Relationships Between Global Warming and Tropical Cyclone Activity in the Western North Pacific

In this work, we investigate the relationships between global warming and tropical cyclone activity in the Western North Pacific (WNP). Our hypothesis is that global warming impacts on TC activity occur through changes in the large scale environmental factors (LSEFs) known to be important in determining the formation and intensity of TCs. The LSEFs on which we focus are: Sea surface temperature (SST) exceeding 26oC Weak vertical shear in horizontal winds Large positive absolute vorticity at low levels Mean upward motion High mid-level humidity We separate the data into weekly 5ox5o region averages. Using a least squares fit, we identify global warming signals in both the SST and vertical wind shear data across the WNP. These signals vary significantly on a 5ox5o scale. Logistic regression was used to determine the LSEFs/TC formation probability relationship. Linear regression was performed to determine the LSEF/ACE relationship. Through the two regression models, we determine that each of the LSEFs is important for both TC formation and ACE. Independent data from that used in the regression modeling was used to validate the models. Our results support our hypothesis, and indicate that global warming has increased TC numbers and intensities in the WNP via the LSEFs.