Abstract Title: Sensitivity of Hadley Circulation to Volcanic Radiative Forcing

Abstract Submitted to: ATMOSPHERIC SCIENCES

Abstract Text:

The direct radiative effects of volcanic eruptions resulting in stratospheric warming, solar dimming, global surface cooling and reduction in rainfall are well documented in earlier studies. However, eruptions also cause indirect dynamic changes that are less well understood. For instance, volcanic aerosols-induced solar-dimming could cause changes in tropical Hadley Circulation (HC) that in turn largely affect evaporation and precipitation patterns. Therefore, understanding the sensitivity of HC to volcanism is essential, as this circulation is directly related to the precipitation changes in the tropics and with other large-scale circulations. Hence, to better understand the post-eruption sensitivity of HC and associated changes in hydrologic cycle, simulations of the El Chichón and Pinatubo tropical eruption are conducted using a High-Resolution Atmospheric Model (HIRAM), effectively at 25km and 50km grid spacing and the simulation results are compared with observational and reanalysis products. Both the model and observational analysis show post-eruption weakening, shrinking and equatorward displacement of the updraft branch of HC caused by the equatorward shift of midlatitude jets and hemispheric land-sea thermal gradient. As Inter-tropical Convergence Zone (ITCZ) is tightly-coupled to the rising branch of HC, hence post-eruption weakening and equatorward displacement of HC cause weakening of the ITCZ that adversely affects rainfall distribution in the monsoon-fed regions, especially the South Asian and African tropical rain belt regions. The model produced the post-eruption distribution of cloud contents suggests a southward shift of the ITCZ. The HIRAM results are largely in agreement with the reanalysis, observations and previous studies indicating that this model performs reasonably well in reproducing the global and regional-scale dynamic changes caused by volcanic radiative forcing.