Planet Four: Derived South Polar Martian Winds Interpreted Using
Mesoscale Modeling
Abstract
For the first time, model-derived and imagery-derived wind directions
and speeds have been compared in Mars’ south polar region. Seasonal
fan-shaped deposits are routinely observed by HiRISE in the polar
regions. They are widely accepted to result from CO 2 gas jet eruptions.
Fan lengths, sizes, and shapes can provide information about wind
directions and strengths at the times such eruptions occur. We utilize a
catalog of those fan-shaped deposits, marked by citizen scientists
within the framework of the Planet Four (P4) project, at 27 regions of
interest (ROIs) for two spring seasons (Mars Year 29 and 30). Fans
change considerably from one HiRISE image to another at most of these
ROIs as wind direction changes over the spring season. Leveraging this
characteristic, intraseasonal variations in near-surface wind speeds and
directions were retrieved and compared to near-surface winds predicted
by a mesoscale atmospheric model (MRAMS) at the same ROIs. At most ROIs
P4-inferred wind directions are consistent with those from MRAMS. The
P4-derived wind speeds are less constrained, but are consistent with
MRAMS wind speeds at the majority of ROIs. The overall consistency
between the P4-inferred and MRAMS wind directions supports the
underlying assumption that fan formation is controlled by the wind, and
is not simply due to ballistic trajectories of material exiting suitably
non-vertical vents. Measurements of seasonal fan-shaped deposits in
HiRISE imagery can thus provide important intraseasonal information
about near-surface winds-invaluable for both validating climate modeling
and quantitatively investigating Mars polar processes.