Development of a high resolution regional climate model

At the Rossby Centre, we are working towards the development of a new Regional Climate Model (RCM), based on the non-hydrostatic NWP model HARMONIE. HARMONIE is specifically developed to allow integrations at convective-resolving resolutions, e.g. ~1-3km per grid box.

The role of increased model resolution

Present day global and regional climate models do not accurately simulate observed intensity and frequency distributions of precipitation, deviating from observations most radically at the extreme (high-intensity) tail of the distribution (e.g. Frei et al. 2006). This is primarily due to the coarse resolution of the models used (e.g. a typical GCM resolution is ~100-200km per grid box, while a typical RCM is in the range ~15-30km).

Furthermore, due to this coarse resolution, convective precipitation processes have to be parameterized, as the model resolution is too coarse to explicitly resolve deep convective processes.

Cloud-resolving models

With increasing computer power, RCM's with a capability of a few kilometers in resolution are becoming possible. Such cloud-resolving models are now in use mainly for numerical weather prediction (NWP) purposes (e.g. Mass et al. 2002, Seity et al. 2010).

When deep convection is explicitly resolved, simulated precipitation patterns are more realistic, especially for moist convection over complex terrain (Hohenegger et al. 2008).

Near future plans

The near future plans are to see how the models represent interactions between the larger-scale circulation, any mesoscale development required to simulate the observed precipitation rates and interactions with topography or other important local forcing features.

We have recently initiated an analysis of precipitation in terms of variability and intensity distributions. The simulations are done on different model grids. Europe with a resolution of 15km and two smaller domains covering the mountainous areas, over Northern Scandinavia and the Alps. Both with a resolution of 2km.

Figure 1 shows mean precipitation for the summer seasons of 1998 to 2002 over Northern part of Sweden for 2 models, Harmonie and RCA. The 2 models are compared to high resolution observations (PTHBV).


Harmonie kartor
Figure 1. Mean precipitation for the summer seasons of 1998 to 2002 over Northern part of Sweden for 2 models, Harmonie and RCA. The 2 models are compared to high resolution observations (PTHBV).
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References

Frei C., R. Scholl, S. Fukutome, J. Schmidli, P. L. Vidale., 2006: Future change of precipitation extremes in Europe: Intercomparison of scenarios from regional climate models., J. Geophys. Res., 111, D06105, doi:10.1029/2005JD005965.

Hohenegger C., Brockhaus P., Schär C, 2008: Towards climate simulations at cloud- resolving scales ., Meteor. Z., 17, 383-394.

Seity Y., P. Brousseau, S. Malardel, G. Hello, P. Benard, F. Bouttier, C. Lac, and V. Masson, 2010: The AROME-France Convective-Scale Operational Model., Mon. Wea. Rev., 139, 976-991.