Greenland annual accumulation along the EGIG line, 1959--2004, from ASIRAS airborne radar and neutron-probe density measurements

We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expeditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and high resolution neutron-probe (NP) density profiles. ASIRAS-NP-derived accumulation rates are not statistically different (95% confidence interval) from in situ EGIG accumulation measurements from 1985 to 2004. ASIRAS-NP-derived accumulation increases by 20% below 3000m elevation, and increases by 13% above 3000m elevation for the period 1995 to 2004 compared to 1985 to 1994. Three Regional Climate Models (PolarMM5, RACMO2.3, MAR) underestimate snow accumulation below 3000m by 16-20% compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modeled density profiles in place of NP densities. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5% of ASIRAS-NP estimates in the dry snow region. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the Operation IceBridge campaign.