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| Titel |
Atmospheric boundary layer top height in South Africa: measurements with lidar and radiosonde compared to three atmospheric models |
| VerfasserIn |
K. Korhonen, E. Giannakaki, T. Mielonen, A. Pfüller, L. Laakso, V. Vakkari, H. Baars, R. Engelmann, J. P. Beukes, P. G. Van Zyl, A. Ramandh, L. Ntsangwane, M. Josipovic, P. Tiitta, G. Fourie, I. Ngwana, K. Chiloane, M. Komppula |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 8 ; Nr. 14, no. 8 (2014-04-30), S.4263-4278 |
| Datensatznummer |
250118645
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| Publikation (Nr.) |
 copernicus.org/acp-14-4263-2014.pdf |
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| Zusammenfassung |
| Atmospheric lidar measurements were carried out at Elandsfontein measurement
station, on the eastern Highveld approximately 150 km east of Johannesburg
in South Africa throughout 2010. The height of the planetary boundary layer
(PBL) top was continuously measured using a Raman lidar, PollyXT
(POrtabLe Lidar sYstem
eXTended). High atmospheric variability together with a large
surface temperature range and significant seasonal changes in precipitation
were observed, which had an impact on the vertical mixing of particulate
matter, and hence, on the PBL evolution. The results were compared to
radiosondes, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization)
space-borne lidar measurements and three atmospheric models that followed
different approaches to determine the PBL top height. These models included
two weather forecast models operated by ECMWF (European Centre for
Medium-range Weather Forecasts) and SAWS (South African Weather Service), and
one mesoscale prognostic meteorological and air pollution regulatory model
TAPM (The Air Pollution Model). The ground-based lidar used in this study
was operational for 4935 h during 2010 (49% of the time). The PBL
top height was detected 86% of the total measurement time (42% of
the total time). Large seasonal and diurnal variations were observed between
the different methods utilised. High variation was found when lidar
measurements were compared to radiosonde measurements. This could be
partially due to the distance between the lidar measurements and the
radiosondes, which were 120 km apart. Comparison of lidar measurements to
the models indicated that the ECMWF model agreed the best with mean relative
difference of 15.4%, while the second best correlation was with the SAWS
model with corresponding difference of 20.1%. TAPM was found to have a
tendency to underestimate the PBL top height. The wind speeds in the SAWS
and TAPM models were strongly underestimated which probably led to
underestimation of the vertical wind and turbulence and thus underestimation
of the PBL top height. Comparison between ground-based and satellite lidar
shows good agreement with a correlation coefficient of 0.88. On average, the
daily maximum PBL top height in October (spring) and June (winter) was
2260 m and 1480 m, respectively. To our knowledge, this study is the first long-term study of PBL top heights and PBL growth rates in South Africa. |
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