AN ANALYSIS OF THE HISTORY OF DUST ACTIVITY ON MARS

A new comprehensive list of possible and probable dust activity has be en compiled from various published lists and additional data. All prev iously listed events have been reviewed and evaluated. For uniformity and clarity, each event is classified using a new system that includes a well-defined nomenclature. Maps showing the reported locations of i ndividual major events, as well as a summary map of the smaller ''loca l'' events, have been compiled. Detailed commentaries describe the eve nts and/or circumstances of their observation. The seasonal distributi on of Martian dust events is diagrammed and discussed together with a seasonal and annual (Mars years) timeline that includes the frequency of photographic coverage. The new compilation shows that major dust st orms have originated in many different regions across the planet, with some evidence of more activity in the southern hemisphere generally a nd in specific regions like Hellas. Regional dust storms have been obs erved in nearly all seasons, except for two relatively narrow periods which occur near times when the polar caps have reached their maximum/ minimum extent. Regional dust storms tend to occur most frequently, an d all planet-encircling dust storms have been observed during the sout hern spring and summer seasons, although there is significant interann ual variability.