MJO Symposium Kelvin Waves and Tropical Cyclones in a ... Kelvin... · 4th MJO Symposium 10–14...
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4 th MJO Symposium 10–14 January 2016, New Orleans, LA [email protected] pdf of this poster NASA PMM Grant NNX13AH47G Poster #852 • Convectively coupled Kelvin waves • Eastward propagation at 10–20 m s −1 • 3–10 day period, 2000–4000 km wavelength • Kelvin Waves modulate key factors for cyclogenesis • Low-level vorticity, convection, vertical wind shear • But net impact on tropical cyclone activity is uncertain • Tropical cyclones inhibited for 3 days before Kelvin wave passage and enhanced 3 days after • Circulation seems to be the dominant factor • Low-level vorticity • Upper-level outflow • Kelvin waves frequently interact with the MJO and easterly waves during genesis Kelvin Waves and Tropical Cyclones Schematic of Kelvin Wave composites from all basins. Adapted from: Schreck, C. J., 2015: Kelvin waves and tropical cyclogenesis: A global survey. Mon. Wea. Rev., 143, 3996–4011, doi:10.1175/MWR-D-15-0111. Pouch Phase Speed • Easterly wave phase speed is estimated from composite Hovmöllers of tropical cyclogenesis with Kelvin waves • This phase speed is subtracted from the composite zonal winds to produce Lagrangian streamlines Composite Hovmöllers of (a) Rainfall, (b) 850-hPa zonal wind, and (c) 200-hPa zonal wind anomalies for tropical cyclones that formed 3.5 days after Kelvin wave passage. Magenta lines denote the estimated phase speed of 4.5 m s −1 . Schematic of an easterly wave’s pouch. Adapted from Wang et al. 2010, J. Atmos. Sci., 67, 1711–1729. Summary Equatorial westerlies from Kelvin waves help close the pouch’s circulation • Kelvin waves are tilted westward with height • Cyclogenesis occurs when the Kelvin wave westerly anomalies reach mid-levels (600 hPa) • This tilt may explain the 0–3 day lag between Kelvin wave passage and genesis. Kelvin Westerlies Composite cross-sections of easterly wave-relative zonal winds Red and blue contours identify are the westerly and easterly phases of the Kelvin waves. Pouch Composites Composite maps of easterly wave-relative zonal winds at 850-hPa (left) and 600-hPa (right). Green and orange contours identify wet and dry envelopes of the Kelvin waves, respectively. Similarly the red and blue are the westerly and easterly phases. • Convection and storm-relative low-level westerlies intersect easterly wave 2–3 days before genesis • Westward tilt of Kelvin waves mean that its midlevel westerlies intersect the easterly wave at genesis • Easterly wave’s westerlies are stronger and deeper from their overlap with the Kelvin wave Kelvin Waves and Tropical Cyclones in a Lagrangian Framework Carl J. Schreck III North Carolina Institute for Climate Studies (NCICS), North Carolina State University
Transcript of MJO Symposium Kelvin Waves and Tropical Cyclones in a ... Kelvin... · 4th MJO Symposium 10–14...
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
