On the relationship between western North Pacific tropical cyclone accumulated cyclone energy and the Pacific‐North American pattern

Abstract

AbstractThis study investigates the influence of the Pacific‐North American (PNA) pattern on the accumulated cyclone energy (ACE) of tropical cyclones (TCs) over the western North Pacific (WNP). There is a significant inverse relationship between ACE during July–October and the simultaneous PNA index during 1970–2020. Lower (greater) basinwide ACE is observed when the PNA is positive (negative), primarily as a result of lesser (greater) TC frequency, while the effects of duration and intensity are found to be relatively minor. When examining the results spatially, we find lower ACE over almost the entire WNP when the PNA index is positive compared with when the PNA is negative. Significant decreases in ACE are observed over the region to the north and east of Guam (10°–35°N, 135°–165°E) and near the Philippines (10°–25°N, 110°–130°E). These decreases when the PNA is positive are primarily induced by a decrease in TC formation as well as a reduction in average intensity in a region north and east of Guam, possibly linked to decreased low‐level vorticity and upper‐level divergence as well as increased vertical wind shear. These changes in dynamic variables are predominantly driven by large‐scale flow patterns related to the PNA.