Support from the U.S. Bureau of Offshore Energy Management; and the Taiwan Foundation for the Advancement of Outstanding Scholarship, the National Science Council, the Ministry of Education, and the National Central University are gratefully acknowledged.
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Corr(A, B, lags) is the maximum lagged correlation coefficient with lags in months and is positive if A leads B. All quoted correlations are above the 95% significance level, and lags are omitted for zero-lagged correlation.
Pr1 may include influences from the strong 1988/89 La Niña. To test this, we repeated the composite and other related analyses taking 1990–94 as the cold-phase period. The results are very similar (details in SM).
The asymmetries are also seen in the ECMWF reanalysis—Fig. 10b (described in greater detail below) plots the differenced SSH, Pr2 minus Pr1, and shows two localized highs: to the south of Puerto Rico consistent with the cyclonically propagating east-side warming scenario during Pr2, and in the Columbian Basin consistent with west-side cooling during Pr1.
While changes in radiative heat fluxes are small (compared to latent heat flux) and unimportant to our argument, NCEP reanalysis data show a slight decrease (4 W m−2) in shortwave radiation during Pr2 (than Pr1) because of increased clouds. However, this is in part compensated by a reduction also of the longwave radiation during Pr2 (so net is very small), consistent with Park et al. (2005) who found positive radiative feedback over the Caribbean Sea during the fall (SON).