XXIX OSTIV congress, Lüsse, Germany, 6-13 August 2008

The role of blocking in the structure The role of blocking in the structure of Mediterranean cyclones which of Mediterranean cyclones which

affect Middleaffect Middle--East and IranEast and Iran

L. Shabrang, F. Ahmadi Givi, P. L. Shabrang, F. Ahmadi Givi, P. IrannejadIrannejad

Institute of Geophysics, University of Tehran, Institute of Geophysics, University of Tehran, IranIran

::OUTLINEOUTLINE

introductionintroduction

DefinitionsDefinitions

MethodologyMethodology

Region of InterestRegion of Interest

Events of Interest and their StructuresEvents of Interest and their Structures

Analysis of Physical and Dynamical Analysis of Physical and Dynamical

Model OutputsModel Outputs

ConclusionConclusion

BLOCKINGBLOCKINGAtmospheric Blocking(Atmospheric Blocking(RexRex, , 19501950), at ), at

500 mb:500 mb:To Sprit the Atmospheric Flow into To Sprit the Atmospheric Flow into two two BranchesBranchesCarrying the Considerable air Mass in Carrying the Considerable air Mass in Each BranchesEach BranchesTo Spread the Jet in at least To Spread the Jet in at least 45 degrees 45 degrees in the zonal Directionin the zonal DirectionConverting the Converting the zonal Flow zonal Flow to to Meridional Meridional FlowFlowAt least At least 10 Days 10 Days period period

Main Locations:Main Locations:Atlantic OceanAtlantic OceanPacific OceanPacific OceanEuropeEurope

Period Time:Period Time:One Week to One monthOne Week to One month

BlockingBlocking

Types of Blocking Events:Types of Blocking Events:Dipole BlockDipole Block

Types of Blocking Events:Types of Blocking Events:Omega BlockOmega Block

Types of Blocking Events:Types of Blocking Events:Stationary, highStationary, high--amplitude amplitude

ridge blockridge block

CyclonesCyclonesCyclones are associated with Cyclones are associated with lowlow

pressure centerspressure centers

The related convergence produces uplift The related convergence produces uplift in the center and divergence aloftin the center and divergence aloft

As we know, divergence isAs we know, divergence is

associated with high pressures,associated with high pressures,

i.e., we find i.e., we find high pressures alofthigh pressures aloft

Remember uplift also producesRemember uplift also produces

adiabatic coolingadiabatic cooling

Low pressures are typicallyLow pressures are typically

associated with weather rangingassociated with weather ranging

from from mild cloud cover to heavymild cloud cover to heavy

precipitationprecipitation

Divergence

Convergence

L

H

MethodologyMethodology

Aَnalysis of surface and Upper Level Analysis of surface and Upper Level synoptic maps During the Wintertime synoptic maps During the Wintertime from 2004 to 2007from 2004 to 2007

Detecting the Region of InterestDetecting the Region of InterestSelecting Two Cyclonic Systems (One Selecting Two Cyclonic Systems (One

in the presence and another in the in the presence and another in the Absence of blocking)Absence of blocking)

Running MM5 Model, Using GFS DataRunning MM5 Model, Using GFS DataAnalysis of Physical and Dynamical Analysis of Physical and Dynamical

MM5 OutputsMM5 Outputs

Region of Interest: 30 WRegion of Interest: 30 W-- 90 E, 15 N90 E, 15 N-- 65N65N

o

o

Iَn the Presence of Blocking: Formation on 26 January 2006, Period: 11 days

In the Absence of Blocking: Formation on 8 February 2007 , Period: 6 days

Path of Movement of the Blocked

Cyclone

Path of Movement of the

nonBlocked Cyclone

Analysis of Synoptic Surface mapsAnalysis of Synoptic Surface maps

hPa1000

Mean Sea Level synoptic map at the

Mature Stage of blocked- cyclone

Mean Sea Level synoptic map at the

Mature Stage of nonblocked- cyclone

hPa1005

Analysis of Geopotentail synoptic mapsAnalysis of Geopotentail synoptic maps

Geopotentail synoptic map at 500 mb at the Mature Stage of

nonblocked- cyclone

dm552

Geopotentail synoptic map at 500 mb at the Mature

Stage of blocked- cyclone

dm544

Generation of Easterlies…

Zonal Component of Horizontal wind Speed (u)Zonal Component of Horizontal wind Speed (u)

“u” Field at 300 mb at the Mature Stage of the

Blocked Cyclone

130 −− ms

“u” Field at 300 mb at the Mature Stage of the non-Blocked Cyclone

0

More Intense Southerlies and Temperature Advection

Meridional Component of the horizontal Wind Speed (v)Meridional Component of the horizontal Wind Speed (v)

110 −ms

“v” Field at 300 mb at the Mature Stage of the Blocked Cyclone

130 −ms “v” Field at 300 mb at the Mature Stage of the non-Blocked Cyclone

110 −ms

)(.yTv

xTuTV

∂∂

+∂∂

−=∇−r

More Intense Relative Vorticity

Vertical Component of the Relative VorticityVertical Component of the Relative Vorticity

Vorticity Field at 500 mb at the Mature

Stage of the Blocked Cyclone

5105.1 −×1−s Vorticity Field at 500

mb at the Mature Stage of the Blocked

Cyclone1−s

5101 −×

)(yu

xv

∂∂

−∂∂

=ξ

Potential Vorticity and Potential TemperaturePotential Vorticity and Potential Temperature

Cross-section of “th” at the

Mature Stage of the Blocked

Cyclone

Cross-section of “th” at the

Mature Stage of the nonBlocked

Cyclone

Cross-section of “PV” at the

Mature Stage of the Blocked

Cyclone

6.5pvu

Cross-section of “PV” at the

Mature Stage of the non-Blocked

Cyclone

5.5pvu

ZPV

∂∂

=θξ

ρ1

More Intense Vertical Motion and Relative Humidity

Cross-section of “RH” at the Mature Stage

of the Blocked Cyclone

Cross-section of “RH” at the

Mature Stage of the non-Blocked

Cyclone

Cross-section of “w”at the Mature Stage

of the Blocked Cyclone 0.1 1−ms

Cross-section of “w” at the

Mature Stage of the non-Blocked

Cyclone

0.021−ms

∝w Temperature Advection

Vertical Motion and Relative HumidityVertical Motion and Relative Humidity

No Difference in the Temperature Fields of Cyclones in This Case Study

Temperature Field at 850 mb at the Mature Stage of the Blocked

Cyclone

278 k

Temperature Field at 500 mb at the Mature

Stage of the non-Blocked Cyclone

278 k

TemperatureTemperature

ConclusionsConclusionsThe Role of Blocking on Cyclogenesis:The Role of Blocking on Cyclogenesis:

Longer CyclonesLonger CyclonesMigration in the Lower LatitudesMigration in the Lower LatitudesGeneration Easterlies and More Intense Generation Easterlies and More Intense

SoutherliesSoutherliesIncrescent in Relative VorticityIncrescent in Relative VorticityMore Intense Warm Temperature Advection, More Intense Warm Temperature Advection,

Static Stability and PVStatic Stability and PVIncrescent in Vertical Motion and relative Increscent in Vertical Motion and relative

HumidityHumidityNo difference in Temperature FieldsNo difference in Temperature Fields

HISTORY OF STUDIESHISTORY OF STUDIESRex(1950):Rex(1950): Blocking action in the middle troposphere and its effect upon rBlocking action in the middle troposphere and its effect upon regional egional

climateclimate. .

Petterssen(1956):Petterssen(1956): Weather Analysis and Forecasting.Weather Analysis and Forecasting.

Trigo et al. (1999Trigo et al. (1999)):: Objective climatology of cyclones in the Mediterranean regionObjective climatology of cyclones in the Mediterranean region

Maheraset al. (2001Maheraset al. (2001 ) ):: A 4 years objective climatology of surface cyclones in the A 4 years objective climatology of surface cyclones in the

Mediterranean region (Spatial and temporal distribution).Mediterranean region (Spatial and temporal distribution).

Barriopedro et al. (2006):Barriopedro et al. (2006): Climatology of Northern Hemisphere blocking.Climatology of Northern Hemisphere blocking.

Nasr Esfahani (2003):Nasr Esfahani (2003): A 1 year Analysis of cyclogenesis over eastern Mediterranean A 1 year Analysis of cyclogenesis over eastern Mediterranean and its effects on Middle east and Iran weather.and its effects on Middle east and Iran weather.

Ahmadi Givi et al. (1385):Ahmadi Givi et al. (1385): Climatology of Blocking (potential Vorticity Thinking).Climatology of Blocking (potential Vorticity Thinking).

Colucci (1986):Colucci (1986): Comparative Diagnostic of Blocking Versus Nonblocking PlanetaryComparative Diagnostic of Blocking Versus Nonblocking Planetary--Scale circulation changes during SynopticScale circulation changes during Synoptic--Scale Cyclogenesis.Scale Cyclogenesis.

Colucci and Alberta (1996):Colucci and Alberta (1996): PlanetaryPlanetary--Scale Climatology of Explosive Cyclogenesis Scale Climatology of Explosive Cyclogenesis and Blocking. and Blocking.