Download - MJO Symposium Kelvin Waves and Tropical Cyclones in a ... Kelvin... · 4th MJO Symposium 10–14 January 2016, New Orleans, LA [email protected] pdf of this poster NASA PMM Grant

4th MJOSymposium10–14January2016,NewOrleans,LA

[email protected] pdf ofthisposter

NASAPMMGrantNNX13AH47GPoster#852

• ConvectivelycoupledKelvinwaves• Eastwardpropagationat10–20ms−1• 3–10dayperiod,2000–4000kmwavelength

• KelvinWavesmodulatekeyfactorsforcyclogenesis• Low-levelvorticity,convection,verticalwindshear• Butnetimpactontropicalcycloneactivityisuncertain

• Tropicalcyclonesinhibitedfor3daysbeforeKelvinwavepassageandenhanced3daysafter

• Circulationseemstobethedominantfactor• Low-levelvorticity• Upper-leveloutflow

• KelvinwavesfrequentlyinteractwiththeMJOandeasterlywavesduringgenesis

KelvinWavesandTropicalCyclones

SchematicofKelvinWavecompositesfromallbasins.Adaptedfrom:Schreck,C.J.,2015:Kelvinwavesandtropicalcyclogenesis:Aglobalsurvey.Mon.Wea.Rev.,143,3996–4011, doi:10.1175/MWR-D-15-0111.

PouchPhaseSpeed

• EasterlywavephasespeedisestimatedfromcompositeHovmöllersoftropicalcyclogenesiswithKelvinwaves

• ThisphasespeedissubtractedfromthecompositezonalwindstoproduceLagrangianstreamlines

CompositeHovmöllersof(a)Rainfall,(b)850-hPazonalwind,and(c)200-hPazonalwindanomalies fortropicalcyclonesthatformed3.5daysafterKelvinwavepassage.Magentalinesdenotetheestimatedphasespeedof4.5ms−1.

Schematicofaneasterlywave’spouch.AdaptedfromWangetal.2010,J.Atmos.Sci.,67,1711–1729.

Summary

EquatorialwesterliesfromKelvinwaveshelpclosethepouch’scirculation• Kelvinwavesaretiltedwestwardwith

height• CyclogenesisoccurswhentheKelvinwave

westerlyanomaliesreachmid-levels(600hPa)

• Thistiltmayexplainthe0–3daylagbetweenKelvinwavepassageandgenesis.

KelvinWesterlies

Compositecross-sections ofeasterlywave-relativezonalwindsRedandbluecontoursidentifyarethewesterlyandeasterlyphasesoftheKelvinwaves.

PouchComposites

Compositemapsofeasterlywave-relativezonalwindsat850-hPa(left)and600-hPa(right).GreenandorangecontoursidentifywetanddryenvelopesoftheKelvinwaves,respectively. Similarly theredandbluearethewesterlyandeasterlyphases.

• Convectionandstorm-relativelow-levelwesterliesintersecteasterlywave2–3daysbeforegenesis

• WestwardtiltofKelvinwavesmeanthatitsmidlevelwesterlies intersecttheeasterlywaveatgenesis

• Easterlywave’swesterlies arestrongeranddeeperfromtheiroverlapwiththeKelvinwave

KelvinWavesandTropicalCyclonesinaLagrangian FrameworkCarlJ.Schreck III

NorthCarolinaInstituteforClimateStudies(NCICS),NorthCarolinaStateUniversity