Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data

B. Maronga, A.F. Moene, D. van Dinther, S. Raasch

Research output: Chapter in Book/Report/Conference proceedingConference paperAcademic

Abstract

Turbulent fluctuations of the refractive index (n) in the atmospheric boundary layer are related to local fluctuations in the air density, which can be expressed by the refractive-index structure parameter (Cn2). Since these fluctuations depend mainly on temperature and humidity, it is possible to relate Cn2 to the structure parameters for temperature (CT2) and humidity (Cq2). Recently, large-aperature scintillometers (LAS) have been increasingly used to measure CT2 over path lengths of several kilometers in the surface layer. By means of Monin-Obukhov similarity theory, the surface fluxes of sensible and latent heat can be estimated from measurements of CT2 and Cq2. However, a validation of these measurements is challenging. We derive CT2 and Cq2 from high-resolution (grid spacing of 2-4 m) large-eddy simulations (LES) of a homogeneously-heated convective boundary layer, driven by measurements at Cabauw (The Netherlands). Three different methods to obtain the structure parameters from LES are investigated. Among others, it is found that the shape of the vertical profiles of the structure parameters compares well with former experimental and modelling results. Depending on the method, deviations in the magnitude up to a factor of two are found and traced back to effects of subgrid-scale modeling in LES. In the presentation we compare the structure parameter profiles with data from an LAS ranging over a distance of 9.8km as well as aircraft measurements along the LAS path in different heights during RECAB 2002 (courtesy of Fred Bosveld at KNMI and courtesy of Beniamino Gioli at Ibimet). In the mixed layer we find that Cq2 compares well between LES and aircraft data, whereas CT2, derived from aircraft data, underestimates the proposed decrease with height. In the surface layer we find a good agreement with the LAS data. Virtual scintillometer measurements are employed in the LES in order to investigate the statistical error in LAS measurements due to the temporal and spatial variability of the path-averaged CT2 as well as its variability along the path. Furthermore we present results from investigations of the similarity relationships for structure parameters in the surface layer. Universal functions, relating the structure parameters to the surface fluxes of sensible and latent heat, by means of Monin-Obkhukov similarity and local free convection similarity are calculated from the LES data and compared with the proposed formulations in literature.
Original languageEnglish
Title of host publication20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA)
Place of PublicationBoston
PublisherAmerican Meteorological Society
Pages5B.2
Publication statusPublished - 2012
Event20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction - Boston, United States
Duration: 9 Jul 201213 Jul 2012

Conference

Conference20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction
CountryUnited States
CityBoston
Period9/07/1213/07/12

Fingerprint

convective boundary layer
large eddy simulation
surface layer
refractive index
surface flux
humidity
aircraft
airborne survey
comparison
parameter
vertical profile
modeling
mixed layer
spacing
boundary layer
temperature
convection
air

Cite this

Maronga, B., Moene, A. F., van Dinther, D., & Raasch, S. (2012). Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data. In 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA) (pp. 5B.2). Boston: American Meteorological Society.
Maronga, B. ; Moene, A.F. ; van Dinther, D. ; Raasch, S. / Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data. 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA). Boston : American Meteorological Society, 2012. pp. 5B.2
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title = "Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data",
abstract = "Turbulent fluctuations of the refractive index (n) in the atmospheric boundary layer are related to local fluctuations in the air density, which can be expressed by the refractive-index structure parameter (Cn2). Since these fluctuations depend mainly on temperature and humidity, it is possible to relate Cn2 to the structure parameters for temperature (CT2) and humidity (Cq2). Recently, large-aperature scintillometers (LAS) have been increasingly used to measure CT2 over path lengths of several kilometers in the surface layer. By means of Monin-Obukhov similarity theory, the surface fluxes of sensible and latent heat can be estimated from measurements of CT2 and Cq2. However, a validation of these measurements is challenging. We derive CT2 and Cq2 from high-resolution (grid spacing of 2-4 m) large-eddy simulations (LES) of a homogeneously-heated convective boundary layer, driven by measurements at Cabauw (The Netherlands). Three different methods to obtain the structure parameters from LES are investigated. Among others, it is found that the shape of the vertical profiles of the structure parameters compares well with former experimental and modelling results. Depending on the method, deviations in the magnitude up to a factor of two are found and traced back to effects of subgrid-scale modeling in LES. In the presentation we compare the structure parameter profiles with data from an LAS ranging over a distance of 9.8km as well as aircraft measurements along the LAS path in different heights during RECAB 2002 (courtesy of Fred Bosveld at KNMI and courtesy of Beniamino Gioli at Ibimet). In the mixed layer we find that Cq2 compares well between LES and aircraft data, whereas CT2, derived from aircraft data, underestimates the proposed decrease with height. In the surface layer we find a good agreement with the LAS data. Virtual scintillometer measurements are employed in the LES in order to investigate the statistical error in LAS measurements due to the temporal and spatial variability of the path-averaged CT2 as well as its variability along the path. Furthermore we present results from investigations of the similarity relationships for structure parameters in the surface layer. Universal functions, relating the structure parameters to the surface fluxes of sensible and latent heat, by means of Monin-Obkhukov similarity and local free convection similarity are calculated from the LES data and compared with the proposed formulations in literature.",
author = "B. Maronga and A.F. Moene and {van Dinther}, D. and S. Raasch",
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Maronga, B, Moene, AF, van Dinther, D & Raasch, S 2012, Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data. in 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA). American Meteorological Society, Boston, pp. 5B.2, 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, Boston, United States, 9/07/12.

Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data. / Maronga, B.; Moene, A.F.; van Dinther, D.; Raasch, S.

20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA). Boston : American Meteorological Society, 2012. p. 5B.2.

Research output: Chapter in Book/Report/Conference proceedingConference paperAcademic

TY - GEN

T1 - Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data

AU - Maronga, B.

AU - Moene, A.F.

AU - van Dinther, D.

AU - Raasch, S.

N1 - recorded presentation: https://ams.confex.com/ams/20BLT18AirSea/flvgateway.cgi/id/21981?recordingid=21981

PY - 2012

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N2 - Turbulent fluctuations of the refractive index (n) in the atmospheric boundary layer are related to local fluctuations in the air density, which can be expressed by the refractive-index structure parameter (Cn2). Since these fluctuations depend mainly on temperature and humidity, it is possible to relate Cn2 to the structure parameters for temperature (CT2) and humidity (Cq2). Recently, large-aperature scintillometers (LAS) have been increasingly used to measure CT2 over path lengths of several kilometers in the surface layer. By means of Monin-Obukhov similarity theory, the surface fluxes of sensible and latent heat can be estimated from measurements of CT2 and Cq2. However, a validation of these measurements is challenging. We derive CT2 and Cq2 from high-resolution (grid spacing of 2-4 m) large-eddy simulations (LES) of a homogeneously-heated convective boundary layer, driven by measurements at Cabauw (The Netherlands). Three different methods to obtain the structure parameters from LES are investigated. Among others, it is found that the shape of the vertical profiles of the structure parameters compares well with former experimental and modelling results. Depending on the method, deviations in the magnitude up to a factor of two are found and traced back to effects of subgrid-scale modeling in LES. In the presentation we compare the structure parameter profiles with data from an LAS ranging over a distance of 9.8km as well as aircraft measurements along the LAS path in different heights during RECAB 2002 (courtesy of Fred Bosveld at KNMI and courtesy of Beniamino Gioli at Ibimet). In the mixed layer we find that Cq2 compares well between LES and aircraft data, whereas CT2, derived from aircraft data, underestimates the proposed decrease with height. In the surface layer we find a good agreement with the LAS data. Virtual scintillometer measurements are employed in the LES in order to investigate the statistical error in LAS measurements due to the temporal and spatial variability of the path-averaged CT2 as well as its variability along the path. Furthermore we present results from investigations of the similarity relationships for structure parameters in the surface layer. Universal functions, relating the structure parameters to the surface fluxes of sensible and latent heat, by means of Monin-Obkhukov similarity and local free convection similarity are calculated from the LES data and compared with the proposed formulations in literature.

AB - Turbulent fluctuations of the refractive index (n) in the atmospheric boundary layer are related to local fluctuations in the air density, which can be expressed by the refractive-index structure parameter (Cn2). Since these fluctuations depend mainly on temperature and humidity, it is possible to relate Cn2 to the structure parameters for temperature (CT2) and humidity (Cq2). Recently, large-aperature scintillometers (LAS) have been increasingly used to measure CT2 over path lengths of several kilometers in the surface layer. By means of Monin-Obukhov similarity theory, the surface fluxes of sensible and latent heat can be estimated from measurements of CT2 and Cq2. However, a validation of these measurements is challenging. We derive CT2 and Cq2 from high-resolution (grid spacing of 2-4 m) large-eddy simulations (LES) of a homogeneously-heated convective boundary layer, driven by measurements at Cabauw (The Netherlands). Three different methods to obtain the structure parameters from LES are investigated. Among others, it is found that the shape of the vertical profiles of the structure parameters compares well with former experimental and modelling results. Depending on the method, deviations in the magnitude up to a factor of two are found and traced back to effects of subgrid-scale modeling in LES. In the presentation we compare the structure parameter profiles with data from an LAS ranging over a distance of 9.8km as well as aircraft measurements along the LAS path in different heights during RECAB 2002 (courtesy of Fred Bosveld at KNMI and courtesy of Beniamino Gioli at Ibimet). In the mixed layer we find that Cq2 compares well between LES and aircraft data, whereas CT2, derived from aircraft data, underestimates the proposed decrease with height. In the surface layer we find a good agreement with the LAS data. Virtual scintillometer measurements are employed in the LES in order to investigate the statistical error in LAS measurements due to the temporal and spatial variability of the path-averaged CT2 as well as its variability along the path. Furthermore we present results from investigations of the similarity relationships for structure parameters in the surface layer. Universal functions, relating the structure parameters to the surface fluxes of sensible and latent heat, by means of Monin-Obkhukov similarity and local free convection similarity are calculated from the LES data and compared with the proposed formulations in literature.

M3 - Conference paper

SP - 5B.2

BT - 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA)

PB - American Meteorological Society

CY - Boston

ER -

Maronga B, Moene AF, van Dinther D, Raasch S. Investigations of structure parameters and their similarity relationships in the convective boundary layer by means of large-eddy simulations and comparison with measurement data. In 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA). Boston: American Meteorological Society. 2012. p. 5B.2