Performance assessment of the Community Climate System Model over the Bering Sea

Abstract

The Community Climate System Model, version 4 (CCSM4) is evaluated against reanalysis data for the late-twentieth century (1955–2005), with a focus on the ecologically and commercially important Bering Sea in the subarctic Pacific. Several atmospheric variables including surface-air temperature, sea level pressure, wind strength, and direction were evaluated due to their relevance to large marine ecosystems. Simulated spatial patterns of climatological surface-air temperature over the Bering Sea are generally well simulated despite some subregional biases as large as +3 °C during autumn and −5 °C during winter. Interannual variability of simulated surface-air temperature exceeds that of the reanalysis by a factor of nearly 1.5. Model simulations show an under-simulated Siberian high and a large northwest displacement of the Aleutian Low-pressure centre. Further, sea level pressure over the Bering Sea is under-simulated in winter and fall by more than 8 hPa, and over-simulated in summer by more than 5 hPa. Interannual variability in simulated sea level pressure is nearly twice as large as observed. In general, the CCSM4 shows an improved representation of both monthly mean surface-air temperature and sea level pressure over the subarctic Pacific relative to its predecessor, the CCSM3. Despite these advances, there is still a clear need for improvements in the model's representation of high-latitude atmospheric circulation in order to achieve proper atmospheric forcing of marine ecosystem models.