Marine signature in West Antarctic climate as seen by AMPS

In East Antarctica, high interior elevations and steep coastal slopes usually confine ocean air masses to the immediate coastal regions. With relatively lower elevations, West Antarctica (WA) exhibits a more ocean-influenced climate as offshore air masses more easily penetrate inland. Here, we use the Antarctic Mesoscale Prediction System (AMPS) forecast archive to investigate the climate of WA over a one-year time period from March 2007 to February 2008. AMPS weather forecasts employed Polar MM5, a version of the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) optimized for polar regions by the Polar Meteorology Group, and whose horizontal resolution over the Antarctic continent was upgraded from 30 km to 20 km in late 2005. The Japanese 25-Year Reanalysis (JRA-25) data set is used to insure the representativeness of the selected time period with respect to climatological values. The present study provides the most detailed climatological description of WA to date and relies on demonstrated AMPS performance in forecasting Antarctic weather to complement scarce observations on this ice sheet.

As evidenced by the distribution of mean annual and seasonal precipitation and potential temperature, ocean influence is constrained by the major topographic divides of WA, with the Amundsen/Bellingshausen Sea (ABS) sector being most affected. Advection of heat and moisture across WA does occur frequently and is associated with depressions moving over the ABS. This transport is found to be greatest in wintertime, at the peak of cyclonic activity over the Southern Ocean, and shifts in longitude with the location of depressions. Inflows of relatively warm and moist air account for the characteristic tongue-shaped pattern which is observed in the spatial distribution of potential temperature and atmospheric moisture variables, and which approximately follows the topographic ridge between the Ross Ice Shelf and the Ronne Ice Shelf catchment areas. Marine air from the ABS can thus extend to the base of the Ross Ice Shelf and upslope beyond the Transantarctic Mountains, where it has known effects on local winds and cloud cover.