|Title:||The origin of summertime crust and surface hoar formation at the WAIS Divide site, West Antarctica|
|Author:||Fegyveresi, J.M., Alley, R.B. and Spencer, M.K.|
|Periodical:||American Geophysical Union, Fall Meeting 2013, abstract #C13B-0670|
Summertime field observations at the WAIS Divide site, West Antarctica, indicate a very active surface. Over five consecutive seasons (2008-2013), daily surface measurements were made along with photography of the surface and of back-lit snowpits, where densities were measured. The Automatic Weather Station in the University of Wisconsin network was supplemented by various independent sensors deployed on site, including pyranometer sensor arrays and net-radiometers in order to better quantify the short-wave and long-wave radiation conditions surrounding near-surface metamorphism. Prominent 'glazed' crusts occur frequently. Surface and pit observations show that such crusts form in summertime during relative low-wind, low-humidity, high-temperature episodes that immediately follow a succession of strong wind events. During each documented case of formation, these episodes were also brought about during clear-sky days with maximum diurnal variability of incoming solar energy. Shallow firn temperature measurements indicate strong inversions during crust formation that likely lead to increased vapor transport. Furthermore, distinct hoar frost growth was observed on crusts that were exposed to multiple clear-sky days, likely as a result of increased insolation, humidity, and vertical vapor transport in the near-surface. There was no obvious indication of melt associated with glazed features during initial inspection. Examination of the WDC06A ice core and its associated ECM record indicates that numerous crusts are present very regularly throughout the core and in all seasons. Crusts are about 40% more abundant in summertime than in wintertime deposits, likely due to the formation of 'glazed' surfaces; formation mechanisms of the less-common wintertime crusts have not been observed and are not known. Over the ice-core record, there is little change in frequency of occurrence of wintertime crusts, but some changes in summertime, perhaps indicating changes in occurrence frequency of those sunny conditions that lead to crust formation. Future work will incorporate the use of SSM/I brightness data to corroborate crust and hoar formation episodes. Additionally it is hoped that a better understanding of wintertime crusting can be achieved.