We combine observations of surface morphology, topography, subsurface stratigraphy, and near surface clouds with mesoscale simulations of south polar winds and temperature to investigate processes governing the evolution of spiral troughs on the South Pole of Mars. In general we find that the south polar troughs are cyclic steps that all formed during an erosional period, contrary to the troughs at the North Pole, which are constructional features. The Shallow Radar instrument (SHARAD) onboard Mars Reconnaissance Orbiter detects subsurface stratigraphy indicating relatively recent accumulation that occurred post trough formation in many locations. Using optical instruments, especially the Thermal Emission Imaging System (THEMIS), we find low altitude trough clouds in over 500 images spanning 6 Mars years. The locations of detected clouds correspond to where recent accumulation is detected by SHARAD, and offers clues about surface evolution. The clouds migrate by season, moving poleward from 71° S at ~ L s 200° until L s 318°, when the last cloud is detected. Our atmospheric simulations find that the fastest winds on the pole are found roughly near the external boundary of the seasonal CO 2 ice cap. Thus, we find that the migration of clouds (and katabatic jumps) corresponds spatially to the retreat of the CO 2 seasonal ice as detected by Titus (2005) and that trough morphology, through recent accumulation, is integrally related to this seasonal retreat.
