Soutenance publique de thèse de doctorat en Sciences physiques - Loïc TROMPET

First analysis of the spectra obtained from the NOMAD instrument onboard ESA’s Trace Gas Orbiter

Jury

Prof. Luc HENRARD (département de physique, UNamur), président
Prof. Muriel LEPERE (département de physique, UNamur), promotrice et secrétaire
Dr Ir Ann Carine VANDAELE (Institut royal d’Aéronomie spatiale de Belgique), co-promotrice
Dr Miguël DHYNE (département de physique, UNamur)
Pr.Dr Jean-Claude GERARD (Université de Liège)
Dr Miguel Ángel LOPEZ-VALVERDE (Instituto de Astrofísica de Andalucia)

Abstract

 

Since April 2018, the Nadir and Occultation for Mars Discovery (NOMAD) instrument on board ESA’s Trace Gas Orbiter has been continuously recording measurements of the atmosphere of Mars. This work focuses on the deduction of vertical profiles (slices of the atmosphere for a range of altitudes) of carbon dioxide density and temperature from the Solar Occultation (SO) channel of NOMAD. Those profiles are necessary to constrain our knowledge of the atmosphere of Mars. They are also necessary for the deduction of the density of other species such as water and carbon monoxide. In remote sensing, this deduction is called a "retrieval" and is an inverse problem, involving the regularisation of the retrieved profiles. The regularisation is performed in this work with the Tikhonov method and the best fine-tuning of this regularisation is achieved with the Expected Error Estimation. Carbon dioxide density profiles are directly retrieved from the spectra of NOMAD-SO while temperature is retrieved from the latter and the hydrostatic equilibrium equation. Up to 1848 profiles of carbon dioxide density and temperature have been retrieved from April, 21st 2018 until December 26th, 2022 and this dataset covers more than two Martian years. Several results will be presented such as the seasonal, latitudinal, longitudinal, and diurnal variations of CO2 density and temperature at the terminator of Mars, focusing on the mesosphere (extending from 50 to 100 km). Specific trends have been identified, such as the CO2 seasonal cycle, the variation with Hadley circulation cells, the polar warmings, and warm and cold pockets. The latter sometimes bear the presence of CO2 ice clouds and their presence is reported. Some strong warm layers are present in the Northern hemisphere at both dawn and dusk and have particularly high amplitudes in the Southern hemisphere at dawn but are absent in the Southern hemisphere at dusk. We also notice strong longitudinal variations which seem to be related to atmospheric tides.

 

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