Photo (above): Maldives sunset: Credit: Asad Photos (Pexels).
Indian Ocean warming is one of the most robust features of anthropogenic warming. Its sea surface temperature is now 1°C warmer than in the mid-20th century, which is more pronounced than other tropical ocean basins. We investigate the effects of this warming on the global climate. By using atmospheric model experiments, we have shown that the warming of the tropical Indian Ocean relative to the other two tropical ocean basins can effectively control Walker Circulation changes in the Pacific and Atlantic oceans and influence climate far beyond the Indian Ocean region.
The warm water from the Indian Ocean evaporates into the atmosphere, creating more precipitation around that basin. The heat thus dissipates in that region, but in doing so, influences prevailing air flows in the tropical Pacific and Atlantic oceans. The subsequent effect is to suppress rainfall over the tropical Atlantic Ocean in particular.
In a warming world, the western Indian Ocean has been observed to heat up more than the eastern Indian Ocean. While this differential warming pattern is important for substantiating the observed precipitation patterns in and around the Indian Ocean basin, it is the overall warming intensity of the tropical Indian Ocean sea surface that influences circulation changes in the other ocean basins.
In the extratropical regions, the most pronounced features include a meridional pressure gradient and strengthening of westerlies in the North Atlantic during austral summer and a zonal wave 3 pattern in the Southern Hemisphere during austral winter. These patterns and associated fields are similar in structure to the circulation trend observed in nature during the last 50 years. This finding suggests a need to take the global influence of the Indian Ocean into greater consideration in observations and climate model studies of the past few decades.
Ongoing work investigates the impact of these circulation trends, driven by a warming Indian Ocean, on interannual modes of climate variability sourced in the tropical Pacific and Atlantic oceans.
- Paper: Dhame, S., A. S. Taschetto, A. Santoso, and K. J. Meissner, 2020: Indian Ocean warming modulates global atmospheric circulation trends. Clim. Dyn., https://doi.org/10.1007/s00382-020-05369-1.