Assessing Satellite-derived Inter-annually Varying Snow/Firn Density
Estimates Over the Greenland Ice Sheet during 2003-2009
Abstract
Knowledge of snow/firn density is important for deriving ice sheet mass
change from satellite altimetry and for surface mass balance modeling.
However, snow/firn densities are largely unknown over the Greenland ice
sheet (GrIS) away from isolated direct measurements in boreholes.
Density assumptions are widely used when converting volume change from
satellite altimetry into mass change, which could introduce errors. Here
we extract the inter-annual anomalies of mass change from Gravity
Recovery And Climate Experiment (GRACE) data and the refined ice
elevation change through the repeat-track analysis of Environmental
Satellite (Envisat) altimetry data retrieved using both the ICE1 and
ICE2 waveform retracking algorithms. By combining these two types of
inter-annual anomalies (GRACE+ICE1 and GRACE+ICE2), we investigate the
inter-annually changing snow/firn density estimates over the GrIS during
the 2003–2009 period. Our results demonstrate that satellite-derived
density is relatively greater over Western GrIS, with magnitude falling
between 300 “kg” ⁄“m” ^“3” and 917 “kg” ⁄“m” ^“3”
occupying more than 71% of the GrIS. At the regional scale, GRACE+ICE1
derived density agrees well with that from density profiles of 9 ice
cores at Summit Station, Central GrIS, with relative errors less than
5%. Satellite-derived densities are further compared with that from 110
ice cores mostly along the central ice divide. The percentage of
GRACE+ICE1 derived densities with relative errors less than 20% exceeds
84%, as opposed to 41% for GRACE+ICE2. Satellite-derived densities
could possibly underestimate the inter-annually varying snow/firn
density over Southern GrIS. This study may provide constraints on the
currently applied density assumptions for the GrIS.