Satellite remote sensing analysis of the 2010 Eyjafjallajökull volcanic ash cloud over the North Sea during 4–18 May 2010

Abstract

Using the Moderate Resolution Imaging Spectroradiometer (MODIS), Spinning Enhanced Visible and Infrared Imager (SEVIRI), Clouds and the Earth's Radiant Energy System (CERES) instrument, and BaE146 aircraft data sets, we provide an overview of volcanic ash spatial distribution for six days (4–18 May 2010) and assess their properties and radiative impacts for 17 May primarily over the North Sea. We describe spectral signatures of volcanic ash, compare the MODIS‐retrieved 550 nm aerosol optical thickness (AOT) and effective radii with the aircraft data, and then assess the change in radiative fluxes at the top of atmosphere using CERES. Our results indicate that the MODIS and SEVIRI thermal channels are adept at identifying volcanic ash near the source. However, the volcanic ash far from the volcanic source, especially over land, is contaminated by surface/atmospheric features. We assess the 17 May case in detail and show that MODIS AOTs (0.23–0.86) are higher than the aircraft values (0.07–0.54), probably due to different aerosol models used in the retrieval process. The MODIS effective radii values are between 0.4 and 0.9 μm with fine mode fraction values between 0.4 and 0.7. The aircraft‐derived effective radii values are between 0.82 and 1.2 μm. The TOA shortwave radiative forcing for unit AOT of volcanic ash aerosols at the time of the satellite overpass is −77 ± 4.0 W m−2 and is larger than the longwave forcing per unit optical depth (11 ± 1.2 W m−2) by seven times indicating that ash could significantly impact radiative energy fluxes.