Sahel precipitation and regional teleconnections with the Indian Ocean

Abstract

AbstractThe drought in the Sahel in the 1980s has been associated with Indian Ocean warming, although the Sahel has experienced a recovery in precipitation since the 1990s, despite continued warming in the Indian Ocean. Using the Community Earth System Model (CESM), we examined the linkages between the pattern of Indian Ocean warming and changes in atmospheric circulation over the Indian Ocean and North Africa to determine how they impact Sahel precipitation. The influence of the Indian Ocean on Sahel precipitation was investigated using a series of sea surface temperature (SST) sensitivity experiments. We identified two mechanisms by which the Indian Ocean can alter Sahel precipitation. The first mechanism is associated with perturbations in SSTs on the equator that alter Sahel precipitation by modulating the Asian monsoon circulation and driving changes in descent in North Africa. The second mechanism is associated with SST perturbations that cover more of the basin and alter the overturning circulation between the Indian and Atlantic Oceans. These two mechanisms result in different precipitation responses in the Sahel: the first induces an increase in precipitation as a result of warming in the Indian Ocean, whereas the second produces a decrease in Sahel precipitation in response to warming. Our results suggest that obtaining robust projections of precipitation in the Sahel will require reliably capturing the scale and spatial patterns of Indian Ocean warming.