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Comparison study of stratospheric volcanic aerosol layers in 2008 and 2009 detected by means of LIDAR in the Arctic

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Hoffmann, A. , Ritter, C. , Stock, M. , Maturilli, M. , Herber, A. and Neuber, R. (2010): Comparison study of stratospheric volcanic aerosol layers in 2008 and 2009 detected by means of LIDAR in the Arctic , Oslo Science Conference 8-12 June 2010 T2-2 Troposphere and stratosphere dynamics and processes and their links with climate. .
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Abstract:

Volcanic eruptions can alter the state of the stratosphere on a timescale of several months to years and can have a significant impact on radiative forcing especially in the climatologically sensitive Arctic regions.The eruptions of the Kasatochi volcano in August 2008 and Sarychev volcano in June 2009 led to an enhanced stratospheric aerosol load which was studied with the Koldewey Aerosol Raman Lidar (KARL) at the AWIPEV Arctic Research Base in Ny-Ålesund, Spitsbergen at 78.9 N, 11.9 E. In both years, distinct layers of enhanced aerosol backscatter in the lower stratosphere and the tropopause region have been observed on subsequent days coinciding with a significant increase in aerosol optical depth (measured with sun photometer) compared to the mean values from 2004 2007.Two case studies some weeks after the eruptions are compared: 1 September 2008 and 13 July 2009. Both days show the lowest layer of enhanced aerosol just above the tropopause with a backscatter ratio of 2-4. Calculations of the lidar ratio as well as the estimation of microphysical parameters of the aerosol particles were performed for these aerosol layers identifying significant differences between the two events. The Kasatochi aerosol showed a much higher lidar ratio indicating a higher index of refraction and hence a higher fraction of absorbing material. Furthermore, on 13 July 2009, the temperature profile obtained with a VAISALA RS98 balloon sounding shows a negative correlation with layers of enhanced backscatter within the stratosphere, which could not be confirmed for 1 September 2008.Our studies imply that, although the spatial distribution of aerosol layers originating from two different volcanic eruptions shows certain similarities, their chemical composition as well as their radiative forcing are very dissimilar. This fact has to be considered in general circulation models to evaluate the climate forcing of volcanic eruptions.

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