Circumglobal wave packets and middle east precipitation dynamics and predictability
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Circumglobal Wave Packets and Middle East precipitation: Dynamics and 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.

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Circumglobal wave packets and middle east precipitation dynamics and predictability l.jpg
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


Slide2 l.jpg

Middle Eastern Precipitation

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


Slide3 l.jpg

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)


Slide4 l.jpg

Middle Eastern precipitation

Composite 300-hPa geopotential height field:

Southern Levant (SL) pattern

H

L

Feldstein and Dayan (2008)


Slide5 l.jpg

-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


Slide6 l.jpg

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


Slide7 l.jpg

-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


Slide8 l.jpg

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?


Slide9 l.jpg

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(


Slide10 l.jpg

Zonal wind response toC andH

A

A

250-hPa [u]

B

B

250-hPa [u]

Eddy-driven jet

Subtropical jet

Son and Lee (2005)




Phase speed of model runs l.jpg
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)


Slide14 l.jpg
\

MODIFIED CS1 EOF1 & EOF2 (300-hPa meridional wind


Composite methodology l.jpg
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


Slide16 l.jpg

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 l.jpg
CTP and non-CTP contributions to eddy kinetic energy during CTP event

Energy fluctuation mostly associated with CTP


Slide18 l.jpg

Non-CTP 300-hPa meridional wind CTP event

Larger Cp

7-day-period

relative to

CTP


Slide19 l.jpg

Anomalous 300-hPa eddy momentum flux [u’v’] CTP event

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


Slide20 l.jpg

Anomalous 850-hPa eddy heat flux [v’T’] CTP event

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


Anomalous e p flux cross sections l.jpg
Anomalous E-P flux cross-sections CTP event

Lag -4 days

Lag -3 days

Lag -2 days

Lag -1 days


Anomalous 300 hpa zonal mean zonal wind l.jpg
Anomalous 300-hPa zonal-mean zonal wind CTP event

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 l.jpg
EOF1 and Composite PC1 (zonal wind) CTP event

EOF1 Annular Mode

Composite PC1

Eddy heat flux strongest when PC1 most negative


Overall picture l.jpg
Overall Picture CTP event

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?


Implications for precipitation in israel l.jpg
Implications for precipitation in Israel? CTP event

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 .



Tropical convection associated with the madden julian oscillation mjo l.jpg
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)



1 7 day forecast of anomalous precipitation in israel l.jpg
1-7 day Forecast of Anomalous Precipitation in Israel phase

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


Conclusions l.jpg
Conclusions phase

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)


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