Comparison of Antarctic Seasonal Variations in GRACE and the RACMO2.1/ant Climate Model

The Gravity Recovery and Climate Experiment (GRACE) is often used to determine long term fluctuations in surface ice and water mass distribution. Most studies of Antarctica using GRACE have addressed long term trends, but literature is scant on Antarctic seasonal cycles. We compared time-variable gravity data from the GRACE mission for 2002-14 with accumulated Antarctic surface mass balance (SMB) from the Regional Atmospheric Climate Model (RACMO2.1/ant). RACMO2 variations are dominantly seasonal and reflect precipitation and ablation but not glacial discharge into the ocean. GRACE processing included conventional spherical harmonic filtering (also applied to the RACMO2 data) and removal of the S2 tidal alias. GRACE and RACMO2 seasonal components were compared for the entire continent and for regions with differing precipitation levels. For dry regions, the GRACE seasonal signal is much higher in amplitude and out of phase with respect to RACMO2, indicating that GRACE detects some other seasonally varying signal. In regions with higher precipitation, there is better but imperfect agreement between RACMO2 and GRACE. Continentally, parts of the GRACE signal match phase and amplitude with RACMO2 but there is extra signal not reflected in RACMO2. These differences provide useful understanding of limitations in both GRACE and RACMO2 at seasonal frequencies in this region.