Change in tropical cyclone size over the western North Pacific

Tropical cyclone (TC) size is a key factor in determining TC destructiveness and a major challenge in understanding changes in TCs. Although much effort has been devoted to investigating TC track and intensity changes, relatively few studies have focused on TC size changes, particularly their responses to natural variability and global warming. Here, we use a metric of TC size in which TCs achieve their lifetime-maximum intensity, which is relatively insensitive to uncertainty in past data. The results show that the Interdecadal Pacific Oscillation (IPO) dominates TC size variability in the western North Pacific, which is the most active region for TCs. Moreover, TC size variability is governed primarily by radial sea surface temperature (SST) gradients rather than absolute SST values. This finding explains not only the difference in TC size between IPO positive and negative years but also the stronger correlation between the IPO and TC size than other climate indices, such as El Niño–Southern Oscillation (ENSO), since the IPO is derived from SST differences and thus gradients, whereas ENSO is determined by absolute SST values. This finding further implies that the pattern rather than the magnitude of the SST change will determine the change in TC size under future global warming.