Cluster analysis of the impact of air back-trajectories on aerosol optical properties at Hornsund, Spitsbergen

摘要

In this paper, spectra of aerosol optical thickness from the AERONET(AErosol RObotic NETwork) station at Hornsund in the southern partof Spitsbergen were employed to study the impact of air mass historyon aerosol optical thickness for wavelength λ=500 nm –AOT(500) – and the ?ngstr?m exponent. Backward trajectoriescomputed, using the NOAA HYSPLIT model, were used to trace airhistory. It was found that in spring, the changes in AOT values overthe Hornsund station were strongly influenced by air masstrajectories 8 days or longer in duration, arriving both in the freetroposphere and at an altitude of 1 km above sea level.Nevertheless, free tropospheric advection was dominant. AOTvariability in summer was best explained by the local direction andspeed of advection (1-day trajectories) and was dominated by theeffectiveness of cleansing processes. During the ASTAR 2007campaign, the aerosols near Hornsund displayed low AOT valuesranging from 0.06 to 0.09, which is lower than the mean AOT(500) forspring seasons from 2005 to 2007 (0.110±0.007; mean ±standard deviation of mean). 9 April 2007 with AOT(500)=0.147 wasexceptional. The back-trajectories belonged to clusters with low andaverage cluster mean AOT. Apart from the maximum AOT of9 April 2007, the observed AOT values were close to or lower thanthe means for the clusters to which they belonged.