熱帯太平洋の海水温変動を考慮した場合としない場合の大気大循環モデルにおける冬期平均降水量と上部対流圏循環の経年変動

Abstract

Interannual variations of winter mean precipitation and upper-tropospheric stationary eddy and the influence of tropical sea surface temperature (SST) on their variability are investigated. The data used are obtained from a series of 15-year general circulation model (GCM) integrations with (theSST runs') and without (thecontrol run') interannual variations of tropical Pacific SST observed during a 15-year period. By comparing the variability appearing in the SST runs to that of the control run, it is shown that the fluctuation of tropical Pacific SST accounts for a large fraction of precipitation variability in localized tropical regions, particularly over the central Pacific and Indonesian subcontinent, and the variability of upper-level stationary eddy over the subtropical central Pacific in both hemispheres. However, the amplitudes of variability in the extratropics are not influenced by the SST. The east-west seesaw between fluctuations of precipitation over the equatorial central Pacific (cp) and the tropical western Pacific (wp) and the induced anomalous Walker circulation owe their existence mainly to the SST fluctuation over cp. Both precipitation anomalies over cp and wp in the SST runs induce the circulation anomaly in the Pacific/North America (PNA) region, but the stronger response results from the precipitation anomaly over cp. Among the tropical regions, the central Pacific is the region where SST has the strongest impact on the large-scale fluctuations of tropical precipitation and midlatitude circulation over the PNA sector. In the control run, however, tropical precipitation anomalies over cp and wp do not result in any organized large-scale circulation pattern in the midlatitudes.