An analysis is carried out of the hydrologic response of a water-rich Mars to climate change and to the physical and thermal evolution of its crust, with particular attention given to the potential role of the subsurface transport, assuming that the current models of insolation-driven change describe reasonably the atmospheric leg of the planet's long-term hydrologic cycle. Among the items considered are the thermal and hydrologic properties of the crust, the potential distribution of ground ice and ground water, the stability and replenishment of equatorial ground ice, basal melting and the polar mass balance, the thermal evolution of the early cryosphere, the recharge of the valley networks and outflow, and several processes that are likely to drive the large-scale vertical and horizontal transport of H2O within the crust. The results lead to the conclusion that subsurface transport has likely played an important role in the geomorphic evolution of the Martian surface and the long-term cycling of H2O between the atmosphere, polar caps, and near-surface crust.

A model for the hydrologic and climatic behavior of water on Mars

The behavior of Mars as observed by the Viking infrared thermal mapper (IRTM) is considered. The IRTM is a 28-channel, 4-telescope radiometer that operated in six spectral bands. The studies considered include observations from the interplanetary phase through data collection on November 7, 1976. During this interval, thermal mapping of the whole Martian surface has been possible. Attention is given to polar temperatures, global albedos, predawn temperatures, a thermal inertia contour map, geometry considerations, clouds, aspects of predawn warming, and observations of earth.

Thermal and albedo mapping of Mars during the Viking primary mission

Direct measurements of the optical depth above the two Viking landers are presented for a period covering the summer, fall, and winter seasons in the Northern Hemisphere, a time period during which two global dust storms occurred. The data are used to define the properties of suspended dust particles in the Martian atmosphere and to assess their role in a number of meteorological and geological processes. Major conclusions are that (1) both the radiative effects of dust particles and the thermodynamical effects of large-scale atmospheric motions have a significant impact on the vertical temperature structure; (2) Pertinent feedback effects play an important part in the generation of some local dust storms, in the expansion of local dust storms to global proportions, and in the subsequent decay of global dust storms; (3) An important mechanism for the removal of dust particles from the atmosphere is the CO2 condensation-sedimentation process; and (4) that the polar laminae are constructed from atmospheric dust and water ice is hypothesized.

Properties and effects of dust particles suspended in the Martian atmosphere

In this paper, we present the results obtained by the general circulation model developed at the Laboratoire de Meteorologie Dynamique which has been used to simulate the Martian hydrological cycle. Our model, which employs a simplified cloud scheme, reproduces the observed Martian water cycle with unprecedented agreement. The modeled seasonal evolution of cloudiness, which also compares well with data, is described in terms of the meteorological phenomena that control the Martian cloud distribution. Whereas cloud formation in the tropical region results from seasonal changes in the overturning circulation, Polar Hood clouds are mostly driven by variations of atmospheric wave activity. A sensitivity study allows us to quantify the effects of the transport of water ice clouds on the seasonal evolution of the water cycle. The residence time of cloud particles is long enough to allow cloud advection over great distances (typically thousands of kilometers). Despite the relatively low proportion of clouds ($10%) in the total atmospheric inventory of water, their ability to be transported over large distances generally acts at the expense of the north polar cap and generates a water cycle globally wetter by a factor of 2 than a cycle produced by a model neglecting cloud transport. Around aphelion season, clouds modulate the north to south migration of water in a significant fashion and participate just as much as vapor in the cross-equatorial transport of total water. Most of the year, atmospheric waves generate an equatorward motion of water ice clouds near the polar vortex boundaries, partially balancing the opposite poleward flux of water vapor. The combination of both effects delays the return of water to the north polar cap and allows water to build up in the Martian tropics.

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Origin and role of water ice clouds in the Martian water cycle as inferred from a general circulation model

A key question regarding the evolution of Mars is related to the behavior of its volatiles. The present investigation is concerned with the global and seasonal abundances of water vapor in the Mars atmosphere as mapped by the Viking Mars Atmospheric Water Detector (MAWD) instrument for almost 1-1/2 Martian years from June 1976 to April 1979. Attention is given to the implications of the observed variations for determining the relative importance of those processes which may be controlling the vapor cycle on a seasonal basis. The processes considered include buffering of the atmosphere water by a surface or subsurface reservior of ground ice, physically adsorbed water, or chemically bound water. Other processes are related to the supply of water from the residual or seasonal north polar ice cap, the redistribution of the vapor resulting from atmospheric circulation, and control of the vapor holding capacity of the atmosphere by the local atmospheric temperatures.

F.Michael Flasar

Papers

Diurnal behaviour of water on Mars