Volcanic impacts on atmospheric dynamics (VolDyn)

• Applicants: Dr. Hauke Schmidt; Dr. Sandra Wallis
• Subject Area: Atmospheric Science
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398006378

There is a large body of scientific literature on the response of stratospheric and troposphericdynamics to volcanic aerosol clouds. Due to the small number of well observed large eruptions and due to the large internal variability of the system, there are still some open questions, but a general picture has emerged which involves in particular an acceleration of the stratospheric meridional overturning circulation, the strengthening of stratospheric vortices and tropospheric responses to this stratospheric anomaly. Much less is known, however, about the mesospheric response. There are indirect indications of temperature anomalies from observations of polar mesospheric clouds (PMC) and direct ones from Lidar observations after the Pinatubo eruption, but little is known about potential mechanisms which may have contributed to this. Our project intends to fill this knowledge gap. In phase I of VolDyn we showed that also the Halogen Occultation Experiment (HALOE) satellite instrument, that started observing shortly after the Pinatubo eruption, indicates a positive upper mesospheric temperature anomaly possibly related to the eruption. First simulations with the upper atmosphere icosahedral non-hydrostatic (UA-ICON) general circulation model have shown for the summer hemisphere a clear influence of stratospheric circulation anomalies on mesospheric dynamics. We are currently analyzing interhemispheric coupling processes.In phase II of VolDyn we will continue using UA-ICON to systematically explore the sensitivity of the mesospheric perturbation to the characteristics of an eruption, such as the emitted sulfur mass, the eruption latitude, or the eruption season.Moreover, as mesospheric anomalies are likely sensitive to specifics of stratospheric circulation anomalies, we want to simulate the historic Pinatubo eruption (the largest volcanic event in the satellite era) and its effects up to the mesosphere as realistically as possible using a nudging approach for the stratosphere. Our aim is to not only make a qualitative but also a quantitative comparison with existing observations – something that is not possible for other historic eruptions such as those of Tambora or Krakatau. To compare the simulation results for the Pinatubo run with observations, we will use virtually all available mesospheric temperature data sets that contain the date of the Pinatubo eruption or the immediate months afterwards. These include data from satellite-borne instruments such as HALOE and the wind imaging interferometer (WINDII), and data from ground-based stations such as Table Mountain, Haute Provence, Hohenpeißenberg, and Wuppertal.Finally, not only circulation but also water vapor anomalies may contribute to the observed PMC signals. To understand this, we want to analyse the transport of volcanic water vapour to the polar summer mesopause in further model simulations.

• DFG Programme: Research Units
• Subproject of: FOR 2820: Revisiting The Volcanic Impact on Atmosphere and Climate – Preparations for the Next Big Volcanic Eruption
• Co-Investigator: Professor Christian von Savigny, Ph.D.