Picture: Above the Indian Ocean. Credit: Imad Boujemaoui Unsplash

Convection over the western near-equatorial Indian Ocean is strongly linked to seasonal rainfall over both Africa and Australia, and the region is influenced by a range of different tropical weather features throughout the year, including the Indian summer monsoon. However, convection in this region is represented poorly in current climate models and the factors leading to the observed annual cycle are poorly understood.

This paper investigated the annual cycle in cloud and rainfall measurements over the western equatorial Indian Ocean. While there is a single period of strong rainfall over the region during December-January each year, there are two periods of increased high-top clouds associated with convection. The second period of increased cloudiness, which occurs during June-August each year, sees less rainfall occurring for the same level of cloud than is seen during the rest of the year.

This reduction in rainfall associated with a given cloud level seems to be related to large scale monsoon circulations, which suppress convection in the region while also moving high-top clouds from areas where convection is occurring. These results give some insight into the aspects controlling the seasonality of convection in the region and possible factors that lead to poor model performance in the region.

  • Paper: King, M.J. and C. Jakob, : Rain and cloud perspectives on the seasonal cycle over the Western Equatorial Indian Ocean. J. Climate, 0, https://doi-org.ezproxy.lib.monash.edu.au/10.1175/JCLI-D-19-0080.1