Constraints on Mars' recent equatorial wind regimes from layered deposits and comparison with general circulation model results

Aeolian modification has been a fundamental surface process on Mars throughout the Amazonian. Orientations of aeolian features such as bedforms and yardangs are controlled by the prevailing wind regime during the feature's formation. Therefore, observation of recently formed bedform orientations provides a way to probe Mars' recent wind regime and constrain/test general circulation models (GCMs). We collect statistical distributions of transverse bedform and yardang azimuths at nine sites on Mars, and compare measured feature orientations to those predicted by using vector wind field output from the MarsWRF GCM. We focus on layered deposits because their erodible nature makes them applicable to determination of Mars' modern wind regime. Our methods of mapping from the long-term wind field to predicted feature orientations include consideration of wind stress thresholds for sand movement to occur, sand flux equations, and the direction of maximum gross bedform-normal transport. We find that all methods examined typically agree with each other to within similar to 15 degrees, though there are some exceptions using high order wind stress weightings with multi-directional annual wind fields. Generally, use of higher wind stress thresholds produces improved matches to bedform orientations. Comparison of multiple yardang orientations to annually variable wind fields is accomplished by inspection of directional maxima in modelled wind vector frequency distributions. Yardangs match well to model predictions and sub-populations in close proximity to each other are shown to match individual directional maxima in GCM output for a single site, implying that topographic effects may produce very localised unidirectional wind fields unresolved by the GCM. (C) 2013 Elsevier Inc. All rights reserved.