Highlights of the 2015-2017 Mars Apparition
Images of the Hellas to Argyre Dust clouds in September are below. In my opinion, these clouds are produced by winds from the continuing sublimation of the CO2 ice cap that began near Ls 112.
The below images from April 5th to May 9th provide evidence for strong South to North straight-line winds in the Hellas basin from Ls 130 to Ls 150. This period is the middle of winter in the Southern Hemisphere. I propose that the sublimation of CO2 ice produces straight-line winds. With the ice exposed to sunlight, the frozen CO2 sublimes, creating enormous winds up to 400 km/h. Each southern winter, the seasonal CO2 ice cap covers the surface to a latitude of 50°. This means that the Northern edge of the cap bisects Hellas. It can be deduced that sublimation winds here contribute to the waves of dust in Hellas. Hellas is immense with the South to North diameter about 1,300 miles that is roughly the distance from the US-Canada border to the Pan-handle of Texas. So with that diameter, a significant temperature gradient is likely in the South to North direction that can produce strong winds that carry immense waves of dust from South polar regions to the Northern wall of Hellas. These detailed images by Clyde Foster and Efrain Riveras Morales show the results of these winds. References are courtesy of Wikipedia.
Also note that the icy floor of Hellas is blue in the April images and white in the May image. A blue color can mean the presence of H2O water vapor. Temperatures get warm enough in the Southern hemisphere during Spring and summer for CO2 sublimation, but it’s too cold for H2O to sublimate. However, the north polar cap of Mars does get warm enough for H2O sublimation. Maybe this is a source of the water vapor, but by May condenses becoming ice fogs. See page 399 of a Traveler’s Guide to Mars by William K. Hartmann published 2003.
Many small features distinguishable on Clyde Foster’s image below!
Images from Feb 17, 2016 to Mar 01, 2016. Have you ever seen
such a broad expanse of white clouds over the Martian disk?