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| Titel |
Mixing-layer height retrieval with ceilometer and Doppler lidar: from case studies to long-term assessment |
| VerfasserIn |
J. H. Schween, A. Hirsikko, U. Löhnert, S. Crewell |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 11 ; Nr. 7, no. 11 (2014-11-08), S.3685-3704 |
| Datensatznummer |
250115944
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| Publikation (Nr.) |
 copernicus.org/amt-7-3685-2014.pdf |
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| Zusammenfassung |
| Aerosol signatures observed by ceilometers are frequently used to derive
mixing-layer height (MLH) which is an essential variable for air quality
modelling. However, Doppler wind lidar measurements of vertical velocity can provide a
more direct estimation of MLH via simple thresholding.
A case study reveals difficulties in the aerosol-based MLH retrieval during
transition times when the mixing layer builds up in the morning and when turbulence decays in the
afternoon. The difficulties can be explained by the fact that the aerosol
distribution is related to the history of the mixing process and aerosol
characteristics are modified by humidification. The results of the case study
are generalized by evaluating one year of joint measurements by a Vaisala
CT25K and a HALO Photonics Streamline wind lidar.
On average the aerosol-based retrieval gives higher MLH than the wind lidar with an overestimation
of MLH by about 300 m (600 m) in the morning (late afternoon).
Also, the daily aerosol-based maximum MLH is larger and occurs later during the day
and the average morning growth rates are smaller than those derived from the
vertical wind.
In fair weather conditions classified by less than 4 octa cloud cover the mean
diurnal cycle of cloud base height corresponds well to the mixing-layer
height showing potential for a simplified MLH estimation. |
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