 |
| Titel |
Elastic-backscatter-lidar-based characterization of the convective boundary layer and investigation of related statistics |
| VerfasserIn |
S. Pal, A. Behrendt, V. Wulfmeyer |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 3 ; Nr. 28, no. 3 (2010-03-22), S.825-847 |
| Datensatznummer |
250016807
|
| Publikation (Nr.) |
 copernicus.org/angeo-28-825-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
We applied a ground-based vertically-pointing aerosol lidar to investigate
the evolution of the instantaneous atmospheric boundary layer depth, its
growth rate, associated entrainment processes, and turbulence
characteristics. We used lidar measurements with range resolution of 3 m and
time resolution of up to 0.033 s obtained in the course of a sunny day (26
June 2004) over an urban valley (central Stuttgart, 48°47' N,
9°12' E, 240 m above sea level). The lidar system uses a
wavelength of 1064 nm and has a power-aperture product of 2.1 W m2.
Three techniques are examined for determining the instantaneous convective
boundary layer (CBL) depth from the high-resolution lidar measurements: the
logarithm gradient method, the inflection point method, and the Haar wavelet
transform method. The Haar wavelet-based approach is found to be the most
robust technique for the automated detection of the CBL depth. Two
different regimes of the CBL are discussed in detail: a quasi-stationary CBL
in the afternoon and a CBL with rapid growth during morning transition in
the presence of dust layers atop. Two different growth rates were found:
3–5 m/min for the growing CBL in the morning and 0.5–2 m/min during
the quasi-steady regime. The mean entrainment zone thickness for the
quasi-steady CBL was found to be ~75 m while the CBL top during the
entire day varied between 0.7 km and 2.3 km. A fast Fourier-transform-based
spectral analysis of the instantaneous CBL depth time series gave a
spectral exponent value of 1.50±0.04, confirming non-stationary CBL
behavior in the morning while for the other regime a value of 1.00±0.06
was obtained indicating a quasi-stationary state of the CBL.
Assuming that the spatio-temporal variation of the particle backscatter
cross-section of the aerosols in the scattering volume is due to number
density fluctuations (negligible hygroscopic growth), the particle
backscatter coefficient profiles can be used to investigate boundary layer
turbulence since the aerosols act as tracers. We demonstrate that with our
lidar measurements, vertical profiles of variance, skewness, and
kurtosis of the fluctuations of the particle backscatter coefficient can be
determined. The variance spectra at different altitudes inside the
quasi-steady CBL showed an f−5/3 dependency. The
integral scale varied from 40 to 90 s (depending on height), which was
significantly larger than the temporal resolution of the lidar data. Thus,
the major part of the inertial subrange was detected and turbulent
fluctuations could be resolved. For the quasi-stationary case, negative values
of skewness were found inside the CBL while positive values were observed in the
entrainment zone near the top of the CBL. For the case of the rapidly
growing CBL, the skewness profile showed both positive and negative values
even inside the CBL. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|