Observations of Martian Tides Over Two Annual Cycles

Abstract

The first four diurnal surface pressure harmonics have been analysed over major portions of two Martian annual cycles (Mars years) at the two Viking lander sites. The diurnal harmonies of surface wind have also been analysed at one of the sites. Since the atmospheric tides have previously been shown to provide a good indication of Martian global dust storms, these results provide a basis for comparing dust storm activity in the two years. Two global dust storms occurred during the first year. During the second year, there was only one major storm, and it closely followed the pattern of the first storm of the first year. A significant feature of the results is the brief, but nearly complete. vanishing of the diurnal pressure tide at the onset of one of the global dust storms. It is proposed that this may have been due to interference between the normal westward-propagating diurnal tide and a topographically forced eastward propagating tide, and that the latter may have helped initiate the global storm.