Variations in the power dissipation index in the East Asia region

This study examines the variability of the powerdissipation index (PDI) for different regions of the EastAsia region during the period 1960–2013. The annualPDI (APDI) in the region is calculated as the sum of thePDI, defined as the cube of the maximum sustained windspeed at landfall of each tropical cyclone (TC) makinglandfall at that region. Upward and downward trends inAPDI are found in the northern and southern parts of EastAsia respectively, suggesting a possible northward shift inTC landfall locations. Interdecadal variations of the APDIcan also be found in some regions. The APDI in variousregions show a close relation with the PDI distribution overthe western North Pacific (WNP) with three characteristicpatterns. The ENSO and basin-wide mode represents thePDI patterns associated with ENSO events and the overall PDI over the WNP. The east–west dipole mode and thenorth–south dipole mode denote the east–west and north–south shifts of PDI respectively. Based on the steering flow(average winds within the 850–300 hPa layer) near the EastAsian coast, a three-cell model for TC landfall in East Asiais proposed, which corresponds to three major modes of theatmospheric circulation in the WNP. Each of these modesshows an anomalous circulation located east of Taiwan,east of Japan and the South China Sea, respectively andeach of which has a significant impact on the APDI in someregions along the coast of East Asia. A northward shift inthe APDI along the East Asian coast is identified in theperiod 1997–2013 as a result of the change in steering flow pattern, northward shift in TC genesis location and weakervertical wind shear over the ocean near the coastal areas.