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 Circumglobal Wave Packets and Middle East precipitation: Dynamics and Predictability

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

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

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

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

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

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

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 with enhanced 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?

Numerical Model  R30L10 but zonal wave number 15 Te(Te( T e (C,H) = T base + ΔT e (C,H); T e (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)  Dissipated by surface friction and 8 th order hyperdiffusion Numerical Model - A dynamic core of GFDL GCM (Gordon and Stern 1982) - Driven by relaxing T toward T e with timescale of 30 days, R30 - Dissipated by surface friction and 8 th order hyperdiffusion ipated by surface friction and 8 th order

Zonal wind response to C and H BB 250-hPa [u] AA Subtropical jet Eddy-driven jet Son and Lee (2005)

EOFs From Idealized Climate Model Runs

Anomalous 300-hPa meridional wind (CS1 Run)

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)

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

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

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

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

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

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

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

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

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

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

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)? Overall Picture WHAT ARE THE IMPLICATIONS FOR THE PRECIPATION 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. Implications for precipitation in Israel?

16 North Pacific sea level pressure cluster patterns

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

Frequency of occurrence for each cluster pattern and MJO phase

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

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 = (w 1 F 1 + w 2 F 2 + w 3 F 3 )/(w 1 + w 2 + w 3 ) FiFi are the model forecasts The weights are determined by w i = P(B|A) =P(A|B)*P(B)/P(A) B= model verification (observations) A= model forecast