Carbon Dioxide Retrievals From NOMAD‐SO on ESA's ExoMars Trace Gas Orbiter and Temperature Profile Retrievals With the Hydrostatic Equilibrium Equation: 2. Temperature Variabilities in the Mesosphere at Mars Terminator

Abstract

The Solar Occultation (SO) channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument scans the Martian atmosphere since 21 April 2018. In this work, we present a subset of the NOMAD SO data measured at the mesosphere. We focused on a spectral range that started to be recorded in Martian year (MY) 35. A total of 968 vertical profiles of carbon dioxide density and temperature covering MY 35 and the beginning of MY 36 were investigated until 135° of solar longitude. We compared 47 profiles with co‐located profiles of the Mars Climate Sounder onboard the Mars Reconnaissance Orbiter. Most profiles show a good agreement as SO temperatures are only 1.8 K higher, but some biases lead to an average absolute difference of 7.4°K. The SO data set is also compared with simulations from the Global Environmental Multiscale‐Mars general circulation model. Both data sets are in good agreement except for the presence of a cold layer in the winter hemisphere and a warm layer at dawn in the Northern hemisphere for solar longitudes between 240° and 360°. Five profiles contain temperatures lower than the limit for CO2 condensation. Strong warm layers were found in 13.5% of the profiles. They are present mainly at dawn and in the winter hemisphere, while the Northern dusks appear featureless. The data set mainly covers high latitudes around 60° and we derived some non‐migrating tides. In the Southern winter hemisphere, we derived apparent zonal wavenumber‐1 (WN‐1) and WN‐3 tidal components with a maximum amplitude of 10% and 5% at 63 km, respectively.

Carbon Dioxide Retrievals From NOMAD‐SO on ESA's ExoMars Trace Gas Orbiter and Temperature Profiles Retrievals With the Hydrostatic Equilibrium Equation: 1. Description of the Method

“…In this first part of a series of two papers dedicated to the observation of CO 2 and temperature from NOMAD-SO observations, we focused on the description of the method and in particular the vertical inversion from slant quantities to vertical local quantities. In the second part of this series (Trompet et al (2023), hereafter called Part II), we will investigate in more detail the results concerning CO 2 and temperature, looking at latitudinal and time variations, as well as comparing them with other instruments' results and GCM. In addition, a companion paper by López-Valverde et al (2022) this issue presents another analysis of temperatures and densities, although focused on MY34.…”

“…In the second part of this series (Trompet et al. (2023), hereafter called Part II), we will investigate in more detail the results concerning CO 2 and temperature, looking at latitudinal and time variations, as well as comparing them with other instruments' results and GCM. In addition, a companion paper by López‐Valverde et al.…”

Depletion of 13C in CO in the Atmosphere of Mars Suggested by ExoMars-TGO/NOMAD Observations

“…The vertical resolution on the temperature profiles is on average around 1.6 km and the uncertainty is about 5 K, which is the total error including the regularization error and the retrieval noise error (Trompet et al 2022a). A comparison between the NOMAD temperature retrievals and those by the Mars Climate Sounder (MCS) on board the Mars Reconnaissance Orbiter shows that the difference is within 5 K (see Figure 2 of Trompet et al 2022b). Even though the number of the orbits for the comparison is not so large (only 47 profiles), it suggests that if there is a systematic bias in the temperature retrievals, which should be less than 5 K. The upper boundary of the temperature profiles (z top ) is controlled by the disappearance of the CO 2 lines, while the lower boundary (z bot ) is controlled by the reduction of the baseline due to the aerosols or the saturation of the CO 2 lines (see Supp.…”