Dust Devils
This figure shows the
signature of a dust devil that passed over the Pathfinder lander on Sol 25. Since then we
have seen several similar features. The black line shows surface pressure plotted over a
period of approximately two minutes. The sharp minimum approximately 0.5% below the
background pressure is very clear. The dashed curves show raw data from two hot wire wind
sensor elements (Blue =3D Wind Sensor 4 =3D East Wind, Red =3D= Wind Sensor 1 =3D West
Wind). When the wind blows directly on an element it cools==2E. It is clear from the
figure that the East wind increases suddenly as the dust devil approaches the lander and
the pressure begins to fall. As the dust devil passes over the lander, pressure begins to
rise, the East wind dies away and the West wind increases suddenly. Finally as the dust
devil moves away, pressure returns to normal and the West wind dies away. This is a
textbook dust-devil signature.
This figure is a very simplified schematic drawing of the dust-devil
that passed over the Sagan Memorial Station on Sol 25. It shows direction of motion and
the graphs of a textbook dust-devil in terms of wind speed and surface pressure.