Seasonal characteristics of diurnal precipitation variation in Krakow (South Poland)

This paper describes the diurnal cycle of liquid precipitation using the amplitude and phase of two precipitation characteristics: frequency and totals. A uniquely long set of uniform hourly precipitation data from Krakow (South Poland) was used. This vast and reliable basic material was collected by the author using pluviographic data covering the period 1886-2002. The role of precipitation type in forming the general diurnal cycle of precipitation was discussed. Two precipitation types, frontal and air mass, were taken into consideration. The role of particular air masses (polar maritime and polar continental) and atmospheric fronts (warm and cold fronts) in the 24-h precipitation cycle was determined. The frontal and air mass precipitation events were identified using a documentation of synoptic situations by Niedzwiedz over the area of southern Poland for the 1951 -2002 period. Depending on the precipitation characteristic (frequency or totals), season of the year and precipitation type, the diurnal precipitation cycle may have one or two modes. The bimodality of the distribution occurs mainly for air mass precipitation. The morning maximum of precipitation frequency in all seasons of the year mimics the diurnal variation of precipitation in maritime polar air masses. Precipitation concentration in the afternoon hours is determined mainly by the intensity of processes in the cold front zone and in the homogeneous polar continental and maritime air masses. Significant differences in precipitation distribution in cold and warm fronts are connected with the time of precipitation concentration within the diurnal period. The type of atmospheric front determines the layout of precipitation clouds, intensity of precipitation formation and the velocity of front movement. Copyright (c) 2006 Royal Meteorological Society.