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Major Saharan dust storms can block out the Sun, Walker Institute reveals – University of Reading

Release Date : 10 January 2007

******EMBARGOED until 00.01am on Thursday 11th Jan****** Scientists from the Walker Institute at the University of Reading have discovered just how dramatically a Saharan dust storm can block out the Sun. The work, which the journal Nature summarised in its Research Highlights section, studied a large Saharan dust storm which raged across the North African desert in March 2006, the largest storm for the previous two years. It reveals how the Sun is blocked out by around a third, causing temperatures at the surface to plummet. For the first time, scientists were able to measure what happens by using both satellites in space and instruments on the ground. Dust storms like this are so large, they can be seen clearly from space, but understanding how they affect the atmosphere has been difficult because of a lack of measurements taken from the ground. The study, led by Professor Tony Slingo, has provided the most comprehensive picture yet of just how large the impact of a dust storm can be. (See pictures available to download on Walker Institute website). "For me the key point is just how large the effects of the dust storm are – this study is the first time that's been shown so clearly. Our models do well in simulating the amount of sunlight absorbed by the dust – that provides crucial information for reducing uncertainties in our predictions of future climate," said Professor Tony Slingo. The study also shows for the first time, that computer models of energy in the atmosphere can simulate the way the dust cloud absorbed the incoming sunlight. This match between models and what was observed, gives greater confidence when these same models are used to predict the climate of say the 2050s. The amount of sunlight absorbed by the dust depends on what the dust is made of and this can vary a lot even within a single dust storm. The dust in the March 2006 storm was found to contain a lot of iron and chalk which made it absorb sunlight strongly. The iron gives the dust its red colour and, when it blows over the Atlantic, some of it ends up in the sea where the iron acts as a fertiliser for microscopic plankton that whales and other creatures feed on. The study makes use of a unique set of observations taken simultaneously from satellites in space and from instruments based on the ground in West Africa during the whole of 2006. Measurements were taken of, for example, energy at the top of the Earth's atmosphere, of energy at the ground, of rainfall and temperature and of clouds and aerosols – tiny particles like fine dust lifted into the air by dust storms. The ground based measurements came from the US Atmospheric Radiation Measurement programme which had its mobile facility based at Niamey, the capital of Niger, on the southern fringes of the Sahara desert from January to December 2006. Notes to editors: (1) For more information and to arrange interviews please contact: Kathy Maskell or Maria Noguer on 0118 3787380. Alternative number: 0118 378 8315. (2) This work is based on the following paper: A Slingo et al (2006). Observations of the impact of a major Saharan dust storm on the atmospheric radiation balance. Geophysical Research Letters, vol. 33, L24817, doi:10.1029/2006GL027869. (3) The Walker Institute for Climate System Research at the University of Reading is concerned with understanding our climate, in order to deliver better knowledge of future climate and its impacts for the benefit of society. It is composed of groups from a number of departments and centres across the University. See the Walker Institute website. (4) Professor Tony Slingo is Deputy Director of the Environmental Systems Science Centre at the University of Reading, a NERC centre of excellence in earth observation.


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