Sensitivity of regional monsoons to idealised equatorial volcanic eruption of different sulfur emission strengths

The impact of volcanic forcing on tropical precipitation is investigated in a new set of sensitivity experiments within the Max Planck Institute Grand Ensemble framework. Five ensembles are created, each containing 100 realizations for an idealized “Pinatubo-like” equatorial volcanic eruption with emissions covering a range of 2.5 - 40 Tg sulfur (S). The ensembles provide an excellent database to disentangle the influence of volcanic forcing on monsoons and tropical hydroclimate over the wide spectrum of the climate's internal variability. Monsoons are generally weaker for two years after volcanic eruptions and their weakening is a function of emissions. However, only a stronger than Pinatubo-like eruption (> 10 Tg S) leads to significant and substantial monsoon changes, and some regions (such as North and South Africa, South America and South Asia) are much more sensitive to this kind of forcing than the others. The decreased monsoon precipitation is strongly tied to the weakening of the regional tropical overturning. The reduced atmospheric net energy input at the ITCZ due to the volcanic eruption and, under negligible changes in the gross moist stability, requires a slowdown of the circulation as a consequence of less moist static energy exported away from the ascent.