Proceedings - C-SRNWP Project

HIRLAM Physics developments
Sander Tijm, HIRLAM project leader for physics
Introduction
The physics developments in HIRLAM are distributed over the synoptic scale and the
mesoscale. In 2006, the synoptic scale developments still received the most attention, but it is
planned that the emphasis of the work will shift more and more on the mesoscale in 2007 and
beyond, as this will become the most area for LAM-NWP. As HIRLAM has chosen to
cooperate with Aladin to develop the mesoscale model AROME, the mesoscale work is aimed
primarily at the development of the schemes in this model.
In this contribution I will describe the main developments of the physics within HIRLAM and
in the HIRLAM-Aladin cooperation in 2006. Also a short overview of the plans for 2007 will
be given.
Synoptic scale
Surface scheme
One of the major developments in 2006 (continued from many years before) has been the
development of a snow/forest scheme. The current ISBA scheme in HIRLAM shows major
problems in winter and spring, when the impact of snow and forests on the temperature and
fluxes are underestimated substantially.
Due to the inadequate description of the isolating properties of a snow pack, the temperatures
do not drop far enough in a clear winter case. Also, the snow melts away too quickly and the
temperature rises too quickly after a snow event.
Figure 1: The temperature over the southwest of Norway as forecasted with the old surface
scheme (left), the new surface scheme (center) and the verifying MSG satellite image (right)
on 10 June 2006, 12 UTC (courtesy Dundee University). Purple is below 4°C, yellow is above
22°C, contour interval is 2°C.
Figure 1 shows the impact of the new surface scheme on the temperatures over southwest
Norway on June 10 2006. With the old surface scheme the temperatures in the Norwegian
mountains are between 16 and 20°C, while the temperatures are much closer to 0°C in the run
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