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| Titel |
Atmospheric circulation patterns associated with extreme precipitation amounts in Greece |
| VerfasserIn |
E. E. Houssos, C. J. Lolis, A. Bartzokas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7340
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| Digitales Dokument |
URL |
| Erschienen |
In: 9th EGU Plinius Conference on Mediterranean Storms (2007) ; Nr. 17 (2008-06-20), S.5-11 |
| Datensatznummer |
250013617
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| Publikation (Nr.) |
 copernicus.org/adgeo-17-5-2008.pdf |
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| Zusammenfassung |
The main synoptic conditions associated with extreme precipitation amounts
in Greece are examined by using a multivariate statistical methodology
comprising S-mode Factor Analysis and k-means Cluster Analysis. The
following data were used : i) daily precipitation amounts (measured at
06:00 UTC) for the meteorological stations of Hellenikon (Athens),
Thessaloniki (northern Greece) and Ioannina (western Greece) and ii) daily
(18:00 UTC) 2.5×2.5 grid point values of 500 hPa geopotential height, mean
sea-level pressure and 1000–500 hPa thickness at 273 grid points over Europe
(10 W to 40 E and 30 N to 60 N), for the period 1970–2002.
The dates corresponding to the upper 5% of the frequency distribution of
precipitation are selected for each one of the three stations. In total, 369
dates are used, some of them being common among the three stations. The
corresponding 369×273 data matrices of 500 hPa geopotential height, mean
sea-level pressure and 1000–500 hPa thickness are constructed. The rows refer
to the 369 extreme precipitation cases and the columns refer to the 273 grid
points. The three matrices are unified into one 369×819 matrix. In order to
reduce the dimensionality of the data set, S-mode Factor Analysis is applied
to the unified matrix, revealing 7 factors accounting for 85% of the
total variance. Finally, k-means Cluster Analysis is applied to the factor
scores matrix, classifying the 369 cases into 9 clusters.
For each one of the 9 clusters, the mean 18:00 UTC patterns of the above
parameters are constructed and presented. These patterns correspond to the
main distinct atmospheric circulation structures favoring extreme
precipitation amounts in Greece. Most of the patterns are characterized by
enhanced cyclonic activity over or near the Greek area. The differences
among the 9 circulation structures refer mainly to the position and the
intensity of the surface and the upper air synoptic systems involved. Some
of the 9 synoptic conditions favor extreme precipitation amounts mainly at
one or two of the three stations while some others equally affect the three
stations. |
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