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- Title
One year of Raman lidar observations of free-tropospheric aerosol layers over South Africa.
- Authors
Giannakaki, E.; Pfüller, A.; Korhonen, K.; Mielonen, T.; Laakso, L.; Vakkari, V.; Baars, H.; Engelmann, R.; Beukes, J. P.; Van Zyl, P. G.; Josipovic, M.; Tiitta, P.; Chiloane, K.; Piketh, S.; Lihavainen, H.; Lehtinen, K. E. J.; Komppula, M.
- Abstract
Raman lidar data obtained over a 1 year period has been analysed in relation to aerosol layers in the free troposphere over the Highveld in South Africa. In total, 375 layers were observed above the boundary layer during the period 30 January 2010 to 31 January 2011. The seasonal behaviour of aerosol layer geometrical characteristics, as well as intensive and extensive optical properties were studied. The highest centre heights of freetropospheric layers were observed during the South African spring (2520±970ma.g.l., also elsewhere). The geometrical layer depth was found to be maximum during spring, while it did not show any significant difference for the rest of the seasons. The variability of the analysed intensive and extensive optical properties was high during all seasons. Layers were observed at a mean centre height of 2100±1000m with an average lidar ratio of 67±25 sr (mean value with 1 standard deviation) at 355 nm and a mean extinctionrelated Ångström exponent of 1.9±0.8 between 355 and 532 nm during the period under study. Except for the intensive biomass burning period from August to October, the lidar ratios and Ångström exponents are within the range of previous observations for urban/industrial aerosols. During Southern Hemispheric spring, the biomass burning activity is clearly reflected in the optical properties of the observed free-tropospheric layers. Specifically, lidar ratios at 355 nm were 89±21, 57±20, 59±22 and 65±23 sr during spring (September-November), summer (December-February), autumn (March-May) and winter (June-August), respectively. The extinction-related Ångström exponents between 355 and 532 nm measured during spring, summer, autumn and winter were 1.8±0.6, 2.4±0.9, 1.8±0.9 and 1.8±0.6, respectively. The mean columnar aerosol optical depth (AOD) obtained from lidar measurements was found to be 0.46±0.35 at 355 nm and 0.25±0.2 at 532 nm. The contribution of freetropospheric aerosols on the AOD had a wide range of values with a mean contribution of 46%.
- Subjects
SOUTH Africa; LIDAR; SCIENTIFIC observation; TROPOSPHERE; RAMAN effect; ATMOSPHERIC aerosols
- Publication
Atmospheric Chemistry & Physics, 2015, Vol 15, Issue 10, p5429
- ISSN
1680-7316
- Publication type
Article
- DOI
10.5194/acp-15-5429-2015