Circumglobal Wave Packets and Middle East precipitation: Dynamics and Predictability

1. Circumglobal Wave Packets andMiddle East precipitation: Dynamicsand Predictability Steven B. Feldstein Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania, U.S.A. Presented at Tel Aviv University, Tel Aviv, Israel on May 11, 2010

2. Middle Eastern Precipitation • Is Middle East precipitation associated with the variability of a particular teleconnection pattern?

3. Middle Eastern precipitation Data and methodology • Data: daily precipitation data averaged over 12 sites in Israel. (Ziv et al. 2006, Quart. J. Roy. Meteorl. Soc.) • Calculatecomposite300-hPa geopotential height field for dates with extreme precipitation • Daily SL (Southern Levant) indexobtained by projecting the daily 300-hPa geopotential height field onto composite pattern Feldstein and Dayan (2008)

4. Middle Eastern precipitation Composite 300-hPa geopotential height field: Southern Levant (SL) pattern H L Feldstein and Dayan (2008)

5. -6 days -4 days -2 days 0 days +2 days +4 days +5 days +7days +9 days Feldstein and Dayan (2008) 300-hPa geopotential evolution - Middle Eastern precipitation

6. Circumglobal Teleconnection Pattern EOF1 Wave packets associated with SL precip wet dry Time-averaged V over persistent event (lag -6 to lag +9 days) 300 Correlation with EOF1 =0.83 Correlation with EOF1 =-0.72

7. -6 days -4 days -2 days 0 days +2 days +4 days +5 days +7days +9 days Feldstein and Dayan (2008) Wave packet evolution & potential vorticity gradient

8. Wave Packet & Middle East precip • Wave packet first observed in the northeast Pacific. The packet travels 3/4 of the distance around the earth before decaying over the northwest Pacific • Wave packet amplifies as it passes over western Europe and the Middle East. This coincides withenhanced precipitation over the Israel. • Wave packets closely associated with east Asian monsoon (e.g., Ding and Wang 2005). • These wave packets related to the circumglobal teleconnection pattern (Branstator 2002). • Questions: What processes account for the formation and decay of circumglobal wave packets (CWPs)? • Why do the wave packets have an eastward group velocity with a near zero phase velocity? Why are the wave packets dominated by zonal wavenumber 5?

9. Numerical Model-A dynamiccore of GFDL GCM (Gordon and Stern 1982)-Driven by relaxing T toward Te with timescale of 30 days, R30 -Dissipated by surface friction and 8th order hyperdiffusion ipated by surface friction and 8th order Numerical Model • Dissipated by surface friction and 8th order hyperdiffusion • R30L10 but zonal wave number 15 Te(C,H) = Tbase + ΔTe(C,H); Te(C,H) is independent of longitude → control the baroclinic zone → control the strength of STJ : high-latitude cooling (K/day) H : tropical heating (K/day) Te(

10. Zonal wind response toC andH A A 250-hPa [u] B B 250-hPa [u] Eddy-driven jet Subtropical jet Son and Lee (2005)

11. EOFs From Idealized Climate Model Runs

12. Anomalous 300-hPa meridional wind (CS1 Run)

13. Phase Speed of Model Runs CS1-CS6 experiments yield wrong latitude for CWP, sometimes the wrong zonal wavenumber (k=4,6), and the phase speed is too large. Reduce midlatitude baroclinicity, which weakens the eddy-driven jet, and strengthens the subtropical jet. (MODIFIED CS1 RUN)

14. \ MODIFIED CS1 EOF1 & EOF2 (300-hPa meridional wind

15. Composite Methodology A Circumglobal Teleconnection Pattern (CTP) Event: 10-day, low-pass filtered, CTP amplitude must (a) exceed a one standard deviation threshold for (b) a minimum number of 15 consecutive days Motivated by the autocorrelation function for the CTP amplitude time series

16. MODIFIED CS1: 300-hPa Meridional Wind Composites Cg eastward Cp near zero K=5 k=5 CTP near 30N

17. CTP and non-CTP contributions to eddy kinetic energy during CTP event Energy fluctuation mostly associated with CTP

18. Non-CTP 300-hPa meridional wind Larger Cp 7-day-period relative to CTP

19. Anomalous 300-hPa eddy momentum flux [u’v’] Anomalous 300-hPa total flux [u’v’] Anomalous 300-hPa total flux [unp’vp’] CTP/non- CTP flux: Constructive Interference Total flux Anomalous 300-hPa total flux [up’vp’] Anomalous 300-hPa total flux [unp’vnp’] CTP flux Non-CTP flux 7-day CTP amplitude fluctuation due to interaction between CTP & non-CTP waves

20. Anomalous 850-hPa eddy heat flux [v’T’] Anomalous 300-hPa total flux [vp’Tp’] Anomalous 300-hPa total flux [vnp’Tnp’] CTP flux Non-CTP flux Anomalous 300-hPa total flux [v’T’] Total flux Slow steady growth of CTP due to CTP eddy heat fluxes

21. Anomalous E-P flux cross-sections Lag -4 days Lag -3 days Lag -2 days Lag -1 days

22. Anomalous 300-hPa zonal-mean zonal wind Anomalous heat flux maxima coincide the zonal wind maxima Anomalous zonal wind driven by the CTP/non-CTP eddy momentum flux

23. EOF1 and Composite PC1 (zonal wind) EOF1 Annular Mode Composite PC1 Eddy heat flux strongest when PC1 most negative

24. Overall Picture Interaction between CTP and non-CTP eddies drives fluctuations in zonal mean zonal wind (between the negative NAM and the climatology). When the subtropical/eddy-driven jet is strengthened and displaced equatorward (negative NAM), the CTP grows baroclinically (baroclinic instability with Cp=0, Cg>0, k=5?) When the jet is near its climatology, the baroclinic growth ceases. CTP decay coincides with an increase in the lower tropospheric zonal wind shear which suppresses subsequent baroclinic growth Barotropic governor (James and Gray 1986; Moon and Feldstein 2009)? WHAT ARE THE IMPLICATIONS FOR THE PRECIPATION IN ISRAEL?

25. Implications for precipitation in Israel? Interaction between small amplitude disturbance on the subtropical jet over North Africa and extratropical eddies over Europe intensifyies the subtropical jet and drive the subtropical jet equatorward. The above process results in a background flow which is favourable for circumglobal wave packet growth via baroclinic instability. This process can be examined with 3-D wave activity flux vectors. The decay of the circumglobal wave packet coincides with an increase in the lower tropospheric zonal wind shear .

26. 16 North Pacific sea level pressure cluster patterns

27. Tropical Convection Associated with the Madden-Julian Oscillation (MJO) Phase 1 Phase 2 • Dominant intraseaonal oscillation in the tropics • MJO cycle: 30-60 days • Shading OLR • Time between phases ~ 6 days Phase 3 Phase 4 Phase 5 Phase 6 Time between Phases ~ 6 days Phase 7 Phase 8 From Wheeler and Hendon (2004) 60۫°W 20۫°E 180۫° From Wheeler andHendon (2004)

28. Frequency of occurrence for each cluster pattern and MJO phase

29. 1-7 day Forecast of Anomalous Precipitation in Israel Phase Number =locationin Israel Lag = 1 to 7 days (Feldstein and Dayan (2008) Pattern Number =cluster pattern Color denotes anomalous precipitation determined from composites for each pattern number

30. Conclusions Precipitation in Israel strongly influenced by circumglobal wave packets Circumglobal wave packet growth triggered by the interaction between CTP and non-CTP eddies which alters the subtropical jet toward a structure that favors baroclinic instability. Circumglobal wave packet decays via the barotropic governor? Based on ideas of the CTP, and the continuum perspective, one may be able to develop a probabilistic 7- day forecast model of precipitation in Israel The forecast model can be extended to a multimodel ensemble which includes the observation features of the cluster model (a Bayesian approach). F = (w1F1 + w2F2 + w3F3)/(w1 + w2 + w3) Fi are the model forecasts B= model verification (observations) A= model forecast The weights are determined by wi = P(B|A) =P(A|B)*P(B)/P(A)