Interbasin Differences in the Median and Variability of Tropical Cyclone MPI in the Northern Hemisphere

Using the 1980-2017 6-hourly best-track tropical cyclone data and global reanalysis data, we studied the interbasin differences in the median and variability of tropical cyclone maximum potential intensity (MPI) as a function of sea surface temperature (SST) in the North Atlantic (NA), eastern North Pacific (ENP), western North Pacific (WNP), and North Indian Ocean (NI). Results show that the MPI median increases by 4.8, 7.7, 6.4, and 4.4 m s(-1) per degree increase in SST in the NA, ENP, WNP, and NI, respectively. The MPI is the largest in the NI at SST between 27 degrees C and 28.5 degrees C and in the ENP at SST above 28.5 degrees C, while is the smallest at SST below 29.5 degrees C in the WNP. The environmental factors that contribute to such interbasin differences were compared among basins. The greatest MPI in the ENP is largely contributed by the colder troposphere and drier boundary layer. The warmer troposphere and wetter boundary layer are responsible for the smallest MPI in the WNP. In the NA, the warmer outflow layer reduces the thermodynamic efficiency and partly offsets the positive contributions by the colder troposphere and drier boundary layer, resulting in the moderate MPI. In the WNP, the variability in MPI decreases with increasing SST across all four basins and is the largest. The large variability at low SSTs is largely contributed by the variability in air temperature, which includes both the air-sea temperature difference and the outflow layer temperature, while the variability at relatively high SSTs is dominantly contributed by boundary layer moisture.