An assessment of NOGAPS performance in Polar Forecasting from SHEBA data

Abstract

This study evaluates the latest Navy Operational Global Atmospheric Prediction System (NOGAPS) version 4.0 with a comparison to data collected during the Surface Heat Budget of the Arctic (SHEBA) project from October 1997 to October 1998. In particular, three periods from this year long study were the focus and included, a winter, spring, and summer case. For each of these cases the first 24-hour period of the forecasts were analyzed for any bias and root mean square difference from the SHEBA data. NOGAPS had no significant biases in pressure and wind speed. During the winter case, the NOPGAPS surface temperature remained near -28 C while observed temperature varied in response to cloud cover changes and was lower by 5.3 C on the average. During the spring the NOGAPS temperatures had a steady increase from -11 C until reaching the melt season temperature of 0 C 11 days earlier than observed. As a result of too warm a surface and less downwelling longwave radiation, the net longwave flux cooling was greater than observed, by an average of -12.4 Wm-2. The NOGAPS net shortwave radiation was greater than observed by an average of 62 Wm-2 for spring and 22.6 Wm-2 for summer.