Aircraft Measurements of Volcanic Aerosol-Cloud Interactions (Vol-ACI)

The Fagradalsfjall eruption in Iceland began on 19th March 2021 and until the 27th of April was characterised by low-altitude continuous degassing of mainly sulfur dioxide. On 27th April, the nature of the eruption changed to continuous lava fountaining, then changed again on 2nd May from continuous to pulsed fountains up to 300m high with a doubled lava discharge rate. Since 27th April, long-range transport of the volcanic plume off the coast of Iceland has occurred and satellite imagery shows that the eruption has been influencing clouds in the North Atlantic. The eruption presents a rare opportunity to make the first ever aircraft measurements of cloud properties perturbed by volcanic activity.

Volcanic eruptions that emit gases such as sulfur dioxide into the lowermost part of our atmosphere have been recognised in the last decade as a perfect natural lab to study how emissions affect cloud amount and the physical properties of clouds, which includes the size of the tiny droplets that make up clouds. Clouds have a net cooling effect on climate because they reflect some of the incoming sunlight back to space. It is also known that emissions of gases such as sulfur dioxide (be they man-made or natural) cause changes to cloud properties once the gas-phase species are converted to airborne particles, but the details of the interplay of clouds, particles and the amount of sunlight reflected back to space are extremely complex and challenging to represent in climate models despite decades of research efforts. This project would deliver the very first measurements of cloud characteristics including changes in the vertical in areas that have been affected by the volcanic emissions. This can then be contrasted to areas that have not been affected by volcanic emissions. When combined with satellite data, our dataset will enable a new understanding of cloud and aerosol particle interactions, which in turn will help to improve model representation of these climate-relevant processes. Better models will provide a more accurate estimate of climate change, which will help to better prepare and mitigate climate change hazards.