Why stratospheric aerosol disproportionately cools the Indian and western Pacific Ocean

In the present publication, the research team points out two reasons for this. First, since large volcanic eruptions often originate in the tropics, the aerosols resulting from these eruptions is concentrated in the tropics, which is also where the sunlight is the strongest. This results in a stronger radiative perturbation and, consequently, a more pronounced cooling effect in the tropics, including the warm pool. However, this effect contributes only weakly to the pronounced warm pool cooling.

Second, the study explores the impact of changes in the stratospheric circulation, particularly the acceleration of the Brewer-Dobson circulation, on temperature patterns. This meridional overturning circulation, a slow-moving process driven by wave dissipation in the stratosphere, is affected by the presence of aerosols. Previous studies have shown that the aerosols locally heat the stratosphere, altering wave propagation and thus the driving force of the circulation, leading to an accelerated overturning. The present study confirms a new idea of the authors: the accelerated Brewer-Dobson circulation exports a substantial amount of energy from the tropics to the extratropics, thus contributing to the additional cooling of the tropical regions, in particular the warm pool.