Radiative effects of volcanic aerosols over Southwestern Iberia

Aerosols are important atmospheric constituents, playing a major role in many atmospheric processes and capable of altering the Earth’s radiation budget, through direct and indirect effects, thus acting as major drivers of climate forcing. Understanding and quantifying the ways in which different types of aerosols interact with radiation is therefore crucial.

The investigation focuses on the radiative effects of transported aerosols originating from the Tajogaite volcanic eruption at La Palma, Canary Islands (Spain), which occurred between September and December 2021. The Iberian Peninsula was on the path of a few occurrences of atmospheric aerosol plumes originating from the eruptive region, with a notable case between 11 and 13 October. The primary aim of the study is to examine the radiative effects of volcanic aerosols in different spectral regions, during this period over Évora and Granada. Sun-photometer and lidar measurements available at these sites provide comprehensive columnar and vertically resolved aerosol data. It was already reported that volcanic ash was limited to regions nearby the source, and that particularly during the 3-day period (11-13 October) considered, the ash cloud covered an area below 100 km². Observations on 12 October indicate that the volcanic plume transport towards Iberia was characterized by low particle depolarization ratios (with a mean value of 0.08±0.02) and a high backscatter-related Angström exponent between 532–1064 nm (with a mean value of 1.4±0.24). These values suggest that the plumes transported for longer distances predominantly contained small spherical sulphate particles. A mean aerosol optical depth of 0.12±0.021 at 532 nm, was registered on 12 October at the sites considered. Lidar measurements revealed a layer of small particles roughly located between 2.5 and 5.0 km above sea level at Évora, with a slightly lower bottom at Granada (~2 km).

The radiative effects in the UV, VIS-NIR, and IR spectral regions will be assessed using the uvspec program within the LibRadtran software package. This tool enables the calculation of radiative fluxes at different vertical levels using measured aerosol properties, including the particle extinction coefficient profiles. The impact of the aerosol vertical distribution on the radiative effects, as well as their assessment at the surface and TOA levels, will be presented.