Branch Seminar Series: Lora Koenig

University of Washington
As temperatures get warmer, global climate models predict an increase in precipitation, and possibly accumulation, on the polar ice sheets. Recent satellite altimeter data on the ice sheets are invaluable for monitoring accumulation changes and validating models but longer data sets are needed to distinguish the natural variability in accumulation rate from a change in climate. Establishing the longest temporal data set of firn properties, including accumulation, motivates the use of passive microwave remote sensing. Over the past 30 years passive microwave sensors have operated over the ice sheets but the complicated signal recorded is not yet fully understood. To better understand the relationship between firn properties and microwave emission we have developed a model relating surface temperature to passive microwave brightness temperature and have collected a comprehensive firn microstructure data set along with radiometer and very-high-frequency radar data at multiple pits in both Greenland and Antarctica. A link between microwave extinction length, firn thermal diffusivity and accumulation rate is shown in West Antarctica and field-measured and strung-fluctuation-theory-modeled extinction lengths are compared at Summit, Greenland. Additionally our very-high-frequency radar measurements indicate the future possibility of monitor accumulation rate and near-surface firn properties at centimeter-scale resolution across polar ice sheets.