Prof. Dr. Christian von Savigny
Universität Greifswald

Atmospheric effects of volcanic eruptions: processes and current questions

Volcanic eruptions are one of the most important drivers for natural climate change on time scales from a few years up to a decade.
Studying the effects of volcanic eruptions allows improving the understanding of the climate system's response to perturbations.
Volcanic eruptions are usually associated with a surface cooling, because the enhanced stratospheric aerosol layer increases the planetary albedo. However, the recent eruption of Hunga-Tonga Hunga-Ha'apai (HTHH) in January 2022 has shown that eruptions with massive H2O injections into the stratosphere may lead to a reduced surface cooling - and perhaps even a warming - due to the radiative effects of the excess H2O.
This presentation will discuss some recent results from the DFG Research Unit VolImpact (FOR 2820) that deals with volcanic effects on the atmosphere and climate. A particular focus will be on the atmospheric effects of the Hunga-Tonga Hunga-Ha'apai (HTHH) eruption that was quite unusual in different respects. The overshooting top of its plume reached the lower mesosphere (about 56 km) and it injected about 150 Mt of H2O into the middle atmosphere, corresponding to about 10% of the stratosphere's H2O load. In a recent study we tracked the HTHH H2O plume through the stratosphere and showed that its temporal evolution can be well reproduced with model simulations. The HTHH H2O anomaly reached the polar summer mesopause in the southern hemisphere in January 2004, constituting an unprecedented and exciting natural phenomenon in the era of global satellite observations. Finally, unusual optical phenomena sometimes occurring after volcanic eruptions, e.g. blue sun or green sunsets, will be discussed.