Typhoon Rainfall over Taiwan Area: The Empirical Orthogonal Function Modes and Their Applications on the Rainfall Forecasting


Distribution of 6-h accumulated typhoon rainfall over Taiwan area is investigated through empirical orthogonal function (EOF) analysis. The data set used includes the rainfall of 20 Central Weather Bureau surface stations when typhoons were inside the domain between 18°N and 18°N, 116°E and 126°E, form 1961 to 1996. Analysis results show that the first three EOF modes are well separated from the other modes. Those three modes contain about 66% of the total rainfall variances. At some stationsk only those three modes can effectively represent the station rainfall. The first EOF mode not only reveals the in-phase increasing or decreasing rainfall at all stations of Taiwan but also shows that larger rainfall occurs at stations with higher elevation and larger slope. The enhancement of rainfall in mountainous areas is an indication of topography effect on redistributing rainfall. The second mode and the third mode both show out-of phase distribution of rainfall over Taiwan when typhoons are nearby. The rainfalls are enhanced on the up-wind sides of the mountain, and the rainfalls are suppressed on the down-wind sides. Those distributions again reveal the effects of redistributing rainfall by Central Mountain Range of Taiwan. 

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