Despite the strong dependence of the Power Dissipation Index (PDI), which is a measure of the intensity of Tropical Cyclone (TC) activity, on tropical sea-surface temperatures (SSTs), the variations in PDI are not completely explained by SST. Here we show, using an analysis of a string of observational data sets, that the variability of the thermocline depth (TD) in the east Pacific exerts a significant degree of control on the variability of PDI in that region. On average, a deep thermocline with a larger reservoir of heat favors TC intensification by reducing SST cooling while a shallow thermocline with a smaller heat reservoir promotes enhanced SST cooling that contributes to TC decay. At interannual time scales, the variability of basin-mean TD accounts for nearly 30% of the variability in the PDI during the TC season. Also, about 20% of the interannual variability in the east Pacific basin-mean TD is due to the El Niño and the Southern Oscillation (ENSO), a dominant climate signal in this region. This study suggests that a better understanding of the factors governing the interannual variability of the TD conditions in the east Pacific and how they may change over time, may lead to an improved projection of future east Pacific TC activity.
Revised: May 1, 2014 |
Published: October 16, 2013