Interdecadal change in the relationship of the western North Pacific tropical cyclogenesis frequency to tropical Indian and North Atlantic Ocean SST in early 1990s

The tropical cyclone (TC) activity over the western North Pacific (WNP) and its year to year variation is a big concern to the society as TCs may cause large damage. In this study, Wu et al. (2020) investigated reasons of interdecadal changes in the relationship between the WNP TC genesis and tropical Indian Ocean (TIO) and tropical North Atlantic Ocean (TNA) sea surface temperature (SST) in early-1990s. It was found that the above interdecadal changes are related to changes in the coherence of TIO and TNA SST variations with equatorial central-eastern Pacific Ocean (EPO) SST variations.

During 1970s through mid-1980s, TIO and TNA SSTs tend to vary in phase with EPO SST on both interannual and interdecadal time scales (Figs. 1a, 1c). The combined effects of TIO and EPO SST anomalies induce opposite environment and TC changes in southeastern and northwestern WNP (Fig. 1a), leading to a weak correlation of basin-wide WNP TC and TIO SST. Similarly, TNA and EPO SST anomalies induce opposite environment and TC changes in northeastern and southeastern WNP (Fig. 1c) and thus basin-wide WNP TC-TNA SST correlation is weak.

During late-1990s through early-2000s, TIO and EPO SST variations have a weak coherence due to their opposite relations on interannual and interdecadal time scales. TIO SST anomalies alone induce anomalous circulation over most WNP (Fig. 1b) so that basin-wide WNP TC-TIO SST relationship is strong. The interannual and interdecadal SST variations remain coherent in TNA and EPO but with a switch of sign in their relationship in early-1990s (Fig. 1d). TNA and EPO SST anomalies induce same environment and TC changes in northeastern and southeastern WNP (Fig. 1d) and thus basin-wide WNP TC-TNA SST relationship is strong.

We et al. (2002) conducted numerical model experiments to validate the importance of coherent regional SST anomalies.The results of numerical experiments confirm that a different combination of the TNA and EPO SST anomalies induce distinct distributions of wind anomalies over the WNP.

Wu, R.*, X. Cao, and Y.-Y. Yang, 2020: Interdecadal change in the relationship of the western North Pacific tropical cyclogenesis frequency to tropical Indian and North Atlantic Ocean SST in early 1990s. Journal of Geophysical Research-Atmospheres, 125(2), e2019JD031493, doi:10.1029/2019JD031493. 2020-1-27.

Figure 1Schematic diagrams showing the relationship of the June-November WNP TC number to (a, b) TIO and (c, d) TNA June-November SST anomalies during (a, c) 1969-1989 and (b, d) 1991-2011.