Initial global dispersion and microphysical variation of the 1991 Mount Pinatubo cloud: A ground-based lidar and interactive modelling analysis.

Explosive volcanic eruptions are capable of injecting huge quantities of sulphur dioxide (SO₂), ash and other components into the stratosphere. This can lead to significant enhancements of the stratospheric aerosol layer and the development of the tropical reservoir of aerosol. Long term observations made by ground based lidar can be used to analyse the vertical distribution of volcanic clouds in the atmosphere over time. Here, using near-tropical (Mauna Loa (MLO)) and Northern hemisphere (Table Mountain (TBM), Toronto (TOR) and Haute Provence (OHP)) ground based lidars, we investigate the initial progression of the 1991 Mount Pinatubo cloud in the first 8 months following the eruption. At MLO, initial filaments of the cloud are apparent as it reached Hawaii in the early phases after the eruption. The volcanic cloud then became more homogeneous with respect to both the vertical and temporal distribution of aerosol as a tropical reservoir of enhanced aerosol formed. Later stages (late 1991) show signs of the Brewer-Dobson circulation affecting the cloud. Northern hemisphere sites show similar vertical structure to MLO, but receive the volcanic signal later indicating these sites receiving the cloud similarly to the evolution of the tropical reservoir. By comparing to daily-mean profiles at the ground-based lidar locations from simulations with an interactive global stratospheric aerosol microphysics model (UM-UKCA), we explore what drives the variability in the observations. The phases and filaments are observed in the model and we consider how particle size distribution evolves through these phases in the global dispersion.