Saarblitz, Wind farm in HDR, flickr.com, creative commons by-nc-sa 2.0

Leipzig

Managed by

Data Provider: 

The data have been extracted from Lettau (1950).

Data accesibility: 

The test case is offered to participants of the IEA Task 31 Wakebench. In the future it will be open for public access.

Site Description: 

The measurements were done on a grass-covered airfield with flat surroundings. Upstream, the air passes over the city of Leipzig.

Instrumentation: 

The Leipzig wind profile results from a set of 28 pitot-balloon observations with two theodolites, between 9:15 and 16:15 on October 20, 1931, during stable weather (Mildner, 1932). During the experiment, the surface isobars were rectilinear indicating that the geostrophic conditions were steady and the horizontal gradients were negligible. 

Measurement Campaign: 

Lettau (1950), performed a reanalysis of the measurements which resulted in a smooth profile, a "representative average" of the original, more scattered data. This classical profile has been discussed extensively in the literature. The boundary layer meteorology folklore considers this profile as a reference for an idealized neutral, barotropic (geostrophic wind constant with height), horizontally homogenous steady-state atmospheric boundary layer (ABL). However, it has been also argued that the profile was obtained in slightly stable conditions with an Obukhov length in the order of 500 m (Sundararajan, 1979) obtained by profile fitting in the lower 150 m. In fact, Lettau (1950) reports a lapse rate of potential temperature of 0.35 K / 100 m.

Remarks: 

The Leipzig wind profile has been extensively used for the analysis and design of ABL models. Blackadar (1962) derived his well known analytical expression for the ABL mixing length profile in flat terrain making use of this profile. The limiting value of the mixing length was found to be proportional to the ratio of the geostrophic wind and the Coriolis parameter. He assumed that the slight stratification of the profile did not influence its turbulence structure. Many mixing-length models of the ABL are based on Blackadar's parameterization ever since. 
Detering and Etling (1985) proposed a k-ε model of the ABL that could reduce the excessive mixing of the default turbulence model of Launder and Spalding (1974). A similar strategy was followed by Apsley and Castro (1997) using a length-scale limiter to avoid the quasy-linear growth of the mixing length beyond the surface layer.
Riopellle and Stubley (1989) used a second-order turbulence closure that included stable stratification and found better agreement with the Leipzig profile than if neutral conditions were assumed.    
Even though it is relatively old, the Leipzig data is useful because of the steady barotropic conditions of the experiment. Being a well-established reference, it is suitable for model intercomparison studies. However, since the dataset is very limited regarding thermal stratification properties, it cannot be used as a complete model validation dataset.   

References: 

Apsley D.D., Castro I.P., 1997, A Limited-Length-Scale k-ε Model for the Neutral and Stably-Stratified Atmospheric Boundary Layer, Boundary Layer Meteorol. 83: 75-78
Blackadar A.K., 1962, The Vertical Distribution of Wind and Turbulent Exchanges in Neutral Conditions, J. Geophys. Res. 67: 3095-3102
Detering H.W., Etling D., 1985, Application of the E-ε Turbulence Model to the Atmospheric Boundary Layer, Boundary Layer Meteorol. 33: 113-133
Launder B.E., Spalding D.B., 1974, The Numerical Computations of Turbulent Flows, Comp. Meih. in Appl. Mech. and Eng. 3: 269-289
Lettau H., 1950, A Re-examination of the Leipzig Wind Profile Considering Some Relations Between Wind and Turbulence in the Frictional Layer, Tellus 2: 125-129
Mildner P., 1932, Über die Reibung in einer speziellen Luftmasse in den untersten Schichten der Atmosphäre, Beitr. z. Phys. d. fr. Atmosph¨are 19: 151–158.
Riopelle G., Stubley G.D., 1989, The Influence of Atmospheric Stability on the 'Leipzig' Boundary-Layer Structure, Boundary Layer Meteorol. 46: 207-227
Sundarajan A., 1979, Some Aspects of the Structure of the Stably Stratified Atmospheric Boundary Layer, Boundary Layer Meteorol. 17: 133-139

NDA: 

Not applicable.