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
4
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)
6
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
8
• 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
9