2023 (JGR) https://doi.org/10.1029/2022EA002429
A. Piccialli, A. C. Vandaele, Y. Willame, A. Määttänen, L. Trompet, J. T. Erwin, F. Daerden, L. Neary, S. Aoki, S. Viscardy, I. R. Thomas, C. Depiesse, B. Ristic, J. P. Mason, M. R. Patel, M. J. Wolff, A. S. J. Khayat, G. Bellucci, J.-J. Lopez-Moreno
The NOMAD-UVIS instrument on board the ExoMars Trace Gas Orbiter has been investigating the Martian atmosphere with the occultation technique since April 2018. Here, we analyze almost two Mars Years of ozone vertical distributions acquired at the day-night terminator. The ozone retrievals proved more difficult than expected due to spurious detections of ozone caused by instrumental effects, high dust content, and very low values of ozone. This led us to compare the results from three different retrieval approaches: (a) an onion peeling method, (b) a full occultation Optimal Estimation Method, and (c) a direct onion peeling method. The three methods produce consistently similar results, especially where ozone densities are higher. The main challenge was to find reliable criteria to exclude spurious detections of O3, and we finally adopted two criteria for filtering: (a) a detection limit, and (b) the Δχ2 criterion. Both criteria exclude spurious O3 values especially near the perihelion (180° < Ls < 340°), where up to 98% of ozone detections are filtered out, in agreement with general circulation models, that expect very low values of ozone in this season. Our agrees well with published analysis of the NOMAD-UVIS data set, as we confirm the main features observed previously, that is, the high-altitude ozone peak around 40 km at high latitudes. The filtering approaches are in good agreement with those implemented for the SPICAM/MEx observations and underline the need to evaluate carefully the quality of ozone retrievals in occultations.
Seasonal evolution of FOEM ozone abundance observed by NOMAD-UVIS for different latitude ranges. Left panels show the ozone retrievals without any filtering; in the middle panels we applied the DL filter; and in the right panels we applied both the DL and Δχ2 filters.
2023 (JGR) https://doi.org/10.1029/2022JE007279
L. Trompet, A.C. Vandaele, I. Thomas, S. Aoki, F. Daerden, J. Erwin, Z. Flimon, A. Mahieux, L. Neary, S. Robert, G. Villanueva, G. Liuzzi, Lopez Valverde, A. Brines, G. Bellucci, J. J. Lopez-Moreno, M. R. Patel
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 are investigated until 135° of solar longitude. We compared 47 profiles with co-located profiles of Mars Climate Sounder onboard 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 dataset is also compared with simulations from GEM-Mars general circulation model. Both datasets 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° to 360°. Five profiles contain temperatures lower than the limit for CO2 condensation. Strong warm layers are 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 dataset mainly covers high latitudes around 60° and we derived some non-migrating tides. In the Southern winter hemisphere, we derived apparent zonal wavenumber-1 and wavenumber-3 tidal components with a maximum amplitude of 10% and 5% at 63 km, respectively.
Panel a) six temperature profiles for diffraction order 148 with some values lower than the temperature limit for CO2
condensation. Panel b) transmittances at pixel 180 corresponding to the profiles in panel a. The second Y-axis provides rough
JGR (2022), https://doi.org/10.1029/2022JE007273
A. Brines, M. A. López-Valverde, A. Stolzenbach, A. Modak, B. Funke, F. G. Galindo, S. Aoki, G. L. Villanueva, G. Liuzzi, I. R. Thomas, J. T. Erwin, U. Grabowski, F. Forget, J. J. Lopez-Moreno, J. Rodriguez-Gomez, F. Daerden, L. Trompet, B. Ristic, M. R. Patel, G. Bellucci, A. C. Vandaele
The water vapor in the Martian atmosphere plays a significant role in the planet’s climate, being crucial in most of the chemical and radiative transfer processes. Despite its importance, the vertical distribution of H2O in the atmosphere has not still been characterized precisely enough. The recent ExoMars Trace Gas Orbiter (TGO) mission, with its Nadir and Occultation for MArs Discovery (NOMAD) instrument, has allowed us to measure the H2O vertical distribution with unprecedented resolution. Recent studies of vertical profiles have shown that high dust concentration in the atmosphere, in particular during dust storms, induces an efficient transport of the H2O to higher altitudes, from 40 km up to 80 km. We study the H2O vertical distribution in a subset of solar occultations during the perihelion of two Martian years (MYs), including the 2018 Global Dust Storm (GDS), in order to compare the same Martian season under GDS and non-GDS conditions. We present our state-of-the-art retrieval scheme, and we apply it to a combination of two diffraction orders, which permits sounding up to about 100 km. We confirm recent findings of H2O increasing at high altitudes during Ls = 190-205° in MY 34, reaching abundances of about 150 ppmv at 80 km in both hemispheres not found during the same period of MY 35. We found a hygropause’s steep rising during the GDS from 30 up to 80 km. Furthermore, strong supersaturation events have been identified at mesospheric altitudes even in presence of water ice layers retrieved by the IAA team.
Seasonal vertical distribution maps of the retrieved water vapor (b,d) during the MY 34 in the Northern (left panels) and the Southern (right panels) hemispheres. The red line indicates the hygropause level. Top panels (a,c) show the latitudes and the Local Solar Time of the observations analyzed.
JGR (2023) https://doi.org/10.1029/2022JE007277
L. Trompet, A.C. Vandaele, I. Thomas, S. Aoki, F. Daerden, J. Erwin, Z. Flimon, A. Mahieux, L. Neary, S. Robert, G. Villanueva, G. Liuzzi, Lopez-Valverde, A. Brines, G. Bellucci, J. J. Lopez-Moreno, M. R. Patel
The SO (Solar Occultation) channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument has been scanning the Martian atmosphere for almost two Martian years. In this work, we present a subset of the NOMAD SO data measured at the mesosphere at the terminator. From the dataset, we investigated 968 vertical profiles of carbon dioxide density and temperature covering Martian Year (MY) 35 as well as MY 36 up to a solar longitude (Ls) of 135° and altitudes around 60 km to 100 km. While carbon dioxide density profiles are directly retrieved from the spectral signature in the spectra, temperature profiles are more challenging to retrieve as unlike density profiles, temperature profiles can present some spurious features if the regularization is not correctly managed. Comparing seven regularization methods, we found that the expected error estimation method provides the best regularization parameters. The vertical resolution of the profiles is on average 1.6 km. Numerous warm layers and cold pockets appear in this dataset. The warm layers are found in the Northern hemisphere at dawn and dusk as well as in the Southern hemisphere at dawn. Strong warm layers are present in more than 13.5% of the profiles. The Southern hemisphere at dusk does not present any warm layer between Ls 50° and 150°. The height and latitudinal distribution of those warm layers are similar in MY 35 and MY 36 during the first half of the year (Ls=0 - 135°).
Retrieved temperature for a pressure of 0.1 Pa over MY 35 and MY 36 until Ls 135° as a function of solar longitude (panels a and b), as a function of local solar time (panel c), and as a function of latitude (panel d). In Panel a, the color code corresponds to the solar local time, and in panel b to the latitude. Local solar time and latitudinal trends are present in panels a and b.
JGR (2002); https://doi.org/10.1029/2022JE007278
Miguel-Angel López Valverde, Bernd Funke, Adrian Brines, Aurèlien Stolzenbach, Ashimananda Modak, Brittany Hill, Francisco González-Galindo, Ian Thomas, Loic Trompet, Shohei Aoki, Gerónimo Villanueva, Giuliano Liuzzi, Justin Erwin, Udo Grabowski, Francois Forget, José Juan Lopez Moreno, Julio Rodriguez-Gómez, Bojan Ristic, Frank Daerden, Giancarlo Bellucci, Manish Patel, Ann-Carine Vandaele, the NOMAD team
We present vertical profiles of temperature and density from solar occultation (SO) observations by the “Nadir and Occultation for Mars Discovery” (NOMAD) spectrometer on board the Trace Gas Orbiter (TGO) during its first operational year, which covered the second half of Mars Year 34. We used calibrated transmittance spectra in 380 scans, and apply an in-house pre-processing to clean data systematics. Temperature and CO2 profiles up to about 90 km, with consistent hydrostatic adjustment, are obtained, after adapting an Earth-tested retrieval scheme to Mars conditions. Both pre-processing and retrieval are discussed to illustrate their performance and robustness. Our results reveal the large impact of the MY34 Global Dust Storm (GDS), which warmed the atmosphere at all altitudes. The large GDS aerosols opacity limited the sounding of tropospheric layers. The retrieved temperatures agree well with global climate models (GCM) at tropospheric altitudes, but NOMAD mesospheric temperatures are wavier and globally colder by 10 K in the perihelion season, particularly during the GDS and its decay phase. We observe a warm layer around 80 km during the Southern Spring, especially in the Northern Hemisphere morning terminator, associated to large thermal tides, significantly stronger than in the GCM. Cold mesospheric pockets, close to CO2 condensation temperatures, are more frequently observed than in the GCM. NOMAD CO2 densities show oscillations upon a seasonal trend that track well the latitudinal variations expected. Results uncertainties and suggestions to improve future data re-analysis are briefly discussed.
Temperature latitude-solar longitude cross sections at 3 different altitudes, 30 km (left panels), 50 km (central column’s panels) and 80 km (right-hand panels). The retrieved temperatures are shown in the central row, while Latitude-Ls cross sections from the LMD-MGCM are shown in the top panel, for reference.
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