Martian Cold Spot Activty in the Northern and Southern Hemispheres and the Effects of the Global Dust Storm of 2001

Introduction: Mariner and Viking were the first to observe cold spot activity in the polar regions of Mars in the 1970s [1]. Cold spots are identified as areas with 20µm brightness temperatures that are as low as 130 K, which is significantly below the CO 2 ice sublimation temperatures [1]. Studies of data from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) [2, 3], Mars Orbital Laser Altimeter (MOLA) [4] and Viking Infrared Thermal Mapper (IRTM) [5] indicate that cold spots are a combination of surface deposits of CO 2 atmospheric condensates and active CO 2 snow storms [2]. This study focuses on differences found between cold spots in the southern hemisphere and the northern hemisphere. We also examined the effects that the 2001 global dust storm had on cold spot formation and activity in both hemispheres. The global dust storm had a significant effect on cold spots in the northern hemisphere [6] and may have also influenced southern hemispheric cold spots. Data: Three Mars years of data from MGS TES were used in this study. Observations were divided into polar ring data (latitudes 86° to 87.2°) and " cold spot only " data, where bolometer brightness temperatures less than 135 K were used. Due to the high-frequency of repeat coverage, polar ring data were used to obtain accurate size and half-life estimations of cold spots. " Cold spot only " data were used to evaluate seasonal and spatial distributions of cold spots outside the polar ring. Analysis techniques: We used data from the TES database and a brightness temperature difference between 18µm and 25µm (T 18-T 25) to analyze the spatial and temporal characteristics of cold spots [2]. Values are obtained by fitting TES data to a two dimensional spatial Gaussian convolved with a temporal exponential decay. These fits provide estimates for both radius and amplitude (intensity) of a cold spot. Results: Polar ring cold spot activity in the northern and southern hemispheres. In the South Polar Ring, cold spot activity is restricted to the perennial cap. Since the perennial cap is not centered at the geographic pole, the south polar ring exhibits less cold spot activity than the north by an average of