Global dispersion and microphysical variation of the 1991 Mount Pinatubo plume: A ground-based lidar and interactive modelling analysis.

Thursday, 22 March 2018
Iriarte (Hotel Botanico)
Sarah Shallcross1, Graham W Mann2, Anja Schmidt3, Ryan Neely2, Sandip Dhomse2, Jim M Haywood4 and Andy Jones5, (1)University of Leeds, ICAS - Earth and Environment, Leeds, United Kingdom, (2)University of Leeds, Leeds, United Kingdom, (3)University of Cambridge, Cambridge, United Kingdom, (4)Met Office, Exeter, United Kingdom, (5)Met Office Hadley Centre for Climate Science and Services, Exeter, United Kingdom
Abstract:
Major volcanic eruptions inject huge quantities of sulphur dioxide (SO2) and ash into the upper atmosphere. Sulphuric acid aerosols, converted from emitted SO2, significantly enhance the stratospheric aerosol layer and have complex effects on the Earth’s climate.

The 1991 eruption of Mount Pinatubo created a plume that spread worldwide within two weeks. The global dispersion of the plume was strongly influenced by the prevailing easterly phase of the quasi-biennial oscillation, assisting in confining the volcanic aerosol plume to the tropics. There was substantial transport to the mid-latitudes over the first post-eruption year.

In this analysis, we examine how the vertical distribution of the Pinatubo plume evolves over time as observed by ground based lidar measurements at tropical (Mauna Loa, MLO) and Northern hemisphere mid-latitude (Table Mountain, TBM and Toronto, TOR) observatories.

At MLO clearly descending strands of the plume are detected in the early phases after the eruption, the lidar signal then becoming more homogeneous as a tropical reservoir of enhanced aerosol forms. With the progression towards winter, the seasonal cycle of the Brewer Dobson transports air masses into northern hemisphere mid-latitudes and only then do the TBM and TOR sites detect the main part of the plume. We identify similar structures within the vertical profile of the MLO lidar signal and Northern hemisphere mid-latitude sites, underlining the donor-receptor relationship between the two latitude regimes.

By comparing to daily-mean profiles from interactive simulations with a global stratospheric aerosol microphysics model, we then explore what drives the variability in the observations. In particular, we consider how particle distribution evolves through these phases in the global dispersion, also considering the effects from new particle formation and coagulation growth in the plume.

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