Opady frontowe na polskim wybrzeżu Bałtyku = Frontal precipitation along the Polish coast

Świątek, Małgorzata

doi:0033-2143

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Opady frontowe na polskim wybrzeżu Bałtyku = Frontal precipitation along the Polish coast Świątek, Małgorzata

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Opady frontowe na polskim wybrzeżu Bałtyku = Frontal precipitation along the Polish coast

Przegląd Geograficzny T. 81 z. 1 (2009)

frontal precipitation ; Polish Baltic coast ; t-Student tests

The climate of the Baltic coastline is strongly affected by prevailing cyclones and frontal activities. Frontal precipitation is shown to dominate in the Baltic area, with about two–thirds of rainfall events being frontal in origin (Walther and Bennartz, 2006). The aim of the work described here was to study precipitation totals in relation to selected atmospheric fronts and days without fronts. The analysis took in the daily precipitation totals recorded during both the cold seasons (October–March) and the warm ones (April-September) in the years 1998–2003, at seven stations along the Baltic coast (i.ee. Szczecin, Świnoujście, Koszalin, Łeba, Hel, Gdynia and Elbląg). The lower weather charts from the years 1998–2003 published by wetterzentrale (www.wetterzentrale.de/topkarten) formed a basis upon which to state the occurrence of different kinds of fronts. Irrespective of kind, the occurrence of a front causes an increase in precipitation totals, while there is a decrease on days without fronts (Table 1). The t-Student test shows that the influence of cold fronts on the precipitation pattern is more important in a warm season than in a cold one, while the effect of warm fronts is greater in a cold season. The highest mean daily precipitation totals along the Polish coast relate to the passage of an occluded front (Tab. 1, Tab. 2). Extreme high totals for precipitation are associated with cold fronts. There are single events with very high totals on days without fronts (Fig. 1) – 27.1 mm was the maximum daily precipitation total (mean for seven stations) recorded for days analyzed in the study. It was noted on September 13th 1999 and was associated with convective rainfall in conditions of a barometric trough. The breakdown of precipitation totals was also studied by size category, with the frequency of occurrence of daily totals within selected size intervals being presented (Fig. 2). The most frequent daily totals were of between 0.01 and 0.50 mm. The probability of moderate precipitation totals (in the 1.01–5.00 range) is higher in the presence of occluded fronts than when warm or cold fronts are passing through. Mean numbers of stations experiencing precipitation as selected fronts pass through were also calculated, as was the frequency of occurrence of precipitation at all stations in days with or without fronts (Figs. 3, 4).

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