Semi-circumglobal teleconnection across Eurasia driven by deep convection over Sahel

The Sahel region, which is located between tropical rainforest Africa and Sahara Desert, has large interannual variability of rainfall in association with extremely deep convection. Several studies have been suggested that interannual variability of the Sahelian convection has an influence on a mid-latitude weather system over Europe. It is also known that an anomalous weather pattern, i.e., a blocking high, over Europe is a source of eastward propagating large scale waves across the Eurasian Continent toward East Asia. Present study examines whether the Sahel convection remotely influences the weather of East Asia through wave propagation over Eurasia.

The outgoing longwave radiation (OLR) is used for the interannual variation of the convective activity over Sahel. The regressed mid-latitude atmospheric fields with the OLR index shows that west-east wave train patterns were seen from West Europe to Siberia in June and September (see figure). We confirmed that these wave train patterns are independent of the tropical oceans such as El Niño. Furthermore, in order to confirm that whether the Sahelian convection drives those wave train patterns, we applied a numerical experiment using a linear baroclinic model. Atmospheric responses to given heating anomalies to the upper troposphere over Sahel shows west-east wave train patterns. These calculated wavy patterns agree well with those of observation. We suggest that the interannual variability of the Sahelian convection might drive the semi-circumglobal teleconnection across Eurasia.