Water-ice clouds and dust in the north polar region of Mars using MGS TES data

Water-ice and dust optical depths in Mars' north polar region are mapped as function of season, latitude and longitude, and their characteristics and variability on a geographic, seasonal, and interannual basis are discussed. We use water-ice and dust optical depth data provided by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES), covering nearly three northern spring and summer periods. We find that interannual variability exists in both the water ice and dust behavior, although there are trends that repeat year to year as well. The optical thickness of the north polar hood (NPH) exhibits interannually varying longitudinal structure, both during springtime recession and late-summer onset. We define the characteristics associated with the transition to and from the NPH and find that the disappearance occurs near L-s = 75 degrees and the reappearance near L-s = 160-165 degrees. We find that the late spring to early summer time frame is characterized by very low water-ice optical depths and enhanced dust activity, with a preference for lower water-ice and higher dust optical depths in the 0-90 degrees W quadrant. We see possible evidence for stationary wavenumber 2 systems in a few of the maps examined. (c) 2007 Published by Elsevier Ltd.