The Influence of South American Monsoon Rainfall on Weather Patterns over the Northern tropical Atlantic, Northwestern Africa and Western Europe

During boreal winter, the South American monsoon system reaches its annual maximum when the upper-level westerly winds prevail over the equatorial Atlantic. Atmospheric dynamic model simulations suggest that Rossby waves generated over South America can propagate to and potentially influence the weather pattern in the Northern Hemisphere. However, observational evidence has been absent previously. Here we identify one of the major modes of variability of pentad precipitation over South America during boreal winter during 1979–2019, which is represented by precipitation anomalies averaged over the southeastern South America (SESA). In the present of the tropical “westerly duct”, by comparing the events associated with both the SESA rainfall and tropical westerlies to the events with tropical westerlies only, we found that Rossby wave trains can be triggered by precipitation anomalies over the SESA and propagate in the southwest–northeast direction crosses the equator. Over a period of 4 days, near-surface temperature over the northwestern Africa and western Europe becomes warmer, accompanied by increased surface downward longwave radiation and precipitable water. The equatorward propagating Eliassen–Palm flux anomalies originated from the SESA supports such cross-equatorial propagation of Rossby wave (CEPRW). Simulations by a time-dependent linear barotropic model forced by prescribing divergence anomalies over the SESA further confirm that the SESA rainfall can influence the Northern Hemisphere weather patterns through the CEPRW. Knowledge of this study will help us better understand and model interhemispheric teleconnections.