Abstract
Abstract. Ground-based spectral measurements of twilight sky brightness were carried out between September 2009 and August 2011 in Georgia, South Caucasus. The algorithm which allowed to retrieve the lower stratospheric and upper tropospheric aerosol extinction profiles was developed. The Monte-Carlo technique was used to correctly represent multiple scattering in a spherical atmosphere. The estimated stratospheric aerosol optical depths at a wavelength of 780 nm were: 6 × 10−3 ± 2 × 10−3 (31 August 2009–29 November 2009), 2.5 × 10−3 ± 7 × 10−4 (20 March 2010–15 January 2011) and 8 × 10−3 ± 3 × 10−3 (18 July 2011–3 August 2011). The optical depth values correspond to the moderately elevated stratospheric aerosol level after the Sarychev eruption in 2009, background stratospheric aerosol layer, and the volcanically disturbed stratospheric aerosol layer after the Nabro eruption in June 2011.
Highlights
Stratospheric and upper tropospheric aerosols are important atmospheric constituents
Volcanic eruptions inject large amounts of sulfur dioxide into the stratosphere where it is oxidized in the presence of water into sulfuric acid that condensates into sulfuric acid droplets forming the stratospheric aerosol layer (SAL)
In this paper we present lower stratospheric and upper tropospheric aerosol extinction profiles retrieved from groundbased spectral measurements of twilight sky brightness
Summary
Stratospheric and upper tropospheric aerosols are important atmospheric constituents. We make use of another technique, the twilight sounding method (Mateshvili et al, 2005) where groundbased measurements of twilight sky brightness are performed to retrieve both lower stratospheric and upper tropospheric aerosol extinction profiles. It is well known that the stratospheric aerosol presence manifests itself by the so-called “purple light”, a reddening of the twilight sky when the Sun is a few degrees below the horizon This effect is especially strong after major volcanic eruptions when the aerosol load in the stratosphere increases dramatically. In this paper we present lower stratospheric and upper tropospheric aerosol extinction profiles retrieved from groundbased spectral measurements of twilight sky brightness. We consider measurements acquired in 1991, after the Pinatubo eruption, to analyse the phenomenon of the “second purple light”, the late reddening of twilight sky that is sometimes visible after the “first purple light”, when the Sun sinks deeper behind the horizon (Mateshvili et al, 2005)
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