HIRLAM-2 Radiation Scheme: Documentation and Tests
Bent Hansen Sass, Danish Meteorological Institute
Laura Rontu, Finnish Meteorological Institute
Petri Räisänen, Department of Meteorology, University of Stockholm
(present affiliation: Department of Meteorology, University of Helsinki)
Abstract
A fast radiation scheme for the HIRLAM-2 model is documented and
tested in one-dimensional and three-dimensional model
runs. Comparisons with more detailed radiation schemes and with the
old HIRLAM-1 scheme are made. In clear sky cases the longwave and
shortwave radiative fluxes and heating given by the HIRLAM-2 scheme
agree well with the reference results. In real cloudy situations the
new scheme seems to overestimate slightly the solar flux penetrating
through cloud layers. The old HIRLAM-1 radiation scheme is shown to
overestimate the total cooling rate especially near the surface,
except when there is a cold and dry layer above the surface. Thus the
old scheme causes in most cases significant excess cooling, while the
new scheme probably produces a small warm bias of the model two-meter
temperature.
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