Branch Seminar Series: John Heinrichs

Fort Hays State University
Observations and predictions of a rapid decline in the extent of multiyear sea ice in the Arctic basin have created an urgent need to understand the dynamic and thermodynamic processes that affect the Arctic sea ice cover. The evolution of multiyear sea ice in the Arctic basin has, however, historically been difficult to study because the ice is difficult to access and moves continuously. In this project, a Lagrangian methodology has been applied in which individual parcels of ice are tracked and their characteristics observed using spaceborne remote sensing data. Sea ice drift tracks were obtained from buoys and passive microwave sensor data and used to obtain time histories of albedo, skin temperature, and ice concentration as functions of location and ice type. Ice age (in years) was derived from the drift tracks and used (by comparison with ICESat data) to derive fields for ice thickness. The results suggest that there are substantial and identifiable differences in environmental conditions experienced by parcels that melt and those that survive over the entire year. From the ice age and thickness fields, it is clear that old ice is no longer surviving summer melt in the Beaufort and Chukchi seas, which means that atmospheric circulation patterns that would previously have acted to rebuild the extent of old ice by moving ice into the western Arctic instead are now causing additional loss of the oldest ice. The Lagrangian approach is also being used to examine how microwave data respond to changing ice conditions, using forward simulation. In particular, a semi-empirical model of sea ice backscatter was employed to estimate backscatter given ice type and cover. It was found that the backscatter of wintertime ice cover is most sensitive to incidence angle and the backscatter of open water in leads. Meltwater in snow and meltponds drastically change the backscatter of the ice surface in summer, and the model performance decreases substantially.