INTERNATIONAL JOURNAL OF CLIMATOLOGY
Int. J. Climatol. 24: 1745–1758 (2004)
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1111
RELATIONSHIP BETWEEN ATMOSPHERIC CIRCULATION TYPES
OVER GREECE AND WESTERN–CENTRAL EUROPE DURING
THE PERIOD 1958–97
a
CHRISTINA ANAGNOSTOPOULOU,a HELENA FLOCAS,b PANAGIOTIS MAHERASa, * and IOANNIS PATRIKASc
Department of Meteorology and Climatology, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece
b Laboratory of Meteorology, Department of Applied Physics, University of Athens, Athens, Greece
c Division of Hydraulics, Faculty of Technology, Aristotle University of Thessaloniki, Thessaloniki, Greece
Received 17 January 2003
Accepted 23 February 2004
ABSTRACT
An attempt is made to examine the relationship of the surface circulation prevailing over Europe with the corresponding
surface and 500 hPa over Greece by correlating Lamb weather types for western Europe and Hess and Brezowsky (HB)
types for central Europe with those derived from a new classification scheme for the Greek area. It was found that
it was difficult to formulate rules controlling the frequency distributions of the circulation types over the Greek area
in relation to the circulation over western and central Europe. However, statistically significant correlation was found
between certain types with high frequency, which is greater between Lamb and HB types with the surface circulation
types over the Greek area, compared with 500 hPa circulation types. For the most correlated pairs, seasonal composites
of mean sea-level pressure and 500 hPa geopotential height anomalies demonstrated that the formation of the circulation
types over the Greek area depends on the extent, intensity of the anticyclonic or cyclonic centres, air mass characteristics,
and stability profile in the lower troposphere over the regions examined, but especially over the central and eastern
Mediterranean. Copyright  2004 Royal Meteorological Society.
KEY WORDS:
circulation types; Greece; western–central Europe; correlation analysis; frequency distribution
1. INTRODUCTION
The relationship between the atmospheric circulation over different regions, in terms of teleconnections
and their implications for the regional climate, is the subject of considerable research in the last few
decades. Atmospheric teleconnection is defined as the correlation between statistically significant and persistent
anomalies of atmospheric circulation at sea level or upper levels over two or more regions, which could be
adjacent or at great distances. Two different approaches have been adopted so far for the identification of
possible teleconnections. In the first approach, the teleconnections of atmospheric pressure or geopotential
height are associated with the occurrence of extreme events with respect to temperature or rainfall over a
specified region on a daily, monthly, seasonal or annual basis (Metaxas, 1974; Metaxas et al., 1992; Maheras
et al., 1999a,b). In the second approach, the teleconnections are investigated independently of the occurrence
of extreme events (Conte et al., 1989; Kutiel and Benaroch, 2002).
The most widely known teleconnection at sea level is that of the southern oscillation being related to the El
Niño phenomenon (ENSO). Xoplaki (2002) has investigated possible impacts of ENSO on the Mediterranean
climate. However, except for northwestern France, non-significant connections for summer air temperature
and precipitation have been found (Xoplaki, 2002). Another widely known sea-level teleconnection is the
North Atlantic oscillation (NAO), which plays an important role in the weather and climate of many
* Correspondence to: Panagiotis Maheras, Department of Meteorology and Climatology, School of Geology, Aristotle University of
Thessaloniki, 54006 Greece; e-mail: [email protected]
Copyright  2004 Royal Meteorological Society
1746
C. ANAGNOSTOPOULOU ET AL.
European regions, mainly during winter (van Loon and Rogers, 1978; Hurrell, 1995, 2001; Stephenson
et al., 2000; Wanner et al., 2001). Other teleconnections with implications in the regional climate of many
European regions include the southern Europe–North Atlantic pattern at sea level (Kutiel and Kay, 1992)
and eastern Atlantic pattern at 700 hPa (Esbensen, 1984). The role of the above-mentioned teleconnections
in influencing the Mediterranean climate is still under investigation, and no definite conclusions have been
drawn.
Furthermore, Conte et al. (1989) suggested the existence of a teleconnection in the annual geopotential
height fields at 500 hPa between the two extremes of the Mediterranean basin that was defined as the
Mediterranean oscillation. Recent studies demonstrated that this oscillation is reflected in the time series of
temperature and rainfall between the western and eastern Mediterranean (Kutiel et al., 1996; Maheras et al.,
1997, 1999a,b; Douguédroit, 1998; Kutiel and Maheras, 1998; Kutiel and Paz, 1998; Maheras and Kutiel,
1999). More recently, Kutiel and Benaroch (2002) and Kutiel et al. (2002) supported the existence of a
new upper level teleconnection, the North Sea–Caspian pattern, that develops between the two regions with
apparent implications for the eastern Mediterranean climate.
The objective of this study is to investigate the relationship between the surface circulation over
western–central Europe and the corresponding circulation at the surface and at 500 hPa over the Greek
area, not in terms of atmospheric teleconnections (a method that has been widely used in the international
literature), but rather by correlating circulation types for the two regions examined, as derived from available
classification catalogues for a period of 40 years (1958–1997).
2. DATA AND METHODOLOGY
The surface atmospheric circulation over the Greek area has been classified on a daily basis according to
Maheras et al. (2000a), and the 500 hPa atmospheric circulation has similarly been classified according to
Maheras et al. (2000b). Both classification schemes are automatic, semi-objective and were developed using
spatial methods of topology and geometry. The schemes employed the 40 year (1958–97) National Centers for
Environmental Prediction reanalysis gridded dataset of mean daily sea-level pressure and 500 hPa geopotential
height, with resolution 2.5° × 2.5° within the European region of 20–65 ° N and 20 ° W–50 ° E. The Greek area
is represented by eight grid points.
More specifically, regarding the surface circulation over the Greek area (hereafter referred to as SLP types,
20 synoptic types have been distinguished according to the location of the anticyclonic and cyclonic centres
with respect to Greece: six anticyclonic, eight cyclonic, two mixed and four special. Regarding the 500 hPa
circulation (hereafter referred to as 500 hPa) over the Greek area, 14 synoptic types have been similarly
distinguished: six anticyclonic and eight cyclonic. Tables I and II describe the main characteristics of the
500 hPa and SLP types, and specify the relative frequency of their appearance per season during the period
examined.
The surface circulation over western Europe has been classified on a daily basis according to Lamb
weather types (Lamb, 1972), following the objective scheme developed by Jenkinson and Collison (1977) that
employed grid point mean sea-level pressure data covering the region 50–60 ° N and 10 ° W–2 ° E. The Lamb
scheme recognizes two basic types, i.e. anticyclonic (A) and cyclonic (C); eight directional types, i.e. westerly
(W), northerly (N), easterly (E), southerly (S), northwesterly (NW), northeasterly (NE), southeasterly (SE),
southwesterly (SW); and 16 hybrid types where more than one individual basic type exists. In this study, the
Lamb scheme was employed for the period 1958–97 as published by Jones et al. (1993).
For the day-by-day classification of the surface circulation over central Europe the Grosswetterlagen scheme,
as described by Hess and Brezowsky (1969), has been employed. This scheme recognizes 29 types: 4 zonal,
18 meridional and 7 mixed (or half-meridional) types. For the purposes of the present study, the updated
catalogue of Hess and Brezowsky (HB) types, as published by the German Federal Weather Service (Deutscher
Wetterdienst), has been used for the period 1958–97 (Hess and Brezowsky, 1969). Table III presents the
characterization of Lamb and HB types, and their relative frequency on a seasonal basis for the period
examined.
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
ATMOSPHERIC CIRCULATION OVER GREECE AND THE WESTERN–CENTRAL MEDITERRANEAN
1747
Table I. Circulation types at 500 hPa level over the Greek area, along with a brief description of their synoptic
characteristics and the relative frequency of appearance on a seasonal basis during the period 1958–97
Code
Type
number
Description
Winter Spring Summer Autumn
(DJF) (MAM)
(JJA)
(SON)
Anticyclonic types
1
A1
An anticyclonic centre is located to the west or northwest of
the Greek area, usually over west, central or northern Europe
2
A2
An anticyclonic centre is located to the northeast of the Greek
area
3
A3
An anticyclonic centre is located over the Balkans and the
Greek area
4
A4
An anticyclonic centre is located to the west or southwest of
the Greek area, over central or western Mediterranean or North
Africa
5
A5
An anticyclonic centre is located to the south or southeast of
the Greek area. It does not occur in summer
6
A6
An anticyclonic centre is located to the east or northeast of the
Greek area
Cyclonic types
7
C
8
Cs
9
Csw
10
11
12
13
Cnw
Cne
Cse
Cn
14
Cw
Relative frequency (%)
A cyclonic centre is located over the Greek area
A cyclonic centre is located south of the Greek area
A cyclonic centre is located west or southwest of the Greek
area
A cyclonic centre is located northwest of the Greek area
A cyclonic centre is located northeast of the Greek area
A cyclonic centre is located southeast of the Greek area
A cyclonic centre is located north of the Greek area, usually
much further north than 50 ° N
A cyclonic centre is located far west (at about 50 ° E) or far
northeast (at about 50 ° N) of the Greek area
3.8
7.0
13.5
8.8
4.6
4.5
8.2
6.1
5.8
6.7
12.0
12.0
11.2
8.7
11.7
13.9
6.1
8.3
11.3
9.0
3.6
4.3
6.3
3.8
11.0
9.1
19.0
13.0
9.7
14.7
13.1
3.9
7.0
13.0
5.2
11.5
4.2
13.5
1.7
0.7
5.8
10.1
2.6
0.9
3.6
7.9
0.5
0.2
4.0
8.6
0.9
0.3
5.5
3.6
1.0
2.9
A first attempt to relate the circulation over the Greek area to the circulation over northwestern and central
Europe has been done, and the possible dependence was studied by means of contingency tables between the
following pairs of circulation schemes for the period 1958–97: (a) 500 hPa and Lamb; (b) 500 hPa and HB;
(c) SLP and Lamb; (d) SLP and HB. In order to account for any seasonal variations, the contingency tables
were further examined on a seasonal basis.
Then, the correlation coefficients between the circulation types for each season were calculated: (a) Lamb
types and each of the 500 hPa types over the Greek area; (b) between Lamb types and each of the SLP types
over the Greek area; (c) the HB types and each of the 500 hPa types over the Greek area; (d) between the
HB types and each of the SLP types over the Greek area. More specifically, the correlation coefficients were
calculated using the frequencies per year for each type of the one classification with each type of the other
classification.
Finally, when high correlation is identified between a circulation pattern over the Greek area and
a circulation pattern over northwestern or central Europe, seasonal composite maps of mean sea-level
pressure and 500 hPa geopotential height anomalies were constructed in order to investigate this relationship
further.
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
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C. ANAGNOSTOPOULOU ET AL.
Table II. Circulation types in SLP over the Greek area, along with a brief description of their synoptic characteristics
and the relative frequency of appearance on a seasonal basis during the period 1958–97
Code
Type
number
Description
Winter Spring Summer Autumn
(DJF) (MAM)
(JJA)
(SON)
Anticyclonic types
1
A1
A high-pressure system is centred to the west or northwest of
the Greek area, usually over west, central or northern Europe
2
A2
A high-pressure system is centred to the northeast of the Greek
area
3
A3
A high-pressure system is centred over the Balkans and the
Greek area
4
A4
A high-pressure system is centred to the west or southwest of
the Greek area, over central or western Mediterranean or North
Africa.
5
A5
A high-pressure system is centred to the east or southeast of
the Greek area
6
A6
A high-pressure system is centred to the west, northwest, north
or northeast of the Greek area. Positive geopotential height
anomaly at 500 hPa over Greece
Cyclonic types
7
C
8
Cs
9
Csw
10
11
12
13
Cnw
Cne
Cse
Cn
14
Cw
Mixed types
15
Mt1
16
Mt2
Relative frequency (%)
A low-pressure centre is located over the Greek area
A low-pressure centre is located south of the Greek area
A low-pressure centre is located west or southwest of the
Greek area
A low-pressure centre is located northwest of the Greek area
A low-pressure centre is located northeast of the Greek area
A low-pressure centre is located southeast of the Greek area
A low-pressure centre is located north, usually much further
north than 50 ° N, of the Greek area
A low-pressure centre is located far west (at about 50 ° E) or far
northeast (at about 50 ° N) of the Greek area
An anticyclone is located to the west of the Greek area
covering most of it and a cyclonic centre to the east of the
Greek area
Anticyclonic circulation covers the whole of Europe and the
Balkans, but to the south over the central and eastern
Mediterranean low-pressure systems dominate
Special types
17
Dsec The thermal low from Southeast Asia extends to the west and
covers the Greek area (from June to September). Positive
geopotential height anomaly at 500 hPa
18
Mb1 Weak pressure gradient over the Mediterranean. Low pressure
values over the Greek area
19
Mb2 Weak pressure gradient over the Mediterranean. High pressure
values over the Greek area
20
Dor During the warm season, similar to A1, A2, A3, Cse, MB1,2,
but a cold pool (cut off low) appears at 500 hPa
Copyright  2004 Royal Meteorological Society
7.3
11
13
13
7.1
4.9
3.3
9.3
4.4
3
2.6
6
3.1
3.3
4
2.6
3
5.5
0.4
1.9
5.8
4.9
7.3
7.9
6.5
3.2
7.3
3.7
4.4
6.9
0.8
0.2
0.8
2.6
1.1
3.5
5.5
10
1.4
5.4
7.2
13
4.5
3.3
2.7
6
7.3
1.4
4.4
4.9
4.6
3.3
5.8
3.8
0
3.3
2.7
3.6
5.1
4.9
9.5
4.3
0
5.1
0
0
23
2.7
2.6
4.2
3.1
9.2
8.5
6.7
0
0
12
4.5
11
3.6
Int. J. Climatol. 24: 1745–1758 (2004)
ATMOSPHERIC CIRCULATION OVER GREECE AND THE WESTERN–CENTRAL MEDITERRANEAN
1749
Table III. Lamb circulation types at mean sea level over western Europe and HB circulation types at mean sea level over
central Europe, along with the relative frequency of appearance on a seasonal basis during the period 1958–97
Lamb type
A
ANE
AE
ASE
AS
ASW
AW
ANW
AN
NE
E
SE
S
SW
W
NW
N
C
CNE
CE
CSE
CS
CSW
CW
CNW
CN
Relative frequency (%)
HB type
Winter
Spring
Summer
Autumn
18.9
1.2
2.0
1.1
1.3
1.2
3.3
1.2
1.3
0.9
5.0
3.0
6.2
5.7
18.9
4.3
3.6
12.7
0.2
1.1
0.4
0.9
0.7
3.0
1.0
1.0
18.2
2.0
3.2
1.2
1.0
1.3
3.2
1.5
2.5
1.8
6.7
2.5
4.9
2.7
12.4
3.7
6.0
15.9
0.8
1.5
0.7
1.5
0.6
1.8
1.1
1.6
22.9
1.1
2.1
0.9
0.8
1.1
5.1
2.2
2.4
1.3
2.2
1.0
2.7
2.7
15.0
5.4
4.6
18.1
0.4
1.2
0.3
0.6
0.6
2.9
1.1
1.2
19.9
1.2
1.2
1.2
1.1
1.4
4.8
1.1
1.5
0.8
2.9
2.5
5.7
4.9
16.9
4.1
4.0
15.4
0.6
1.3
0.4
1.4
0.7
2.9
0.7
1.2
WA
WZ
WS
WW
SWA
SWZ
NWA
NWZ
HM
BM
TM
NA
NZ
HNA
HNZ
HB
TRM
NEA
NEZ
HFA
HFZ
HNFA
HNFZ
SEA
SEZ
SA
SZ
TB
TRW
Relative frequency (%)
Winter
Spring
Summer
Autumn
5.5
19.3
5.2
2.8
2.7
4.4
1.2
6.0
7.8
8.9
1.3
0.6
2.9
2.5
2.2
2.9
3.4
0.5
0.9
2.2
1.7
0.8
2.4
3.1
2.3
1.9
1.7
1.3
2.0
2.9
11.7
2.4
2.4
2.4
3.9
1.7
5.1
4.4
8.7
3.9
1.2
3.5
2.8
3.0
3.1
4.2
2.3
2.1
4.6
2.4
2.5
2.3
2.4
1.8
1.7
0.6
2.5
7.2
8.1
15.0
2.3
1.7
2.8
2.3
2.6
5.1
6.6
10.9
1.9
1.1
2.3
2.2
2.2
3.6
4.9
3.1
2.7
3.5
1.6
1.9
1.9
0.7
0.1
0.5
0.1
2.7
5.6
6.3
18.2
2.1
2.8
4.1
4.5
3.1
2.6
8.6
10.3
1.9
0.2
2.2
1.7
0.6
3.6
5.1
0.4
1.0
2.2
1.5
0.3
1.1
2.2
1.2
3.2
1.1
2.7
4.9
3. FREQUENCY DISTRIBUTION ANALYSIS
Figure 1(a) shows the frequency distribution of the 500 hPa circulation types over the Greek area in winter.
It can be seen that the cyclonic types occur most frequently over the Greek area (Figure 1(a)) during this
season, with the maximum frequency (19%) being attributed to type Csw. Figure 1(b)–(d) presents the
frequency distribution of the same types when the most frequent Lamb types (see Table III), A, W and C
respectively, predominate over western Europe in winter, as derived from the contingency tables between the
two classification schemes. The comparison of these with Figure 1(a) reveals that the frequency distribution
of the 500 hPa types over Greece does not change significantly when different circulation types prevail over
western Europe. Likewise, the frequency distributions of the 500 hPa circulation types in winter when the
most frequent HB types WZ and BM (see Table III) prevail over central Europe (Figure 1(e) and (f)) seem
to be slightly affected compared with Figure 1(a). Similar results are obtained for the frequency distributions
of 500 hPa types when they are associated with different Lamb and HB types for other seasons, i.e. spring,
summer and autumn (not shown).
Regarding the SLP types over the Greek area, Figure 2(a) shows their frequency distribution in autumn,
where A1 and Mb2 show higher frequencies. It can be seen that the connection of the SLP types to Lamb
types A and C (see Figure 2(b) and (c)) that principally dominate over western Europe in autumn, as well
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
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C. ANAGNOSTOPOULOU ET AL.
(b) Lamb type A, winter
35
30
30
relative frequency (%)
relative frequency (%)
(a) 500hPa, winter
35
25
20
15
10
5
0
25
20
15
10
5
0
A1
A2
A3
A4
A5
A6
C
Cs Csw Cnw Cne Cse Cn Cw
A1 A2
A3 A4 A5 A6
(c) Lamb type W, winter
(d) Lamb type C, winter
relative frequency (%)
relative frequency (%)
30
25
20
15
10
5
A1 A2 A3 A4 A5 A6
C
30
25
20
15
10
5
0
Cs Csw Cnw Cne Cse Cn Cw
A1 A2 A3 A4 A5 A6
(e) Hess and Brezowsky type WZ, winter
C
Cs Csw Cnw Cne Cse Cn Cw
(f) Hess and Brezowsky type BM, winter
35
35
relative frequency (%)
relative frequency (%)
Cs Csw Cnw Cne Cse Cn Cw
35
35
0
C
30
25
20
15
10
5
0
30
25
20
15
10
5
0
A1 A2 A3 A4 A5 A6
C
Cs Csw Cnw Cne Cse Cn Cw
A1 A2 A3 A4 A5 A6
C
Cs Csw Cnw Cne Cse Cn Cw
Figure 1. (a) Frequency distribution of 500 hPa types over the Greek area in winter. (b) Frequency distribution of 500 hPa types over
the Greek area in winter when Lamb circulation type A prevails over western Europe. (c) As in (b), but for type W. (d) As in (b),
but for type C. (e) Frequency distribution of 500 hPa type over the Greek area in winter when HB circulation type WZ prevails over
central Europe. (f) As in (e), but for type BM
as the connection to the most frequent HB types WZ and BM over central Europe (see Figure 2(d) and (e)),
does not seem to affect their frequency distribution considerably. However, it should be mentioned that the
derived differences are enhanced more than those derived from the comparison between 500 hPa types and
Lamb types or HB types (see Figure 1). This could be attributed to the fact that the surface circulation over
western Europe is expected to be related more to the surface circulation over Greece, rather to the 500 hPa
circulation. Similar results are deduced for the relationship between the SLP and Lamb and HB types for the
other seasons (not shown).
Therefore, it is suggested that the frequency distribution of the SLP and 500 hPa types over Greece does
not depend substantially on the circulation type prevailing over western and central Europe. Moreover, it
can be supported that, in terms of frequency distributions, no remarkable connection rules can be formulated
between the circulation of western–central Europe and the circulation over Greece for individual seasons. A
further approach is to examine the correlation coefficients in order to identify any possible relationship.
4. CORRELATION ANALYSIS
The correlation coefficients were calculated for the pairs of types Lamb–500 hPa, HB–500 hPa, Lamb–SLP
and HB–SLP for every season separately. The estimated correlation coefficients were then checked for their
statistical significance at the α = 0.05 level, employing the t-distribution with n − 2 degrees of freedom
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
ATMOSPHERIC CIRCULATION OVER GREECE AND THE WESTERN–CENTRAL MEDITERRANEAN
(a) SLP, autumn
(b) Lamb type A, autumn
20
relative frequency (%)
relative frequency (%)
20
15
10
5
0
A1
A3
A5
C
Csw Cne
Cn
15
10
5
0
Mt1 Dsec Mb2
A1
(c) Lamb type C, autumn
A3
A5
C
Csw
Cne
Cn
Mt1 Dsec Mb2
(d) Hess and Brezowsky WZ, autumn
20
20
relative frequency (%)
relative frequency (%)
1751
15
10
5
15
10
5
0
0
A1
A3
A5
C
Csw
Cne
Cn
A1
Mt1 Dsec Mb2
A3
A5
C
Csw
Cne
Cn
Mt1 Dsec Mb2
(e) Hess and Brezowsky BM, autumn
relative frequency (%)
20
15
10
5
0
A1
A3
A5
C
Csw
Cne
Cn
Mt1 Dsec Mb2
Figure 2. (a) Frequency distribution of SLP (surface) circulation types over the Greek area in autumn. (b) Frequency distribution of
SLP types over the Greek area in autumn when Lamb type A prevails over western Europe. (c) As in (b), but for type C. (d) Frequency
distribution of SLP types over the Greek area in autumn when WZ HB type prevails over central Europe. (e) As in (d), but for type
BM
(where n is the number of correlated pairs between Lamb and HB circulation types with SLP and 500 hPa
types for each season). Positive correlation means that the increase (or decrease) of the frequency of SLP
(or 500 hPa) classification types corresponds to an increase (or decrease) of the frequency of Lamb or HB
classification types. On the other hand, negative correlation means that an increase of the frequency of SLP or
500 hPa classification types corresponds to a decrease of the frequency of Lamb or HB classification types,
and a decrease of the frequency of SLP or 500 hPa classification types corresponds to an increase of the
frequency of Lamb or HB classification types.
Table IV displays the statistically significant correlations between Lamb and HB types with 500 hPa types
for each season. It can be seen that stronger positive correlations are observed in winter, when the highest
positive correlation (0.63) is observed between type SW over western Europe and anticyclonic type A2
over the Greek area. No negative correlation was found in winter; the most statistically significant negative
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
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C. ANAGNOSTOPOULOU ET AL.
Table IV. Statistically significant (at the 0.05 level) seasonal correlation between Lamb types over western Europe and
HB types over central Europe with 500 hPa types over Greek area and with SLP types over Greek area. The corresponding
correlation coefficients are included in parentheses
Lamb–500 hPa
HB–500 hPa
Lamb–SLP
HB–SLP
Winter
AW–A1 (0.46)
AW–Csw (0.4)
SW–A2 (0.63)
W–A2 (0.4)
WA–A2 (0.4)
WA–A6 (0.43)
WA–Cs (−0.41)
WA–Cne (−0.4)
WZ–Cw (−0.53)
HM–A1 (0.47)
A–A1 (0.59)
A–Csw (−0.45)
AE–Cnw (0.49)
E–Cnw (0.43)
E–Cne (0.41)
E–Mb2 (−0.44)
S–A2 (0.47)
SW–A3 (0.42)
W–A4 (0.58)
W–Cnw (−0.45)
NW–Cn (0.41)
N–Csw (0.4)
C–A1 (−0.43)
Spring
S–A3 (−0.43)
N–Cs (0.52)
C–A1 (0.4)
WW–Csw (0.46)
HFA–C (0.43)
E–Cs (0.44)
SE–Csw (0.4)
W–A1 (0.4)
Summer
NE–A3 (0.49)
N–A1 (−0.4)
BM–A4 (−0.46)
NWZ–Csw (0.51)
NEA–C (0.43)
Autumn
W–A1 (0.48)
A–Cnw (−0.45)
A–Dsec (−0.57)
CE–Dsec (0.43)
CNW–Dsec (0.45)
A–A1 (0.5)
SE–Mt2 (0.43)
N–Cnw (0.43)
C–A1 (−0.5)
CNE–Mb2 (0.49)
WA–A3 (0.52)
WA–A4 (0.41)
WA–A6 (0.5)
WA–Csw (−0.45)
WA–Mb2 (0.54)
WZ–A4 (0.53)
WZ–Cnw (−0.47)
WS–Cn (0.51)
TRM–Csw (0.51)
HNFZ–Cne (0.56)
HNFZ–Cw (0.51)
SEA–A2 (0.56)
SEZ–A2 (0.42)
SA–A2 (0.64)
WA–A6 (0.41)
NEA–Dor (0.44)
HFA–Cs (0.54)
HMFZ–Cne (0.52)
TRW–Mb2 (0.47)
HFZ–Cne (0.43)
WZ–A6 (0.44)
BM–Dor (0.44)
coefficients are observed in spring between S and A3 (−0.43), and in summer between N and A1 (−0.4).
The only statistically significant correlation in autumn is found between W and A1 (0.48).
Similar to Lamb types, the best correlations between HB types over central Europe and the 500 hPa types
over the Greek area are also achieved in winter, with the pairs HM–A1 and WZ–Cw being associated with
the highest coefficients, 0.47 and −0.53 respectively (Table IV). However, a higher percentage of statistically
significant correlations is observed for HB types in winter, compared with Lamb types, indicating that the
surface circulation over central Europe, rather than over western Europe, is related better to the 500 hPa
circulation over the Greek area during this season. No statistically significant correlation is found for autumn.
The statistically significant correlations between Lamb and HB types with SLP types for each season are
also displayed in Table IV. In general, greater correlations are observed between the surface circulation over
western Europe and the Greek area, compared with 500 hPa circulation over the Greek area. This is consistent
with the results that the frequency distribution of the 500 hPa types remained almost unchanged for different
Lamb types, whereas the SLP distribution appears rather affected occasionally. Particularly high percentages
of statistically significant correlation coefficients are observed during winter. The highest positive correlation
coefficients (0.59) were found for Lamb type A with the SLP type A1 and for W with A4 (0.58). Also
worth mentioning is the association of type E (which denotes an anticyclone stretching from Scandinavia to
Iceland) with types Cnw and Cne in winter but with type Cs in spring, leading to the formation of Saharan
depressions.
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
ATMOSPHERIC CIRCULATION OVER GREECE AND THE WESTERN–CENTRAL MEDITERRANEAN
1753
Similar to Lamb types, a higher correlation is also found between the HB types with surface circulation over
the Greek area, compared with 500 hPa circulation, and a high percentage of statistically significant correlation
coefficients was estimated for winter. Lower correlations were found in the other seasons (Table IV).
5. SEASONAL COMPOSITE MAPS
In order to investigate further the relationship between the circulation over western and central Europe
and the circulation over the Greek area, seasonal composite maps of mean sea-level pressure and 500 hPa
geopotential height anomalies were constructed for the most statistically significant correlated pairs of
Lamb–SLP types, Lamb–500 hPa types, HB–SLP types and HB–500 hPa types (Table IV). The composite
maps were constructed for each case where there were common appearances for both classification types for
each season.
Figure 3 displays seasonal composites of mean sea-level pressure for selected correlated pairs of Lamb
and SLP types. Lamb type A presents statistically significant correlation with more than one SLP type over
the Greek area: in winter with A1 (Figure 3(a)) and Csw (Figure 3(b)); in summer with Dsec (Figure 3(e))
and Cnw (Figure 3(f)); in autumn with A1 (not shown). This can be attributed to its large spatial extent
and the different types of air mass that it consists of. In this type of correlation, the most significant role
is played by the stability structure of the atmosphere. When the atmosphere is stable over the whole of
Europe and the Mediterranean, then type A1 dominates over the Greek area. When the atmosphere is
stable over the whole of Europe but rather unstable over the central Mediterranean, then the Greek area
is characterized by the cyclonic types Csw or Cnw. Finally, when the atmosphere over the whole of
western–central Europe is stable, but unstable over the eastern Mediterranean, due to thermal factors in
summer, then type Dsec prevails over the Greek area. Lamb type W, which occurs when an anticyclone is
centred south of the British Isles and low pressure to the north, results in zonal flow over western Europe
in winter that steers depressions into central Europe and mainly over northern Italy, and is thus associated
with the predominance of the type Cnw over the Greek area (Figure 3(d)). However, if the zonal flow is
strong and extends along northern Europe, then anticyclonic circulation of type A4 is established over the
Mediterranean (Figure 3(c)).
Figure 4 displays seasonal composites of mean sea-level pressure for selected correlated pairs of HB and
SLP types. As can be seen, HB types WA and WZ are related to various types of circulation over the Greek
area, since both are characterized by zonal flow over central Europe, but are combined with different circulation
patterns over the Mediterranean and eastern Europe. When the zonal flow WA is combined with anticyclonic
circulation over the Mediterranean, then high-pressure values are also established over the Greek area in
winter and spring. Depending on the location of the anticyclonic centre and the extent of the anticyclone,
this type of circulation can be related to Mb2 type (Figure 4(a)) when the centre is located over the western
basin of the Mediterranean, to A3 (Figure 4(b)) when the centre is located over the Balkans, or to A6
(Figure 4(c)) when the centre is located over the western basin but the anticyclone is rather extended to
the east. When the zonal flow WZ is combined with cyclonic circulation over the Mediterranean, then type
Cnw is more likely to occur over the Greek area in winter (Figure 4(d)). However, if the zonal flow extends
further east, then type A4 prevails over the Greek area (Figure 4(e)). In autumn, the WZ type is more likely
related to an anticyclone being centred over central Europe, resulting in the predominance of the A6 type
over the Greek area (Figure 4(f)). Figure 5 displays seasonal composites of geopotential height anomalies
at 500 hPa for selected correlated pairs of Lamb and 500 hPa types. It can also be seen that the same type
of circulation over western Europe can lead to different types of 500 hPa circulation over the Greek area
or vice-versa. For example, Lamb type N, which is characterized by an anticyclonic anomaly over western
Europe, is related to either the cyclonic type Cs in spring (Figure 5(d)) or the anticyclonic type A1 in summer
(Figure 5(f)). Furthermore, type A2 prevails over the Greek area when two different Lamb types occur over
western Europe in winter, SW (Figure 5(b)) and W (Figure 5(c)). These differences are associated with the
location of the cyclonic or anticyclonic centres, the extent and intensity of the corresponding circulation over
western Europe, and also to the stability structure of the atmosphere over the two regions. It can also be
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
1754
C. ANAGNOSTOPOULOU ET AL.
(b) A - Csw, winter
(a) A - Al, winter
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
(d) W - Cnw, winter
(c) W - A4, winter
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
10.00 20.00 30.00 40.00 50.00
10.00 20.00 30.00 40.00 50.00
(f) A - Cnw, summer
(e) A - Dsec, summer
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
Figure 3. Seasonal composites of mean sea-level pressure for correlated pairs of Lamb–SLP types: (a) A–A1 for winter; (b) A–Csw
for winter; (c) W–A4 for winter; (d) W–Cnw for winter; (e) A–Dsec for summer; (f) A–Cnw for summer
seen that Lamb type AW is characterized by an anticyclonic anomaly over central Europe in winter, which
is strongly related to the formation of an anticyclonic center to the northwest of the Greek area (type A1;
Figure 5(a)). However, type A1 also prevails when a cyclonic anomaly forms over the British Isles (Lamb
type C; Figure 5(e)).
Similar results can be obtained with respect to seasonal composites of geopotential height anomalies at
500 hPa for selected correlated pairs of HB and 500 hPa types (Figure 6). For example, type WA can be
related both to the anticyclonic type A2 (Figure 6(a)) and the cyclonic type Cs (Figure 6(b)) over the Greek
area in winter, depending on the extent and intensity of the westerly flow over central Europe.
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
ATMOSPHERIC CIRCULATION OVER GREECE AND THE WESTERN–CENTRAL MEDITERRANEAN
(a) WA - Mb2, winter
(b) WA - A3, winter
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
(f) WZ - A6, autumn
(e) WZ - A4, winter
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
(d) WZ - Cnw, winter
(c) WA - A6, spring
20.00
-20.00 -10.00 0.00
1755
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
Figure 4. Seasonal composites of mean sea-level pressure for correlated pairs of HB–SLP types: (a) WA–Mb2 for winter; (b) WA–A3
for winter; (c) WA–A6 for spring; (d) WZ–Cnw for winter; (e) WZ–A4 for winter; (f) WZ–A6 for autumn
6. CONCLUSIONS
In this study an attempt was made to relate the surface atmospheric circulation over western and central
Europe to the surface and upper air atmospheric circulation over the Greek area in terms of synoptic types.
For this purpose, the Lamb classification scheme of weather types was employed for western Europe, the HB
scheme for central Europe and the SLP and 500 hPa classification schemes of Maheras et al. (2000a,b) for
the Greek area, using a common period of 40 years (1958–97).
The analysis demonstrated that it is difficult to formulate rules controlling the circulation over the Greek
area in relation to the circulation over western and central Europe for individual seasons. This can be partially
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
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C. ANAGNOSTOPOULOU ET AL.
(a) AW - A1, winter
(b) SW - A2, winter
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
(c) W - A2, winter
(d) N - Cs, spring
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
60.00
60.00
50.00
50.00
40.00
40.00
30.00
30.00
10.00 20.00 30.00 40.00 50.00
10.00 20.00 30.00 40.00 50.00
(f) N - A1, summer
(e) C - A1, spring
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
20.00
-20.00 -10.00 0.00
10.00 20.00 30.00 40.00 50.00
Figure 5. Seasonal composites of geopotential height anomalies at 500 hPa for correlated pairs of Lamb–500 hPa types: (a) AW–A1
for winter; (b) SW–A2 for winter; (c) W–A2 for winter; (d) N–Cs for spring; (e) C–A1 for spring; (f) N–A1 for summer
attributed to the fact that different classification schemes were employed for the three regions examined, due
to different synoptic characteristics of the prevailing surface circulation.
However, statistically significant correlation was found between types with high frequency. Higher
percentages of significant correlation coefficients are observed in winter for all pairs of types examined,
compared with other seasons. Moreover, greater correlations are observed between Lamb and HB types
with the surface circulation types SLP over the Greek area, compared with 500 hPa circulation types
(except between SW Lamb type and A2 of 500 hPa anticyclonic type; correlation coefficient of 0.63).
This is consistent with the results that the frequency distribution of the 500 hPa types remained almost
unchanged for different Lamb types, while the SLP distribution appears rather affected occasionally. The
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
ATMOSPHERIC CIRCULATION OVER GREECE AND THE WESTERN–CENTRAL MEDITERRANEAN
1757
(a) WA-A2, winter
60.00
50.00
40.00
30.00
20.00
-20.00
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
30.00
40.00
50.00
(b) WA-Cs, winter
60.00
50.00
40.00
30.00
20.00
-20.00
-10.00
0.00
10.00
20.00
Figure 6. Seasonal composites of geopotential height anomalies at 500 hPa for correlated pairs of HB–500 hPa types: (a) WA–A2 for
winter; (b) WA–Cs for winter
highest correlation coefficients were estimated in winter between Lamb type SW and 500 hPa anticyclonic
type A2, Lamb type A and SLP type A1, HB type SA and SLP type A2, HB type WZ and 500 hPa
Cw. The highest correlation coefficients can be explained for the first case by the southwesterly circulation
over western Europe (Lamb type SW), which establishes an anticyclonic circulation over eastern Europe
(A2). In the second case, the appearance of one expanded anticyclone, whose centre is over Britain,
covers both western Europe (A) and the Greek region (A1). There are similar explanations for HB
and Lamb classification for the other seasons. However, owing to the low values of the correlation
coefficients, the practical possibility of predicting a classification from another one is very limited. Thus,
one should use this classification for climate evolution studies with care and only for each validation
region.
For the most correlated pairs, seasonal composites of mean sea-level pressure and 500 hPa geopotential
height anomalies demonstrated that the formation of the circulation types over the Greek area depends on
the extent and intensity of the anticyclonic or cyclonic centres, the air mass characteristics, and the stability
profile in the lower troposphere over the regions examined, but especially over the central and eastern
Mediterranean.
Copyright  2004 Royal Meteorological Society
Int. J. Climatol. 24: 1745–1758 (2004)
1758
C. ANAGNOSTOPOULOU ET AL.
ACKNOWLEDGEMENTS
This research was funded by the EC project STARDEX, under contract EVK2-CT-2001-00115. We would
like to express our gratitude to the referees for their constructive comments and suggestions.
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