Adv. Geosci., 12, 87–93, 2007
www.adv-geosci.net/12/87/2007/
© Author(s) 2007. This work is licensed
under a Creative Commons License.
Advances in
Geosciences
Extreme precipitation related to circulation types for four case
studies over the Eastern Mediterranean
K. Tolika1 , Chr. Anagnostopoulou1 , P. Maheras1 , and H. Kutiel2
1 Department
2 Department
of Meteorology and Climatology, School of Geology, Aristotle University of Thessaloniki, 54124 Greece
of Geography and Environmental Studies, University of Haifa, Israel
Received: 26 February 2007 – Revised: 5 July 2007 – Accepted: 6 August 2007 – Published: 8 August 2007
Abstract. The analysis of the links between the extreme precipitation and the associated atmospheric conditions through
an aloft circulation type approach at the 500-hPa geopotential level, for the time period of 1958-2000, is the main motivation for the present study. Four stations in the eastern
Mediterranean (17.5◦ E to 37.5◦ E and 30◦ N to 40◦ N) were
selected as separate case studies. The extreme precipitation
conditions were defined by the two most widely used indices:
the 90th and 95th percentiles. It was found that two cyclonic
types (C – with its centre over the station and Cwsw – with
its centre at the WSW of the station) were mainly associated
with extreme rainfall conditions for all the selected stations.
Generally, these circulation types are deepening during days
with extreme precipitation in comparison to the general mean
field of the type.
1
spheric circulation, and the statistical downscaling models
use mainly these parameters as predictors for their future
projections (Tolika et al., 2006), it becomes evident that the
knowledge of the climatic features of extremes and their links
with the atmospheric conditions could be helpful for the development of more valid future climate change scenarios of
the extremes (Hellstrom, 2005). Moreover, the study and the
association of the occurrence of extremes and the large-scale
circulation could reveal novel information about the physical
processes that dominate during extreme conditions (Santos
et al., 2007).
The main motivations for the present study are a) the statistical analysis of the extreme precipitation conditions over
the eastern Mediterranean and their association with the circulation types, and b) the analysis of the dynamic processes
in the fields of these circulation types during the extreme precipitation events.
Introduction
Extreme precipitation and temperature events have been
recently the subject of numerous climate studies, since
they have severe environmental and socioeconomic consequences, as well as impacts on the hydrological cycle, water
resources, agriculture and tourism. Furthermore, in a future
warmer climate, where there will probably be a change in the
extremes, the assessment of these changes, particularly of the
frequency and intensity of the extreme events receives great
importance. Especially in the case of precipitation, Santos
et al. (2007) have demonstrated that an estimation of the
changes in the rainfall extremes in a modified future climate
could be helpful for the development of appropriate adaptation and mitigation strategies.
Since the General Circulation Models were found quite
skilful in reproducing the general and the regional atmoCorrespondence to: P. Maheras
([email protected])
2
Data and methodology
The data used in the study consist of daily precipitation time
series derived from four meteorological stations over the
eastern Mediterranean region (Fig. 1). The selected time period covers the years from 1958 to 2000 and due to the fact
that eastern Mediterranean is characterized by very low precipitation totals (or even absence of rainfall) during summer,
the study focuses only on the cold – wet period from October
to April. All the time series used contain no missing values
and were found homogeneous according to the Alexandersson test (Alexandersson, 1986).
A new automatic classification, based on the previous classification by Maheras and Anagnostopoulou (2003), was applied for the computation of the daily calendars of the circulation types. The main improvements of this classification
are the number of the circulation types, which are reduced
now to 12 and the fact that the scheme is flexible all over the
Published by Copernicus Publications on behalf of the European Geosciences Union.
88
K. Tolika et al.: Extreme precipitation related to circulation types
65.0
62.5
60.0
57.5
55.0
52.5
50.0
47.5
45.0
42.5
40.0
37.5
35.0
32.5
30.0
27.5
25.0
22.5
20.0
-20.0 -15.0 -10.0 -5.0
a
Kerkyra
Larnaca
Milos
0.0
5.0
10.0
15.0
20.0
25.0
Tel Aviv
30.0
35.0
40.0
45.0
50.0
Figure 1. Location Map.
Fig. 1. Location Map.
Mediterranean. The 500-hPa geopotential data (2.5◦ ×2.5◦
spatial resolution) from the NCEP/NCAR (Kalnay et al.,
1996) were employed, covering a large spatial window over
the whole European region, for the development of the daily
circulation type’s calendar. The centre of each classification
changed according to the geographical location of the station and the selected grid point was the one closest to the
station (Fig. 2). Thus, the following centres were chosen:
a) Kerkyra classification centre (20◦ W and 40◦ N), b) Milos
classification centre (25◦ W and 37.5◦ N), c) Larnaca classification centre (32.5◦ W and 35◦ N) and d) Tel Aviv classification centre (35◦ W and 32.5◦ N).
Finally, extreme precipitation was defined with the application of two extreme indices, the 90th and the 95th percentile. The selection of these two indices was made based
on the fact that they are the most commonly used ones in the
literature for the analysis of extreme precipitation. Also, percentiles were preferred instead of a fixed threshold, in order
to make the indices comparable and transferable in regions
with different climatic characteristics and different local precipitation regimes.
65.0
62.5
60.0
57.5
55.0
52.5
50.0
47.5
45.0
42.5
40.0
37.5
35.0
32.5
30.0
27.5
25.0
22.5
20.0
-20.0 -15.0 -10.0
Anw
Ane
A
Asw
-5.0
0.0
5.0
10.0
15.0
Ase
20.0
25.0
30.0
35.0
40.0
45.0
50.0
b
65.0
62.5
60.0
57.5
55.0
52.5
50.0
47.5
45.0
42.5
40.0
37.5
35.0
32.5
30.0
27.5
25.0
22.5
20.0
-20.0 -15.0 -10.0 -5.0
Cnnw
Cwnw
Cne
C
Cwsw
Cse
Cssw
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Fig. 2. The locations of the circulation types, anticyclonic (a) and
Figure
2. The
locations
of the over
circulation
cyclonic
(b) with
a centre
of the classification
Kerkyra. types,
a centre of the classification over Kerkyra.
Statistical analysis of the extreme precipitation and the
related circulation types
found with precipitation amounts greater than the 90th percentile and 4.3 days per year with precipitation higher than
the 95th percentile. Tel Aviv follows with a 90th percentile of
24.2 mm and a 95th of 34.6 mm. Moreover, while the highest absolute maximum precipitation (130.6 mm) was found
in Kerkyra as well, the minimum was observed in Larnaca
with only 99.1 mm. Finally, the calculated ratios of the absolute maximum precipitation and the 90th percentile (maxprec/90th) varied from 4.35 (Tel Aviv) to 6.69 (Milos). The
equivalent results for the second index showed that the maxprec is three to almost five times greater than the 95th percentile, with values between 3.04 (Tel Aviv) to 4.57 (Milos).
Table 1 summarizes the results of the computation of the two
percentiles, the averaged number of rain days (total number/years) with rainfall greater than these percentiles, the absolute maximum daily precipitation (maxprec) and the ratio
of the maxprec/Xth perc, for the four stations under study.
Kerkyra was considered as the rainiest station, as it presented
the highest 90th and 95th percentile values reaching 28.1 mm
and 38.8 mm respectively. This station presented also the
greatest number of days with rainfall higher than the examined percentiles. More specifically, 8.6 days per year were
In a further analysis, the trends in the precipitation time
series during the selected period (October–April) and in the
number of events with precipitation greater than the two percentiles, as well as their rainfall totals were estimated (only
the results of the 95th percentile are presented). It was found
that Kerkyra differed from the rest of the stations as all the
above parameters showed statistically significant decreasing
trends during the years 1958–2000 (Fig. 3). Conversely, in
all the other three stations,
11 the precipitation and the extreme
events do not change significantly. Generally, they present
small positive trends (not statistically significant).
3
3.1
Results
Adv. Geosci., 12, 87–93, 2007
www.adv-geosci.net/12/87/2007/
anticy
K. Tolika et al.: Extreme precipitation related to circulation types
89
Table 1. The extreme precipitation characteristics of the four stations used in the study.
K erkyra
To ta l a n n u a l p r e c i p i ta ti o n > = 9 5 th p e r c e n ti l e
L arn aca
N u m b e r o f e v e n ts w i th p r e c > = 9 5 th p e r c e n ti l e
y = 0.016x + 2.0616
10
Te l Av i v
P r e c i p i ta ti o n fo r th e w e t p e r i o d O c t - Ap r i l
12
y = 0.0293x + 2.1312
10
1998
1995
1992
1986
1989
1998
1995
1992
1989
1998
1995
1992
1989
1986
1983
1980
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
0
1965
2
1962
4
1967
y = 1.4423x + 107.52
1959
6
200
0
700
600
500
400
300
200
100
0
8
1964
Te l Av i v
To ta l a n n u a l p r e c i p i ta ti o n > = 9 5 th p e r c e n ti l e
Te l Av i v
N u m b e r o f e v e n ts w i th p r e c > = 9 5 th p e r c e n ti l e
y = 1.116x + 487.8
1977
1959
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
1967
1964
1961
1958
0
1974
2
1971
4
1968
6
1961
y = 0.8452x + 71.086
500
400
300
200
100
0
8
1958
700
600
1962
y = -0 . 4 3 6 x + 3 2 3 . 9 3
1000
800
600
400
200
0
1983
L arn aca
To ta l a n n u a l P r e c i p i ta ti o n > = 9 5 th p e r c e n ti l e
12
1400
1200
1000
800
600
400
y = 0.7041x + 93.702
1986
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
1967
1964
1961
1958
L arn aca
P r e c i p i ta ti o n fo r th e w e t p e r i o d O c t - Ap r i l
700
600
500
400
300
200
100
0
1962
y = 0.0173x + 2.4623
8
6
4
2
0
1980
1959
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
12
10
y = 0.2191x + 381.19
1400
1200
Milo s
To ta l a n n u a l p r e c i p i ta ti o n > = 9 5 th p e r c e n ti l e
Milo s
N u m b e r o f e v e n ts w i th p r e c > = 9 5 th p e r c e n ti l e
1959
Milo s
P r e c i p i ta ti o n fo r th e w e t p e r i o d O c t - Ap r i l
1968
1965
1962
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
1967
1964
1961
1958
1959
2
0
1983
4
200
0
y = -4 . 6 1 5 7 x + 3 4 3 . 0 1
1980
8
6
700
600
500
400
300
200
100
0
1965
y = -0 . 0 7 0 8 x + 5 . 8 5 6
10
y = -9 . 1 2 3 x + 1 1 2 6 . 7
1000
800
600
400
1400
1200
1000
800
600
400
200
0
3.37
4.57
3.84
3.04
K erkyra
N u m b e r o f e v e n ts w i th p r e c > = 9 5 th p e r c e n ti l e
12
1400
1200
4.65
6.69
5.63
4.35
1962
K erkyra
P r e c i p i ta ti o n fo r th e w e t p e r i o d O c t - Ap r i l
130.6
115.1
99.1
105.3
1977
4.3
2.8
2.4
2.8
1974
8.6
5.8
4.8
5.5
1977
38.8
25.2
25.8
34.6
95th
1971
28.1
17.2
17.6
24.2
90th
1974
95th
1968
90th
1971
95th
Ratio
Maxprec/Xth
percentile
1968
90th
Absolute Max
precipitation
(mm)
1968
Kerkyra
Milos
Larnaka
Tel Aviv
Mean Number
of days with
prec>Xth perc.
(days)
1965
Xth Perc.
(mm)
1965
Stations
th
Figure
3. The
trends
of precipitation
the precipitation
the October-April
(1st column),
the number
of extreme
with precipitation
Fig.
3. The
trends
of the
of theofOctober-April
periodperiod
(1st column),
of theofnumber
of extreme
events events
with precipitation
>95th > 95
percentile
column) and
and the
the annual
annual precipitation
column), for
percentile(2nd
(2nd column)
precipitation of
of these
these extreme
extreme events
events (3th
(3th column),
for the
the four
four stations
stations under
under study.
study.
According to the results (number of days and percentage
of occurrence %) presented in Table 2, extreme rainfall conditions were found mainly during the circulation types C and
Cwsw. The characterization of each circulation type refers
to the location of a positive (anticyclonic) or a negative (cyclonic) centre in relation to the examined area (e.g. Greece)
(Maheras and Anagnostopoulou, 2003; Anagnostopoulou et
al., 2007). So, the cyclonic type C has a negative centre over
this area with northerly sector winds blowing over it. Respectively, the circulation type Cwsw, if the study is for the Ionian
Isles, it presents a negative centre over the central Mediterranean and northern Africa with a westerly – south-westerly
flow over Greece. The relative precipitation of each circula-
www.adv-geosci.net/12/87/2007/
tion type was computed as well as the ratio (maximum daily
prec of each ct/Xth percentile) and the results are presented
in Table 2.
13
For both percentiles, over 55% of the extreme precipitation
cases were found at the occurrence of these two circulation
types, for all the stations. In Kerkyra, Milos and Larnaca, the
Cwsw type presents a greater number of extreme episodes,
while in Tel Aviv the circulation type C prevails. Furthermore, it should be mentioned that the average precipitation
amounts of these circulation types is higher for both percentages in the case of Kerkyra, which is the station with the
greatest precipitation totals. However, the calculated ratio
(Table 2) presents its highest value in Milos ((6.4) circ. type
Adv. Geosci., 12, 87–93, 2007
90
K. Tolika et al.: Extreme precipitation related to circulation types
Table 2. Statistical analysis of two most frequent circulation types at the occurrence of precipitation extremes, for the two percentiles (90th
and 95th).
Stations
Circulation Types
(CTs)
C
Kerkyra
Cwsw
C
Milos
Cwsw
C
Larnaka
Cwsw
C
Tel Aviv
Cwsw
Percentiles
No. of cases with
prec>Xth percentile
CTcases/Total cases
(%)
CTprec/Ct cases
CTmax prec/Xth perc.
90th
95th
90th
95th
89
43
114
57
24.7
23.6
31.6
31.3
43.3
54.7
47.2
61
3.9
2.8
4.6
3.4
90th
95th
90th
95th
72
38
76
31
29.6
31.9
31.3
26.1
30.9
40
27.6
37.9
6.4
4.4
4.7
3.2
90th
95th
90th
95th
46
21
77
43
22.7
20.8
37.9
42.6
27.8
36.2
29.6
36.9
2.9
2
5.6
3.8
90th
95th
90th
95th
113
59
43
16
48.5
50
18.5
13.8
39.9
50.4
36.5
49.6
4.4
3
2.7
1.9
C for the 90th percentile) and its lowest value (1.9) in Tel
Aviv for the 95th Cwsw.
3.2
Dynamical Analysis of the extreme precipitation and
the related circulation types
In the final step of this study, an attempt is made to examine
the dynamic changes, at the 500-hPa level, of the fields of
these two prevailing circulation types that may cause these
extreme precipitation conditions in the four selected areas.
For this reason, the general mean anomaly field of the selected circulation types was plotted as well as the equivalent
fields only from the cases with daily rainfall amounts greater
than the two percentiles. Finally, the differences between the
general mean field and the field of the selected cases (gen.
mean field – mean cases field) were computed and mapped.
At this point it should be mentioned that all the anomaly values in Figs. 4 and 5 were multiplied by 100.
The first case examined was the circulation type C for the
station of Kerkyra. As it could be seen from the composite maps in Fig. 4 (a1–a5), although the mean cases fields
do not seem to differ much from the general field, it was
found that during extreme precipitation conditions they become less deep (negative differences). The centre of these
negative anomaly differences is located at the northeast of
the examined area (Kerkyra) and they present greater absolute values in the case of the 95th percentile. The analysis of
the second prevailing type (Cwsw, Fig. 4 b1–b5) led to different conclusions. This time, the dynamic field of the circuAdv. Geosci., 12, 87–93, 2007
lation type seemed to be deeper at the occurrence of extreme
precipitation (higher negative anomalies). The differences
found were positive, covering the selected area. The positive
centre was slightly moved to the west (Fig. 4 b1–b5).
Concerning Milos, the anomaly fields of both circulation
types presented a similar behaviour, with higher negative
anomalies during days with heavy rainfall. Quite a strong
positive differences centre is placed at the north of Greece,
covering the island of Milos as well. Due to space limitations, only the differences are presented (Fig. 5 a1–a4). The
results of the two other study areas (Larnaca and Tel Aviv)
showed that also in these cases the circulation types occurring during rainfall extreme totals are deepening in comparison with their general mean field of the period October–
April. The centre of the positive differences was situated
almost over the locations of the two selected stations (differences, Fig. 5 b1–c4).
4
Discussion and conclusions
The present study aimed at exploring the relationships of the
extreme precipitation conditions over the eastern Mediterranean region and the circulation types that prevail during the
occurrence of extremes. The 90th and the 95th percentiles
were selected as extreme precipitation indices and were computed for four stations, in Greece (Kerkyra, Milos), in Cyprus
(Larnaca) and in Israel (Tel Aviv).
www.adv-geosci.net/12/87/2007/
K. Tolika et al.: Extreme precipitation related to circulation types
91
Kerkyra
a1) C _ G.M.A. FIELD FOR OCT-APRIL
a2) C _ M. A. FIELD OF THE CASES > 90th
a3) C _ DIFF. (mean gen.field - mean cases field)
a4) C _ M.A. FIELD OF THE CASES > 95th Perc
a5) C _ DIFF. (mean gen.field - mean cases field)
67.5
67.5
67.5
67.5
67.5
62.5
62.5
62.5
62.5
62.5
57.5
57.5
57.5
57.5
57.5
52.5
52.5
52.5
52.5
52.5
47.5
47.5
47.5
47.5
47.5
42.5
42.5
42.5
42.5
42.5
37.5
37.5
37.5
37.5
37.5
32.5
32.5
32.5
32.5
32.5
27.5
27.5
27.5
27.5
22.5
-22.5 -17.5 -12.5 -7.5 -2.5
22.5
-22.5 -17.5 -12.5 -7.5 -2.5
2.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
b1) Cwsw_ G.M.A. FIELD FOR OCT-APRIL
2.5
22.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5 -22.5 -17.5 -12.5 -7.5 -2.5
2.5
27.5
22.5
-22.5 -17.5 -12.5 -7.5 -2.5 2.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
b2) Cwsw _ M. A. FIELD OF THE CASES > 90th b3) Cwsw _ DIFF. (mean gen.field - mean cases field) b4) Cwsw _ M. A. FIELD OF THE CASES > 95th Perc
22.5
-22.5 -17.5 -12.5 -7.5 -2.5 2.5
67.5
67.5
67.5
67.5
62.5
62.5
62.5
62.5
62.5
57.5
57.5
57.5
57.5
57.5
52.5
52.5
52.5
52.5
52.5
47.5
47.5
47.5
47.5
47.5
42.5
42.5
42.5
42.5
42.5
37.5
37.5
37.5
37.5
37.5
32.5
32.5
32.5
32.5
32.5
27.5
27.5
27.5
27.5
22.5
-22.5 -17.5 -12.5 -7.5 -2.5 2.5
22.5
-22.5 -17.5 -12.5 -7.5 -2.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
2.5
22.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5 -22.5 -17.5 -12.5 -7.5 -2.5
200 150 100 50
2.5
22.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5 -22.5 -17.5 -12.5 -7.5 -2.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
b5) Cwsw _ DIFF. (mean gen.field - mean cases field)
67.5
27.5
2.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
22.5
-22.5 -17.5 -12.5 -7.5 -2.5
2.5
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5
0 -50 -100-150-200-250-300-350-400-450-500
Figure 4. The composite map of the general mean anomaly (G.M.A.) field of the two prevailing circulation types (C and Cwsw), their mean
Fig.
4. The
composite
map
the general
anomaly
(G.M.A.) field
of thedifferences
two prevailing
circulation
(C and
Cwsw),
their mean
anomaly
(M.A.)
field in
theofcases
> of themean
90th and
95th percentiles
and their
(G.M.A.
– M.A.)types
for the
station
of Kerkyra.
All
anomaly (M.A.) field in the cases > of the 90th and 95th percentiles and their differences (G.M.A. – M.A.) for the station of Kerkyra. All
anomalies
are
multiplied
by
100.
anomalies are multiplied by 100.
From the four stations under study, Kerkyra was found to
have the highest 90th and 95th percentiles, followed by Tel
Aviv, Larnaca and Milos. Kerkyra presented also the largest
number of cases (events) with extreme precipitation. The
precipitation totals, the extreme precipitation and the number of events of extreme precipitation presented a statistically
significant negative trend only for the station of Kerkyra.
For the other three stations, extreme precipitation did not
show any significant change during the period of October–
April (1958–2000). This is in accordance with the findings
of Alpert et al. (2002), demonstrating also that in the eastern Mediterranean, and especially for stations over Cyprus
and Israel, extreme precipitation does not present significant
trends. Moreover, in their study on the extreme temperature
and precipitation conditions over the Middle East (including Cyprus), Zhang et al. (2005) showed that the trends of
the precipitation indices and the maximum daily precipitation events were less coherent and weaker than the ones concerning extreme temperature.
Heavy rainfall occurred during the circulation types C and
Cwsw in all the stations under study. These circulation types
are characterized by warm and cold air sequences, as well
as by potential and kinetic energy exchanges. Rainfall conditions depend on evolving airmass, the wind direction at
500 hPa, the trajectory of the low pressure system, and the
upper trough, on the orography and the distance from the sea
of each specific area of interest, and on surface roughness. In
the majority of the cases of the aforementioned circulation
types, the depressions have a Mediterranean origin (Maheras
1982, 1983) and they are well developed when they reach
the study areas. Their impact on rainfall is related to the intensity of the cold air intrusion, as well as to the depth of
the associated low–pressure system. In fact, this characterwww.adv-geosci.net/12/87/2007/
istic was concluded from the dynamic analysis of the types,
which were deepening during days with extreme precipitation (higher negative anomalies in comparison with the general mean field of the type). The only exception was found
for the circulation type C, in the case of Kerkyra.
In this station, the trajectories of the depressions that rep14
resent the C and Cwsw types, and are related to extreme
precipitation, are divided into two categories: a) depressions
with a SW to NE trajectory and b) depressions with a NW-SE
trajectory (Maheras, 1983). In both these categories, there
is a trough at the 500-hPa level, whose axis is located at
the west of the Greek area. In the case of the SW-NE depressions, the cyclones are moving along the east side of
the trough. The deeper these cyclones are, the more intense
the rainfall is. Also, the 500-hPa geopotential anomalies are
more intense over Greece and the southern Balkans than the
anomalies of the general mean field of type C. In the case
of the NW-SE depressions, the axis of the trough is usually
located at the west of Greece with a NW-SE slope. As a surface cyclone is moving towards SE, defining a C type, it is
obvious that the 500-hPa geopotential values are relatively
high over the southern Balkans, resulting in the appearance
of higher anomalies at the 500-hPa level, in comparison to
the mean anomaly values of this type. The fact that the greatest percentage of the depressions associated with extreme
rainfall in Kerkyra follows a NW-SE trajectory reinforces the
above conclusions. However, it should be also taken under
consideration at this point that the “peculiar” result found for
this station could as well be attributed to the fact that the
frontal activity in that area may play a more important role in
the rainfall intensity and the extremes than the depth of the
depressions.
Adv. Geosci., 12, 87–93, 2007
92
K. Tolika et al.: Extreme precipitation related to circulation types
Milos
Larnaca
Tel Aviv
b1) C_ DIFFERENCIES
a1) C _ DIFFERENCIES
c1) C _ DIFFERENCIES
62.5
60.0
60.0
52.5
50.0
50.0
42.5
40.0
40.0
32.5
30.0
30.0
22.5
-17.5
-7.5
2.5
12.5
22.5
32.5
42.5
20.0
-10.0
0.0
10.0
20.0
30.0
40.0
50.0
20.0
-10.0
60.0
60.0
52.5
50.0
50.0
42.5
40.0
40.0
30.0
30.0
32.5
22.5
-7.5
2.5
12.5
22.5
32.5
42.5
20.0
-10.0
10.0
20.0
30.0
40.0
50.0
-10.0
30.0
40.0
50.0
0.0
10.0
20.0
30.0
40.0
50.0
c3) Cwsw_ DIFFERENCIES
62.5
60.0
52.5
50.0
42.5
40.0
35.0
32.5
30.0
25.0
22.5
-17.5
20.0
20.0
0.0
b3) Cwsw_ DIFFERENCIES
a3) Cwsw_ DIFFERENCIES
10.0
c2) C _ DIFFERENCIES
62.5
-17.5
0.0
b2) C_ DIFFERENCIES
a2) C _ DIFFERENCIES
55.0
-7.5
2.5
12.5
22.5
32.5
42.5
20.0
-10.0
45.0
15.0
0.0
10.0
20.0
30.0
40.0
-7.5
50.0
a4) Cwsw _ DIFFERENCIES
2.5
12.5
22.5
32.5
42.5
52.5
62.5
c4) Cwsw _ DIFFERENCIES
b4) Cwsw _ DIFFERENCIES
60.0
62.5
55.0
52.5
50.0
42.5
40.0
35.0
32.5
30.0
25.0
22.5
-17.5
-7.5
2.5
12.5
22.5
32.5
42.5
20.0
-10.0
45.0
15.0
0.0
10.0
20.0
30.0
40.0
50.0
-7.5
2.5
12.5
22.5
32.5
42.5
52.5
62.5
Fig. 5. Composite maps of the differences (G.M.A. – M.A.) for both circulation types and the two percentiles for of Milos (1st column),
Larnaca
(2nd 5.
column)
and Tel Aviv maps
(3rd column).
Figure
Composite
of the differences (G.M.A. – M.A.) for both circulation
types and the two percentiles for of Milos (1st column), Larnaca (2nd column) and Tel
As a future work, the authors plan to investigate more thorrd
oughly
of other characteristics of the circulation
Avivthe(3changes
column).
types (frequency, wind speed, changes in other geopotential levels, as well as the isentropic potential vorticity (IPV)
advection) that could also play an important role in the occurrence of extreme precipitation conditions over the study area.
Also, it could be of great interest to examine whether in other
parts of the Mediterranean region, the same circulation types
are associated with the extreme indices.
Adv. Geosci., 12, 87–93, 2007
Acknowledgements. This work was funded by the European
Commission under the frame of the “ENSEMBLES” project
(GOCE –CT-2003-505539).
Edited by: P. Alpert, H. Saaroni, and E. Heifetz
Reviewed by: two anonymous referees
www.adv-geosci.net/12/87/2007/
K. Tolika et al.: Extreme precipitation related to circulation types
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