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| Titel |
Turbulence vertical structure of the boundary layer during the afternoon transition |
| VerfasserIn |
C. Darbieu, F. Lohou, M. Lothon, J. Vilà-Guerau de Arellano, F. Couvreux, P. Durand, D. Pino, E. G. Patton, E. Nilsson, E. Blay-Carreras, B. Gioli |
| 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 ; 15, no. 17 ; Nr. 15, no. 17 (2015-09-09), S.10071-10086 |
| Datensatznummer |
250120023
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| Publikation (Nr.) |
 copernicus.org/acp-15-10071-2015.pdf |
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| Zusammenfassung |
We investigate the decay of planetary boundary layer (PBL) turbulence in the
afternoon, from the time the surface buoyancy flux starts to decrease until
sunset. Dense observations of mean and turbulent parameters were acquired
during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field
experiment by several meteorological surface stations, sounding balloons,
radars, lidars and two aircraft during the afternoon transition. We analysed a case study based on some of
these observations and large-eddy simulation (LES) data focusing on the
turbulent vertical structure throughout the afternoon transition.
The decay of turbulence is quantified through the temporal and vertical
evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic
length scales of turbulence and (3) the shape of the turbulence spectra. A
spectral analysis of LES data, airborne and surface measurements is performed
in order to characterize the variation in the turbulent decay with height and
study the distribution of turbulence over eddy size.
This study highlights the LES ability to reproduce the turbulence evolution
throughout the afternoon. LESs and observations agree that the afternoon
transition can be divided in two phases: (1) a first phase during which the
TKE decays at a low rate, with no significant change in turbulence
characteristics, and (2) a second phase characterized by a larger TKE decay
rate and a change in spectral shape, implying an evolution of eddy size
distribution and energy cascade from low to high wave number.
The changes observed either in TKE decay (during the first phase) or in the
vertical wind spectra shape (during the second phase of the afternoon
transition) occur first in the upper region of the PBL. The higher within the
PBL, the stronger the spectra shape changes. |
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