The Effect of Surface Heterogeneity on the Structure Parameters of Temperature and Specific Humidity: A Large-Eddy Simulation Case Study for the LITFASS-2003 Experiment

Abstract

We conduct a high-resolution large-eddy simulation (LES) case study in order to investigate the effects of surface heterogeneity on the (local) structure parameters of potential temperature C 2 T and specific humidity C 2 q in the convective boundary layer (CBL). The kilometre-scale heterogeneous land-use distribution as observed during the LITFASS-2003 experiment was prescribed at the surface of the LES model in order to simulate a realistic CBL development from the early morning until early afternoon. The surface patches are irregularly distributed and represent different land-use types that exhibit different roughness conditions as well as near-surface fluxes of sensible and latent heat. In the analysis, particular attention is given to the Monin-Obukhov similarity theory (MOST) relationships and local free convection (LFC) scaling for structure parameters in the surface layer, relating C 2 T and C 2 q to the surface fluxes of sensible and latent heat, respectively. Moreover we study possible effects of surface heterogeneity on scintillometer measurements that are usually performed in the surface layer. The LES data show that the local structure parameters reflect the surface heterogeneity pattern up to heights of 100-200 m. The assumption of a blending height, i.e. the height above the surface where the surface heterogeneity pattern is no longer visible in the structure parameters, is studied by means of a two-dimensional correlation analysis. We show that no such blending height is found at typical heights of scintillometer measurements for the studied case. Moreover, C 2 q does not follow MOST, which is ascribed to the entrainment of dry air at the top of the boundary layer. The application of MOST and LFC scaling to elevated C 2 T data still gives reliable estimates of the surface sensible heat flux. We show, however, that this flux, derived from scintillometer data, is only representative of the footprint area of the scintillometer, whose size depends strongly on the synoptic conditions.

Surface-Layer Similarity Functions for Dissipation Rate and Structure Parameters of Temperature and Humidity Based on Eleven Field Experiments

“…Note that the function from Maronga (2014) is partially hidden by the flux-profile-derived function. The fact that the MOST functions are very similar to those found by Maronga et al (2014) based on idealized turbulence in a LES model strengthens our case that the selected data indeed follow MOST.…”

“…A potential powerful approach is that of Maronga (2014) and Maronga et al (2014) using LES modelling. Such an approach allows the quantification of the effect of non-local conditions on MOST relations.…”

“…Although LES modelling results are restricted to near-free convection conditions, Maronga (2014) demonstrated in his LES study that when entrainment was simulated, f C q 2 diverges from f C T 2 . Maronga et al (2014) quantified the effects of surface heterogeneity on C T 2 and C q 2 and found that an heterogeneous surface generates additional temperature and moisture fluctuations leading to higher C T 2 and C q 2 values. This effect did modify the MOST functions but the effect was very small.…”

The marine atmospheric boundary layer under strong wind conditions: Organized turbulence structure and flux estimates by airborne measurements

“…This work will be completed in the future with a large eddy simulation, from which we would be able to better quantify the impact of the coherent structures on the vertical exchanges. This is particularly important since coherent structures, or secondary circulations, are certainly more frequent than is expected, even over continental heterogeneous surfaces [ Maronga et al , ].…”

The Parallelized Large-Eddy Simulation Model (PALM) version 4.0 for atmospheric and oceanic flows: model formulation, recent developments, and future perspectives

“…The investigation of effects of land surface heterogeneity on the convective boundary layer has been one of the core areas of research with PALM. The early studies used idealized surface heterogeneity, i.e., stripes or checkerboard patterns (Raasch and Harbusch, 2001;Kim et al, 2004;Letzel and Raasch, 2003;Inagaki et al, 2006), whereas recent studies incorporated more complex surface configurations using the irregularly distributed land use classes as observed during the LITFASS-2003 field experiment (see Beyrich and Mengelkamp, 2006;Maronga and Raasch, 2013;Sühring and Raasch, 2013;Maronga et al, 2014;Sühring et al, 2015). Moreover, PALM has been applied to study the flow over Arctic ice leads and during cold-air outbreaks (e.g., Lüpkes et al, 2008;Gryschka et al, 2008Gryschka et al, , 2014.…”