気象庁全球モデルでシミュレートされた北半球夏の熱帯の30-60日季節内振動

Abstract

The JMA global model at T106 horizontal resolution has been integrated for 10 years with observed SST. Intraseasonal variations in the tropics during N.H. summer have been examined using 30-60 day filtered anomalies from the model simulated results. Eastward propagation of velocity potential anomalies on a 30-60 day time scale has been noticed throughout the equatorial region with a period of about 38 days. Composite analyses have been made using the principal components of an EOF analysis of the upper tropospheric velocity potential anomalies. The observed characteristics of the oscillation have been simulated by the model reasonably well. The equatorial oscillation modulates the strength of the Indian monsoon and plays an important role in deftning its intraseasonal variability on a 30-60 day time scale. The model simulates well the northward propagation of the rainfall anomalies from the equatorial Indian Ocean to the Indian region. An EOF analysis has been made using the filtered rainfall anomalies in the Indian longitudes. Composite analyses of rainfall, wind and surface fields have been made using the principal components of the EOF analysis. Circulation features in the different phases of the northward propagation resemble that of active and weak monsoon conditions and agree well with the observed analyses. It it noticed that latent heat flux variations over the sea on a 30-60 day time scale associated with the modulation of large scale monsoon circulation by the eastward propagating equatorial intraseasonal mode play a more important role than the land surface processes in the northward propagation.