Verification of the climatic features of a regional climate model with BAIM

Abstract

Verification of local climatic features produced by a regional climate model (JSM-BAIM) that includes a Biosphere-Atmosphere Interaction Model (BAIM) in the Japan Spectral Model (JSM) was performed. The data used in the verification were the results of a six-year integration calculated by the JSM-BAIM. In the time integration of the JSM-BAIM, the spectral boundary coupling (SBC) method was used. The reproducibility of horizontally distributed features, and local and seasonal changes in the principal climatic elements of the model, were investigated in finer detail than that of our previous study. Comparisons of the model results with JMA objective analysis data were performed with respect to geopotential heights, temperatures, and winds at the 850-hPa and 500-hPa levels. Statistically significant differences appeared, mainly in the summer temperature field, and in the summer and the winter wind fields. It was considered that the statistically significant differences in the summer temperature field were due to the effects of land surface processes, and the summer convection process over the southern ocean area. The statistically significant differences in the wind field were mainly due to the influence of differences in topography between the regional model field and the analysis field, especially when interacting with the strong wind flow during the winter season. Comparisons of the model results with the data of dense surface meteorological observation network (AMeDAS) were performed with respect to precipitation, surface air temperature, and radiation at the land surface over four typical climate areas in the Japanese Islands. The model reproduced reasonably well the features of the seasonal and interannual variations of each variable, in each area. There were, however, some seasonal and regional features in the differences between the model results and the AMeDAS data. The JSM-BAIM, with the use of the spectral boundary coupling (SBC) method in a long period time integration, had sufficient accuracy for use in investigations of the interaction mechanisms between the terrestrial ecosystems and climate; temporally at least on the level of the seasonal and interannual variations, and spatially at least on the level of the climatic classification of the Japanese Islands. There is, however, the necessity for further verification using observed data, especially with respect to the near land surface air temperature in a natural vegetation environment, and the atmospheric variables over the ocean.