Lidar and Sun photometer observations of atmospheric boundary-layer characteristics over an urban area in a mountain valley |
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Authors: | Nikolay Kolev Ivan Grigorov Ivan Kolev P C S Devara P Ernest Raj K K Dani |
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Institution: | (1) Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsarigradsko shosse Blvd, Sofia, 1784, Bulgaria;(2) Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune, 411008, India |
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Abstract: | We present measurements of the vertical aerosol structure and the aerosol optical depth in the lower troposphere performed
above the city of Sofia (an urban area situated in a mountain valley), western Bulgaria by means of a ground-based aerosol
lidar operating continuously for a number of years. The lidar measurements were accompanied by measurements of the aerosol
optical depth (AOD) in the visible and near infrared regions of the spectrum performed in October 2004 using Microtops II
radiometers. The maximum values of the AOD were found to occur 1–2 h before the complete development of the atmospheric boundary
layer, i.e. during the residual layer destruction, which confirms our hypothesis concerning the slope circulation effect on
the processes taking place in the atmospheric boundary layer. The AOD values obtained by the lidar are lower than those taken
by the sun photometer. Further, the AOD exhibits two different types of behaviour. In the case of a ‘clear atmosphere’ (i.e.
in the absence of volcanic eruptions and/or dust transport from the Sahara) most of the aerosol accumulated within the atmospheric
boundary layer over the urban area considered. The combined use of the two instruments allows the comparison between the optical
characteristics of the atmospheric aerosol (e.g. aerosol extinction coefficient, etc.) obtained by the lidar and through an
independent method (sun photometer). |
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Keywords: | Aerosol optical depth Atmospheric boundary layer Lidar Mixing layer Residual layer Sun photometer |
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