Interdecadal Variability of Western North Pacific Tropical Cyclone Activity

This study investigates the relationship between the interdecadal variation of the annual tropical cyclone (TC) activity over the western North Pacific (WNP) and the springtime (March–May) oceanic and atmospheric conditions of the North Pacific. Variations in the annual TC activity, with active periods during 1962–75 and 1989–97 and an inactive period during 1976–88, are linked to those of the March–May sea-surface temperature (SST) anomalies in the tropical central North Pacific (CNP) and 850-hPa geopotential height anomalies over the subtropical CNP. Negative 850-hPa geopotential height anomalies and positive SST anomalies are generally associated with above-normal annual TC activity. Inactive TC seasons are related to opposite signs of these anomalies.

The springtime SST anomalies in the tropical CNP apparently persist into the main TC season. These subsequent anomalies are related to the summertime tropical 850-hPa zonal winds over the tropical WNP, which then affect the strength of the monsoon trough. The 850-hPa geopotential height anomalies are part of the anomalous low-level atmospheric circulation pattern over the subtropical WNP and hence related to the strength of the subtropical high, which again persists into the summer. Interdecadal variations in the strength of the subtropical high and the monsoon trough associated with these atmospheric and oceanic conditions in the North Pacific are therefore apparently responsible, at least in part, for the interdecadal variation of annual TC activity.