Observations at 0.3--3.0 μm by the Viking infrared thermal mapper have been used to determine the temporal and spiral variations of the albedo of the Martian surface and atmosphere. These data were collected into 1¿¿1¿ latitude, longitude bins, for local times of 6--10 H, 10--14 H, and 14--18 H (24 H equals 1 Martian day), and for 10¿ Ls bins th the two global dust storms of 1977. The first storm began near Ls 205 ¿, and the second storm began between Ls 273.5¿, and 274.0¿, consistent with Viking imaging and thermal observations. For optically thick atmospheric dust, the observed albedo was 0.37--0.40. Over all regions the atmosphere cleared substantially between the two storms, with many southern hemisphere regions returning to their prestorm albedos. In general, the northern hemisphere atmosphere had a higher dust content throughout the storm phase, and retained dust longer during the decay phases, then the southern hemisphere. Southern hemisphere dark regions were not measurably brighter following the global storms, suggesting little net deposition of dust. In contrast, the northern hemisphere dark regions of Syrtis Major and Acidalia Planitia were measurably brighter following the storm, indicating the deposition of ~7--45 μm of dust per year. These surfaces subsequently darkened over the following months, returning to prestorm albedo values prior to the next dust storm season.

The material raised from these surfaces, and atmospheric dust observed locally over several other dark regions during the clear periods, may account for the general dust haze observed throughout the year. It appears that dust is also deposited in bright, low-inertia regions, where it remains. The albedo data suggest active dust transport into the north, with net deposition in the bright, low-inertia regions. This south-to-north transport of dust during global storms is consistent with atmospheric circulation models, which predict the presence of cross-equatorial Hadley circulation during this season. Because of the close connection between dust transport and atmospheric circulation at present, it is possible that under reversed conditions of north-to-south circulation during epochs when the maximum solar heating occurs in the north, the current deposits would be eroded and transported back to the south. This continual reworking of an active, surface dust layer would therefore not require substantial erosion of the surface to account for the high level of aeolian erosion and transport observed at present. ¿ American Geophysical Union 1988