Journal of Ecology and Protection of the Coastline

Comments

Transcription

Journal of Ecology and Protection of the Coastline
99
of Słupsk
B A L T I CTheCclimate
OASTAL ZONE
Journal of Ecology and Protection of the Coastline
40th academic year of the University
ISBN 1643-0115
Vol. 14
2010
pp. 99-120
ISBN 1643-0115
© Copyright by Institute of Biology and Environmental Protection of the Pomeranian University in Słupsk
Received:
Accepted:
Original research paper
1.12.2009
3.03.2010
THE CLIMATE OF SŁUPSK
Dariusz Baranowski, Małgorzata Kirschenstein
Institute of Geography, Pomeranian University in Słupsk,
ul. Partyzantów 27, 76-200 Słupsk, Poland,
e-mail: [email protected]
Abstract
This study is an attempt to provide a comprehensive and synthetic characterisation of Słupsk climate based on a homogeneous series of daily measurements covering the longest possible period.
Apart from the temperature and precipitation profiles derived from a 58-year examination record
(1950-2007), the climate analysis also presents the distribution of other key weather components
(atmospheric pressure, wind, relative humidity and cloud cover) in a shorter (1991-2007) time-span.
The paper, which is a summary of the existing research into Słupsk climate, is directed not only at
geographers (for whom it may be a significant reference in research concerning weather conditions
in other Polish towns), but also at local residents and tourists, who choose Słupsk as their holiday
destination.
Key words: Słupsk, climate, Baltic coast
INTRODUCTION
Słupsk is situated on PobrzeŜe Południowobałtyckie (the South Baltic Shoreland).
According to Okołowicz’s classification (1978) Słupsk belongs to the region mostly
shaped by the influence of the Atlantic Ocean and the Baltic Sea. The local climate
has a transitional character between maritime and continental. The geographical position of the city and the general flow of air masses (mostly zonal), governed by the
large-scale patterns of atmospheric circulation, are the main causes of the great variability in weather conditions, high precipitation and abrupt air temperature fluctuations. The most characteristic features of the Polish sea-coast climate (in comparison
to the other regions of the country) are: strong winds, relatively high amount of precipitation (especially in autumn-winter period) and cold springs and summers.
Słupsk is located near the sea coast, where the amount of precipitation exceeds the
total evaporation. Almost all year round air humidity is higher than in offshore regions of Poland. What is more, the area is distinguished by a high frequency of
100
Dariusz Baranowski, Małgorzata Kirschenstein
strong winds which are favourable for orographic and dynamic lifting of air masses
over the north-western slopes of Pojezierze Pomorskie (the Pomeranian Shoreland).
Due to the geographical position of PobrzeŜe Południowobałtyckie, within a transitional zone from maritime to continental climate, in the typical course of air masses
(governed by prevailing zonal circulation) there is a great variability of weather
conditions.
In this paper the most important meteorological elements were investigated: wind
velocity and direction, air temperature, relative air humidity, amount and frequency
of precipitation, snow cover and atmospheric pressure. A detailed analysis of the
climatic features of Słupsk (φ = 54º28'N; λ = 17º02'E; elevation – 17 m.a.s.l.) was
based on mean monthly, seasonal and annual data from the 1991-2007 period.
Trends of annual and multiyear changes in precipitation and air temperature were
determined using observations from the years 1950-2007. In order to verify the homogeneity of 58-yr meteorological series a non-parametric Smirnov-Kolmogorov
test was used. The obtained results of the test (λ = 0.81 for precipitation totals and
λ = 1.88 for air temperature values) are lower than the critical values for the level of
significance 0.001 (λ0,001 = 1.96).
Atmospheric pressure
Atmospheric pressure rate can be considered as a basis for further analysis of local
climate. Low pressure systems are usually accompanied by “bad” and changeable
weather conditions, whereas anticyclonic systems create more stable weather. For that
reason the characteristics of atmospheric pressure fluctuations should be an indispensable part of the comprehensive climatological analyses (Baranowski 2008b).
The distribution of atmospheric pressure over Poland varies greatly with the seasons.
It follows from the fact that the major centres of action on the Atlantic Ocean – the
Icelandic Low and the Azores High – influence weather and climatic patterns not
only in Poland but over the whole Europe. Usually in January the Icelandic Low
extends (and mean atmospheric pressure over Iceland drops below 995 hPa) while
the High (with the pressure at the centre of about 1020 hPa) moves to the south of
the Azores. These fluctuations in pressure result in more variable weather. In addition, especially during autumn and winter periods, an increase in cyclone activity
and the high frequency of westerlies was observed over the Baltic region during the
20th century (Sepp 2009). In summer the Icelandic Low is relatively weak. At the same
time the Azores High extends (atmospheric pressure exceeds 1025 hPa) and starts to
play a significant role in the determination of weather conditions in Poland.
In Słupsk the annual average sea-level pressure value in the period 1991-2007 exceeded 1012.3 hPa and in particular years ranged from 1008.4 hPa to 1019.2 hPa
(Fig. 1a). During the annual course (Fig. 1b) the highest mean monthly value of atmospheric pressure was recorded in March (1012.9 hPa), the smallest – in April
(1010.6 hPa). According to Parczewski (1965) rising frequency of high-pressure
systems over Poland in March is normally observed. In April their occurrence goes
down and from May until October yet again grows. However, most often in July and
August a small decrease in atmospheric pressure is recorded. Its mostly a result of
The climate of Słupsk
101
Fig. 1. Mean annual (a) and monthly (b) atmospheric pressure (1991-2007)
strong heating of the lowest air layers by the ground surface, favouring the creation
of low pressure systems. The highest average monthly pressure (1028.0 hPa), for the
period under consideration, was recorded in June 2006, while the lowest (1000.4 hPa)
– in December 1993.
Wind
In Poland, mostly due to its geographical location (within the temperate zone) and
the distribution of atmospheric pressure over the North Atlantic and Europe, prevail
102
Dariusz Baranowski, Małgorzata Kirschenstein
winds from the west (however their role
varies considerably throughout the year).
According to Woś (1999) in the structure
of air masses over Poland winds from
the western sector predominate (24%). The
frequency of winds from the northern (NWNE), eastern (NE-SE) and southern (SESW) quadrants constitutes about 21%, 21%
and 18% respectively. In contrast, in northern Poland winds from the western and
southern sector prevail (both about 30%),
while advection from the northern and
Fig. 2. Frequency of wind directions (in %) eastern quadrant represents respectively
without calms (1991-2007)
15% and of 20% of the total annual inflow.
In Słupsk, in the analysed period, winds
from the south (24.1%), west (18.8%) and south-west (17.3%) prevail (Fig. 2). The
north-western sector was the least represented (NW – 4.1%, N – 6.3%, NE – 4.5%).
Consequently, in Słupsk winds with the southern (SE, S, SW – 51.7%) and western
(SW, W, NW – 40.2%) component were most frequent; air flow from the eastern
(SE, E, SW – 29.4%) and northern sector (NW, N, NE – 14.8%) occurred rarely.
In spring (Fig. 3a) the flow from the south to north prevail (19.9%), but in the local
climate winds from other directions are quite frequent too (e.g. from the west –
18.4%, east – 17.8% and south-west – 15.5%). During summer winds from the
south-western sector (S, SW and W) are most numerous, exceeding 65.2% of all
cases (Fig. 3a). In autumn (Fig. 3b), apart from the dominant winds from the south
(27.8%), an increased frequency of easterlies is usually recorded (17.4%). In wintertime, the wind blows predominantly from the south (27.8%), even though directions from the south-west and west amount to 19.8% and 19.4% respectively (Fig.
3b). Moreover, in the winter months (Dec.-Feb.) decreasing frequency of advection
from the eastern sector is observed (NE, E i SE – 24.5% altogether).
Fig. 3a. Frequency of wind directions (in %) without calms in spring and summer (19912007)
The climate of Słupsk
103
Fig. 3b. Frequency of wind directions (in %) without calms in autumn and winter (1991-2007)
Fig. 4. Mean annual (a) and monthly (b) wind velocity (1991-2007)
104
Dariusz Baranowski, Małgorzata Kirschenstein
In Słupsk during the whole year and in all seasons winds from the southern sector
are recorded more often than from the northern one, as well as winds blowing from
the western sector are more frequent (apart from autumn) than from the eastern one.
The second most important feature of the horizontal air movement (besides the direction) is its velocity, which can be affected by a number of factors and situations,
operating on varying scales. These include the pressure gradient, Rossby waves and
jet streams as well as local weather conditions. In most regions of Poland the average annual wind velocity varies within the limits of 3.0-4.0 m/s (Atlas klimatu Polski 2005). In Słupsk the mean annual wind velocity – 2.3 m/s in the given period
1991-2007 ranged between 1.6 m/s and 3.8 m/s (Fig. 4a). In the annual course the
maximum velocity during winter months is usually observed, with the maximum
value in January – 2.9 m/s and minimum in September – 1.6 m/s (Fig. 4b). Higher
than average wind velocity during winter is mostly linked to the seasonal increase in
pressure gradient over Poland.
Air temperature
The study of temperature conditions was based on mean monthly and extreme air
temperature values (tmax, tmin). The mean annual temperature in Słupsk in the years
1950-2007 was about 7.8ºC and ranged from 6.0ºC in 1987 to 9.7ºC in 2000 (Fig. 5).
Most often January is the coldest month (Table 1) even though the lowest mean
monthly temperatures are also recorded in February (34.5% of years), December
(22.4%), March (3.4%) and November (1.7%). The highest average temperature in
Słupsk usually occurs in July, August and from time to time in June. The frequent
occurrence of maximum air temperatures in August and minimum ones in February
is typical for the cities situated on the Polish sea coast (Atlas współzaleŜności…
2002, Paszyński and Niedźwiedź 1991, Baranowski 2001, Baranowski 2008a, Baranowski and Kirschenstein 2008). This one-month delay (in comparison to central
and southern Poland) is mostly attributed to the strong influence of the Atlantic
Ocean and the Baltic Sea.
Fig. 5. Mean annual air temperature in the years 1950-2007 (Kirschenstein and Baranowski 2008)
The climate of Słupsk
105
106
Dariusz Baranowski, Małgorzata Kirschenstein
In Słupsk the annual range of air temperature (the difference between mean temperatures of the warmest and the coldest month) for the investigated period
amounted to 18.3ºC and ranged from 14.9ºC in 2000 to 26.7ºC in 2006 (Table 1). In
the annual course the biggest variations in amplitudes (>13ºC) are typical for January and February; the lowest fluctuations are usually recorded in April (5.3ºC).
Taking into consideration the absolute maximal and minimal values the greatest differences occurred in January and February, the smallest – in July. The difference
between the absolute minimum (-31.2ºC in January 1963) and the absolute minimum (37.5ºC in August 1992) amounted to 68.7ºC.
The analysis of air temperature in different seasons of the year has shown its great
variability in the studied period (1950-2007). Warm summers, with an average temperature over 18ºC, only four times were recorded – in 1992, 1997, 2002 and 2006;
relatively cold ones (below 15ºC) – in the years: 1962, 1965, 1974 and 1987. The
warmest summer, with an average temperature over 18,9ºC was registered in 2002,
the coldest (14.6ºC) – in 1962. What is more in Słupsk, for the last twenty years of
the analysed period, warm winters were characteristic. Only in 1991, 1996 and 2003
the average winter temperature was negative.
To determine the variation in air temperature coefficients of linear trend were calculated (Table 2). The obtained results reveal a marked rise of mean temperatures in all
seasons of the year, especially in spring (0.0318ºC/year) and winter (0.0314ºC/year).
In the analysed 58-yr period the average air temperature during the winter-spring
season has raised by about 1.8ºC. The highest increase in temperature during this
part of the year is mostly caused by a rapid growth of temperature in January
(0.0377ºC/year), February (0.0422ºC/year) and May (0.0345ºC/year). In summer
and autumn linear temperature trends revealed a slow-growth tendency.
Fig. 6. Average seasonal temperature in the years 1950-2007 (Kirschenstein and Baranowski 2008)
The analysis of changes in the maximum and minimum temperature levels has revealed the highest tmax increase in January-May period, with a falling tendency in
September and November. Consequently, in winter and spring an increase in maximum temperature was recorded (on average 0.0332ºC and 0.0474ºC per year respectively) and a decrease in autumn (-0.0198ºC/year). As far as tmin is concerned,
107
The climate of Słupsk
a very steep rise was recorded in February (0.0977ºC), March (0.0575ºC) and June
(0.0662ºC) versus a drop in January (-0.0067ºC) and October (-0.0013ºC).
The research has shown that in the long-term course of average temperature the
greatest rise in spring and winter was observed (particularly in February). In contrast
summer and autumn are marked by the smallest rise in temperature (especially June
and November). Furthermore, in the studied period 1950-2007 the value of linear
trend accounted to 0.0217ºC/year, resulting in an increase of mean annual temperature in Słupsk by about 1.3ºC (Table 2).
Table 2
Linear trend coefficients and changes in air temperature and in precipitation amount
in the years 1950-2007 (Kirschenstein and Baranowski 2008)
Air temperature
linear trend coefficient
Precipitation totals
changes in temp.
(58 years)
changes
in precip.
amount
(58 years)
Tavg
Tmax
Tmin
Tavg
Tmax
Tmin
linear
trend
coefficient
Jan.
0.0377
0.0495
-0.0067
2.2
2.9
-0.4
0.2243
13.0
Feb.
0.0422
0.0435
0.0977
2.4
2.5
5.7
0.1583
9.2
Mar.
0.0327
0.0561
0.0575
1.9
3.3
3.3
0.3219
18.7
Apr.
0.0283
0.0397
0.0102
1.6
2.3
0.6
-0.1015
-5.9
May
0.0345
0.0463
0.0347
2.0
2.7
2.0
0.1329
7.7
Jun.
0.0003
0.0162
0.0662
0.0
0.9
3.8
0.2116
12.3
Jul.
0.0286
0.0310
0.0436
1.7
1.8
2.5
-0.4015
-23.3
Aug.
0.0246
0.0263
0.0240
1.4
1.5
1.4
-0.1743
-10.1
Sep.
0.0096
-0.0448
0.0287
0.6
-2.6
1.7
0.1752
10.2
Oct.
0.0072
0.0105
-0.0013
0.4
0.6
-0.1
0.3354
19.5
Nov.
0.0001
-0.0250
0.0020
0.0
-1.5
0.1
0.1122
6.5
Dec.
0.0143
0.0066
0.0496
0.8
0.4
2.9
0.3277
19.0
Spring
0.0318
0.0474
0.0342
1.8
2.7
2.0
0.3532
20.5
Summer
0.0179
0.0245
0.0446
1.0
1.4
2.6
-0.3641
-21.1
Autumn
0.0057
-0.0198
0.0098
0.3
-1.1
0.6
0.6228
36.1
Winter
0.0314
0.0332
0.0469
1.8
1.9
2.7
0.7103
41.2
Year
0.0217
0.0213
0.0339
1.3
1.2
2.0
1.3223
76.7
Period
Relative air humidity
The geographical location of Słupsk, and typical course of air masses are the most
important factors influencing the local climate. Prevailing winds from the western
108
Dariusz Baranowski, Małgorzata Kirschenstein
sector transport humid air from the Atlantic Ocean and the Baltic Sea. On the other
hand dry air masses quite frequently arrive here from the eastern part of Europe. It
can therefore be concluded that the air humidity in this region is considerably influenced by atmospheric circulation (Baranowski and Kirschenstein 2010).
Fig. 7. Mean annual (a) and monthly (b) relative air humidity (1991-2007)
The research has revealed that the average annual relative humidity in Słupsk, in the
analysed period was rather high (80%) and ranged from about 78% in 2002 and
2003 to 85% in 1991 (Fig. 7a). From September to February mean air humidity
usually exceeds 83%, with the highest value in December – 88% (Fig. 7b). In
the remaining months the average humidity is lower than the mean annual value. The
driest season is usually recorded in late spring or early summer, with the minimum
relative air humidity in May (78%). In the 18-yr period the mean monthly values of
humidity varied from 64% in May 2000 up to 93% in November 1991 and December 2000.
The climate of Słupsk
109
The seasonal variation in relative humidity in Słupsk shows that in autumn and
winter air humidity (85% and 86% respectively) is usually about 10% higher then in
spring (75%) and summer (76%). In consequence the warm half-year (Apr.-Sep.) is
about 5% drier than the cold one (Oct.-Mar.).
Cloud cover
Cloud amount is the extent to which the sky is obscured by clouds. The total cloud
cover is usually reported in eighths (octas) or in percent notation. Cloudiness is a comprehensive indicator of the state of the atmosphere and one of the most important
components of weather and climate. This exerts influence on the radiation balance
of the Earth and of the atmosphere and in consequence on the ground and air temperature as well as on precipitation.
Fig. 8. Mean annual (a) and monthly (b) cloud cover (1991-2007)
110
Dariusz Baranowski, Małgorzata Kirschenstein
The average annual cloud cover over a wide area of Poland ranges between 5.0-5.4
(Atlas klimatu Polski 2005). In Słupsk the mean long-term cloudiness in the period
1991-2007 exceeded 5.4 (in the 0-8 scale) and in particular years varied within the
limits of 5.0-5.9 (Fig. 8a). Usually, in an annual course (Fig. 8b), higher cloud
amount is recorded in autumn (5.6) and winter (6.2%), with a maximum in December (6.4). Lower values are typical of spring (4.9) and summer (4.7), with an annual
minimum in May (4.4). As a result, in the cold half-year an average cloud cover is
much larger (5.8) than in the warmer one (4.8) – a regularity indicated by most
weather stations in Poland. Due to an intensification of process of cloud formation in
the warm half-year, when masses of warm unstable air rapidly rise (producing convective clouds), clouds do not usually cover the sky completely. Furthermore, heavy
precipitation tends to increase air transparency, so recorded cloud cover is usually
relatively small. In contrast, in the colder half of the year, usually due to the relatively cold land-surface a decrease in the rate of convective cloud formation is observed. However, in this period, frequent advection of warm and humid air masses
from the Atlantic Ocean and the Baltic Sea is favourable for stratiform clouds formation, which are usually connected with rather frequent low-intensity precipitation.
Precipitation
The average annual precipitation in Słupsk in 58-years period accounted to 1 261
mm, varying from 522 mm in 1959 (65.7% of multi-annual average) to the highest
sum – 1 261 mm in 1981 (158.8%), (Fig. 9). In 1950-2007 period 50% of the analysed years amount of precipitation exceeded the mean long-term value.
Fig. 9. Mean annual precipitation totals (in mm) in the years 1950-2007 (Kirschenstein and
Baranowski 2008)
Normally, in an annual course the highest average rainfall in Słupsk are recorded
in July. March usually stands out with the smallest amount of precipitation (Fig. 10). In
different years the mean monthly maximum values varied from 77 mm (March
1951) to 279 mm (July 1965), while the minimum in the range of about 0 mm in
The climate of Słupsk
111
Fig. 10. Mean monthly precipitation totals (in mm) in the years 1950-2007
June 1992 to 42 mm in May 1998. Quite fregrently in Słupsk the mid-summer peak
is very often accompanied by another one that occurs in the autumn months, particularly in September (13.8%) or October (17.2%). This specific situation might be
attributed to the strong influence of the Atlantic Ocean and the Baltic Sea. The
minimum of precipitation is mostly dependent on circulation factors. In spite of
the fact that the average minimum in the analysed period occurred in March (12.1%
of the studied years), more frequently it was recorded in April (22.4%). Quite often
it was also noted in January (10.3%), February (12.1%) or in May (10.3%).
Fig. 11. Types of seasonal distribution of precipitation in the years 19502007, (Kirschenstein and Baranowski 2008)
To determine the asymmetry of the annual variation in precipitation amount in the
years 1950-2007, the annual period was divided into two half-years (cold and warm)
as well as into four meteorological seasons: spring (March-May), summer (JuneAugust), autumn (September-November) and winter (December-February). Consid-
112
Dariusz Baranowski, Małgorzata Kirschenstein
ering the sum of precipitation in different seasons in comparison to the average annual amount 3 types of seasonal distribution of rainfall in Poland (KoŜuchowski and
Wibig 1988) have been determined: the Pomeranian type (LJZW), the type of Polish
central zone (LJWZ) and the type characteristic for the south of Poland (LWJZ). The
seasonal distribution of precipitation in Słupsk (Fig. 11) revealed that the local climate belongs to the Pomeranian type (with the shares in particular seasons: summer
– 30.4%; autumn – 29.8%; winter – 21.9%; spring – 17.9%).
In Słupsk, besides relatively high summer precipitation, large amount of autumn
rainfall in the analysed period was recorded. Higher than normal precipitation sums
in autumn months are usually caused by frequent advection of warm and humid air
from the Atlantic Ocean and the Baltic Sea (because of extremely intensive cyclonic
activity over the southern Baltic). A low amount of spring precipitation refers mostly
to the presence of large water bodies near the coastline (cooling effect). What is
more, the long-term analysis of particular seasons’ contributions to the annual total
Fig. 12. Percentage of average spring and autumn rainfall in annual precipitation totals in the
years 1950-2007 (Kirschenstein and Baranowski 2008)
Fig. 13. Percentage of average summer and winter rainfall in annual precipitation totals in the
years 1950-2007 (Kirschenstein and Baranowski 2008)
The climate of Słupsk
113
precipitation has shown significant variation. The level of spring precipitation sums
varied from 4.4% in 1974 to 30.5% in 1983, summer from 10.3% in 1983 to 46.1%
in 1980, autumn from 12.4% in 1966 to 45.8% in 1974 and winter from 2.9% in
1972 to 35.7% in 1982 (Fig. 12, 13). Further calculations has showed that the highest precipitation variability was recorded in summer (35.8%) and autumn (33.4%),
the smallest – in spring (26.1%).
In the period under consideration the share of the warm half-year (May-October)
rainfall in the annual precipitation sum in Słupsk was 57.7% and in different years
ranged from 39.9% in 1969 to 73.1% in 1996 (Fig. 14). Moreover, in half of the
analysed years the amount of rainfall in the cold semi-annual period was higher than
in the warm one (what is typical for the oceanic type of precipitation).
Fig. 14. Percentage of warm half-year precipitation in annual precipitation totals in the years
1950-2007 (Kirschenstein and Baranowski 2008)
In Słupsk an increasing tendency in precipitation amount was observed (1.3223 mm
per year). The mean annual precipitation totals during the analysed 58-yr period has
risen by about 76.7 mm. The highest upward trend the city has experienced in winter
and in autumn (0.7103 mm/year and 0.6228 mm/year respectively).
Frequenc y of p rec ip ita tion
The frequency of rainy days (≥ 0.1 mm) in the northern part of Poland depends
mostly on atmospheric circulation, fronts which are usually associated with some
form of precipitation, influence of the Baltic Sea and local factors (especially topography and presence of large water basins). According to Kirschenstein (2004), the
average annual number of days with precipitation in the north-western part of Poland amounts to 163 and ranges from 127 days by the Noteć River to 188 days on
the north-western slope of Pojezierze Pomorskie (Pomeranian Lake District).
Moreover, along with Olechnowicz-Bobrowska the average number of precipitation
days in Poland varies within the limits 140-240. In Słupsk the mean annual number
of days with precipitation in the studied period 1991-2007 ranged from 163 in 2003
114
Dariusz Baranowski, Małgorzata Kirschenstein
to 211 in 2001, with a long-term average – 190 days (Fig. 15a). In an annual course
(Fig. 15b) rainfall days most frequently were recorded in December (19.4 days);
least often – in April (12.6 days). In particular years the variation in the mean
monthly number of wet days ranged from 2 in July 1994 to 29 in January 2007.
Fig. 15. Average monthly (a) and annual (b) numbers of rainy days (≥ 0.1
mm) in the years 1991-2007
Further analysis of the frequency of rainy days in different seasons has revealed that
in winter and autumn precipitation days were most common (respectively 29.5% and
26.3% of annual number of these days), in summer and spring rainy days are less
frequent. Consequently, in Słupsk rainfall days in the cold half year prevail (54% of
the total number).
The climate of Słupsk
115
Snow cover
The average number of days with snow cover mostly depends on thermal and wind
conditions, air humidity, precipitation and topography. It is also influenced by the
atmospheric circulation. According to Paszyński and Niedźwiedź (1991), the distribution of the number of days with snow cover shows great variability in Poland. In
general (except for the mountain regions) the mean annual number of snow-lying
days decreases from the east (>50 days) to the west (30-40 days). In Słupsk the annual number of these days in the studied period (1991-2007) ranged from 18 in 1992
to 90 in 1996 (Fig. 16).
Fig. 16. Mean annual (a) and monthly (b) number of days with snow
cover (1991-2007)
116
Dariusz Baranowski, Małgorzata Kirschenstein
Fig. 17. Mean annual (a) and monthly (b) depth of snow cover (1991-2007)
Fig. 18. Maximum depth of snow cover (1991-2007)
117
The climate of Słupsk
Every year snow cover in Słupsk was noted in January and February (Table 3).
Twice in the analysed period it did not appear in December (1997, 2006) and March
(2003 i 2007), while in October occurred occasionally (in 1997 and 2003).
The average depth of snow cover in Słupsk exceeded 6 cm (Fig. 17a). The greatest
accumulation of snow was usually observed in January (Fig. 17b), however the
maximum value (46 cm) was recorded in March (2005). The highest depth of snow
cover (≥40 cm) was recorded in 1991, 2001, 2002 and 2005 (Fig. 18).
Table 3
Maximum depth (in cm) of snow cover in the 1991-2007 period
Year
Jan.
Feb.
Mar.
Apr.
MaySep.
Oct.
Nov.
Dec.
1991
1
40
1
1
-
-
-
4
1992
1
12
13
-
-
-
-
5
1993
8
16
7
2
-
-
2
2
1994
10
14
16
-
-
-
-
2
1995
19
4
4
-
-
-
16
10
1996
14
17
15
2
-
-
2
27
1997
17
7
2
2
-
5
-
-
1998
5
10
4
-
-
-
11
25
1999
24
18
10
-
-
-
1
17
2000
10
1
13
-
-
-
-
8
2001
8
18
15
-
-
-
-
40
2002
41
8
5
-
-
-
-
11
2003
16
6
-
11
-
1
-
13
2004
15
20
7
-
-
-
1
15
2005
7
22
46
-
-
-
7
15
2006
11
10
7
-
-
-
-
-
2007
25
12
-
-
-
-
-
6
CONCLUSIONS
The main purpose of the paper was to determine the characteristics of the most important meteorological elements in Słupsk. The climatic analysis, besides the longterm characteristics of the air temperature and precipitation in the years 1950-2007,
includes the distribution of other principal meteorological elements (pressure, wind,
cloud cover or relative humidity) in the 1991-2007 period. The research has revealed
118
Dariusz Baranowski, Małgorzata Kirschenstein
the great annual variability in these elements, resulting mostly from the variable impact of circulation from the Atlantic Ocean and the Baltic Sea as well as from the local factors. What is more, the studies have shown the local regularities to the spatial
distribution of weather elements.
• Great seasonal variation in atmospheric pressure throughout the year is characteristic for the local climate. The highest difference is most often registered
in the cold half-year. In Słupsk the annual average sea-level pressure in the
period 1991-2007 amounted to 1012.3 hPa. In the annual course the highest
mean monthly value was recorded in March (1012.9 hPa), the lowest – in
April (1010.6 hPa). The highest average monthly pressure – 1028.0 hPa was
observed in June 2006, while the lowest – 1000.4 hPa – in December 1993.
• Słupsk is located not far (about 18 km) from the Baltic Sea coast, where the
horizontal pressure gradient is relatively high. What is more, due to dynamic
convection, constrained convergence and less friction over water, the average
wind velocity remains significantly higher than in central Poland. In Słupsk
the wind from the south, south-west and west prevail. In contrast the wind
from the north is less frequent. In spring and autumn, apart from the dominant
wind from the south, increased frequency of air masses from the eastern sector
is recorded. The average long-term wind velocity in Słupsk is about 2.3 m/s.
In an annual course relatively strong winds during winter months are observed (seasonal increase in pressure gradient); the slowest – usually occurs
in September.
• The most characteristic feature of the local climate are relatively cold springs
and summers as well as warm autumns and mild winters. Temperatures in
summer rarely exceed 25oC. Usually July is the hottest month, even though
the highest mean monthly temperatures of June and August in particular years
were also recorded. Ordinarily, the lowest average temperatures are characteristic for January or February, and from time to time – for December. In
Słupsk autumn is normally warmer than spring (in 84.5% of studied years).
The analysis of long-time series (1950-2007) has shown high increase in air
temperature in spring and winter months (with maximum in February). In
autumn a slow-growth tendency was more characteristic (especially in November). During the 58-yr period the average annual temperature in Słupsk
has increased by 1.3ºC.
• The analysed station is located in a short distance from the sea, therefore air
humidity is relatively high (mean annual – 80%). Normally from September
to February relative air humidity exceeds 83%, with the highest value in December. Late spring and early summer are usually the driest seasons.
• The annual course of cloud cover is very similar to that of relative humidity.
The average annual cloudiness is relatively high (5.4 in the 0-8 scale). Generally, the skies are the clearest in late spring and early summer, and cloud
amount tend to reach the highest values in autumn (5.6) and winter (6.2).
• Frequent occurrence of maximum precipitation totals not only in July, but
also in September and October is characteristic for the local climate. The
lowest maximum values, mostly due to strong influence of the Baltic Sea, are
usually recorded in February, March and April. The sea decreases the amount
The climate of Słupsk
119
of precipitation in spring and early summer, however from July to November
growing contrast in temperature between the land and sea contribute to a considerable increase in precipitation. Consequently, in autumn a relatively high
amount of precipitation is normally recorded. In the analysed 58-yr period
mean annual precipitation amount in Słupsk has risen by 76.7 mm. The highest increase was observed in winter and in autumn (with maximum in October
and December). During summer (mostly due to the negative trend in July)
a significant decrease in precipitation amount was observed. The average annual number of wet days in Słupsk was relatively high (about 190). Precipitation predominantly occurred in the cold half-year, with maximum in December (on average 19.4 rainy days). The average number of days with snow
cover in the studied period exceeded 47 but in particular years ranged from 18
to 90 days. The average snow depth was about 6 cm; maximum (46 cm) was
recorded in March 2005.
REFERENCES
Atlas klimatu Polski. (Climatic Atlas of Poland), 2005. IMGW, Warszawa, (in Polish).
Atlas klimatycznego ryzyka uprawy roślin w Polsce. (Atlas of climatic risk to crop cultivation in Poland), 2001. AR Szczecin, (in Polish and English).
Atlas współzaleŜności parametrów meteorologicznych i geograficznych w Polsce. XVI.
Prognozy zmian klimatu Polski, 2002. (Atlas of interdependence of meteorological and
geographical parameters in Poland. Vol. 16: Prognoses of the climate changes in Poland).
(Eds) J. Boryczka et al. Warsaw University Press, (in Polish).
Baranowski D., 2001. ZróŜnicowanie warunków atmosferycznych w Polsce w zaleŜności od
typu cyrkulacji. (The diversification of weather conditions in Poland depending on the
type of atmospheric circulation). Słupskie Pr. Geogr. 1, 121-131, (in Polish).
Baranowski D., 2008a. Cechy dynamiczne klimatu Polski i ich wpływ na pole temperatury.
(Dynamic features of the Polish climate and their influence on the air temperature field
distribution). AP Słupsk, 149, (in Polish).
Baranowski D., 2008b. The climate of Łeba. Balt. Coast. Zone, 12. 75-84.
Baranowski D., Kirschenstein M., 2008. Częstość występowania oraz cyrkulacyjne uwarunkowania dni charakterystycznych pod względem termicznym w Ustce. W: Świadomość ekologiczna a rozwój regionalny w Europie Środkowo-Wschodniej. (Frequency of
days with characteristic air temperature values in Ustka and their relation to atmospheric
circulation. In: Ecological consciovsness and regional deve Coment in Central Eastern
Europe). AP Słupsk, 433-439, (in Polish).
Baranowski D., Kirschenstein M., 2010. Wilgotność względna powietrza w Łebie i jej cyrkulacyjne uwarunkowania. (Relative air humidity in Łeba and its dependence on atmospheric circulation). Słupskie Pr. Geogr., 7, (in Polish, article in press).
Chomicz K., 1971. Struktura opadów atmosferycznych w Polsce. (The structure of atmospheric precipitation in Poland). Pr. PIHM, 25-66, (in Polish).
Kirschenstein M., 2004. Rola cyrkulacji atmosferycznej w kształtowaniu opadów w północno-zachodniej Polsce. (The role of atmospheric circulation in precipitation formation in
north-western Poland). AP Słupsk, 193, (in Polish).
Kirschenstein M., 2005. Wieloletnie zmiany sum opadów atmosferycznych na wybranych
stacjach północno-zachodniej Polski. (Long-term variations in precipitation totals at the
selected stations in north-western Poland). Słupskie Pr. Geogr., 2, 199-214, (in Polish).
120
Dariusz Baranowski, Małgorzata Kirschenstein
Kirschenstein M., Baranowski D., 2008. Wahania roczne i tendencje zmian opadów atmosferycznych i temperatury powietrza w Słupsku. (Annual variations and trends of changes
in atmospheric precipitation and air temperature in Słupsk). Dokum. Geogr., 37, 76-82,
(in Polish).
KoŜuchowski K., Wibig J., 1988. Kontynentalizm pluwialny w Polsce, zróŜnicowanie
geograficzne i zmiany wieloletnie. (Pluvial continentalism in Poland, geographic diversity and long-term variations), Acta Geogr. Lodziensia, 55, 9-91, (in Polish).
Okołowicz W., 1978. Mapa regionów klimatycznych. W: Narodowy atlas Polski. (Map of
climatic regions. In: National atlas of Poland). PAN, Instytut Geografii, Wrocław-Warszawa-Kraków-Gdańsk, 29, (in Polish).
Parczewski W., 1965. Fronty atmosferyczne nad Polską. (Atmospheric fronts over Poland).
Wiad. Sł. Hydrol. i Meteor., 59, 20-36 (in Polish).
Paszyński J., Niedźwiedź T., 1991. Klimat. W: Geografia Polski. Środowisko przyrodnicze.
(Climate. In: Geography of Poland. Natural environment). (Ed.) L. Starkel. PWN, Warszawa, 296-355, (in Polish).
Sepp M., 2009. Changes in frequency of Baltic Sea cyclones and their relationships with
NAO and climate in Estonia. Boreal Env. Res., 14, 143-151.
Woś A., 1999. Klimat Polski. (The climate of Poland). PWN, Warszawa, (in Polish).
KLIMAT SŁUPSKA
Streszczenie
Opracowanie jest próbą kompleksowej, syntetycznej charakterystyki klimatu Słupska
opartej na moŜliwie długiej, jednorodnej serii codziennych danych pomiarowych z posterunku meteorologicznego IMGW w Słupsku. Analiza klimatyczna oprócz charakterystyk termicznych i opadowych badanych w 58-letnim okresie (1950-2007) uwzględnia równieŜ rozkład innych podstawowych elementów meteorologicznych (ciśnienia atmosferycznego, wiatru, wilgotności względnej powietrza oraz zachmurzenia) w krótszym przedziale czasowym
(1991-2007).
Niniejsza praca, będąca podsumowaniem dotychczasowych badań nad klimatem Słupska,
skierowana jest nie tylko do klimatologów i geografów (dla których moŜe być istotnym
punktem odniesienia w badaniach warunków klimatycznych innych miast Polski), ale równieŜ do mieszkańców Słupska oraz turystów, którzy w ostatnich latach coraz liczniej odwiedzają to miasto.