Local and Remote Influences on Atlantic Hurricane Potential Intensity

Recently, the role of remote vs. local SST on hurricane activity in the Atlantic attracted some interest in the climate research community, with a focus on their different effects on tropical cyclone activity in the 21st century under a global warming scenario. Here we examine this topic further, using a set of long historical sea-surface temperature (SST) experiments (1856 - 2006) with the CCM3 atmospheric model. Each experiment comprised of a set of 16 ensemble members forced with by the same prescribed SSTs. The 3 types of SST forcings considered were: GOGA (global observed SST), TAGA (tropical Atlantic observed SST, everywhere else climatological SST) and POGA (tropical Pacific observed SST, in other locations climatological SST). We calculated Emanuel's theoretical maximum potential intensity (PI) in these simulations, with a focus on the tropical Atlantic. The ensemble mean GOGA PI is similar to the PI obtained from 3 reanalysis products, in the period in which the simulations and the reanalysis are available. Differences between the Atlantic PI in the GOGA and TAGA simulations are due to the remote effect of the other basins in the tropical Atlantic PI. The TAGA PI in the tropical Atlantic is consistently higher than the GOGA PI in the same region. In order to separate the influence of the remote SST in the Atlantic PI due to natural variability and anthropogenic forcing, we regressed the Atlantic PI onto the two indices derived by Ting et al. (2009). The first index represents the AMO (Atlantic multi-decadal Oscillation), i.e. the natural climate variability in the region in decadal time-scales. While the 2nd index shows the trend in the region due to anthropogenic forcing in the 20th century. Both for AMO and for anthropogenic forcing, it is shown that the SST remote influence in the Atlantic PI leads to a statistically significant reduction of the PI value in specific regions of the tropical Atlantic.

Reference: Ting, M., Y. Kushnir, R. Seager, and C. Li, 2009: Forced and natural 20th Century SST trends in the North Atlantic. J. Climate, 22, 1469–1481.