Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 25 Precipitation: Measurement, Climatology, Remote Sensing, and Modeling (EGU Session 2009) 2010 10.5194/adgeo-25-45-2010 http://www.adv-geosci.net/25/45/2010/ http://www.adv-geosci.net/25/45/2010/adgeo-25-45-2010.html http://www.adv-geosci.net/25/45/2010/adgeo-25-45-2010.pdf 45 50 2010-03-09 Cyclic modes of the intra-annual variability of precipitation in Greece P. T. Nastos nastos@geol.uoa.gr C. S. Zerefos Laboratory of Climatology and Atmospheric Environment, Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens, Greece National Observatory of Athens, Athens, Greece Research Center for Atmospheric Physics and Climatology of the Academy of Athens, Athens, Greece The application of harmonic analysis to the annual variability of precipitation is the object of this study, so that the modes, which compose the annual variability, be elicited. For this purpose, monthly precipitation totals from 30 meteorological stations of the Hellenic National Meteorological Service (HNMS), for the period 1950–2000, were used. <br><br> The initial target is to reduce the number of variables and to detect structure in the relationships between the variables. The most commonly used technique for this purpose is the application of Factor Analysis (FA) resulted in five main factors (sub-regions) with common precipitation characteristics, explaining 77% of the total variance. For each sub-region, a representative station is selected for the analyses, mainly, as the station within the sub-region with the highest factor loading. In the process, the Fourier Analysis is applied to the mean monthly precipitation, so that 2 harmonic components are derived, which explain more than 90% of the total variability of each station, and are due to different synoptic and thermodynamic processes associated with Greece's precipitation regime. 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