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REGIONAL & GLOBAL SCALE PATTERNS ASSOCIATED WITH RAINFALL ANOMALIES IN ISRAEL Baruch Ziv Uri Dayan Chaggi Rot Yohanan Kushnir Yehouda Enzel Ziv et al (2006)

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Presentation on theme: "REGIONAL & GLOBAL SCALE PATTERNS ASSOCIATED WITH RAINFALL ANOMALIES IN ISRAEL Baruch Ziv Uri Dayan Chaggi Rot Yohanan Kushnir Yehouda Enzel Ziv et al (2006)"— Presentation transcript:

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

2 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

3 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 The study area and the rain stations used Average annual rainfall Mediterranean Sea Dead Sea

4 Most of the rainfall results from Cyprus Lows Their signature appears in the Long-Term Mean SLP

5 Cyprus Low is most pronounced in composite maps for days with ~50 mm in Israel Dates 500 hPa SLP The low is accompanied by pronounced upper-trough

6 Difference (wettest-driest) Main Feature: WE-EM dipole Seasonal Signature: composite SLP maps 10 wettest years – Cyprus Low dominates 10 driest years – Cyprus Low is hardly discerned

7 Composite 500-hPa gph Difference (wettest-driest) Main Feature: WE-EM dipole 10 wettest years – Main trough at East-Med 10 driest years – Main trough at Central Med

8 Correlation maps of Israel rainfall (DJF) with: 700 mb temp 500 mb gph SLP Main Feature : WE-EM dipole!

9 The correlation patterns resemble the Mediterranean Oscillation ( Dunkeloh and Jacobeit, 2003 ) Similar dipole in the upper-level The SLP resembles the AO Associated rainfall anomaly: negative over the MG, except for the SE Med

10 Correlation with known global circulation LevelPeriodLocation of DipoleName Corr 700 hPa1950- 2002 England and – Caspian Sea E Atlantic/ W Russia (EA-WR) 0.51 500 hPa1958- 1998 North Sea - N. Caspian Sea North Caspian Pattern (NCP) 0.40 700 hPa1950- 2002 Europe - NE ChinaPolar/ Eurasian 0.30 SST1950- 2002 Tropical PacificENSO 0.29 700 hPa1979- 2002 Gulf of Alaska- Hudson Bay Tropical North Hemisphere -0.24 Sea Level1950- 2002 Azoreans-IcelandNorth Atlantic Oscillation (NAO) 0.09 Kutiel&BenarochPrice et al.Ben Gai, Eshel The E coast of Meds rainfall is not determined by NAO

11 -0.4 -0.6 Correlation with 925 hPa temperature Prominent remote feature: Pacific Warm Pool

12 Global 50 hPa zonal-wind correlation with Israel DJF rainfall Band-anomalies along polar stratospheric jets in both N & S hemispheres

13 Height-latitude correlation cross-section of zonally averaged zonal wind with Israel DJF rainfall The stratospheric anomalies at both sub-polar regions are prominent

14 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

15 500 hPa gph Correlation maps for DJF with In all of them the WE-EM dipole appears S Polar Jet Pacific Warm Pool N Polar Jet

16 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

17 Nino 1+2 NAO In both the WE- EM dipole is insignificant 500 hPa gph correlation maps for other global circulations previously suggested to affect Israel rainfall:

18 Correlation between global-scale systems and the EM upper-trough EM Upper trough North Polar Jet R=-0.50 South Polar Jet R=-0.38 Pacific Warm Pool R=-0.38 R=0.41 R=0.66R=0.61 All factors - EM trough R = 0.69 EM trough–Israel rainfall R = 0.74

19 CONCLUSIONS The EM upper-trough explains > 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 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 No significant tele-connection exists between Israel rainfall and NAO or ENSO, direct or indirect

20 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

21 10 wettest years 10 driest years 250 hPa speed of composite wind The Atlantic & African jets are more detached in wet years

22 Stratospheric Polar Jet (50 mb) Normal 10 Dry Years 10 Wet Years

23 Fig. New: Tropical-Subtropical moisture transport 1.E nhanced Hadely circulation over W-africa – positive, over E-Africa – negative 2. Wave No. 2 seems to play a role 400 mb 600 mb 850 mb Correlation maps with Spec. Humidity

24 Another global correlation map with Israel DJF rainfall - 250 hPa meridional wind Note the dominance of wave 5 in NH and 4 in SH

25 Fig. 4: Latitudinal-height cross-section of zonally averaged geopotential height anomaly over 80°S-80 N – 1000-50 hPa domain for: a) the 10 driest seasons and b) the 10 wettest seasons abab

26 Height-latitude cross-section of the correlation between the zonal average of geopotential height and rainfall in Israel

27 Correlation with jets 150 mb North STJ 50 mb S- PJ

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