Tropical Atlantic Contributions to Strong Rainfall Variability Along the Northeast Brazilian Coast

Figure 4

Distributions of lagged linear regression coefficients (1974–2008) between the interannual rainfall anomalies for very wet (>+0.5) and very dry (<−0.5) years in Fortaleza-NNEB (red star) during March-April and the interannual SST anomalies during the years selected above in the tropical Atlantic for March-April (zero lag), February-March, January-February, December-January, and November-December (4-month lag) (mm·month⁻¹/°C). The vectors (mm·month⁻¹/m²·s⁻²) represent linear regressions between the interannual rainfall anomalies and the interannual PWS (PWSx and PWSy) anomalies. The 95% significance level of correlation, according to a student -test (and higher than 0.5), is plotted with a dotted line (negative) and a solid line (positive) for SSTA. Before averaging and plotting by 2-month periods, the linear trends are removed from all anomalies. The black box (NEA) relative to January-February (JF) represents a strongly influential SST variability area. NEA, which presents significant negative anomalies of SST from December-January to March-April, is used in the following for testing the forecasts of the rainfall season over NNEB.