The Invisible Winds that Shape the Fans

Today we have a guest post by Tim Michaels. Tim is a research scientist at the SETI Institute who studies how the weather and climate of other worlds affects their surface features.

The Planet Four science team has recently been using the catalog of your fan markings to compare to the wind speed and direction estimated by computer calculations of how Mars’ atmosphere moves around.  These wind estimates are calculated by a complex computer program known as a mesoscale atmospheric model, very similar to those that forecast the daily weather on Earth.  There are no actual wind measurements in the southern polar regions of Mars, so we use these modeled wind estimates to better interpret what your fan markings tell us about the planet’s weather and climate.

The figure below shows an example of the modeled wind estimates near the Manhattan Classic fan site (86.4S, 99.0E) in the early evening at Ls 190.  The area shown is about 135 km by 135 km, south is toward the upper right side, and every arrow is about 1.5 km apart (every model gridpoint; the numbers on the sides count these).  This area is at the head (top) of the great south polar valley Chasma Australe, and the white topographic contours (in meters) show the upper reaches of that valley running downhill from center right toward the lower left.  The arrows show wind direction and speed (arrow length, see the 10 m/s scale in the upper right corner).  Wind speed is also indicated by the color of the arrows — cooler colors (like blue and purple) for the slower winds, warmer colors (like red and orange) for the faster winds.  The fastest wind speeds in this scene are about 11 m/s.

You can see how the wind directions and speeds vary a lot across this area — those patterns change quite a bit with the time of day, as well.  Our preliminary results show that the strong winds from the east near the center of this figure may be related to the formation of the fans in this area.  Much more work still needs to be done to better understand what all of your markings of fans and blotches tell us about the winds on Mars, but we wanted to give you a glimpse of what the (invisible) winds that sculpt the fans may look like.