Detection of Hunga Tonga volcanic aerosols in Northern Hemisphere stratospheric westerlies for the first time

The Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences has led an international team that has made a significant discovery. They detected aerosols from the Hunga Tonga eruption in the Northern Hemisphere stratospheric westerlies, which has never been done before. This discovery, published in Science Bulletin, will aid in simulating the physical and chemical processes in volcanic plumes.

The Hunga Tonga-Hunga Ha’apai volcano erupted in January 2022, spewing ash and gas into the atmosphere. It was closely monitored by scientists worldwide. The eruption was one of the largest in recent years.

The team made this discovery unexpectedly during the Sounding Water vapor, Ozone, and Particle (SWOP) campaign. The purpose of the SWOP campaign is to better understand the temporal and spatial distribution characteristics of atmospheric compositions over the Tibetan Plateau.

Prof. Bian Jianchun, an IAP scientist and a team leader of the SWOP campaign, said, “We happen to have captured the volcanic aerosols from the Hunga Tonga eruption 12 weeks after it erupted. To my knowledge, this is the first time that it’s been detected at the stratospheric westerlies in the Northern Hemisphere.”

However, uncertainties still remain in understanding the physical properties and evolutionary process of volcanic aerosols in the stratosphere, particularly SO2 oxidation in volcanic plumes and clouds and the interaction between ash and sulfate aerosols after volcanic eruptions. In-situ measurements obtained in volcanic plumes, especially measurements of the microphysical parameters of volcanic aerosols, provide compelling evidence that reduces these uncertainties. Obtaining these parameters during the occurrence of volcanic eruptions is difficult.

As part of the SWOP campaign, a balloon-borne payload containing the Compact Optical Backscatter Aerosol Detector (COBALD) and Portable Optical Particle Spectrometer (POPS) was released in Lijiang, Yunan province on April 9, 2022. Unexpectedly, the balloon captured the size spectrum of volcanic aerosols at 24-25 km.

The volcanic aerosol from the Hunga Tonga eruption was identified by the size distribution of the aerosol diameter, which was larger than the background mode of stratospheric aerosols. The particle number densities were around 1 cm-3. The COBALD measurements at 455 nm and 940 nm showed enhanced aerosol signals between 24 and 25 km. Measurements also indicated that the aerosol and water vapor layers were separated in the Hunga Tonga plume.

These findings suggest that volcanic eruptions can have an impact on regional and global atmospheric circulation and climate, even if they occur thousands of kilometers away from the source. Further research will examine the possible mechanisms that led to the separation of the aerosol and water vapor layers in the Hunga Tonga plume.

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