Relative Roles of Land and Ocean Cooling in Triggering an El Niño Following Tropical Volcanic Eruptions

Abstract

AbstractPaleoclimate evidence suggests that tropical volcanic eruptions could increase the likelihood of El Niño occurrence. Previous numerical model studies with zonally uniform volcanic aerosol forcing suggested the roles of land cooling‐induced monsoon suppression and ocean cooling‐induced air‐sea interaction in triggering an El Niño following the eruption. Here, we perform targeted sensitivity experiments by confining aerosol forcing over land or ocean only in the fully coupled Community Earth System Model to assess relative roles of these land and ocean cooling. Our results indicate that volcanic aerosol over land, especially over the large landmass of tropical Africa, is more effective in exciting an El Niño than over ocean. The suppressed African monsoon excites Kelvin‐wave westerly wind anomalies over the tropical central Pacific, triggering an El Niño through the Bjerknes feedback. Under the uniform ocean aerosol forcing, the Indian Ocean's fast dipole response induces a slow western Pacific El Niño‐like cooling in the second year.