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Extracting point forecasts from TIGGE-LAM grib archives
The European Centre for Medium Range Weather Forecasting (ECMWF) provides an archive of high-resolution forecasts generated by several limited-area numerical weather prediction models, as part of the TIGGE-LAM (The International Grand Global Ensemble - Limited Area Model) project.
One of these forecast datasets is generated by HIRLAM, run by the Danish Meteorological Institute . The TIGGE-LAM datasets are freely available for research purposes from ECMWF.
For wind energy forecasting studies, the TIGGE-LAM datasets are preferable to more well-known numerical weather prediction datasets such as ERA-Interim because TIGGE-LAM contains pure forecasts at multiple lead times, rather than reanalysis data. The HIRLAM forecasts of TIGGE-LAM also have very high horizontal resolution (approximately 0.05 degrees in latitude and longitude). The wider TIGGE project is described in detail in [1].
The HIRLAM data is provided in GRIB format on a rotated lat/lon grid (south pole co-ordinate 40 degrees S, 10 degrees E). If you want to extract data for a particular point location you have to either (a) transform the dataset to an "unrotated" grid, or (b) transform your particular co-ordinates to the HIRLAM grid. The second option, (b) seemed more expedient, and I found a very useful Matlab script, rotated_grid_transform() , by Simon Funder to do this.
Once the location was transformed to HIRLAM's rotated grid co-ordinates (and reverse transformed to check everything worked properly!) , I ran grib_ls with the "-l" command line option to extract the four nearest neighbouring grid cells' values from the grib file.
Some other points to consider are:
- HIRLAM's grid is Arakawa-C, so the grids for u and v are staggered. I think this means that u and v should be separately spatially interpolated to the point of interest, but the spatial resolution of HIRLAM is good, so that for now I just took the nearest grid cell of each field (u and v).
- the wind direction calculated from u and v will be rotated because the native HIRLAM grid is rotated. Again, I'm not (currently) interested in wind directions (just wind speeds) so I didn't try to "unrotate" this .
[1] Swinbank, R.; Kyouda, M.; Buchanan, P.; Froude, L.; Hamill, T. M.; Hewson, T. D.; Keller, J. H.; Matsueda, M.; Methven, J.; Pappenberger, F.; Scheuerer, M.; Titley, H. A.; Wilson, L. & Yamaguchi, M. The TIGGE Project and Its Achievements. Bulletin of the American Meteorological Society, 2016, 97, 49 - 67