TY - JOUR

T1 - 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

AU - Maronga, Björn

AU - Moene, Arnold F.

AU - van Dinther, Daniëlle

AU - Raasch, Siegfried

AU - Bosveld, Fred C.

AU - Gioli, Beniamino

N1 - Funding Information: Acknowledgments This study was supported by the German Research Foundation (DFG) under grant RA 617/20-1. All simulations were performed on the SGI Altix ICE at The North-German Supercomputing Alliance (HLRN), Hannover/Berlin. Aircraft data were obtained within the European Commission research project RECAB (EVK2-CT-1999-00034). We appreciate the two anonymous reviewers for their numerous valuable comments that helped to improve the manuscript. The first author would like to thank Oscar Harto-gensis for providing assistance with the spectra and scintillometer analyses. Copyright: Copyright 2013 Elsevier B.V., All rights reserved.

PY - 2013/2/12

Y1 - 2013/2/12

N2 - We derive the turbulent structure parameters of temperature CT2 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 CT2 in the mixed layer and surface layer and its implications for airborne and LAS measurements. A high variability of CT2 along a given horizontal path in the LES data is associated with plumes (high values) and downdrafts (low values). The path average of CT2 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 CT2.

AB - We derive the turbulent structure parameters of temperature CT2 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 CT2 in the mixed layer and surface layer and its implications for airborne and LAS measurements. A high variability of CT2 along a given horizontal path in the LES data is associated with plumes (high values) and downdrafts (low values). The path average of CT2 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 CT2.

KW - Convective boundary layer

KW - Large-eddy simulation

KW - Turbulent structure parameter

KW - Virtual scintillometer

UR - http://www.scopus.com/inward/record.url?scp=84873452785&partnerID=8YFLogxK

U2 - 10.1007/s10546-013-9801-6

DO - 10.1007/s10546-013-9801-6

M3 - Article

AN - SCOPUS:84873452785

VL - 148

SP - 1

EP - 30

JO - Boundary-Layer Meteorology

JF - Boundary-Layer Meteorology

SN - 0006-8314

IS - 1

ER -