THE REINFORCING INFLUENCE OF THE WALKER CIRCULATION
In addition, there is a transverse circulation over the South American continent, which is also known as the Walker circulation. Due to the southern shift of the ITCZ, which goes back to the positive temperature anomalies of the sea water off the coast of Ecuador and Peru, there is a rise of warm, humid air masses over the Amazon basin. These vertical air movements are intensified by the high solar radiation in the area of the high heating surfaces of the Bolivian Altiplano as well as by the latent heat stored in the air as a result of the high transpiration capacities of the Amazon rainforest, which is released during the condensation as a result of the ascent. Correspondingly, the descending branch of this circulation system over north-east Brazil is also strengthening. So there are two descending branches of different air circulations there, one of which comes from the north from the North Atlantic and the other from the west from the area of the Amazon rainforest and its western foothills. This exacerbates the drought in the region, as descending air leads to warming and corresponding cloud dissolution. The southern high pressure areas are also initially strengthened.
The increased South Atlantic high will be sustained for a certain time by the Walker circulation over South America even if the circulation anomalies over the South Pacific normalize again. It also deflects the ectropic disturbances coming from the south with their cold and warm fronts, which otherwise with their precipitation sometimes penetrate as far as northeastern Brazil, into the interior of the continent.
All in all, the El Niño phenomenon in northeastern Brazil not only reduces tropical precipitation linked to the zone of maximum intra-tropical convergence, but also trade wind precipitation and ectropic frontal precipitation. In addition, there is a reduction in confluence precipitation from onshore trade winds and nocturnal land winds, which often occurs in winter. The reason for this is a weakening of the land wind as a result of the cooler water temperatures of the South Atlantic off the coast of northeast Brazil. For more information about the continent of South America, please check estatelearning.com.