Fourth Study Conference on BALTEX Scala Cinema Gudhjem

investigated in the seaside of the Baltic Sea (the highest
west-east gradients of precipitation amounts) as well as in
the region of carved relief (relief peculiarities re-forms
precipitation field and increases its heterogeneity).
%
40
35
30
25
20
15
10
5
0
y = 17,529x + 9,7535
r = 0,84
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Figure 2. Mean error of precipitation amount measured
in the rain gauge station, that is the nearest from
geometric center of catchment (%, from mean
precipitation amount in whole catchment area)
dependence on parameter k.
The highest dispersion of precipitation field during D
type synoptic process was observed. Discrete convective
cells in the periphery of anticyclones or non-gradient
pressure fields predetermine high uneveness of
precipitation field. Precipitation dispersion values of
other types synoptic processes are quite similar in whole
Lithuanian teritorry, however some regional differences
associated with their movement trajectory are noticeable.
The later is access of barical systems to different parts of
Lithuania, the higher is uneveness of precipitation.
Precipitation field of southern cyclones (type B) is mostly
uneven in Zemaiciai Highland, whereas western cyclones
(type A) - in Middle Plain and South-East hydrological
regions.
4. Prevailing synoptic processes
Maximum rainfall runoff formation is usually caused by
a complex of synoptic processes that last more than 5
days (type E - 34%) in the Lithuanian territory. In the
k
- 58 -
result of such type of synoptic process the greatest
amount of precipitation fell down, however, precipitation
intensity was relatively low because of its duration. Type
E the most frequently occurred in the Middle Plain and
South-East hydrological regions of Lithuania – 41%,
whereas such synoptic processes occurred more rarely in
the Zemaiciai Highland region – 22%.
Western cyclones are the most important synoptic system
influencing RIR formation in Zemaiciai Highland
(A type – 39%). Low pressure systems, moving from the
Atlantic Ocean, bring extremely high amount of
precipitation to the western part of Lithuanian territory
(16,2 mm/per day of average precipitation – during the
maximum RIR formation). This situation is especially
characteristic for September – it makes 74% of the cases.
In spring it is opposite – influence of southern cyclones
(type B) is stronger. Warm and wet air vortexes come
from Subtropics, whereas the Atlantic Ocean as well as
the Baltic Sea are not warm enough.
RIR in April and May are mostly related to Southern
cyclones (type B) in the Middle Plain. Influence of
Western cyclones increases towards autumn (35% in
September). Unlike Western Lithuania, type E is very
frequent in the Middle Plain: type E influenced 61% of
RIR formation in July there.
RIR has been mostly formed due to the influence of
complex of synoptic processes (type E) in South-East
hydrological region. Influence of Western cyclones is
less (hardly 13%), whereas Southern cyclones (type B)
are more frequent than in other regions of Lithuania
(28%). RIR influenced by Southern cyclones in spring
and summer prevails over type E, frequency of which
increases towards autumn.
RIR, related to undulate atmosphere fronts in low
pressure fields (type C) occurred rarely (15%). Frequency
and duration of the rainy period (based on type C) is
similar and comparable in all Lithuanian territory,
however amount of precipitation is slightly higher in
Zemaiciai Highland.
Maximum RIR due to D-type synoptic processes is
possible only in case of relatively rainless period and low
intensity cyclonic circulation. D type synoptic processes
were estimated barely 1%.