Siegfried Raasch博士による超並列LES講演会は、多数の方のご出席のもと、


CREST特別講演会() in東工大のご案内 (終了しました)

超並列Large Eddy Simulation (PALM)で著名なドイツ・ハノーバー大学のSiegfried Raasch博士

日時 2005916日(金)15:00

場所 東京工業大学 石川台4号館地下B04会議室


講師 Siegfried Raasch (ドイツ・ハノーバ大学気象学科)

題目 High resolution Large Eddy Simulations on the effects of land surface heterogeneities

参加 無料

要旨 Orography and differences in landuse represent inhomogeneities of the land surface, which range
from continental scale to micro scale. In operational weather forecast models, the orography of the land
surface is already well-implemented, being a crucial factor for success of the forecast. Despite the effects of
large-scale heterogeneities like land and sea (e.g. land-see breeze), it is still an open question if the heterogeneous
of meso- to micro- scale produce significant effects on local weather (e.g. convectively-induced rainshowers).
Therefore, several experiments have been carried out in the last decades, e.g. Yates et al. (2001), Isaac et al. (2004).

Until now, a “heterogeneous effect” of landuse on the CBL could not be clearly captured in any of these experiments.
Reasons for this are e.g. a coarse instrumentation, synoptic-driven events like frontal clouding and rainfall, or high
wind speeds during the campains. Simulations with mesoscale models suffer from the coarse grid resolution of a few
(Lynn et al., 1995; Arola, 1999), while turbulence resolving large eddy simulation (LES) models were
mostly used to investigate the effects of idealized heat flux inhomogeneites on the convective boundary layer (CBL),
e.g. Albertson et al. (2001), Avissar and Schmidt (1998), Raasch and Harbusch (2001), Letzel and Raasch (2003).

Therefore, the intention of our project was to carry out an LES study of the effects of actually observed heatflux
heterogeneities on the CBL structure. We primarily focused on secondary circulations set off by the heterogeneities.
As appropriate initial and boundary conditions for the simulations we used data from the LITFASS-2003 experiment
which was part of the German EVA_GRIPS project (Beyrich et al., 2004). This project investigates the evaporation
at scales of about 0.1 - 20 km over the heterogeneous area around Lindenberg southeast of Berlin/Germany,
continuously recorded with 13 energy balance stations during May/June 2003. Orography plays only a minor role in
this area, whereas differences in landuse represent strong heterogeneities. The size of the experimental domain (
was 20 x 20 km2. Using the experimental data, the daytime development of the CBL has been simulated for four days
of the experimental period (2003/05/30, 06/02, 06/13, 06/17). Because the simulations have to resolve the small scale
boundary layer turbulence as well as to use a large computational domain, they require very large computational
resources. These can be satisfied only by massively parallel computers.