Huge Dust Devil Northwest of Spirit - Sol 1919

Caption NASA:"Researchers used the NavCam on NASA's Mars Exploration Rover Spirit to look for Dust Devils near the Rover during the Mission's 1919th Sol (May 27, 2009). This shot from that day's sequence, presented here with three different levels of processing, caught a large Dust Devil about 1,5 Km (a little less than 1 mile) North-West of Spirit.

The top frame is the original image, the middle frame has been processed enhance the visibility of the Dust Devil, and the bottom frame is a merged version. The image was taken in the early afternoon (note: such as in that period of time comprised between 12:30 and 15:30) from Spirit's position at the "Troy" sand trap beside "Home Plate", looking northwest across the floor of Gusev Crater.
The large Dust Devil shows a typical central core (brightest area) surrounded by a more diffuse sand and dust "skirt" about 415 mt (such as about 1350 feet) across. The Dust Devil is moving toward the North-East (toward the right in this image) at about 0,75 meter-per-second (meaning 1,7 miles-per-hour).
This Dust Devil is some 20 times larger than the average Dust Devil on Earth. A smaller Dust Devil is seen on the right leading the larger DD.
More than 650 DDs have been recorded by Spirit since its operation began in 2004. The Mission is currently in its third "season" for DDs on Mars, which typically begin in Martian Spring".