Variations in the power dissipation index in the East Asia region

Abstract

This study examines the variability of the power dissipation index (PDI) for different regions of the East Asia region during the period 1960–2013. The annual PDI (APDI) in the region is calculated as the sum of the PDI, defined as the cube of the maximum sustained wind speed at landfall of each tropical cyclone (TC) making landfall at that region. Upward and downward trends in APDI are found in the northern and southern parts of East Asia respectively, suggesting a possible northward shift in TC landfall locations. Interdecadal variations of the APDI can also be found in some regions. The APDI in various regions show a close relation with the PDI distribution over the western North Pacific (WNP) with three characteristic patterns. The ENSO and basin-wide mode represents the PDI patterns associated with ENSO events and the overall PDI over the WNP. The east–west dipole mode and the north–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 East Asian coast, a three-cell model for TC landfall in East Asia is proposed, which corresponds to three major modes of the atmospheric circulation in the WNP. Each of these modes shows an anomalous circulation located east of Taiwan, east of Japan and the South China Sea, respectively and each of which has a significant impact on the APDI in some regions along the coast of East Asia. A northward shift in the APDI along the East Asian coast is identified in the period 1997–2013 as a result of the change in steering flow pattern, northward shift in TC genesis location and weaker vertical wind shear over the ocean near the coastal areas.