Impact of Major Volcanic Eruptions on Stratospheric Water Vapor -- Analysis of Chemistry-Climate Model Simulations

Abstract

The eruptions of El Chich~on in Mexico in 1982 and Mount Pinatubo in the Philippines in 1991 are two of the strongest volcanic eruptions in the last century. Those major volcanic eruptions had signi�cant impact on earth's weather and climate system. Besides the subsequent tropospheric changes also the stratosphere was in uenced. The aim of this thesis is to improve the knowledge about how volcanoes are able to a�ect water vapor in the stratosphere. Within the scope of this study changes in stratospheric water vapor and its related chemical constituents like ozone, methane and OH are investigated. To understand the occurring changes, also the variation of dynamical patterns is analyzed. Additionally, an evaluation of the gathered results is conducted. For this study a sensitivity analysis was carried out, using results from two EMAC simulations of which one includes the volcanic forcing through prescribed aerosol extinction rates. The results show a signi�cant increase in stratospheric water vapor after the eruptions, resulting from increased heating rates and the subsequent changes in stratospheric temperatures. The tropical upwelling and the South Asian summer monsoon are identi�ed as important sources for water vapor in the stratosphere. The volcanic forcing changes the model's dynamics in similar ways after both eruptions, but this has to be interpreted with care, as the extracted results are in uenced by the simulations' set-up with an applied Newtonian relaxation technique. The dynamical changes due to the volcanoes are already implied through the nudging in both simulations. Consistent changes in the abundance of ozone, methane and OH in the stratosphere are identi�ed, which also agree with �ndings in the literature. The same is valid for changes in water vapor. This con�rms, that the used EMAC model realistically reproduces the volcanic e�ects in a comprehensive chemistry-climate simulation.