Mars GCM Experiments: Application to the Transport and Behaviour of Water

M.I. Richardson (UCLA), R.J. Wilson (GFDL), D.A. Paige, S.E. Wood (UCLA)

The Martian water cycle is highly asymmetric with regard to season. Spacecraft and telescopic observations show peak column water vapour abundances over the northern summer high latitudes ( tex2html_wrap_inline17  90pr tex2html_wrap_inline19 m) with the southern summer peak being smaller ( tex2html_wrap_inline17 20pr tex2html_wrap_inline19 m) and appearing further from the pole. This distribution of vapour results in an annual average meridional vapour gradient whose means of maintenance has yet to be conclusively determined (Jakosky and Haberle, 1992). Hypotheses thus advanced include a net annual transfer of water from north to south, more vigourous meridional transport during southern summer (Davies 1981, James 1985), and trapping of vapour in the northern summer hemisphere by the circulation (Haberle and Jakosky 1990), water condensation (Clancy tex2html_wrap_inline25 tex2html_wrap_inline27 1996), or subsurface adsorption (Houben tex2html_wrap_inline25 al. 1997).

The GFDL Mars General Circulation Model (Wilson and Hamilton 1996 and Wilson tex2html_wrap_inline25 al. 1997, this volume) has been augmented with water processes including: atmospheric water vapour transport, water exchange with surface ice, atmospheric vapour condensation, and subsurface water exchange. This model represents the first treatment of the water cycle in a full General Circulation Model including the effects of topography, diurnal cycle, and interactive atmospheric dust. Results will be shown from model experiments designed to assess the ability of the atmosphere to extract water from the north polar cap source and effect equatorward transport. The role of atmospheric vapour condensation in limiting the transport of water, its effect on the spatial distribution of dust (via the use of dust for water condensation nuclei), and consequently its influence on the vigour of circulation (by altering the amount of solar radiation absorbed by airborne dust) will be examined.