Change in relationship between western North Pacific tropical cyclone frequency and the tropical Pacific SST

摘要

We examine the relationship between the number of tropical cyclones (TCs) inthe western North Pacific and the tropical Pacific sea surface temperature (SST) duringthe main TC season (from July to November). Results show that there are periodswhen TC frequency and the tropical Pacific SST are well correlated and periods whenthe relationship breaks down. Therefore, decadal variation is readily apparent in therelationship between the TC frequency and the SST variations in the tropical Pacific.We further examine the oceanic and atmospheric states in the two periods whenmarked contrast in the correlation between the TC frequency and the tropical PacificSST is observed. The analysis indicates that before 1990 oceanic conditions largelyinfluenced anomalous TC frequency, whereas atmospheric conditions had little impact.After 1990, there the reverse appears to be the case. A role of atmosphere and ocean inrelation to the TC development in the western North Pacific changes, which isconsistent with change of the correlations between the TC frequency and the tropicalPacific SST.