A Spectral Nudging Technique for Dynamical Downscaling Purposes
Hans von Storch, Heike Langenberg, and Frauke Feser, 2000: Monthly Weather Review, 128 (19), 3664-3673.
Abstract.
Institute of Hydrophysics; GKSS Research Center; D-21502 Geesthacht; Germany.
hvonstorch(at)web.de, H.Langenberg(at)nature.com, frauke.feser(at)hzg.de
The ``spectral nudging'' method imposes time-variable large-scale
atmospheric states on a regional atmospheric model. It is based on the idea
that regional-scale climate statistics are conditioned by the
interplay between continental-scale atmospheric conditions and such
regional features as marginal seas and mountain ranges. Following
this ``downscaling'' idea, the regional model is forced to satisfy not
only boundary conditions, possibly in a boundary sponge region, but
also large-scale flow conditions inside the integration area.
In the present paper the performance of spectral nudging in an extended climate
simulation is examined. Its success in keeping the simulated state close to
the driving state at larger scales, while generating smaller-scale features
is demonstrated, and it is also shown that the standard boundary forcing
technique in current use allows the regional model to develop internal states
conflicting with the large-scale state. It is concluded that spectral nudging
may be seen as a suboptimal and indirect data assimilation technique.