Data handling
Due to the enormous amount of data that comes along with computationally expensive LES, the data handling plays a key role for the performance of LES models and for data analysis during post-processing. PALM is optimized to pursue the strategy of performing data operations to great extent online during the simulation instead of postpone these operations to the post-processing. In this way, the data output (e.g., of huge 4-D data, or temporal averages) can be significantly reduced. In order to allow the user to perform own calculations during runtime, the user interface offers a wide range of possibilities, e.g., for defining user-defined output quantities (see Sect. user interface).
PALM allows data output for different quantities as time series, (horizontally-averaged) vertical profiles, 2-D cross sections, 3-D volume data, and masked data (see Sect. user interface ). All data output files are in netCDF format, which can be processed by different public domain and commercial software. NetCDF data can also be easily read from Fortran programs, provided that a netCDF library is available. The netCDF libraries currently support three different binary formats for netCDF files: classic, 64-bit offset, and netCDF-4. The latter was introduced in netCDF version 4.0 and is based on the HDF5 (http://www.hdfgroup.org/HDF5) data format. PALM is able to handle all three netCDF formats and also supports parallel I/O for netCDF-4.
For visualization of the netCDF data generated by PALM, several NCAR Command Language (NCL, http://www.ncl.ucar.edu) scripts are available that allow a quick overview of the simulation data. For advanced visualizations, we recommend the Open Source software VAPOR (http://www.vapor.ucar.edu, Clyne et al., 2007). Animations using PALM data and VAPOR have been recently published by Maronga et al. (2013), Knoop et al. (2014), and Kanani et al. (2014a, b).
References
- Clyne J, Mininni P, Norton A, Rast M. 2007. Interactive desktop analysis of high resolution simulations: application to turbulent plume dynamics and current sheet formation. New. J. Phys. 301: 1–28.
- Maronga B, Hoffmann F, Riechelmann T, Raasch S. 2013. Large-eddy simulation of dust devils: Animation of dust devils in the convective boundary layer using a virtual dust. Computer animation. doi
- Knoop H, Keck M, Raasch S. 2014. Urban large-eddy simulation - influence of a densely build-up artificial island on the turbulent flow in the city of Macau, Computer animation. doi.
- Kanani F, Maronga B, Knoop H, Raasch S. 2014a. Large-eddy simulation of a forest-edge flow -- adjustment of a turbulent flow to the changing surface conditions at a clearing-to-forest transition. Computer animation. doi.
- Kanani F, Maronga B, Knoop H, Raasch S. 2014b. Large-eddy simulation of the scalar transport in a forest-edge flow -- spatial variability of the scalar distribution and the scalar transport downstream of a clearing-to-forest transition. Computer animation. doi.
