Discrete events at Viking-2 Mars site, northern summer

The Viking-2 Mars Lander landed at 48 deg N 226 deg W, northern summer. During the summer period the wind vector exhibited a repetitive clockwise turning with a period of one Sol (Mars day). Occasionally, however, the rotation ceased and wind became principally northeasterly. These events were always multiples of a Sol in duration, and all began around local midnight. The exact reason for this behavior is not clear, but it is suggested that small variations in the strength of the global circulation may be responsible.