A study on the intra-annual variation and the spatial distribution of precipitation amount and duration over Greece on a 10 day basis

The intra-annual variation of precipitation amount and duration and their spatial distribution during the year are studied on a 10 day basis for the Greek region, using S-mode and T-mode factor analysis. (i) For the intra-annual variation of precipitation amount, two modes were revealed: the first shows one broad maximum during the conventional winter in stations affected by the sea; the second presents two maxima, the first during late autumn-early winter and the second during late spring, corresponding to the northern mainland stations. (ii) For the spatial distribution of precipitation, three main patterns were revealed: the first one is the 'winter' pattern, with the maximum over the west windward area; the second is the 'summer' pattern, with a maximum over the north inland region; and the third is the 'autumn' pattern, with the maximum over northwestern Greece. (iii) For precipitation duration, two types of intra-annual variation were revealed. The first one is similar to the first of the analysis for precipitation amount; the second presents two maxima, the first during the beginning of December and the second during the middle of February, corresponding to the areas of northwestern and northeastern Greece. (iv) For the spatial distribution of precipitation duration, three main patterns were revealed: the first is the 'summer' pattern, which is similar to the second of the analysis for precipitation amount; the second is the 'winter' pattern, with the spatial maximum located over the eastern mainland and western Crete; finally, the third one is the 'autumn' pattern, with the maximum in northwestern Greece. During the third 10 day period of October and the second 10 day period of February, precipitation seems to present singularities, possibly due to fluctuations in atmospheric circulation, The above intra-annual variations and spatial distribution patterns are connected to the seasonal variations of the depression trajectories, the atmospheric instability, the influence of sea-surface temperature as a cyclogenesis factor, and the windward or leeward character of the various areas (orographic effect). Copyright (C) 2003 Royal Meteorological Society.