November 16, 2020: Online Ocean Circulation and Climate Dynamics Colloquium

online 2 pm
Webex meeting room: https://geomar.webex.com/geomar/j.php?MTID=mb71324901b4e0c9108ba3630cb5f6f71
Meeting number (access code): 174 374 4128
Meeting password: AMteyNJm278

Eastern South America can experience severe droughts that are accompanied by heatwaves as well as marine heatwaves in the western South Atlantic. Here, we show that these multivariate events have the same driver and modulator. Tropical convection in the Indian and Pacific oceans can cause persistent anticyclonic circulation over eastern South America that not only leads to severe droughts and heatwaves but also generates marine heatwaves in the adjacent ocean. The anomalous anticyclonic circulation prevents synoptic systems reaching the region while inhibiting the development of the South Atlantic Convergence Zone and its associated rainfall in austral summer. Increased shortwave radiation due to reduced cloud cover and reduced ocean heat loss from weaker winds are the main contributors to the establishment of marine heatwaves in the region. The proposed mechanism, which involves atmospheric blocking and droughts, explains approximately 60% of the heatwaves over land and marine heatwaves in the western South Atlantic. Their impacts include water and power shortages in southeast Brazil, a region that is heavily populated, home to more than 80 million people, and responsible for 60% of the Brazilian gross domestic product. They can reduce Brazilian soy, coffee and sugarcane production, impacting food supplies globally and increasing worldwide prices. They decrease the production of oysters and the catch of some commercially important fish species, while decimating clams along the southern coast of Brazil. They can affect human health by driving dengue fever outbreaks in urban areas. In addition, these compound events degrade ecosystems causing loss of land and marine biodiversity.

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