J.-P. Huot

Improved general circulation models of the Martian atmosphere from the surface to above 80 km

We describe a set of two “new generation” general circulation models of the Martian atmosphere derived from the models we originally developed in the early 1990s. The two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations. The vertical resolution near the surface has been refined, and the vertical domain has been extended to above 80 km. These changes are accompanied by the inclusion of state-of-the-art parameterizations to better simulate the dynamical and physical processes near the surface (boundary layer scheme, subgrid-scale topography parameterization, etc.) and at high altitude (gravity wave drag). In addition, radiative transfer calculations and the representation of polar processes have been significantly improved. We present some examples of zonal-mean fields from simulations using the model at several seasons. One relatively novel aspect, previously introduced by Wilson [1997], is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi-global, angular-momentum conserving Hadley cell which has no terrestrial equivalent. Within such a cell the Coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km. This winter polar warming had been observed but not properly modeled until recently. In fact, thermal inversions are generally predicted above one, and often both, poles around 60–70 km. However, the Mars middle atmosphere above 40 km is found to be very model-sensitive and thus difficult to simulate accurately in the absence of observations.

A climate database for Mars

A database of statistics which describe the climate and surface environment of Mars has been constructed directly on the basis of output from multiannual integrations of two general circulation models developed jointly at Laboratoire de Meteorologie Dynamique du Centre National de la Recherche Scientifique, France, and the University of Oxford, United Kingdom, with support from the European Space Agency. The models have been developed and validated to reproduce the main features of the meteorology of Mars, as observed by past spacecraft missions. As well as the more standard statistical measures for mission design studies, the Mars Climate Database includes a novel representation of large-scale variability, using empirical eigenfunctions derived from an analysis of the full simulations, and small-scale variability using parameterizations of processes such as gravity wave propagation. The database may be used as a tool for mission planning and also provides a valuable resource for scientific studies of the Martian atmosphere. The database is described and critically compared with a representative range of currently available observations.

Atmospheric hazards for entry, descent and landing of future missions to Mars: numerical simulations of fine-scale meteorological phenomena

In order to allow safe entry descent and landing, as well as mission surface operations, constraints apply to the selection of suitable landing sites. These constraints are defined in terms of general characteristics related to the specific mission profile (interplanetary transfer, waiting orbit injection and orbital waiting period and eclipse mitigation strategies) and to the EDL operations (entry conditions and environment, safe operation of the descent system with parachute deceleration, controlled rockets braking, touchdown with vented airbags). Most constraints are relative to « static » properties such as the geographical location, the altimetry, and the soil thermophysical constants. Few constraints are relative to the « dynamical » properties of the atmosphere, i.e. meteorological variations of density, temperature and winds, notwithstanding these are the most crucial characteristics to predict so as to ensure the success of the EDL phase. Martian mesoscale and microscale meteorological models are one of the relevant tools that can be used to predict the local and regional meteorological variability likely to be encountered at several proposed landing ellipses during Entry, Descent, and Landing. Most of the atmospheric hazards in the Martian lower atmosphere are not evident in current observational data and general circulation model simulations and can only be ascertained through mesoscale modeling of the region. The Laboratoire de Meteorologie Dynamique (LMD) Mesoscale Model is a versatile simulator of the Martian atmosphere and environment at horizontal scales ranging from hundreds of kilometers to tens of meters. Specific simulations with relevancy to assessment of atmospheric hazards possibly encountered in Martian landing sites can be carried out with such a tool. The need for accurate and realistic Martian mesoscale modeling remains critical for the design of upcoming missions to Mars (e.g., Mars Science Laboratory, ExoMars).