Derivation of Structure Parameters of Temperature and Humidity in the Convective Boundary Layer from Large-Eddy Simulati
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Derivation of Structure Parameters of Temperature and Humidity in the Convective Boundary Layer from Large-Eddy Simulations and Implications for the Interpretation of Scintillometer Observations Björn Maronga · Arnold F. Moene · Daniëlle van Dinther · Siegfried Raasch · Fred C. Bosveld · Beniamino Gioli Received: 27 August 2012 / Accepted: 22 January 2013 / Published online: 12 February 2013 © The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract We derive the turbulent structure parameters of temperature C T2 and humidity Cq2 from high-resolution large-eddy simulations (LES) of a homogeneously-heated convective boundary layer. Boundary conditions and model forcing were derived from measurements at Cabauw in The Netherlands. Three different methods to obtain the structure-parameters from LES are investigated. The shape of the vertical structure-parameter profiles from all three methods compare well with former experimental and LES results. Depending on the method, deviations in the magnitude up to a factor of two are found and traced back to the effects of discretization and numerical dissipation of the advection scheme. Furthermore, we validate the LES data with airborne and large-aperture scintillometer (LAS) measurements at Cabauw. Virtual path measurements are used to study the variability of C T2 in the mixed layer and surface layer and its implications for airborne and LAS measurements. A high variability of C T2 along a given horizontal path in the LES data is associated with plumes (high values) and downdrafts (low values). The path average of C T2 varies rapidly in time due to the limited path length. The LES results suggest that measured path averages require sufficient temporal averaging and an adequate ratio of path length to height above the ground for the LAS in order to approach the domain average of C T2 .
B. Maronga (B) · S. Raasch Institut für Meteorologie und Klimatologie, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany e-mail: [email protected] A. F. Moene · D. van Dinther Meteorology and Air Quality Section, Wageningen University, Wageningen, The Netherlands F. C. Bosveld Regional Climate Division, Royal Netherlands Meteorological Institute, De Bilt, The Netherlands B. Gioli Institute of Biometeorology, National Research Council, Florence, Italy
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Keywords Convective boundary layer · Large-eddy simulation · Turbulent structure parameter · Virtual scintillometer
1 Introduction A number of measurement systems have been used to observe the turbulence structure of the atmospherice boundary layer, including radars, sodars, lifted kites and aircraft (Petenko and Shurygin 1999; Muschinski 2004; Muschinski et al. 2004; Martin et al. 2010, among others). Recently, scintillometers have been increasingly employed to measure the optical interference along a horizontal path (e.g. Ochs and Wang 1978; Kohsiek 1982; Beyrich et al. 2002; among others). Scintillometers are operated in the atmospheric surface la
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