ASurveyofSynop-cWavesoverWestAfrica

Yuan-MingCheng,ChrisThorncro<andGeorgeKiladis

•  Whatareeasterlywaves?–  synop&cdisturbancespropaga&ngwestwardintheITCZ–  responsibleforday-to-dayweathervariabilityinthetropics–  alsoknownasthetropicaldepression(TD)-typewaves–  e.g.,Africaneasterlywaves(AEWs)

Introduc-on

Kiladis et al. (2006)

105 m2 s-1; m s-1;+/- 6 W s-2

Frank and Roundy (2006)

TD-TypeMRG

2

!

Mo-va-on

WeknowliFleaboutstructuralvariabilityofthesynop&cwaves 3

•  EmpiricalOrthogonalFunc&ons(EOFs)– highlightthedominantwavestructure

•  3kindsofEOFs•  TbEOF2-6-day-westward-filteredbrightnesstemperature(Tb)

•  v700EOF2-6-day-filteredmeridionalwindat700hPa

•  v200EOF2-6-day-filteredmeridionalwindat200hPa

Methods

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TbEOF(commonlyrecognizedAEW)

2X105 m2 s-1; ms-1; 0.5 K

•  Convec&onandcircula&oncenteredandconfinedaroundtheITCZ•  AtypicalAEWevolu&onstronglycoupledwithconvec&on

Tb EOF-PC1; 700 hPa

5

A

B

MoroccanVortexMixedRossbyGravitywave(MRG)

AB

2X105 m2 s-1; ms-1; 0.5 K v700 EOF-PC1; 700 hPa

•  Broadmeridionalextent

v700EOF(MRG-AEWHybrid)

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TbEOF v700EOF

•  ThetwokindsofEOFcapturedifferentbehaviorsofAEWs•  Thermodynamicalvs.dynamicalemphasis

-TbEOF:centeredandconfinedaroundtheITCZ-v700EOF:interac&onwiththeequatorialwaveandsubtropics:A-MoroccanVortexandB-MRG

A

B

2X105 m2 s-1; ms-1; 0.5 K

7

v200EOF(upper-levelMRG)

Thecircula&onshowsacoherentMRGstructureinbothconvec&veandkinema&cfields•  centeredat5S–meteorologicalequator(PV=0)•  locallyspinningupoverAfrica•  interac&ngwithmid-la&tudeRossbywavesintheSouthernHemisphere

2X105 m2 s-1; ms-1; 0.5 K v200 EOF-PC1; 200 hPa

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•  TheEOFanalysisdepictsmarkedstructuralvariabilityofsynop&cwavesoverWestAfrica

•  CommonlyrecognizedAEW(TbEOF)–  stronglyconvec&vely-coupledcircula&on,centeredandconfinedaround

theITCZ•  AEW-MRGhybrid(v700EOF)

–  broadmeridionalextentofthewave-interac&ngwithMoroccanvortexandMRG

•  Upper-levelMRG(v200EOF)–  ahintofmid-lowlevelAEWstructure–  stronginterac&onwithmid-la&tudeRossbywavesintheSouthern

Hemisphere•  TheseresultshighlightsthedifferentbehaviorsofAEWand

coexistenceofAEW-MRGstructureoverWestAfrica

Summary

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