Karen Schmidt awarded the PhD degree
Karens G. Schmidt's thesis describes the efforts to construct a model that models the water cycle on Mars. Water is present on Mars mainly as polar ice deposits. During the seasonal cycle of the Martian year, water evaporates from the "summer pole" ice cap and is transported through the atmosphere to the "winter pole" ice cap. Getting a grip on this water transport is thus important for the understanding of the Martian climate.
Both the Viking Mission's Mars Atmospheric Water Detector (MAWD) and Mars Global Surveyor's Thermal Emission Spectrometer (TES) observed the Martian atmospheric water abundance through the Martian seasonal cycle. Studies of the MAWD and TES data indicate that there is a net transport of water from the north to the south during northern summer, which is not balanced by a similar northward transport at other seasons.
An atmospheric diffusion model, representing atmospheric mixing caused by the Hadley circulation on Mars, was coupled with a model where the ice caps and most of the regolith in the northern hemisphere exchange water with the atmosphere. In general, the results agree well with the measured data as the magnitude and the general pattern of the spatial and temporal water distribution were reproduced. However, some features were not reproducible, and it was concluded that the model representing an advection process, where vapour is transported like a tracer with the wind, would be better suited to describe the annual water cycle.
The surface exchange model coupled with the atmospheric advection of water vapour shows that the ice caps alone are not sufficient for retaining the present level of water in the atmosphere. In an experiment based on the Mars Odyssey Gamma Ray Spectrometer measurements of ground ice in the regolith, it is shown that the model using the GRS values as percentages of a clean ice surface overestimates the evaporation of water to the atmosphere. This indicates that the water is bound more strongly to the reservoirs than in the model experiment.
Download the thesis here