At the
University of Basel, numerical weather forecasts for Europe are
computed twice daily using the NMM, and are made
available on the internet [www.meteoblue.ch]. A
visualization system was developed and
some
animations are now used daily by national television. Special focus
lies on the Alpine region, which is covered by two
nested domains running at resolutions of 4 and 2 km, respectively.
A parameterization for radiation in complex topography was developed
and tested. The interactions of radiation
fluxes with the terrain due to sky view restriction, slope and aspect
angle as well as shadows are computed
based on a digital elevation model that has a higher resolution than
the mesoscale model. Runtime computational
costs are negligible, and temperature differences as high as 3 K are
found in complex topography. Especially
at night, the cold bias in valleys is significantly reduced.
Current research efforts focus on fog and low stratus clouds. An
assimilation and ensemble system for 1D-modelling
was developed, but a 3D approach seems more promising for the
topography in Switzerland. Therefore, detailed
microphysics of the 1D fog model PAFOG were implemented into the
Non-hydrostatic Mesoscale Model (NMM). This
introduces total droplet number concentration as a new prognostic
variable and a sophisticated determination
of condensation/evaporation as well as size dependent droplet settling.
The nature of radiation fog requires a
high vertical resolution to model the steady growth from the surface. A
thickness of approximately 4 meters in
the lowest layers combined with the stable stratification during a fog
event can cause problems in the standard
turbulent exchange, resulting in a cold bias. In the case of liquid
water advection, boundary conditions for the droplet
number concentration have to be specified. In general, the new
microphysics decrease fog water content to a more
realistic value and the complex spatial distribution of simulated fog
underlines the importance of the 3D approach.