MARTIAN AEOLIAN FEATURES AND DEPOSITS - COMPARISONS WITH GENERAL-CIRCULATION MODEL RESULTS

The development of a general circulation model (GCM) of Mars' atmosphere allows questions to be addressed concerning the relationships between near-surface winds and the distribution of wind-related features and deposits. Predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks, yardangs, and rock abundance on the surface. The occurrence and orientation of bright streaks are well accounted for by the GCM. Results suggest that bright streaks form during southern hemisphere summer by Hadley cell circulation, in which dust is raised in the southern hemisphere, carried northward at high altitudes, then deposited in the wake of craters and other topographic obstacles by the descending Hadley cell. The reduction in the number of bright streaks southward from 30-degrees-N is interpreted to reflect the depletion of dust by near-surface winds blowing to the south. Although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by GCM simulations, a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season (southern hemisphere summer). Yardang orientations do not match the GCM simulations for any season; their orientation is attributed to either structural control in the rocks (such as joint patterns) or to a change in wind patterns from the time when the yardangs formed. The global distribution of rocks on the surface is correlated well with predicted wind stress, particularly during dust storm season; the rocky areas are sites of strong winds, suggesting that fine material is swept away by the wind, leaving rocks and coarser material behind.