RCA - Rossby Centre regional Atmospheric climate model: model description and results from the first multi-year simulation.

Type: Report
Series: RMK 83
Author: Markku Rummukainen, Jouni Räisänen, Anders Ullerstig, Björn Bringfelt, Ulf Hansson, Phil Graham and Ulrika Willen Rossby Centre, SMHI


The first version of the Rossby Centre regional climate model (RCA) has now been developed. The RCA model is based on a parallel coding of the operational weather forecast model HIRLAM. Some modifications have been done on the model formulation, especially in its surface/snow/soil scheme, in an attempt to include the regional and local scale climate-modifying forcing up to time scales of several years. The physical parameterization choices in HIRLAM and in RCA are discussed in some detail. One of the notable features in RCA is that the regional sea ice climate, as well as ice on the numerous lakes in the region, has been included in a crude, but time-efficient fashion. It appears that realistic modeling of the sea/lake ice is most important for modeling the regional climate in the Nordic region.

The RCA model has been run fora ten-year period, focusing on the Nordic region, using results from a coupled ocean-atmosphere general circulation model. In this first multi-year simulation, the regional resolution was 44 km.  Several results are illustrated from this regional simulation and they are compared to the driving global model data, to analyzed observations and to Swedish station data for the 1961-90 period. The apparent model development needs are also discussed briefly.