The impacts of the 2014 eruption of Holuhraun in Iceland: the tropospheric equivalent of Mount Pinatubo

Thursday, 17 December 2015: 09:30
3014 (Moscone West)
James Matthew Haywood1, Florent Malavelle2, Andy Jones3, Nicolas Bellouin4, Olivier Boucher5, Sophie Bauduin6, Ken S Carslaw7, Lieven Clarisse8, Hugh Coe9, M Dalvi3, Sandhip Dhomse7, Andrew Gettelman10, Dan Grosvenor7, Margaret E Hartley11, Ben Thomas Johnson3, Colin Johnson3, Jeff Knight3, Jon Egill Kristjansson12, Graham Mann7, Fiona M O'connor13, Steven E Platnick14, Anja Schmidt7, Graeme L Stephens15, Hanii Takahashi16, Richard Philip Allan17 and Matt Hawcroft18, (1)University of Exeter, Exeter, EX4, United Kingdom, (2)University of Exeter, Exeter, United Kingdom, (3)Met Office Hadley center for Climate Change, Exeter, United Kingdom, (4)University of Reading, Department of Meteorology, Reading, United Kingdom, (5)LMD, Paris Cedex 05, France, (6)Université Libre de Bruxelles, Brussels, Belgium, (7)University of Leeds, Leeds, United Kingdom, (8)Université Libre de Bruxelles, Bruxelles, Belgium, (9)University of Manchester, School of Earth, Atmospheric and Environmental Sciences, Manchester, United Kingdom, (10)National Center for Atmospheric Research, Boulder, CO, United States, (11)University of Cambridge, Cambridge, United Kingdom, (12)University of Oslo, Department of geosciences, Oslo, Norway, (13)UK Met Office, Exeter, United Kingdom, (14)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (15)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (16)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (17)University of Reading, READING, United Kingdom, (18)University of Exeter, CEMPS, Exeter, United Kingdom
During the period 31st August September 2014- 28th February 2015, a significant fissure eruption occurred in the Holuhraun area of Iceland. Unlike the well documented eruption of Eyjafjallajökull in 2010, this eruption has received relatively little public attention as the emissions are at low altitude, there is little accompanying ash, and thus there has not been any impact on trans-Atlantic air-traffic. However, the emission rates of sulphur dioxide from the eruption during the first two months was at least four times those from the entire 28 European member states and the continuous nature of the eruption means that by the end of the eruption, the emissions of sulphur dioxide exceeded the total annual emission targets of all of Europe. We provide a comprehensive global modelling estimate of the impact on cloud microphysics and show that the empirical relationship between degassed sulphur and TiO2/FeO ratios derived from prior Icelandic basaltic flood lava has undoubted utility. The impact of the sulphur dioxide cloud droplet size is clearly identified in satellite retrievals over the entire North Atlantic. Pristine clouds of lesser reflectivity were replaced by polluted clouds of higher reflectivity. This eruption provides an ideal test bed for validating models and inter-comparing observations of aerosol-cloud-interactions. Simulations with HadGEM3 including a detailed aerosol-microphysical scheme show excellent agreement with observations of cloud effective radius and cloud droplet number concentration and we use the model to assess the detectability of other variables such as aerosol optical depth, cloud liquid water path, cloud optical depth and radiation forcing. We conclude that, just as the explosive eruption of Pinatubo into the stratosphere provided the basis for many model and satellite analysis and inter-comparisons, the Holuhraun eruption provides a similar counterpart for focussing analyses of tropospheric cloud-aerosol interactions.