Water heavily fractionated as it ascends on Mars as revealed by ExoMars/NOMAD

sotopic ratios and, in particular, the water D/H ratio are powerful tracers of the evolution and transport of water on Mars. From measurements performed with ExoMars/NOMAD, we observe marked and rapid variability of the D/H along altitude on Mars and across the whole planet. The observations (from April 2018 to April 2019) sample a broad range of events on Mars, including a global dust storm, the evolution of water released from the southern polar cap during southern summer, the equinox phases, and a short but intense regional dust storm. In three instances, we observe water at very high altitudes (>80 km), the prime region where water is photodissociated and starts its escape to space. Rayleigh distillation appears the be the driving force affecting the D/H in many cases, yet in some instances, the exchange of water reservoirs with distinctive D/H could be responsible

The PROMOTE 3D ozone record service: Overview and first evaluation of stratospheric ozone reanalyzes based on satellite observations between 1992 and 2004

Data assimilation of atmospheric constituents is becoming more and more important as the number and quality of satellite observations increases. New assimilation methods allow us to derive continuous four-dimensional depictions of the atmos-phere’s chemical state. Within the European ESA/GMES project PROMOTE three CTM-based assimilation systems have been applied to derive long-term records of stratospheric ozone and related species from UARS/MLS, ERS2-GOME/NNORSY and ENVISAT/MIPAS ozone observations covering a time period from 1992 to 2004. Using ROSE/DLR (sequential), SACADA and BASCOE (both 4D-VAR) daily chemi-cal analyzes and error statistics have been generated. We present first validation re-sults using independent ground-based and satellite observations. With respect to cli-mate research the benefit of data assimilation is sometimes called into question: e.g., forcing the model with observations may lead to inconsistencies in derived parame-ters, e.g. chemical ozone depletion rates. By means of cross-comparison we there-fore discuss the possible model influence on final analysis results. We show that in most cases results are highly consistent showing errors well within expected error bars. However, under certain conditions and/or if observational coverage is poor, e.g., at the polar vortex edge during spring, specific model limitations have to be ad-dressed and taken into account. Concerning stratospheric ozone, we discuss the ap-plicability and potential of the PROMOTE data record for the SPARC community

Impact of gradients at the martian terminator on the retrieval of ozone from SPICAM/MEx

International audienceRapid variations of pressure, temperature and illumination at the day-night terminator have the potential to cause asymmetries in the abundance distribution of the atmosphere constituents along the line of sight (LOS) of a solar occultation experiment. Ozone, in particular, displays steep density gradients across the terminator of Mars due to photolysis. Nowadays, most of the retrieval algorithms for solar and stellar occultations rely on the assumption of a spherically symmetrical atmosphere. However, photochemically induced variations near sunrise/sunset conditions need to be taken into account in the retrieval technique in order to prevent inaccuracies.We investigated the impact of gradients along the LOS of the solar occultation experiment SPICAM/Mars Express for the retrieval of ozone under sunrise/sunset conditions. In order to test the impact of different gradients, we selected four occultations at sunrise and at sunset each. Sunset occultations are located near the equator, while sunrise observations are situated at high latitudes in the South, because of the geometry of the orbit.We used the diurnal variations in the ozone concentration obtained from a three-dimensional General Circulation Model (GEM-Mars) together with an adapted radiative transfer code (ASIMUT). The General Circulation Model (GCM) suggests that ozone variations strongly depend on latitude, altitude, and season. As shown by the model, near the equator and below 25 km, ozone changes only slightly with local time. Around 45 km, the density changes by several orders of magnitude across the terminator. At high latitudes in the South, during northern winter time, ozone variations at the terminator are negligible.The impact of gradients on ozone retrievals is strongly related to the local atmospheric structure as predicted by the GCM. Sunset ozone retrievals are smaller than retrievals obtained assuming a spherically symmetrical atmosphere , with a maximum change of about 20%. At sunrise, the impact of gradients on the retrievals is negligible. This behavior can be explained by the specific geometry of sunrise observations, all situated at high latitudes in the South

Probing the Atmospheric Cl Isotopic Ratio on Mars: Implications for Planetary Evolution and Atmospheric Chemistry

Following the recent detection of HCl in the atmosphere of Mars by ExoMars/Trace Gas Orbiter, we present here the first measurement of the 37Cl/35Cl isotopic ratio in the Martian atmosphere using a set of Nadir Occultation for MArs Discovery (NOMAD) observations. We determine an isotopic anomaly of −6 ± 78‰ compared to Earth standard, consistent with the −51‰–−1‰ measured on Mars’ surface by Curiosity. The measured isotopic ratio is also consistent with surface measurements, and suggests that Cl reservoirs may have undergone limited processing since formation in the Solar Nebula. The examination of possible sources and sinks of HCl shows only limited pathways to short‐term efficient Cl fractionation and many plausible reservoirs of “light” Cl