Zgryźliwość kojarzy mi się z radością, która źle skończyła.
Chapter 15
Multi-Annual Variability of Cloudiness
and Sunshine Duration in Cracow Between
1826 and 2005
Piotr Lewik, Dorota Matuszko, and Maria Morawska-Horawska
15.1 Introduction
The Cracow series of nephologic and heliographic observations is unique on a
global scale, due to its uniformity as to the place of measurements, their uninter-
rupted continuity, as well as its length and the reliability of data. Only on the basis
of long and uninterrupted climatologic series is it possible to obtain reliable infor-
mation about trends and tendencies with a certain level of significance and Cracow’s
observations belong to such a series.
The present study aims at characterizing the multi-annual variability of cloudi-
ness and sunshine duration in Cracow on the basis of archive data from the
1826–2005 period.
15.2 Cloudiness
The commencement of the uninterrupted observation series dates back to 1826.
However, “The records of daily meteorological observations” (“Dzienniki co-
dziennych spostrzeżeń meteorologicznych”) only includes the results of fixed time
observations of cloudiness on a 0–10 scale starting on 1 December 1862.
The present study uses archive materials from the following sources: the cloudi-
ness in the 1826–1852 period has been reconstructed on the basis of a publication
P. Lewik
Pedagogical University of Cracow, Podchorążych 2, 30-084, Cracow, Poland
e-mail: lewik@up.krakow.pl
D. Matuszko
Institute of Geography and Spatial Management, Jagiellonian University, Gronostajowa 7,
30-387, Cracow, Poland
e-mail: d.matuszko@geo.uj.edu.pl
M. Morawska-Horawska
Institute of Meteorology and Water Management, P. Borowego 14, 30-215, Cracow, Poland
R. Przybylak et al. (eds.),
The Polish Climate in the European Context:
An Historical Overview
, DOI 10.1007/978-90-481-3167-9_15,
© Springer Science + Business Media B.V. 2010
341
342
P. Lewik et al.
by Wierzbicki
(1873)
concerning the monthly number of clear and overcast days;
the data for 1853–1862 come from a manuscript by Karliński (Morawska
1963)
which lists the mean monthly values of cloudiness; and data for the years 1863–
2005 have been obtained from “The records of daily meteorological observations”
with fixed time observations of cloudiness. The amount of cloudiness in the initial
period of the observations has been reconstructed by means of two methods: by
using the following formula:
zabskn
/
s
– number of overcast days,
k
– number of clear days,
n
– number of days in a
given period,
a
,
b
– calculated numerical parameters (Gorczyński and Wierzbicka
1916)
, as
well as by applying regression analysis.
The regression equation has the following form:
=+⋅+⋅
The cloudiness calculated by means of both methods was almost identical. The
correctness of the applied method has been verified on the basis of the values of
actual cloudiness for the 1854–2005 period (Fig.
15.1
). A similar course of oscilla-
tions has been registered in all months. Clear and overcast days for the entire
1826–2005 period have been identified according to the guidelines provided by
Wierzbicki
(1873)
and valid in the nineteenth century
.
According to the guidelines,
the mean daily cloudiness on clear days equalled from 0.0 to 3.3, whereas on over-
cast days it amounted to 6.7–10.0. The application of the data concerning the num-
ber of clear and overcast days permitted to lengthen the examination period by 37
years, that is move back to 1826.
The amount of cloudiness recorded from 1826 to 1852 has been assessed on a
4-degree scale (Morawska
1963)
, from 1853 to 31 December 1990 on a 1–10 scale
z a bk cs
Fig. 15.1
Mean annual cloudiness in Cracow between 1853 and 2005 – actual and calculated by
extrapolation for the years 1826–2005
( )
=+⋅ −
15 Multi-Annual Variability of Cloudiness and Sunshine Duration
343
and from 1 January 1991 onwards on a 1–8 scale. In order to obtain comparable
data, the values of cloudiness have been standardized according to a 10-degree
scale and converted to percentage values.
The mean annual cloudiness in Cracow during the entire series (1826–2005)
totals 67.5% and thus, it is 0.4% lower than the mean calculated on the basis of the
results of fixed-time observations carried out between 1863 and 2005. In the analy-
sed multi-annual period, the value of the mean annual cloudiness repeatedly under-
went considerable changes (Fig.
15.2
). The course of cloudiness, smoothed by
means of a Gaussian filter, is a sinusoid with a changing amplitude (Fig.
15.3
). The
segmentation of the course of the cloudiness data series according to Alexandersson
(1986)
, refers to the division into NAO circulation epochs and splits the series into
the following intervals: 1826–1846 (mean cloudiness, ca. 68%), 1847–1858 (mean
cloudiness, ca. 60%), 1859–1921 (mean cloudiness, ca. 67%), 1922–1966 (mean
Fig. 15.2
Mean annual cloudiness in Cracow between 1826 and 2005 and its segmentation
according to the Alexandersson test
Fig. 15.3
Cloudiness (C) and sunshine duration (S) in Cracow between 1826 and 2005, smoothed
by Gaussian filter.
Solid line
– actual values,
broken line
– extrapolated values
344
P. Lewik et al.
cloudiness > 70%), 1967–1981 (mean cloudiness, ca. 68%), 1982–1994 (mean
cloudiness <65%), 1995–2005 (increase in cloudiness >65%). All the tests used for
the segmentation of the series indicated a breakthrough in the amount of cloud
cover: first, between 1921/1922 and to a lesser degree in 1966/1967. In the analy-
sed multi-annual period, the mean annual cloudiness minimum equalled ca. 56%
(1856, 1858, 1982), and the maximum, 78% (1941, 1952). The highest values of
mean monthly cloudiness reached 98% and were registered in February 1913 and
1952, as well as in December 1959. The absolute minimum (32%) was recorded in
March 1921.
The entire analysed period is characterized by a small increase in cloudiness in
Cracow, which is statistically significant at a confidence level of 0.05. The course
of cloudiness in the twentieth century, and especially in its second half, exhibits a
significantly greater variability than it does in the nineteenth century. This can be a
result of the significantly greater dynamics and the range of changes in circulation
conditions (Ustrnul
2007)
. The course of cloudiness, both in terms of the mean
values and the extreme phenomena, seems to be correlated with the cyclonicity
index. The index has been calculated by means of a method presented by
Nied´wied´
(1981)
and on the basis of data received from the same author. This can
be illustrated using the year 1921 as an example, in which the minimum (−228) of
the index within the entire investigated period occurred. The mean annual cloudi-
ness (57%) in that year was close to the absolute minimum. In the years character-
ized by the greatest cloudiness (1941 and 1952), high values of the index could be
observed. The values of the index increase from 1922 onwards, with a maximum in
the 1960s, when western circulation is also weakened (Ustrnul
2007)
.
In the first half of the twentieth century, a growing trend in cloudiness was
observable. It was especially clearly visible in autumn. The second half of the cen-
tury was characterized by a downward trend, very pronounced in wintertime. The
decrease in cloudiness observed since the beginning of the 1950s was also recorded
at other stations in Poland (Wibig
2004)
and in the countries of the former Soviet
Union (Sun and Groisman
2000)
, as well as in Potsdam and other regions of the
globe. The presented results from Cracow are also concurrent with the results of
work by Henderson-Sellers
(1986)
regarding the changes in cloud cover in
Europe.
The occurrence of similar tendencies everywhere in Europe indicates that circu-
lation is the predominant reason for cloudiness variability in Cracow, which is also
modified by local factors. In addition, it confirms earlier conclusions concerning
this issue (Morawska
1963)
. The role of local factors intensified after World War
II, during a period of territorial and industrial growth of the city, which occurred
during the years with the greatest cloudiness. The increase in the emission of air
pollutants caused a greater concentration of condensation nuclei in the atmosphere
and contributed not only to the increase in cloudiness but to a change in its structure
as well. The emission of anthropogenic heat, amelioration of land and replacing
vegetation areas with artificial ones caused a decrease in the frequency of occur-
rence of morning fogs and stratus clouds as well as an increase in the amount of
convective ones (Morawska-Horawska
1985
; Matuszko
2003)
.
15 Multi-Annual Variability of Cloudiness and Sunshine Duration
345
Cracow’s cloudiness is most strongly correlated with the cyclonicity index
(
r
= +0.38) and to a lesser degree with the optical thickness of volcanic aerosol
(
(
r
= −0.32). These two factors
account for 34% of cloudiness variability. The cyclonicity index reflects the fre-
quency of occurrence of cyclonic meteorological situations, irrespective of the
direction of advection (Niedźwiedź
1981)
. However, if the directions of the influx
of air are taken into account, it is easy to state that advections in cyclonic systems
from all directions except SE (
r
= −0.01) contribute to high cloudiness. The advec-
tions which are especially strongly correlated with cloudiness are the ones originat-
ing from the following directions: E (
r
= +0.37), N (
r
= +0.33), W (
r
= +0.33). An
anti-cyclonic wedge is an especially unfavourable situation (
r
= −0.38). The fluc-
tuations of cloudiness in Cracow are cyclical, exhibiting the following periods,
expressed in years: 3.0–3.6, 5.7–8.9, 16.4, 20 and 60, on the basis of a harmonic
analysis. These results are similar to those obtained for the 1880–1979 period
(Morawska-Horawska
1985)
.
15.3 Clear and Overcast Days
The number of clear and overcast days, calculated according to Wierzbicki’s crite-
rion and used in his work (Wierzbicki
1873)
, is greater in comparison to the number
of such days determined according to the currently valid guidelines (Matuszko
2007)
.
On average, 69 clear days occur in Cracow. This value varies in individual years,
because in certain years with little cloudiness the number of clear days was twice
as high or twice as low (Fig.
15.4
). The curve of the multi-annual course of the
annual number of clear days exhibits a downward trend, although in the second half
of the twentieth century an increase in the number of such days could be observed.
Fig. 15.4
The number of clear (B) and overcast (A) days in Cracow between 1826 and 2005,
leveled by a 31-element Gaussian filter, and their trends
zanotowane.pl doc.pisz.pl pdf.pisz.pl hannaeva.xlx.pl
Multi-Annual Variability of Cloudiness
and Sunshine Duration in Cracow Between
1826 and 2005
Piotr Lewik, Dorota Matuszko, and Maria Morawska-Horawska
15.1 Introduction
The Cracow series of nephologic and heliographic observations is unique on a
global scale, due to its uniformity as to the place of measurements, their uninter-
rupted continuity, as well as its length and the reliability of data. Only on the basis
of long and uninterrupted climatologic series is it possible to obtain reliable infor-
mation about trends and tendencies with a certain level of significance and Cracow’s
observations belong to such a series.
The present study aims at characterizing the multi-annual variability of cloudi-
ness and sunshine duration in Cracow on the basis of archive data from the
1826–2005 period.
15.2 Cloudiness
The commencement of the uninterrupted observation series dates back to 1826.
However, “The records of daily meteorological observations” (“Dzienniki co-
dziennych spostrzeżeń meteorologicznych”) only includes the results of fixed time
observations of cloudiness on a 0–10 scale starting on 1 December 1862.
The present study uses archive materials from the following sources: the cloudi-
ness in the 1826–1852 period has been reconstructed on the basis of a publication
P. Lewik
Pedagogical University of Cracow, Podchorążych 2, 30-084, Cracow, Poland
e-mail: lewik@up.krakow.pl
D. Matuszko
Institute of Geography and Spatial Management, Jagiellonian University, Gronostajowa 7,
30-387, Cracow, Poland
e-mail: d.matuszko@geo.uj.edu.pl
M. Morawska-Horawska
Institute of Meteorology and Water Management, P. Borowego 14, 30-215, Cracow, Poland
R. Przybylak et al. (eds.),
The Polish Climate in the European Context:
An Historical Overview
, DOI 10.1007/978-90-481-3167-9_15,
© Springer Science + Business Media B.V. 2010
341
342
P. Lewik et al.
by Wierzbicki
(1873)
concerning the monthly number of clear and overcast days;
the data for 1853–1862 come from a manuscript by Karliński (Morawska
1963)
which lists the mean monthly values of cloudiness; and data for the years 1863–
2005 have been obtained from “The records of daily meteorological observations”
with fixed time observations of cloudiness. The amount of cloudiness in the initial
period of the observations has been reconstructed by means of two methods: by
using the following formula:
zabskn
/
s
– number of overcast days,
k
– number of clear days,
n
– number of days in a
given period,
a
,
b
– calculated numerical parameters (Gorczyński and Wierzbicka
1916)
, as
well as by applying regression analysis.
The regression equation has the following form:
=+⋅+⋅
The cloudiness calculated by means of both methods was almost identical. The
correctness of the applied method has been verified on the basis of the values of
actual cloudiness for the 1854–2005 period (Fig.
15.1
). A similar course of oscilla-
tions has been registered in all months. Clear and overcast days for the entire
1826–2005 period have been identified according to the guidelines provided by
Wierzbicki
(1873)
and valid in the nineteenth century
.
According to the guidelines,
the mean daily cloudiness on clear days equalled from 0.0 to 3.3, whereas on over-
cast days it amounted to 6.7–10.0. The application of the data concerning the num-
ber of clear and overcast days permitted to lengthen the examination period by 37
years, that is move back to 1826.
The amount of cloudiness recorded from 1826 to 1852 has been assessed on a
4-degree scale (Morawska
1963)
, from 1853 to 31 December 1990 on a 1–10 scale
z a bk cs
Fig. 15.1
Mean annual cloudiness in Cracow between 1853 and 2005 – actual and calculated by
extrapolation for the years 1826–2005
( )
=+⋅ −
15 Multi-Annual Variability of Cloudiness and Sunshine Duration
343
and from 1 January 1991 onwards on a 1–8 scale. In order to obtain comparable
data, the values of cloudiness have been standardized according to a 10-degree
scale and converted to percentage values.
The mean annual cloudiness in Cracow during the entire series (1826–2005)
totals 67.5% and thus, it is 0.4% lower than the mean calculated on the basis of the
results of fixed-time observations carried out between 1863 and 2005. In the analy-
sed multi-annual period, the value of the mean annual cloudiness repeatedly under-
went considerable changes (Fig.
15.2
). The course of cloudiness, smoothed by
means of a Gaussian filter, is a sinusoid with a changing amplitude (Fig.
15.3
). The
segmentation of the course of the cloudiness data series according to Alexandersson
(1986)
, refers to the division into NAO circulation epochs and splits the series into
the following intervals: 1826–1846 (mean cloudiness, ca. 68%), 1847–1858 (mean
cloudiness, ca. 60%), 1859–1921 (mean cloudiness, ca. 67%), 1922–1966 (mean
Fig. 15.2
Mean annual cloudiness in Cracow between 1826 and 2005 and its segmentation
according to the Alexandersson test
Fig. 15.3
Cloudiness (C) and sunshine duration (S) in Cracow between 1826 and 2005, smoothed
by Gaussian filter.
Solid line
– actual values,
broken line
– extrapolated values
344
P. Lewik et al.
cloudiness > 70%), 1967–1981 (mean cloudiness, ca. 68%), 1982–1994 (mean
cloudiness <65%), 1995–2005 (increase in cloudiness >65%). All the tests used for
the segmentation of the series indicated a breakthrough in the amount of cloud
cover: first, between 1921/1922 and to a lesser degree in 1966/1967. In the analy-
sed multi-annual period, the mean annual cloudiness minimum equalled ca. 56%
(1856, 1858, 1982), and the maximum, 78% (1941, 1952). The highest values of
mean monthly cloudiness reached 98% and were registered in February 1913 and
1952, as well as in December 1959. The absolute minimum (32%) was recorded in
March 1921.
The entire analysed period is characterized by a small increase in cloudiness in
Cracow, which is statistically significant at a confidence level of 0.05. The course
of cloudiness in the twentieth century, and especially in its second half, exhibits a
significantly greater variability than it does in the nineteenth century. This can be a
result of the significantly greater dynamics and the range of changes in circulation
conditions (Ustrnul
2007)
. The course of cloudiness, both in terms of the mean
values and the extreme phenomena, seems to be correlated with the cyclonicity
index. The index has been calculated by means of a method presented by
Nied´wied´
(1981)
and on the basis of data received from the same author. This can
be illustrated using the year 1921 as an example, in which the minimum (−228) of
the index within the entire investigated period occurred. The mean annual cloudi-
ness (57%) in that year was close to the absolute minimum. In the years character-
ized by the greatest cloudiness (1941 and 1952), high values of the index could be
observed. The values of the index increase from 1922 onwards, with a maximum in
the 1960s, when western circulation is also weakened (Ustrnul
2007)
.
In the first half of the twentieth century, a growing trend in cloudiness was
observable. It was especially clearly visible in autumn. The second half of the cen-
tury was characterized by a downward trend, very pronounced in wintertime. The
decrease in cloudiness observed since the beginning of the 1950s was also recorded
at other stations in Poland (Wibig
2004)
and in the countries of the former Soviet
Union (Sun and Groisman
2000)
, as well as in Potsdam and other regions of the
globe. The presented results from Cracow are also concurrent with the results of
work by Henderson-Sellers
(1986)
regarding the changes in cloud cover in
Europe.
The occurrence of similar tendencies everywhere in Europe indicates that circu-
lation is the predominant reason for cloudiness variability in Cracow, which is also
modified by local factors. In addition, it confirms earlier conclusions concerning
this issue (Morawska
1963)
. The role of local factors intensified after World War
II, during a period of territorial and industrial growth of the city, which occurred
during the years with the greatest cloudiness. The increase in the emission of air
pollutants caused a greater concentration of condensation nuclei in the atmosphere
and contributed not only to the increase in cloudiness but to a change in its structure
as well. The emission of anthropogenic heat, amelioration of land and replacing
vegetation areas with artificial ones caused a decrease in the frequency of occur-
rence of morning fogs and stratus clouds as well as an increase in the amount of
convective ones (Morawska-Horawska
1985
; Matuszko
2003)
.
15 Multi-Annual Variability of Cloudiness and Sunshine Duration
345
Cracow’s cloudiness is most strongly correlated with the cyclonicity index
(
r
= +0.38) and to a lesser degree with the optical thickness of volcanic aerosol
(
(
r
= −0.32). These two factors
account for 34% of cloudiness variability. The cyclonicity index reflects the fre-
quency of occurrence of cyclonic meteorological situations, irrespective of the
direction of advection (Niedźwiedź
1981)
. However, if the directions of the influx
of air are taken into account, it is easy to state that advections in cyclonic systems
from all directions except SE (
r
= −0.01) contribute to high cloudiness. The advec-
tions which are especially strongly correlated with cloudiness are the ones originat-
ing from the following directions: E (
r
= +0.37), N (
r
= +0.33), W (
r
= +0.33). An
anti-cyclonic wedge is an especially unfavourable situation (
r
= −0.38). The fluc-
tuations of cloudiness in Cracow are cyclical, exhibiting the following periods,
expressed in years: 3.0–3.6, 5.7–8.9, 16.4, 20 and 60, on the basis of a harmonic
analysis. These results are similar to those obtained for the 1880–1979 period
(Morawska-Horawska
1985)
.
15.3 Clear and Overcast Days
The number of clear and overcast days, calculated according to Wierzbicki’s crite-
rion and used in his work (Wierzbicki
1873)
, is greater in comparison to the number
of such days determined according to the currently valid guidelines (Matuszko
2007)
.
On average, 69 clear days occur in Cracow. This value varies in individual years,
because in certain years with little cloudiness the number of clear days was twice
as high or twice as low (Fig.
15.4
). The curve of the multi-annual course of the
annual number of clear days exhibits a downward trend, although in the second half
of the twentieth century an increase in the number of such days could be observed.
Fig. 15.4
The number of clear (B) and overcast (A) days in Cracow between 1826 and 2005,
leveled by a 31-element Gaussian filter, and their trends