Circulation Types and Their Influence on the Interannual Variability
233
characterized by much lower than the average precipitation amounts (-50%). Only
the regions of south east Aegean Sea and Thessaly reveal precipitation amounts
between 70 and 80% of the average.
The spatial distribution of the precipitation amounts for the wettest year (19621963, Fig. 22) reveals a very important enhancement of precipitation over Greece
with a minimum over the meridional Aegean Sea (Cyclades -110%) and two
maxima, the first over
Crete (-185%) and the
second over Ionian
Islands (-185%).
In order to analyse
the seasonal evolution
of extreme drought
episode, the mean
values of precipitation
for every month of
hydrological year and
the corresponding
values of the driest
episode 1989-1990 are
compared in Fig. 23 a
and b. This extreme
case presents a very
pronounced dry winter
period with close to
normal precipitation
during autumn, late
spring and summer. An
analysis of the
corresponding values of
frequency of C, C sw ,
C NW and C w types
circulation may be
observed in the same
figure (23 b). The
agreement between the
corresponding figures
(monthly precipitation
and
monthly
frequencies
of
circulation types) is
obvious and in this case
of extreme event shows
the decisive role that is
41
20
21
22
23
24
2S
26
27
28
Fig. 21. Geographical distribution of percentage of precipitation
amount of the driest year 1989/90 in relation to the annual mean for
the period 1958-1997
played by the identified 35 1--,------r-----,--,.."---=-r--=-r----;r----1
links
between
20
21
22
23
24
2S
26
27
28
anomalies monthly
Fig. 22. Same as Fig. 21 but for the wettest year 1962/63