HR: 1340h
AN: C33C-0355    [Abstracts]
TI: Co-Variations of Ice Sheet Elevation and Slope with Accumulation, Radar Backscatter, and Temperature in West Antarctica
AU: * Haran, T
EM: tharan@nsidc.org
AF: National Snow and Ice Data Center, CIRES, University of Colorado, 449UCB, Boulder, CO 80309 United States
AU: Scambos, T
EM: teds@icehouse.colorado.edu
AF: National Snow and Ice Data Center, CIRES, University of Colorado, 449UCB, Boulder, CO 80309 United States
AB: Maps of surface slope and elevation of the West Antarctic Ice Sheet (WAIS) may be refined by applying calibrated image pixel brightnesses to existing DEMs. Using these image-enhanced elevation models, and existing models of regional katabatic air flow, we investigate the relationship of accumulation, radar backscatter, and temperature to surface slope in the catchment area of the Ross Embayment ice streams. MODIS (Moderate Resolution Imaging Spectroradiometer) images were combined with the RAMP (Radarsat Antarctic Mapping Project) DEM and airborne laser altimeter profiles (from the ALICE/CASERTZ/SOAR aerogeophysics programs) to create a new 250-meter resolution slope and elevation DEM of the study region. The DEM fully resolves the surface undulation field of 2 - 10 km spatial scale, and permits an investigation of air-surface interaction effects in greater detail. Coupling this slope map with the regional mean wind pattern (Bromwich, pers. comm.), we compare local slope variations in the wind direction with accumulation variations derived from a 180-km ground-penetrating radar profile (Spikes, Hamilton, and Arcone, pers. comm.) and point accumulation measurements (Giovinetto, and Vaughan, pers. comm.). We also compare wind-direction slope and accumulation with radar backscatter intensity derived from the RAMP AMM-1 data set. Correlation between RAMP backscatter and accumulation along the traverse is very high (r = 0.8). Regions of higher accumulation are associated with lower backscatter. Accumulation varied as much as 3-fold over just 15 km in regions of significant local relief. Both backscatter and accumulation show high correlation (r= 0.7) with surface slope in the mean wind direction: higher accumulation occurs on windward slopes. This relationship suggests that slope, backscatter, and mean wind direction may be used to infer accumulation in high spatial detail throughout the continent. Mean surface temperature under clear-sky conditions also shows a significant correlation with surface structure, in this case elevation. Using 60 clear-sky AVHRR images, we compile a map of mean surface temperature under clear-sky conditions. Locally high areas on the ice sheet show consistently warmer surface temperatures, by 1 to 4 C, under clear-sky conditions. Katabatic winds arise from surface radiative cooling under clear conditions; so the relationship between surface elevation and clear-sky temperature is an indicator of inversion-layer air-flow. We infer that katabatic airflow dominates accumulation via snow re-distribution and may also impact mean annual snow temperature via its interaction with surface morphology at the 2 - 10 km spatial scale. We hypothesize that flow of the inversion layer slows over the upwind face of hills, causing a loss of entrained sediment (snow). Greater concentration of subsurface layering (wind-crust, hoar, or glaze layers per meter depth in the firn) on low-accumulation lee faces leads to higher radar backscatter. Steep, inverted lapse rates in the inversion layer result in persistent temperature-elevation relationships of several degrees C over elevation changes of just a few tens of meters.
DE: 9310 Antarctica
DE: 3307 Boundary layer processes
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting