Precipitation in the baiu season, which is with typhoons, is prerequisite for summer water resources in East Asia including Japan. It is therefore of great importance to prolong the prediction for baiu precipitation, even if the latest regional forecast models providing practical predictions on a synoptic scale. The present work diagnostically examines the predictability of the baiu precipitation in the western North Pacific.
Quite recently, Tomita et al. (2004) proposed that the meridional fluctuation of baiu front has two dominant interannual time scales of 4 or 5 years and of about 2 years. The differences between the two variations are attributed to the spatial phase of horseshoe sea surface temperature anomalies in the western Pacific, which are related to the ENSO events. This work diagnoses the predictability focusing not only on the meridional fluctuation of the baiu front but also on the horizontal variation pattern of the baiu precipitation.
In order to investigate the dominant precipitation variability from May to July in the western North Pacific, we first applied the extended empirical orthogonal function (EEOF) analysis to the continuous three-month precipitation field. Based on the consistence between the EEOFs and the rms of precipitation near the baiu front in June that is the central month of the baiu season, we chose the first (11.7%), fourth (8.2%), and fifth (7.2%) EEOF modes, all of which well correspond to the interannual variability of the baiu front in June. Other EEOF modes explain the dominant interannual variability in May and/or July.
The 1st EEOF mode shows the continuous precipitation anomalies in June and July. The 4th EEOF mode explains the baiu precipitation anomalies only in June, and the 5th mode indicates the precipitation anomalies persisting for three months near the baiu front. The regression analysis based on the EEOF time coefficients clearly shows that the sea surface temperature anomalies (SSTAs) from May to July off Philippines and SSTAs from the South China Sea to the south of Japan in May are significant for the three EEOF modes. Large scale air-sea interaction in the tropical western Pacific and rather local interaction near Japan seem to effectively modify the baiu precipitation. We may consider them as a precursor of the interannual variability of baiu precipitation.
Submittal Information
Name :
Date :
Tomohiko Tomita
09-Aug-04-16:40:48
Organization :
Theme :
Kumamoto Univ./FRCGC, JAMSTEC
Theme 3
Address :
Presentation :
Department of Environmental Sciences, Faculty of Science, Kumamoto Univ., Kumamoto 860-8555