Abstract
HDO and the D/H ratio are essential to understand Mars past and present
climate, in particular with regard to the evolution through ages of the
Martian water cycle. We present here new modeling developments of the
HDO cycle with the LMD Mars GCM. The present study aims at exploring the
behaviour of the D/H ratio cycle and its sensitivity to the modeling of
water ice clouds and the formulation of the fractionation by
condensation. Our GCM simulations are compared with observations
provided by the Atmospheric Chemistry Suite (ACS) on board the
ESA/Roscosmos Trace Gas Orbiter, and reveal that the model quite well
reproduces the temperature and water vapor fields, which offers a good
basis for representing the D/H ratio cycle. The comparison also
emphasizes the importance of modelling the effect of supersaturation,
resulting from the microphysical processes of water ice clouds, to
correctly account for the water vapor and the D/H ratio of the
middle-to-upper atmosphere. This work comes jointly with a detailed
comparison of the measured D/H profiles by TGO/ACS and the model
outputs, conducted in the companion paper of Rossi et al. 2022 (this
issue).