Raikoke Volcanic Sulfate/SO 2 Anticyclonic Contained Circulations: In Situ Proof, Morphology, and Radiative Signature

Source abstract

Abstract We present an analysis of the stratospheric cloud from the June 2019 Raikoke volcanic eruption. The cloud is observationally characterized herein as consisting primarily of and sulfuric acid droplets, and marked by multiple distinctive, quasi‐circular cloud features 300–400 km in diameter. Previous reports showed that one of these entities was traceable for 3 months. Anticyclonic circulation was also previously reported. We present multiple lines of evidence to characterize these cloud subelements by their spatial confinement, morphology, and sulfate‐dominated aerosol aspect, which was evident from plume onset. In addition, we show that they were ably identifiable in geostationary satellite “cirrus channel” reflectance imagery and had an enduring signal of window infrared absorption, detectable for at least 1 month. The term we apply to this phenomenon is “sulfate/SO 2 anticyclonic contained circulation,” abbreviated SSACC. Anticyclonic circulation is first detectable on 24 June, 2 days posteruption. Two SSACCs persist beyond June. One is traceable until mid‐August over Canada. The other SSACC was discernible until 5 October after having completed three global circumnavigations. The internal SSACC circulation aspect is gleaned from geostationary‐based visible image animations and confirmed in situ via a novel application of high‐resolution radiosonde wind direction and balloon position data. We also examine diabatic lofting of both SSACCs in relation to their individual geographic and constituent morphologies. Thermal infrared observations show that SSACC aerosols produce brightness temperature depressions of 2.6 K, opening a new line of investigation into the source of heating that contributes to diabatic rise.