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Ann. Geophys., 20, 2047-2066, 2002
www.ann-geophys.net/20/2047/2002/
© European Geosciences Union 2002
Numerical study of the October 2000 torrential precipitation event over eastern Spain: analysis of the synoptic-scale stationarity
V. Homar1, R. Romero1, C. Ramis1, and S. Alonso1,2
1Meteorology Group, Dept. de Física, Univ. de les Illes Balears, Palma de Mallorca, Spain
2IMEDEA, UIB-CSIC, Palma de Mallorca, Spain
Correspondence to: V. Homar (victor.homar@uib.es)
Abstract. A torrential
precipitation event affected eastern Spain during 21 to 24 October 2000. Total
accumulated rainfall higher than 500 mm was registered at some locations, with
values up to 300 mm in a 24-h period. The synoptic-scale charts for these days
show the presence of a cold cutoff low aloft, south of the Iberian Peninsula,
as a part of an W-blocking structure over Europe. At
low levels, persistent easterly winds, established between a dominant
anticyclone over eastern Europe and a cyclone over Morocco, are found over the
western Mediterranean throughout the entire period. Satellite images show the
advance and breaking away of a trough, with an associated cold front, over the
Iberian Peninsula, which resulted in the cutoff low formation. Later, scattered
convective cells are detected along the eastern Spanish coast during more than
3 days. Numerical simulations reveal that the convective environment was
developed by the low-level advection of warm and moist air from central
Mediterranean, being charged of moisture by evaporation from the sea.
Sensitivity runs confirm that the synoptic-scale persistent low-level easterly
flow, and specifically, the presence of a low level jet, was crucial for the
subsynoptic processes leading to the long lasting torrential rainfall over the
exposed terrains of eastern Spain. The stagnancy of the low-level flow is
attributed to the quasi-stationary characteristics of the upper level cutoff
low located south of the Iberian Peninsula. Experiments with modified
upper-level potential vorticity distributions reveal that slight deviations
from the observed configuration result in enhanced mobility of the low-level
flow pattern, and thereby a reduction of the precipitation persistence. This
suggests the major importance of a correct representation in the model initial
conditions of the intensity and location of the upper level features, in order
to obtain valuable numerical forecasts of these heavy rainfall events.
Key words. Meteorology and
atmospheric dynamics (convective processes; mesoscale meteorology;
precipitation)
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