An Exploratory Study of the Relationship Between Annual Frequency of Invaded Typhoons in Taiwan and EI Nino/Southern Oscillation

Abstract

In this study, a nonlinear association between the characteristics of invaded t}·phoons (hereafter, referred to as IT Ys) in Taiwan and sea surface temperature anon1alies (SSTAs) over the equatorial eastern Pacific is ident.ified. rf he relation is such that the years with a warmer-than-normal SSTA condition in the late season generally correspond to fewer annual IT Ys (< 4), while those with a cooler SSTA are basically associated with more IT Ys (>=4). \iVhen the SSTA becomes too cold C:S-l.0°C), how·ever, the annual total number of IT'\' s is, in fact, greatly reduced (r-v 1-2) instead of being increased.

It is suggested that such a phenomenon is caused by different large-scale atmospheric responses to the underlying sea surface temperature conditions. A lower-level anti-cyclonic circulation with strong divergence suppresses the usual activities of tropical C),clones over the western North Pacific (WNP) in the cold years. An opposite mechanism occurs in the early season of the cool years. During the \Varm years, the typhoon activities over the \\1NP are not necessarily suppressed but are rather displaced eastward in response to an anomalous cyclonic circulation over the eastern part of WNP. Under such a configuration, ho\vever, Taiwan is not in the path of the preferential storm track.

T his observat.ion appears to be useful in the long term forecasting of typhoon activities in the rfaiwan area, as long as the SSTAs can be predicted.

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