A robust equatorial Pacific westerly response to tropical volcanism in multiple models

• After each of the 1963 Agung, 1982 El Chichon, and 1991 Pinatubo eruptions, an El Nino was observed. The increased likelihood of an El Nino after a tropical eruption has also been found in long-term reconstructed proxy data. Through examining simulations over the last millennium by 11 different models, we show that a tropical volcano eruption can robustly excite a western-to-central equatorial Pacific (WCEP) westerly anomaly at 850 hPa in eight out of the 11 models; such a westerly anomaly is favorable for El Nino development. Under the volcanic forcing, there are significant extratropical continent surface cooling and tropical drying with negative precipitation anomalies over the South-South East Asia (SSEA), West African monsoon, and Intertropical Convergence Zone (ITCZ) regions. This common precipitation suppression response occurs in most of the models. Sensitivity experiments show that a WCEP westerly anomaly can be excited by the tropical land cooling, especially the SSEA cooling induced precipitation suppression rather than by the extratropical land surface cooling. Theoretical results show that a WCEP westerly anomaly is excited due to a Gill response to reduced precipitation over the SSEA and West African monsoon regions; and the SSEA contributes more than the West African monsoon does. The ITCZ weakening, however, excites an easterly wind anomaly. The models with more sensitive convective feedback tend to simulate an El Nino more easily, while a failed simulation of an El Nino after a robust westerly anomaly in some models calls for further studies on these models' delayed responses to radiative forcing induced by volcano eruptions.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

El Nino

Large tropical volcanic eruption

Westerly anomaly

South-South

East Asia

West African Monsoon

Precipitation suppression

climate forcing reconstructions

sea-surface temperature

earth system

model

el-nino

intercomparison project

pmip simulations

coupled

model

in-situ

millennium

impact

Meteorology & Atmospheric Sciences

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