Changes in Greenland Ice Surface Roughness and Relationships to Melting and Glacial Acceleration --- Analyses Using Altimeter Data from ICESat, CryoSat-2 and ICESat-2 Simulator Instruments

Abstract:

Spatial ice surface roughness is an indicator of many processes that affect the ice surface, including glacial acceleration, ice deformation, crevassing, snowfall, melting, and wind deposition and erosion. We derive ice-surface roughness from satellite observations and investigate the relationships of surface roughness and its changes to the main manifestations of climate-induced changes in the Greenland ice sheet: (a) glacial accelerations and (b) melting. Results are relevant for assessment of sea-level change through mass loss from the Greenland ice sheet and for understanding relationships between observations and physical processes. The analysis is based on ICESat GLAS data 2003-2009, CryoSat-2 SIRAL data (since 2010) and data from ICESat-2 simulator instruments MABEL and SIMPL. The approach uses a spatial statistical concept of generalized spatial surface roughness and characteristic parameters, which are mathematically related to physical concepts including crevassing, deformation and aerodynamic roughness length. To derive micro-topographic and roughness information from MABEL and SIMPL data, the Density-Dimension-Poisson Algorithm (DDA) is introduced. Results demonstrate the expected capabilities of NASA's future ICESat-2 mission to map even spatially complex ice-surface topography with unprecedented resolution and accuracy. The remote-sensing data analysis lays the foundation for applied case studies: (1) Roughness and elevation changes in Ilulissat Ice Stream and other outlet glaciers are analyzed to investigate links between glacial acceleration and its causes. (2) Roughness changes during the recent acceleration of the margin of the Greenland ice sheet are analyzed together with other synoptic observations, such as those of surface water. (3) Energy balance calculations are carried out to relate surface roughness changes and changes in melt energy, for regions with small-scale roughness typical of uncrevassed snow and ice surfaces.