Submitted as: model evaluation paper 14 Aug 2020

Submitted as: model evaluation paper | 14 Aug 2020

Review status: a revised version of this preprint is currently under review for the journal GMD.

Validation of the PALM model system 6.0 in real urban environment; case study of Prague-Dejvice, Czech Republic

Jaroslav Resler1, Kryštof Eben1, Jan Geletič1, Pavel Krč1, Martin Rosecký1, Matthias Sühring2, Michal Belda3, Vladimír Fuka3, Tomáš Halenka3, Peter Huszár3, Jan Karlický3, Nina Benešová4, Jana Ďoubalová4, Kateřina Honzáková4, Josef Keder4, Šárka Nápravníková4, and Ondřej Vlček4 Jaroslav Resler et al.
  • 1Institute of Computer Science, Czech Academy of Sciences, Prague, Czech Republic
  • 2Institute of Meteorology and Climatology, Leibniz University Hannover, Hannover, Germany
  • 3Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
  • 4Czech Hydrometeorological Institute, Prague, Czech Republic

Abstract. The PALM 6.0 model system has been rapidly developed in the recent years with respect to its capability to simulate physical processes within urban environments. In this regard, it includes e.g. energy-balance solvers for building and land surfaces, a radiative transfer model to account for multiple reflections and shading, as well as a plant-canopy model to consider the effects of plants on the (thermo)dynamics of the flow. This study provides a thorough evaluation of modelled meteorological, air chemistry and wall-surface quantities against dedicated in-situ measurements taken in an urban environment in Prague, Dejvice, Czech Republic. Measurements included e.g. monitoring of air quality and meteorology in street canyons, surface temperature scanning with infrared camera and monitoring of wall heat fluxes. Large-eddy simulations (LES) for multiple days within two summer and three winter episodes that are characterized by different atmospheric conditions were performed with the PALM model driven by boundary conditions obtained from a mesoscale model. For the simulated episodes, the resulting temperature, wind speed and concentrations of chemical compounds within street canyons agreed well with the observations, except the LES did not adequately capture nighttime cooling near the surface at certain meteorological conditions. In some situations, less turbulent mixing was modelled resulting in higher near-surface concentrations. At most of the surface evaluation points the simulated wall-surface temperature agreed fairly well with the observed one regarding its absolute value as well as daily amplitude. However, especially for the winter episodes and for modern buildings with multi-layer walls, the heat transfer through the wall is partly not well captured leading to discrepancies between the modelled and observed wall-surface temperature. Furthermore, we show that model results depend on the accuracy of the input data, particularly the temperatures of surfaces affected by nearby trees strongly depend on the spatial distribution of the leaf area density, land-surface temperatures at grass surfaces strongly depend on the initial soil moisture, or wall-surface temperatures depend on the correct prescription of wall material parameters, though these parameters are often not available with sufficient accuracy. Moreover, we also point out current model limitations, here we particularly focus on implications with respect to the discrete representation of topography on a Cartesian grid, complex heterogeneous facades, as well as glass facades that are not well represented in terms of radiative processes.

With these findings presented, we aim to validate the representation of physical processes in PALM as well as to point out specific shortcomings. This will help to build a baseline for future developments of the model and for improvements of simulations of physical processes in an urban environment.

Jaroslav Resler et al.

Status: final response (author comments only)
Status: final response (author comments only)
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Jaroslav Resler et al.

Model code and software

PALM 6.0 revision 4508 Resler et al. (2020)

Jaroslav Resler et al.


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Short summary
We describe validation of the PALM model v6.0 against measurements collected during two observational campaigns in Prague-Dejvice quarter. The study focuses on evaluation of the newly developed or improved radiative and energy balance modules in PALM related to urban modelling. The article is partially a follow-up paper of our previous GMD paper PALM-USM v1.0: A new urban surface model integrated into the PALM large-eddy simulation model.