Testing the downscaling ability of a one-way nested regional climate model in regions of complex topography |
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Authors: | S Antic R Laprise B Denis R de Elía |
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Institution: | (1) Département des sciences de la Terre et de l’Atmosphére, Université du Québec á Montréal, 550 Sherbrooke St. West, 19th Floor, Montréal, Québec, Canada H3A 1B9;(2) Canadian Meteorological Centre, Meteorological Service of Canada, Dorval, Québec, Canada |
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Abstract: | The downscaling ability of a one-way nested regional climate model (RCM) is evaluated over a region subjected to strong surface
forcing: the west of North America. The sensitivity of the results to the horizontal resolution jump and updating frequency
of the lateral boundary conditions are also evaluated. In order to accomplish this, a perfect-model approach nicknamed the
Big-Brother Experiment (BBE) was followed. The experimental protocol consists of first establishing a virtual-reality reference
climate over a fairly large area by using the Canadian RCM with grid spacing of 45 km nested within NCEP analyses. The resolution
of the simulated climate is then degraded to resemble that of operational general circulation models (GCM) or observation
analyses by removing small scales; the filtered fields are then used to drive the same regional model, but over a smaller
sub-area. This set-up permits a comparison between two simulations of the same RCM over a common region. The Big-Brother Experiment
has been carried out for four winter months over the west coast of North America. The results show that complex topography
and coastline have a strong positive impact on the downscaling ability of the one-way nesting technique. These surface forcings,
found to be responsible for a large part of small-scale climate features, act primarily locally and yield good climate reproducibility.
Precipitation over the Rocky Mountains region is a field in which such effect is found and for which the nesting technique
displays significant downscaling ability. The best downscaling ability is obtained when the ratio of spatial resolution between
the nested model and the nesting fields is less than 12, and when the update frequency is more than twice a day. Decreasing
the spatial resolution jump from a ratio of 12 to six has more benefits on the climate reproducibility than a reduction of
spatial resolution jump from two to one. Also, it is found that an update frequency of four times a day leads to a better
downscaling than twice a day when a ratio of spatial resolution of one is used. On the other hand, no improvement was found
by using high-temporal resolution when the driving fields were degraded in terms of spatial resolution.
Figure legends were missing in original article. Climate Dynamics (2005) 23: 473-493. The complete article is given here.
DOI: 10.1007/s00382-004-0438-5 |
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