Climate responses to volcanic eruptions assessed from observations and CMIP5 multi-models

Abstract

This study analyzes climate responses to four volcanic eruptions that occurred since 1960s using observations (including reanalyses) and CMIP5 multi-model simulations. Changes in surface air temperature, specific humidity, and precipitation over the global land are examined during pre- to post-eruption years using a composite analysis. Observations exhibit consistent decreases in temperature, humidity, and precipitation following eruptions, which are reasonably captured by CMIP5 multi-models simulated including volcanic forcing. The observed and simulated decreases in temperature and humidity are stronger than the internal variability ranges (estimated from pre-industrial control simulations), indicating robust responses. On the other hand, the observed precipitation decrease is significant but the CMIP5 models considerably underestimate it, as reported by previous studies. In order to explore important physical processes determining climate responses to volcanic forcing, a surface energy budget is analyzed together with inter-model relationship between variables. A strong inter-model correlation (r = 0.89) appears between temperature and humidity, representing the Clausius-Clapeyron relation. Interestingly, precipitation is found to be closely related with latent heat flux (r = -0.50) and vertical motion (omega) at 500 hPa level (r = -0.68), changes of which are also underestimated by models. Further, by comparing estimates of precipitation minus evaporation between land and ocean, which is significantly correlated with vertical motion (r = -0.73), it is found that monsoon circulation weakens after volcanic eruptions but CMIP5 models substantially underestimate it. Our results suggest that this dynamic response via monsoon circulation weakening can be a critical factor for models' underestimation of precipitation reduction to volcanic forcing.