Areal classification concerning patterns of global radiation and cloudiness variations in Hungary

Factor Analysis (FA) in S-mode is applied to classify the global radiation and the cloud distribution patterns derived from METEOSAT digital images. The aim of the areal classification is to construct a meta-archive of days with different cloud coverage for the derivation of surface climate parameters and also for the special needs of weather analysis. Another aim is to intercompare the large-scale patterns of global radiation, derived from the visible channel, with the other investigated parameter, the cloud covearge, that employs infrared information, too. The investigated areas cover 4×8 and 4×9 spatial elements corresponding to app. 70×70 km and 50×50 km resolution in Central Europe, respectively. Regions are defined, where for any point within each region, the analysed meteorological variable covaries. Results of the two classifications indicate a similar number, 3–5, of characteristic regions, but their spatial arrangements are different. Another difference is that, for the cloudiness, the fourth rotated factor (having already been rejected according to the Guttman criterion i.e. the rule to keep the factors with eigenvalues >1) does not influence the patterns in case of cloud coverage, but yields completely different structure in case of global radiation.