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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.
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