Work package M2: Large- and micro-scale nesting

Contact information

Principal investigators: Dr. Björn Maronga mail.gif, Prof. Dr. Siegfried Raasch mail.gif

Staff: Dr. Matthias Sühring mail.gif

Institution: Institute of Meteorology and Climatology (, Leibniz Universität Hannover (

Goals of WP-M2

To evaluate the turbulent flow in an urban area, all relevant processes that affect the local environment need to be considered in a simulation, which cover a wide range of spatial scales, reaching from the small scale (e.g. effects of single tree or buildings) up to the regional (e.g. urban heat island) or even the synoptic scale. To resolve all those spatial scales, the simulation has to run on a fine grid as well as for a large model domain, however, today this is still hardly possible in terms of the available computational resources. Here, the nesting technique offers an alternative, where the larger-scale processes are simulated on a coarse grid for a large model domain and the smaller-scale local processes are simulated on a fine grid only for the domain of interest, so that all relevant processes can be considered. The main goal of this subproject is to implement different nesting methods, which allow to force PALM-4U with simulation data from larger-scale models, as well as to allow a recursive PALM-4U self-nesting. The first approach enables PALM-4U to incoorporate external data from e.g. regional climate scenarios or even measured data, while the second approach provides a kind of magnifying lens feature applied for a small limited area, e.g. to study effects of local buildings on the local environment.

Work program

WP-M2.1: PALM-4U nesting with larger scale models

Larger-scale models will provide synoptic or mesoscale data for PALM-4U as time-dependent mean wind-, temperature-, and humidity-profiles, which are further used to force the PALM-4U simulation by applying the large-scale forcing and nudging technique. Nesting will first be implemented for RANS-mode and realized in two different ways, first using time-dependent profiles at the lateral boundaries, and second, adding larger-scale tendencies and subsidence to the horizontally averaged model state. Moreover, the second method has to be adjusted to be used for heterogeneous surfaces. A data interface will be implemented for COSMO and ICON, in cooperation with work package D3. The large-scale forcing will be extensively tested and evaluated.

WP-M2.2: Recursive nesting – PALM-4U-ZOOM

The recursive self-nesting will allow to run coarse- and fine-resolution simulation simulataneously, while the coarse-resolution simulation will provide full 2d-data at the lateral boundaries of the fine-resolution run. Interfaces between coarse and fine resolution runs will be implemented. The recursive nesting will be extensively tested and evaluated.

WP-M2.3: Nesting in LES mode

Nesting in LES-mode will provide a fully 3d-coupling between coarse- and fine- resolution simulation, using the post-insertion method, where the 3d data is bi-laterally exchanged between the coarse- and the fine-resolution simulations. In case of nesting a turbulence resolving LES in a larger domain running in RANS-mode, where the turbulence is fully parametrized, turbulence at lateral boundaries of the LES has to be generated. This will be done either by a turbulence recycling method or by a synthetic turbulence generator. The fully 3d nesting in LES mode will be extensively tested and evaluated.

Last modified 11 months ago Last modified on Apr 11, 2017 8:55:35 AM
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