Martian surface winds: Insensitivity to orbital changes and implications for aeolian processes

Abstract

. The primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long-term wind indicators (for example, the misalignment of rock tail and ventifact orientations at the Mars Pathfinder landing site). Specifically, we assess whether changes in planetary obliquity, precession, or global dust opacity could significantly alter patterns of surface wind directions. In all cases we find the seasonal and annual average wind direction patterns to be highly invariable. While changes in the dust loading (hence the partitioning of solar absorption between the surface and atmosphere) and in the surface latitude of maximum solstitial insolation cause the vigor of the large-scale circulation to increase (especially the Hadley cell), the spatial patterns of the surface wind orientations remain essentially unchanged. In the case of perihelion during northern summer (opposite of the current perihelion position), the northern summer Hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere. Taken together, these results cast significant doubt on orbital explanations for surface wind changes. It is thus suggested that significant changes in topography (e.g., Tharsis uplift, true polar wander) or climate (e.g., the existence of a significantly thicker atmosphere or an ocean at some point in the past) are more likely explanations for long-term wind indicators such as the ventifact orientations at the Mars Pathfinder landing site.

Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux

“…Atmospheric models on various scales show that the circulation at Nili Patera is dominated by a combination of the tropicalmean overturning ('Hadley') circulation, thermal tides and slope flows associated with the dichotomy boundary and the Isidis basin [28][29][30][31] . Nili Patera is located roughly 9°N of the equator within the seasonally reversing Hadley circulation.…”

A comparison of methods used to estimate the height of sand dunes on Mars

“…We currently have the capability to collect data on aeolian dune type, location, sediment size, lithology, and provenance and to search for evidence of dune migration (e.g., Anderson et al, 1999;Bourke et al, 2004a;Edgett and Christensen, 1991;Edgett, 2002;Garvin et al, 1999;Langevin et al, 2005;Zimbelman, 2000). We can use atmospheric models to predict wind regimes at decadal, seasonal, and even diurnal timescales (e.g., Bourke et al, 2004b;Fenton and Richardson, 2001;Fenton et al, 2005;Haberle et al, 1999;Raflíin and Michaels, 2003;Toigo and Richardson, 2003). At a more local scale, the Lander and Rover data sets have made possible the detailed examination of small-scale aeolian dunes (centimetre to meter scale) and detection of aeolian grain size and mineral composition (e.g., Greeley et al, 1999Greeley et al, , 2002Greeley et al, , 2004Sullivan et al, 2005).…”

Morphology of Slope Streaks within Nicholson Crater, Mars:Records of Recent Wind Activity

“…Extensive presence of yardangs and of slope streaks at various locations on Mars have been detected and studied earlier 4,5 . In some cases the aeolian features are completely ephemeral and relate only to the lifting and settling of atmospheric dust, whereas certain features like dune fields, yardangs and ventifacts are more persistent and require significant time for their development 6 . Understanding of landform morphology helps reveal how in combination with previous active processes the sedimentary history of a region has eventually modified itself in response to a complex alternating process of dust accumulation and erosion brought down due to still active aeolian processes 7 .…”