ICESat-2 Oceanic & Sea Ice Responses to Atmospheric Forcing

NASA's ICESat-2 mission will measure and monitor the heights of sea ice and oceans as well as the heights over land, vegetation and land ice. In order to avoid aliasing high-frequency variations into averages of Sea Surface Height (SSH), science-directed oceanic data products require systematic correction to account for various geophysical signals such as tides and atmospheric forcing. The focus here is on the temporal surface responses to atmospheric pressure and wind field forcing. We present evaluations of modeled oceanic responses from the MOG2D Dynamic Atmospheric Correction (DAC) model, which includes both the atmospheric pressure and wind stress effects, and from ECMWF and NCEP atmospheric pressure alone through the Inverted Barometric (IB) effect pressure. We evaluate for both the ice-covered and ice-free ocean. The influence of wind stress relative to IB increases with latitude north and south, likely due to increased Coriolis and the associated effectiveness of Ekman pumping. However, we show examples where wind field stresses in the DAC appear to extend further onto sea-ice covered zones than we anticipated. Additional examples of anomalous variability between along-track, point-value DAC & IB values found on Cryosat-2 data records will be shown. Comparison of monthly samples across three years (2012-2014) of Arctic Ocean mean sea level pressure data from ECMWF and NASA's GMAO GEOS-5 FP-IT (V5.12.4) reveals pressure differences of up to ±9.5 mbar between them. Up to ±10.6 mbar differences are noted in the oceans surrounding Antarctica. The magnitude of these differences, between assimilation sources, when considered as an IB correction (1 mbar ≈ 1 cm IB), create a challenge when attempting to achieve 1 cm, satellite-borne, LIDAR oceanographic and sea ice geodesy.