id : insu-03919073 , version 1

Cite

Sumedha Gupta, Roger V. Yelle, Nicholas Mccord Schneider, Sonal K. Jain, Francisco Gonzalez-Galindo, et al.. Diurnal Thermal Structure of the Martian Atmosphere from MAVEN/IUVS Stellar Occultations. AGU Fall Meeting 2022, Dec 2022, Chicago, United States. pp.P35A-06. ⟨insu-03919073⟩
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