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| Titel |
Profiles of second- to fourth-order moments of turbulent temperature fluctuations in the convective boundary layer: first measurements with rotational Raman lidar |
| VerfasserIn |
A. Behrendt, V. Wulfmeyer, E. Hammann, S. K. Muppa, S. Pal |
| 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. 10 ; Nr. 15, no. 10 (2015-05-20), S.5485-5500 |
| Datensatznummer |
250119738
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| Publikation (Nr.) |
 copernicus.org/acp-15-5485-2015.pdf |
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| Zusammenfassung |
| The rotational Raman lidar (RRL) of the University of Hohenheim (UHOH)
measures atmospheric temperature profiles with high
resolution (10 s, 109 m). The data contain low-noise
errors even in daytime due to the use of strong UV laser light
(355 nm, 10 W, 50 Hz) and a very efficient
interference-filter-based polychromator. In this paper, the first profiling of the second- to fourth-order moments of
turbulent temperature fluctuations is presented. Furthermore, skewness profiles and
kurtosis profiles in the convective planetary boundary layer (CBL) including the
interfacial layer (IL) are discussed. The results demonstrate that the UHOH
RRL
resolves the vertical structure of these moments. The data set which
is used for this case study was collected in western Germany
(50°53'50.56'' N,
6°27'50.39'' E;
110 m a.s.l.) on
24 April 2013 during the Intensive Observations Period (IOP) 6 of the
HD(CP)2 (High-Definition Clouds and Precipitation
for advancing Climate Prediction) Observational Prototype Experiment (HOPE).
We used the data between 11:00 and 12:00 UTC corresponding to 1 h around
local noon (the highest position of the Sun was at 11:33 UTC).
First, we
investigated profiles of the total noise error of the temperature measurements and compared them with
estimates of the temperature measurement uncertainty due to shot noise
derived with Poisson statistics. The comparison confirms that
the major contribution to the total statistical uncertainty of the temperature measurements originates from shot noise. The
total statistical uncertainty of a 20 min temperature measurement
is lower than 0.1 K up to 1050 m a.g.l. (above ground level) at
noontime; even for single 10 s temperature profiles, it is smaller
than 1 K up to 1020 m a.g.l. Autocovariance and spectral analyses of the atmospheric
temperature fluctuations confirm that a temporal resolution of 10 s
was sufficient to resolve the turbulence down to the inertial
subrange. This is also indicated by the integral
scale of the temperature fluctuations which had a mean value of about
80 s in the CBL with a tendency to decrease to smaller values towards
the CBL top. Analyses of profiles of the second-,
third-, and fourth-order moments show that all
moments had peak values in the IL around the mean top of the CBL which was located
at 1230 m a.g.l. The maximum of the variance profile
in the IL was 0.39 K2 with 0.07 and 0.11 K2
for the sampling error and noise error, respectively. The
third-order moment (TOM) was not significantly different from zero in
the CBL but showed a negative peak in the IL with a minimum of
−0.93 K3 and values of 0.05 and 0.16 K3 for
the sampling and noise errors, respectively. The fourth-order moment (FOM)
and kurtosis values throughout the CBL were not significantly different to
those of a Gaussian distribution. Both showed also maxima in the IL but these
were not statistically significant taking the measurement uncertainties into
account. We conclude that these measurements permit the validation of large
eddy simulation results and the direct investigation of turbulence
parameterizations with respect to temperature. |
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