Regional Climate Response of Middle Eastern, African and South Asian Monsoon Regions to Explosive Volcanism and ENSO Forcing

It is well observed that the monsoon climate experiences substantial climatic changes following explosive volcanism. Likewise, previous studies show that the monsoon climate regimes, especially, the African and South Asian tropical regions, are adversely affected by El Niño-Southern Oscillation (ENSO) events. Hence, studying the sensitivity of the monsoon regions to the effect of these forcing factors, that is, explosive volcanism and volcanic-induced ENSO forcing, is essential for better understanding the driving mechanism and climate variability in these regions. Using observations and a high resolution atmospheric model, effectively at 50- and 25-km grid spacing, this study shows that ENSO and tropical eruptions together weaken the upward branch of Northern Hemisphere (NH) Hadley cell, that is, Intertropical Convergence Zone. This results in a significant decrease of monsoonal precipitation, suggesting severe drought conditions over the NH tropical rain belt regions. The volcanic-induced direct radiative cooling and associated land-sea thermal contrast result in significant warming and drying due to the reduction of clouds over the monsoon regions in boreal summer. The posteruption ENSO circulation also results in warming and drying over NH tropical rain belt regions. This study confirms that the monsoon climate regime responds vigorously to posteruption direct radiative and indirect circulation impacts caused by volcanic-induced ENSO forcing. Hence, quantification of magnitude and spatial pattern of these postvolcanic direct and indirect climatic responses is important for better understanding of climate variability and changes in Asian and African monsoon regions.