| Summary: | Volcanic eruptions have a variety of impacts on the climate, from short-term reductions in temperature lasting only days, to longer term impacts due to the influence of stratospheric aerosols lasting 2-3 years, and even decadal scale effects arising from the impact on the oceans. Large tropical eruptions have the biggest impact on the stratosphere and have the potential to have long lasting global impacts. These large eruptions allow sulphate aerosols to be formed within the tropical stratosphere and transported globally by the stratospheric circulation, not only causing the well-known global averaged surface cooling, but also heating within the stratosphere due to the aerosols which can cause significant dynamical feedbacks. In this thesis, I investigate the impact of such large tropical eruptions on the North Atlantic wintertime climate. I analyse observational and reanalysis datasets for periods within 1870-2010 using multiple linear regression to try to isolate the volcanic response from other forms of climate variability in sea level pressure (SLP), sea surface temperature (SST), the North Atlantic jet latitude and speed, and atmospheric blocking. I do this at various lags from 0 to 5 years following an eruption, which shows the initial wintertime surface response similar to a positive North Atlantic Oscillation (NAO) phase as found in previous studies. However, the strongest signal appears during the first winter and doesn’t persist as strongly into the second as these studies have suggested. Focusing on time periods centred on specific eruptions shows the strongest response comes from the Mount Pinatubo eruption of 1991, and that the eruption of Agung in 1963 shows a very different response pattern. A ‘lag 4 response’ also appears during the 5th post-eruption winter in several fields, which, if real, could suggest the influence of other mechanisms, possibly involving the ocean, and warrants further investigation.
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