Wintertime westward-traveling planetary-scale perturbations over the Euro-Atlantic region |
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| Authors: | F J Doblas-Reyes M A Pastor M J Casado M Déqué |
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| Institution: | (1) Centro de Astrobiologia, INTA, Ctra. de Ajalvir km 4, 28850 Torrejon, Madrid, Spain E-mail: mep@ecmwf.int, ES;(2) Instituto Nacional de Meteorologia, P° de las Moreras s/n, 28040 Madrid, Spain, ES;(3) CNRM, Météo-France, 42 Av. G. Coriolis, 31057 Toulouse Cedex, France, FR |
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| Abstract: | The features of the wintertime westward-traveling planetary scale perturbations over the Euro-Atlantic region are examined
through the use of space–time spectral analysis applied to the 500 hPa geopotential height field. The intention is to understand
the nature of these phenomena and the performance of climate models. Data from both ECMWF re-analyses and a simulation from
the ARPEGE general circulation model are used. Westward-traveling planetary scale transients are found over the region as
local perturbations resembling Rossby normal modes, with a maximum power over the Eastern Atlantic. The westward-traveling
planetary scale transients north of 40∘N have periods larger than 20 days. South of this latitude, wave periods are shifted to a band around 10 days, so that they
can be related to subtropical transient waves. The atmospheric model used, like other models which exhibit reasonable mean
climatic properties, tend to have less overall intraseasonal variability than observed. Nevertheless, the model is able to
capture most of the features of the westward-traveling low-frequency transients. The differences in basic state, partially
produced by scale interactions, would lead to the generation of westward-traveling waves in the model distinct from the observed.
However, it is suggested that the improvement of the present model version with regard to previous model versions is due to
a better simulation of the time–mean state. The reasonable simulation of the synoptic-scale variability south of 50∘N, and thus of its barotropic forcing on the basic state, may also help to explain the realistic westward-traveling transients
in the model.
Received: 17 May 2000 / Accepted: 1 December 2000 |
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