Correlated error reduction in GRACE data over Greenland using extended empirical orthogonal functions

Abstract

Surface mass change estimates from Gravity Recovery and Climate Experiment (GRACE) spherical harmonic solutions are contaminated by north-south stripe noise due largely to aliasing of high-frequency variations into monthly samples. These meridional stripes are especially troubling for ice mass balance studies of the Greenland Ice Sheet (GrIS) where large ice mass variations are known to occur along north-south trending coastlines. By assuming that mass variations and noise have different patterns in both space and time over Greenland, we use extended empirical orthogonal functions (EEOFs) to filter out this noise. The method is compared with a conventional approach, by examining both continent-wide estimates and regional changes. GRACE results are compared with independent regional estimates derived from a climate model. The EEOF filter is effective at separating ice mass change signals from meridional stripe noise, with better rejection of high temporal frequency noise and less signal attenuation and spatial smoothing compared to a conventional method. We use EEOF-filtered GRACE data to examine regional seasonal variations. Consistent with surface and other data, results show ice mass loss along the west, southwest, and east coasts during summer and gain in these regions during winter. In addition, there is summer ice mass gain in the central region of the GrIS.