Seasonal Skill Comparison between Operational Ocean Thermal Structure Products inthe Northeast Atlantic/Norwegian Sea

摘要

The U.S Navy's Fleet Numerical Oceanography Center has several operationalproducts available for thermal structure nowcasts in the northeast Atlantic/Norwegian Sea. These include regional nowcasts and short forecasts at 40 km resolution, global nowcasts and short forecasts at 190 km resolution, and two thermal climatologies at 50 km and 380 km resolutions. We propose two hypotheses: (1) that the inclusion of real-time data in the nowcasts and forecasts improves nowcast skill over the use of climatology alone and (2) that increased realtime product resolution increases nowcast skill. This study addresses these hypotheses by comparing the six products listed above in the northeast Atlantic/Norwegian Sea region an a seasonal basis. We extracted daily bathythermograph (BT) data from the real-time operational database in a 2,000 km diameter region centered on the Iceland-Faeroe Front from July 1989 through June 1990. We then compared each BT to the spatially-interpolated results from each of the six operational products. All comparisons were made prior to the BTs assimilation into the real-time products. For each season, we then accumulated three months of results to form a root-mean-square deviation of a given product relative to the verifying BTs. In this region, the results indicate that the real-time nowcasts perform better than both climatologies in autumn and winter. The results also demonstrate the advantage of increased resolution in fall and winter, but not as strongly. The spring and summer results do not produce definitive conclusions.