Sensitivity of Martian Southern polar cap edge winds and surface stresses to dust optical thickness and to the large-scale sublimation flow

Abstract

Strong surface thermal contrasts of up to 90 K occur in the spring and early summer between the retreating seasonal polar caps and the adjacent ice-free regolith. This contrast should drive strong winds. Observations indicate local dust storms being common near at least the Southern cap edge in the springtime. Models of the polar cap edge winds have not included dust in the atmosphere. Some NASA Ames Mars Global Circulation Model (MGCM; Pollack et al., 1990; Haberle et al., 1993) results indicate sensitivity of the surface stress at Southern subtropical latitudes to changes in dust optical thickness (τ) in the 0 < τ < 1 range. In this work we have modelled the sensitivity of the Southern polar cap edge circulation and surface stress to both the dust optical thickness and the springtime sublimation flow. Models used are the MGCM and an improved version of the University of Helsinki 2-D Mars Mesoscale Model (MMM2D; Savijärvi and Siili, 1993). Model results indicate that even when both thermal contrast and mass sublimation wind generation mechanisms are invoked, calculated surface stress values remain too weak to lift dust from a topographically flat surface under conditions of low dust optical thickness.