Post-Volcanic Aerosol Altitude and Particle Size Measurements Basing on Twilight Sky Polarimetry

Measurements of the background intensity and polarization of the twilight sky were conducted during the "purple lights" epoch that was potentially caused by the Raikoke volcano eruption in the summer of 2019. An increase in sky brightness paired with a decrease in polarization was registered, especially noticeable in the dusk segment. Using techniques developed in previous works, altitude distribution and the mean particle size of additional aerosol was found. The mean radius of (0.11 micrometers) is typical for background or moderate eruption conditions, however, aerosols were mostly observed in the upper troposphere and near the tropopause rather than in the stratosphere. A comparison with existing aerosol data after mid-latitude eruptions like the Kasatochi volcano eruption one decade ago showed similar properties, which can be used as confirmation that the "purple lights" event in 2019 was of volcanic nature.