Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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The Influence of Synoptic Situations on Extreme Precipitation in the Raba
Valley (Gaik-Brzezowa)
Agnieszka Saramak
Jagiellonian University, Institute of Geography and Spatial Management, Department of Climatology, ul. Grodzka 64,
31-044 Cracow, Poland, e-mail: janusz@uj.edu.pl
1. Introduction
Atmospheric circulation is a factor, which affects the climate
both in global and local scale. The type of synoptic situation
determines direction of air movement as well as atmospheric
front motion. The type of synoptic situation affects also
radiation, which is closely connected with air movement,
Niedźwiedź (1981).
The aim of the paper is to describe dependence between
precipitation (mainly heavy precipitation) and the type of
synoptic situation in Gaik-Brzezowa, located in the drainage
basin of the Baltic.
Analysis is based on 30-year database of precipitation.
2. <strong>Study</strong> area and database
The area of research represents a fragment of the Raba river
basin, with the relief of the Carpathians Foothills, in the
South of Poland, which belongs to the drainage basin of the
Baltic. The research station Gaik-Brzezowa is the station of
Department of Climatology, Institute of Geography and
Spatial Management, Jagiellonian University.
Analysis includes database of precipitation in warm months
of year (April-October) during the period 1971-2000. Total
sum of precipitation was gathered by using two measuring
devices: Hellman’s rain-gauge and pluviograph, situated
about 2 meters away one from another.
3. Methods of analysis
In this study, the types of synoptic situations formulated by
Niedźwiedź were used. They describe the character of
pressure system (cyclone, anticyclone) and direction of air
movement. There are 21 types of atmospheric circulation:
Na, NEa, Ea, SEa, Sa, SWa, Wa, NWa, Ca, Ka, Nc, NEc,
Ec, SEc, Sc, SWc, Wc, NWc, Cc, Bc, X, where:
a – anticyclone system;
c – cyclone system;
N, NE, E, SE, S, SW, W, NW – direction of air movement;
Ca – centre of anticyclone;
Ka – a ridge of high pressure;
Cc – centre of cyclone;
Bc – a trough of low pressure;
X – situations unclassified
According to research concerning meteorological reasons of
high precipitation in this area, made by some Polish
researchers, e.g. Cebulak (1992), Milata (1955), Niedźwiedź
(1972, 1981, 1988), there are three genetic types of extreme
precipitation:
� local, short-lasting downpours, rainstorm – connected
with convection or dislocation of atmospheric front,
mainly cold front;
� continuous rainfalls, which comprise large parts of the
territory and last some days – related to the cyclone
system, moving from the Mediterranean Sea trajectory
V-b (van Bebbera); additional factor of increasing total
amount of precipitation is the mountain’s barrier causes
convection;
� short-lasting downpours superimpose on continuous
rainfalls, spatially diverse – connected with
dislocation of atmospheric front, mainly warm front
4. Individual precipitation
The analysis concerning the influence of the type synoptic
situations on the precipitation is based on studies of the
single precipitation. The rainfall is considered as being
single (also called as individual), when the duration
between two falls of rain is at least two hours. Such
duration was established in order to compare the results
obtained with the standardized works done in the Institute
of Meteorology and Water Resources in Poland.
The analysis based on individual downpours presents
more detailed description of extreme phenomena of
precipitation.
5. Results
The analysis of frequency of variable amount rainfalls
showed, that the most common precipitation was the one
with the total amount less or equal than 5,0 mm (Fig.1). It
was 76,1% of all rainfalls. Among these rainfalls almost
60% there were rains of amounts 0,1-1,0 mm. However
for instance rains higher than 20,0 mm made up only 4,6%
of the precipitation total during the April-October period
in the years 1971-2000. Therefore, despite the fact that
extreme downpours make up only some percent of total
sum of precipitation, they are the most crucial for
hydrological and morphological processes.
76,1%
0,4%
11,3%
4,8%
3,2%
1,6%
1,2%
0,5%
0,4%
0,3%
0,3%
0,1 - 5,0 5,1 - 10,0 10,1 - 15,0 15,1 - 20,0
20,1 - 25,0 25,1 - 30,0 30,1 - 35,0 35,1 - 40,0
40,1 - 45,0 45,1 - 50,0 < 50,0 mm
Figure 1. Average frequency of rainfalls of variable
amounts (each group represents 5 mm) at the Gaik-
Brzezowa Station, April-October, 1971-2000