Active dust devils in Gusev crater, Mars: Observations from the Mars Exploration Rover Spirit
[1] A full dust devil "season" was observed from Spirit from 10 March 2005 (sol 421, first active dust devil observed) to 12 December 2005 (sol 691, last dust devil seen) this corresponds to the period Ls 173.2deg to 339.5deg, or the southern spring and summer on Mars. Thermal Emission Spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in Gusev and that Spirit landed in the waning stages of a dust devil season as temperatures decreased. 533 active dust devils were observed, enabling new characterizations; they ranged in diameter from 2 to 276 m, with most in the range of 10 20 m in diameter, and occurred from about 0930 to 1630 hours local true solar time (with the maximum forming around 1300 hours) and a peak occurrence in southern late spring (Ls 250deg) Horizontal speeds of the dust devils ranged from <1 to 21 m/s, while vertical wind speeds within the dust devils ranged from 0.2 to 8.8 m/s. These data, when combined with estimates of the dust content within the dust devils, yield dust fluxes of 3.95 x 10 9 to 4.59 4 kg/m2/s. Analysis of the dust devil frequency distribution over the inferred dust devil zone within Gusev crater yields ~50 active dust devils/km2/sol, suggesting a dust loading into the atmosphere of ~19 kg/km2/sol. This value is less than one tenth the estimates by Cantor et al. (2001) for regional dust storms on Mars.