The land-surface scheme of the Rossby Centre regional atmospheric climate model (RCA3)

Typ: Rapport
Serie: Meteorologi 122
Författare: Patrick Samuelsson, Stefan Gollvik, Anders Ullerstig


This report describes the physical processes as part of the Land-Surface Scheme (LSS) in the Rossby Centre Regional Atmospheric Climate Model (RCA3). The LSS is a tiled scheme with the three main tiles with respect to temperature: forest, open land, and snow. The open land tile is divided into a vegetated and a bare soil part for latent heat flux calculations. The individual fluxes of heat and momentum from these tiles are weighted in order to obtain grid-averaged values at the lowest atmospheric model level according to the fractional areas of the tiles. The forest tile is internally divided into three sub-tiles: forest canopy, forest floor soil, and snow on forest floor. All together this gives three to five different surface energy balances depending on if snow is present or not. The soil is divided into five layers with respect to temperature, with a no-flux boundary condition at three meters depth, and into two layers with respect to soil moisture, with a maximum depth of just above 2.2 meters. Runoff generated at the bottom of the deep soil layer may be used as input to a routing scheme. In addition to the soil moisture storages there are six more water storages in the LSS: interception of water on open land vegetation and on forest canopy, snow water equivalent of open land and forest snow, and liquid water content in both snow storages. Diagnostic variables of temperature and humidity at 2m and wind at 10m are calculated individually for each tile.