REGIONAL

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REGIONAL GLOBAL SCALE PATTERNS ASSOCIATED WITH
RAINFALL ANOMALIES IN ISRAEL
Baruch ZivUri DayanChaggi Rot Yohanan Kushnir
Yehouda Enzel Ziv et al (2006) Regional and
Global Atmospheric Patterns Governing Rainfall in
the Southern Levant, Int. J. Clim., 26
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MOTIVATION

• The sensitivity of the region to water shortage

• The linkage of the rainfall to single synoptic
  system facilitates the analysis

Enzel et al. (2003) showed that the Dead-Sea
level responds to Israel rainfall. Therefore

• If tele-connection is found between Israel
  rainfall and the conditions in other regions, the
  Dead Sea level can serve as proxy for past
  climate variations for these regions

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The study area and the rain stations used
12 stations with continuous record were
selected 2/3 of the annual rainfall is obtained
in DJF Therefore, each season is represented by
DJF rainfall Study period 1950-2002
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Most of the rainfall results from Cyprus Lows
Their signature appears in the Long-Term Mean SLP
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Cyprus Low is most pronounced in composite maps
for days with 50 mm in Israel
The low is accompanied by pronounced upper-trough
Dates
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Seasonal Signature composite SLP maps
10 wettest years Cyprus Low dominates
10 driest years Cyprus Low is hardly discerned
Difference(wettest-driest)
Main Feature WE-EM dipole
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Composite 500-hPa gph
10 wettest years Main trough at East-Med
10 driest years Main trough at Central Med
Difference(wettest-driest)
Main Feature WE-EM dipole
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Correlation maps of Israel rainfall (DJF) with
Main Feature WE-EM dipole!
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The correlation patterns resemble the
Mediterranean Oscillation (Dunkeloh and
Jacobeit, 2003)
Associated rainfall anomaly negative over the
MG, except for the SE Med
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Correlation with known global circulation
KutielBenaroch
Price et al.
Ben Gai, Eshel
The E coast of Meds rainfall is not determined
by NAO
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Correlation with 925 hPa temperature
Prominent remote feature Pacific Warm Pool
-0.6
-0.4
-0.4
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Global 50 hPa zonal-wind correlation with Israel
DJF rainfall
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The stratospheric anomalies at both sub-polar
regions are prominent
Height-latitude correlation cross-section of
zonally averaged zonal wind with Israel DJF
rainfall
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• Correlations farther from Israel are weaker, but
  remote distinct patterns are discerned
• North and South stratospheric polar jets
• SST over the tropical subtropical W Pacific

Suspecting that direct relationships between them
and Israel exist, we searched for an indirect,
through the W-Europe-E-Med dipole
We constructed a time series for each factor and
derived 500 hPa gph correlation map, searching
for a fingerprint of the WE-EM dipole
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In all of them the WE-EM dipole appears
500 hPa gph Correlation maps for DJF with
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Explanations for the indirect tele-connections
N Polar Jet Graf et al. (1994) found this
relationship, suggested that this wave is
enhanced by the increase in stratospheric
reflectivity when the jet intensifies
Indo-Pacific Warm Pool Increase in SST at certain
region along the ITCZ enhances the Hadley
Circulation there, subsequently the subtropical
ridge downwind, such as over W Europe, with the
associated enhanced EM trough
S Polar Jet No explanation exists
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500 hPa gph correlation maps for other global
circulations previously suggested to affect
Israel rainfall
In both the WE-EM dipole is insignificant
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Correlation between global-scale systems and the
EM upper-trough
EM troughIsrael rainfall R 0.74
All factors - EM trough R 0.69
EM Upper trough
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CONCLUSIONS
The EM upper-trough explains gt 0.54 of the DJF
rainfall variation in the N half of Israel
It is activated by 3 external factors N Polar
jet S Polar jet Indo-Pacific Warm Pool
No significant tele-connection exists between
Israel rainfall and NAO or ENSO, direct or
indirect
The EM trough is combined with ridge over W
Europe, hence Cold wet winters in south Levant
coincide with warm dry winters in W Europe and
vice versa
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SPECULATION
Since the Dead-Sea level reflects the rainfall
variations in Israel, the anti-correlation
between Israel W-Europe in the winter suggests
that
Under similar climatic regime periods of rise in
the Dead-Sea level indicates retreat of icebergs
in Western Europe and S-West Scandinavia
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250 hPa speed of composite wind
The Atlantic African jets are more detached in
wet years
10 wettest years
10 driest years
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Stratospheric Polar Jet (50 mb)
10 Dry Years
Normal
10 Wet Years
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Correlation maps with Spec. Humidity
400
mb 600 mb 850 mb

• Fig. New Tropical-Subtropical moisture transport
• Enhanced Hadely circulation over W-africa
  positive, over E-Africa negative
• Wave No. 2 seems to play a role

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Another global correlation map with Israel DJF
rainfall - 250 hPa meridional wind
Note the dominance of wave 5 in NH and 4 in SH
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a b
Fig. 4 Latitudinal-height cross-section of
zonally averaged geopotential height anomaly over
80S-80N 1000-50 hPa domain for a) the 10
driest seasons and b) the 10 wettest seasons
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Height-latitude cross-section of the correlation
between the zonal average of geopotential height
and rainfall in Israel
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Correlation with jets 150 mb North STJ
50 mb
S- PJ