| Summary: | Combined measurements of Global Positioning System (GPS) surface positions and in situ measurements of ice deformation advance understanding of ice dynamics on the Greenland ice sheet by allowing the for the partitioning of surface motion into its basal and deformation components. We analyzed winter motion by partitioning the surface into sliding and deformation. Here, we present GPS positions from a five station GPS array and of ice tilt in two orthogonal directions and azimuth through a vertical column extending from the ice surface to the bed at eight boreholes drilled at location western Greenland and collected over the 2015-16 winter. We find that sliding dominates ice motion, comprising 96% of the total surface motion during the winter. Interestingly, we find time variations in the tilt rates of the near basal inclinometers, which are attributable to the effects of basal roughness on the local stress field as the ice slides across the basal boundary.
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