Self-similarity patterns of precipitation in the Iberian Peninsula |
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Authors: | A Morata M L Martín M Y Luna F Valero |
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Institution: | (1) Instituto Nacional de Meteorología, Servicio de Desarrollos Climatológicos, Madrid, Spain;(2) Departamento Matemática Aplicada, Escuela de Informática, Campus de Segovia, Universidad de Valladolid, Spain;(3) Departamento Astrofísica y CC de la Atmósfera, Facultad de CC Físicas, Universidad Complutense de Madrid, Spain |
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Abstract: | Summary An objective classification of the precipitation field over the Iberian Peninsula and the Balearic Islands is obtained. Data
are derived from a high-resolution daily precipitation dataset obtained from in-situ measurements. The dataset, Iberian monthly
Precipitation Dataset (IPD), consists of monthly precipitation data over a 25 km × 25 km grid from 1st January 1961 to 31st December 2003. Therefore, 960 data series over the Iberian Peninsula and the Balearic Islands are disposed over the grid
for 43-year period. Multi-resolution wavelet analysis is used to extract similar information in the precipitation field at
different timescales. An objective classification of the obtained wavelet coefficient series is carried out by means of the
Kohonen’s neural network, also named Self-Organizing Map (SOM). SOM is formed by an unsupervised learning algorithm that may
be used to find clusters of similar events in the input data and is able to identify some underlying dynamic structures of
the multi-dimensional datasets. SOM is applied to the wavelet coefficients for intramonthly, intermonthly and interannual
oscillations, obtaining self-organised maps which objectively identify similar zones of precipitation behaviour over the Iberian
Peninsula. The homogeneity of the patterns is also studied by means of non-parametric correlations, energy scalograms and
tests of significance. The intramonthly, intermonthly and interannual waves resulted in seven, five and three SOM patterns,
respectively. As timescale increases, the wavelet series coefficients tend to be highly clustered. The results indicate that
as the oscillation frequencies decrease, the Iberian precipitation behaves more linearly. |
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