Abstract

In response to the need for improved weather prediction capabilities in support of the U.S. Antarctic Program's Antarctic field opera tions, the Antarctic Mesoscale Prediction System (AMPS) was implemented in October 2000. AMPS employs a limited-area model optimized for use over ice sheets, the Polar MM5. The modeling system consists of several domains ranging in horizontal resolution from 90 km covering a large part of the Southern Hemisphere, to 3.3 km over the complex terrain surrounding McMurdo, the hub of U.S. operations . The performance of the 30-km AMPS Polar MM5 domain versus observations from manned and automatic stations is statistically evaluat ed for a 2-y period from September 2001 through August 2003. The simulated 12-36 h surface pressure and near-surface temperature at most sites have correlations of r>0.95 and r>0.75, respectively, and small biases. Surface wind speeds reflect the complex topograph y and generally have correlations between 0.5-0.6, and positive biases of 1-2 m s-1. In the free atmosphere, r>0.95 (geopotential he ight), r>0.9 (temperature), and r>0.8 (wind speed) at most sites. Over the annual cycle, there is little interseasonal variation i n skill. Over the length of the forecast, a gradual and nearly linear decrease in skill is observed from hour 0-72. An exception to this is for the surface pressure, which improves slightly in the first few hours from the initial condition, due in part to the mode l adjusting from the surface pressure biases in the initial conditions that are caused by the initialization technique over the high, cold terrain.

The impact of the higher resolution model domains over the McMurdo region is also evaluated. It is shown that the 3.3-km domain is m ore sensitive to spatial and temporal changes in the winds than the 10-km domain, which represents an overall improvement in forecast skill especially on the windward side of the island where the Williams Field and Pegasus runways are situated, and in the lee of Ros s Island, an important area of mesoscale cyclogenesis. i