Dust Devils are cleaning Spirit

Caption NASA originale:"One Sol before this image was taken, power output from Spirit's solar panels went up by about 50% when the amount of dust on the panels decreased. Was this a coincidence, or did a helpful Dust Devil pass over Spirit and lift off some of the dust?
By comparing the separate images from the Rover's different cameras, team members estimate that the Dust Devils moved about 500 mt (1.640 feet) in the 155' between the navigation camera and hazard-avoidance camera frames; that equates to about 3 mt per second (i.e.: 7 miles per hour). The Dust Devils appear to be about 1.100 meters (almost three-quarters of a mile) from the Rover".