Analysing changes in stratospheric water vapour following Pinatubo-like volcanic eruption using UK Earth System Model

Large tropical volcanic eruptions can significantly alter stratospheric water vapour either with direct injection or modifying entry pathways and the quantitative magnitude and time evolution of these changes remain uncertain. Using an ensemble volcanic forcing experiment carried out with version 1 of the UK Earth System Model (UKESM1), we explore the changes in the stratospheric water vapour (SWV) by a Pinatubo-like volcanic eruption via modification of the entry pathway. Our simulations show significant increases in SWV three months after the volcanic eruption for the ensemble mean. The increase peaks at 1 ppmv (~17% of the background levels) in the second post-eruption winter and then decays slowly, in accordance with the tropical cold point temperature anomalies. By decomposing the volcanic heating into diabatic aerosol heating and adiabatic dynamical heating, we show that the timing of tropopause heating after the eruption is determined by the seasonal variation of a general decelerated tropical upwelling imposed on the significant direct aerosol heating lasting two years.