Long-term atmospheric circulation variability in the tropics linked to climate changes in the Amazon and Congo
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Presently, there has not been an attempt to holistically understand regional manifestations of tropical atmospheric circulation systems or how long-term changes in these systems have influenced the climate in the Amazon or the Congo. This study provides insight into long-term (1900–2010) changes in the Hadley Circulation and Walker Circulation with a focus on connecting these tropical circulation changes to regional and seasonal climate change in the Amazon and Congo tropical forests. Based on the results of this study, it can be concluded that the Hadley Circulation has distinct regional manifestations and has not changed uniformly across different regions. Globally, the Hadley Circulation has strengthened in the Southern Hemisphere and weakened in the Northern Hemisphere for the 1900–2010 time period. However, the Hadley Circulation over the Amazon indicates strengthening in both hemispheres and weakening in both hemispheres over the Congo. A strengthening of the Walker Circulation has also been identified in the Pacific and Atlantic Ocean and over the Maritime Continent. However, long-term changes of the Walker Circulation over the Atlantic are indicative to Atlantic Niño (Atlantic counterpart of the El Niño) conditions, as represented in substantial reversals of climatological zonal wind patterns. These wind reversals indicate less moisture influx into the Amazon from the Atlantic Ocean and more moisture influx into the Congo from the Atlantic although long-term precipitation trends indicate more drying in the Congo than the Amazon. This study provides valuable insight into how interactions between oceans and atmospheric circulation systems influence regional climate in the Amazon and Congo as well as large-scale changes in the full tropical belt. These findings will help to improve climate projections in the tropics by providing an essential foundation of seasonal and regional manifestations of tropical atmospheric circulation systems and how long-term changes in these systems have influenced climate in the Amazon and the Congo forests.