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The Ups and Downs of Tropical Cyclone Activity in the Western Hemisphere
Wang, C. and Lee, S.-K. 2009. Co-variability of tropical cyclones in the North Atlantic and the eastern North Pacific. Geophysical Research Letters 36: 10.1029/2009GL041469.

The authors write that in the Western Hemisphere, tropical cyclones (TCs) "can form and develop in both the tropical North Atlantic (NA) and eastern North Pacific (ENP) Oceans, which are separated by the narrow landmass of Central America," and that "in comparison with TCs in the NA, TCs in the ENP have received less attention although TC activity is generally greater in the ENP than in the NA (e.g., Maloney and Hartmann, 2000; Romero-Vadillo et al., 2007)."

What was done
In exploring how the TC activities of the NA and ENP ocean basins might be related to each other over the period 1949-2007, as well as over the shorter period of 1979-2007, Wang and Lee employed a number of different datasets to calculate the index of accumulated cyclone energy (ACE), which accounts for the number, strength and duration of all TCs in a given season.

What was learned
The two U.S. scientists discovered that "TC activity in the NA varies out-of-phase with that in the ENP on both interannual and multidecadal timescales, "so that "when TC activity in the NA increases (decreases), TC activity in the ENP decreases (increases)." And they found that "the out-of-phase relationship seems to [have] become stronger in the recent decades," as evidenced by the fact that the interannual and multidecadal correlations between the NA and ENP ACE indices were -0.70 and -0.43, respectively, for the period 1949-2007, but -0.79 and -0.59, respectively, for the period 1979-2007.

What it means
In terms of the combined TC activity over the NA and ENP ocean basins as a whole, there is little variability on either interannual or multidecadal timescales; and real-world empirical data suggest that the variability that does exist over the conglomerate of the two basins has grown slightly weaker as the earth has warmed over the past six decades, which runs counter to climate-alarmist claims that earth's hurricanes or tropical cyclones should become more numerous, stronger and longer-lasting as temperatures rise.

Maloney, E.D. and Hartmann, D.L. 2000. Modulation of eastern North pacific hurricanes by the Madden-Julian Oscillation. Journal of Climate 13: 1451-1460.

Romero-Vadillo, E., Zaytsev, O. and Morales-Perez, R. 2007. Tropical cyclone statistics in the northeastern Pacific. Atmosfera 20: 197-213.

Reviewed 3 November 2010