[1806] - Scale dependence of atmosphere-surface coupling through similarity theory

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Ansorge, C., 2018. Scale dependence of atmosphere-surface coupling through similarity theory. 23rd Symposium on Boundary Layers and Turbulence, June 11 - 15, 2018, Oklahoma City. Accessed from https://www.tr32db.uni-koeln.de/data.php?dataID=1806 at 2020-08-10.
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Title(s):Main Title: Scale dependence of atmosphere-surface coupling through similarity theory
Description(s):Abstract: Surface-layer similarity theory is derived under the assumptions of horizontal heterogeneity and stationarity, but it is used in ever more complex and heterogeneous configurations. We independently assess the scale-dependence of surface-layer similarity theory by obtaining values of the surface friction from wind- and velocity fields within the surface layer. A classical set of Monin-Obukhov similarity functions is inverted analytically; this allows to investigate the joint convergence of individual samples of the wall-friction and its estimate from similarity theory as a function of the spatial and temporal filter scale. Spatially and temporally resolved data originate from a direct numerical simulation of turbulent Ekman flow, an idealized representation of the atmospheric boundary layer. This work focuses on the stable stratification and the neutrally stratified limit. In neutral conditions, a systematic underestimation of variance in surface fluxes estimated through similarity theory versus the actual flux is found and quantified as a function of height, averaging time and length scale. A sufficient convergence of the local friction estimate by similarity theory to the actual local surface friction is only obtained for averaging box sizes of several thousand wall units, and only for data filtered along both horizontal dimensions; the three-dimensional structure of the turbulence elements appears to limit the convergence of data filtered along any of the single dimensions time, the streamwise or the spanwise direction. In stable conditions, the bulk profiles agree with similarity theory until the maximum buoyancy flux is reached and the turbulence becomes intermittent. Due to the non-stationarity, convergence is only considered in the spatial domain and only for two-dimensional horizontal box-averages. Due to the turbulence intermittency and a frictional decoupling associated to the inertial oscillation, similarity theory does not govern the joint fluctuation of wind in the lower part of the surface layer and friction at the surface at any scale; in fact, the skill of similarity in predicting local variations decreases with increasing averaging scale while the mean values are still constrained to within 10\%. While similarity theory appears appropriate to represent fluctuations for weak stratification and at large scales, the present results suggest a scale on the order of thousands of wall units below which the coupling of fluctuations at the surface and within the surface layer is no longer governed by surface-layer similarity theory such as the Monin-Obukhov Stability Theory. Further, the applicability limit of similarity in terms of a critical stratification is also confirmed in this analysis be a negative skill of similarity in predicting local fluctuations in strongly stable conditions.
Identifier(s):URL: https://ams.confex.com/ams/23BLT21ASI/meetingapp.cgi/Paper/345059
URL: https://ams.confex.com/ams/23BLT21ASI/videogateway.cgi/id/48190?recordingid=48190
Responsible Party
Creator(s):Author: Cedrick Ansorge
Publisher:CRC/TR32 Database (TR32DB)
TR32 Topic:Atmosphere
Related Sub-project(s):C7
Subject(s):CRC/TR32 Keywords: Atmosphere–Land Interaction, Turbulence, 10m-Wind Speed, Surface Fluxes, Turbulent Fluxes, Numerical Simulation
DDC: 532 Fluid mechanics; Liquid mechanics, 550 Earth sciences, 551 Geology, hydrology, meteorology
Topic Category:ClimatologyMeteorologyAtmosphere
File Details
File Name:talk.pdf
Data Type:Text
File Size:21346 kB (20.846 MB)
Date(s):Issued: 2018-06-15
Mime Type:application/pdf
Data Format:PDF
Download Permission:Free
General Access and Use Conditions:According to the TR32DB data policy agreement.
Access Limitations:According to the TR32DB data policy agreement.
Licence:Creative Commons Attribution-NonCommercial-NoDerivs 4.0 Unported (CC BY-NC-ND 4.0)
North:-no map data
Measurement Region:None
Measurement Location:--None--
Specific Informations - Presentation
Presenter:Cedrick Ansorge
Presentation Date:2018-06-15
Presentation Type:Invited talk
Event Name:23rd Symposium on Boundary Layers and Turbulence
Event Type:Conference
Event Location:Oklahoma City
Event Period:11th of June, 2018 - 15th of June, 2018
Event Url:https://www.ametsoc.org/index.cfm/ams/meetings-events/ams-meetings/23rd-symposium-on-boundary-layers-and-turbulence-21st-conference-on-air-sea-interaction/21st-conference-on-air-sea-interaction-call-for-papers/
Metadata Details
Metadata Creator:Cedrick Ansorge
Metadata Created:2018-08-02
Metadata Last Updated:2019-08-02
Funding Phase:3
Metadata Language:English
Metadata Version:V43
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