Tropical Plumes and Their Interaction with the Extratropics (AOS 935 ...
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Tropical Plumes and Their Interaction with the Extratropics (AOS 935 ...

Tropical Plumes and theirInteraction with theExtratropicsZachary HandlosUniversity of Wisconsin - Madison

Outline:Define Tropical Plumes (TP)/CharacteristicsWhat causes TPs? TP TheoryCase studies with TPsSummaryFuture Work

Outline:Define Tropical Plumes (TP)/CharacteristicsWhat causes TPs? TP TheoryCase studies with TPsSummaryFuture Work

What is a Tropical Plume?McGuirk et al (1987):1) Continuous middle toupper-troposphericclouds2) Cross 15 deg N fromeither north or south3) ~2000 km in length4) Poleward orequatorward progression(ie: deep convection vs.frontal band)Iskenderian (1995):1) Continuous middle toupper-troposphericclouds2) Cross 20 deg N fromthe south3) Horizontal extent ~2000km4) Originates in tropics5) Includes cirrus from

Early Climatology

TP ClimatologyTPs last on average between 1-3 daysOccur most frequently in the Central and EastPacific as well as AtlanticOriented Southwest to NortheastOccur most commonly during cool season(NDJFMA)

Outline:Define Tropical Plumes (TP)/CharacteristicsWhat causes TPs? TP TheoryCase studies with TPsSummaryFuture Work

McGuirk et al (1987)ConclusionsZonal average of moisturebursts → amplification ofthermally direct circulationLooks like Hadley Cell!Anomalous westerlies →“Westerly Duct”Fig 6b,c McGuirk et al (1987)

Necessary for TP formation (Iskenderian 1995):1) Favorable planetary-scale flow configuration2) Synoptic scale transientsIskenderian (1995) fig 5c

Blackwell (2000)Hypothesis: Local cyclonic Rossby Wave Sources(RWSs) that form in local upper tropospheric (UT)convergence and subsidence regions, promote TPformationUsed barotropic shallow water modelInvestigates composite of 5 TP simulations

Figure 13a from Blackwell (2000)

Figures 13b and 13c from Blackwell (2000)

Blackwell (2000) ConclusionsUpper tropospheric TCEP convergent forcingprerequisite for TP formationAgeostrophic forcing → large advection of mass →PC/PD couplet (PD source region of TP)TP genesis sensitive to size of forcing, notmagnitude

Mecikalski and Tripoli (1998)Hypothesize that inertial instability, IAKEsignificant in TP genesisInertial Stability (example from Holton 1992):f ∂ M∂ y =f ( f − ∂ u g∂ y )with M = fy-u gIAKE = Inertial Available Kinetic Energy> 0 → stable=0 → neutral 0 for:1) Small f (Coriolis Parameter)2) Low PV3) Anticyclonic Shear4) Diabatic source of PV (v cu≠ 0)

Geopotential Height (thick black contours); PV gradient (dark fill)ITCZ convection (hashed); Equilibrium Distance for outflow (dashed)Fig9 Mecikalski and Tripoli (1998)

Summary Mecikalski andTripoli (1998)●IAKE necessary for TP development● TP genesis region: surface convergence, high θ e, andIAKE > 0●●Poleward directed outflow with easterly momentumtransport (follows max CAPE + IAKE)Midlatitude wave more responsible for TP destruction

Outline:Define Tropical Plumes (TP)/CharacteristicsWhat causes TPs? TP TheoryCase studies with TPsSummaryFuture Work

Case Studies: Knippertz andMartin (2005)Investigate three cases of cool season extremeprecipitation in Western AfricaBack trajectories with UW-NMS modelKey ingredients in all three events:Upper tropospheric trough from midlatitudesSubtropical Jet streakTPLow level trade wind surges

STJTPIsotachs at θ = 345K in white (m/s)Streamlines in black00 UTC 9 Jan 2002Fig2b Knippertz and Martin (2005)

STJmaxIsotachs at θ = 345K in white (m/s)Streamlines in black00 UTC 10 Jan 2002Fig2c Knippertz and Martin (2005)

Trade Wind SurgeStreamlines in black solid at θ = 310KPressure in black dashConvergence in shading12 UTC 7 Jan 2002Fig6a Knippertz and Martin (2005)

ω vs. QG-ω: Trough 1500 hPa geo hght (thin solid lines)ω (thick solid lines) and QG-ω (fill)00 UTC 7 Jan 2002Fig11a Knippertz and Martin (2005)

ω vs. QG-ω: Trough 2500 hPa geo hght (thin solid lines)ω (thick solid lines) and QG-ω (fill)00 UTC 9 Jan 2002Fig11b Knippertz and Martin (2005)

Summary Case Study 1Amplification of Subtropical Jetstreak due to:PV ridge amplification over Atlantic (fig 14)Trade Wind “Surge” of CAA from northwestAgeostrophic mass flux + negative PV advectionForm TP, extreme precipitation in West AfricaMix of poleward Hadley Cell and RWS theories

Case Study 2: Knippertz(2005)●●●Goal: investigate evolution of pronounced TP andSubtropical Jetstreak over North HemisphereAtlantic Ocean in March 2002Utilizes back trajectoriesAnother heavy rain event in West Africa

θ ~ 345KV ageoNegative PVadvectionPoleward TPgenerationEquatorward TPgenerationNegative PVadvectionV ageoθ ~ 300K

θ ~ 345KGray fill = high cloudsShort black arrows: jet maximaC/D = convergence/divergence centersThick black arrows: trajectoriesH/L = SLP extremaHatching = low inertial stabilityBlack solid lines = PV contoursThin arrows = streamlines of divergent (full) wind at upper (lower) level

Summary Case Study 2●●●●Northern (southern) trajectory from subtropical airfed into Hadley cell (ITCZ convective outflow)Low PV advection → gain of kinetic energyZonal ridge/trough contractionAmplification of Subtropical Jetstreak

Outline:Define Tropical Plumes (TP)/CharacteristicsWhat causes TPs? TP TheoryCase studies with TPsSummaryFuture Work

Summary:TP's are synoptic scale features that generate fromeither deep tropical convection or midlatitude frontsCase studies demonstrate importance of– Trade Wind Surge– RWS and IAKE– Negative PV advection– Subtropical Jetstreak– Hadley Cell/Thermally Direct Circulationamplificationwith respect to TP genesis

Future WorkTP latent heating/vertical motion profilesMore in-depth climatology of TP/middle latitudewave interactionRole of TPs with respect to “Superjets”

ReferencesBlackwell, K. G., 2000: Tropical plumes in a barotropic model: A product of Rossby wave generation in the tropical upper troposphere. Mon. Wea.Rev., 128, 2288–2302.Holton, J. R., 1992: An Introduction to Dynamic Meteorology. 3d ed. Academic Press, 507 pp.Iskenderian, H., 1995: A 10-year climatology of Northern Hemisphere tropical cloud plumes and their composite flow patterns. J. Climate, 8, 1630–1637.Kiladis, G. N., 1998: Observations of Rossby waves linked to convection over the eastern tropical Pacific. J. Atmos. Sci., 55, 321–339.Knippertz, Peter, 2005: Tropical–Extratropical Interactions Associated with an Atlantic Tropical Plume and Subtropical Jet Streak. Mon. Wea. Rev.,133, 2759–2776. doi:, P., and J. E. Martin, 2005: Tropical plumes and extreme precipitation in subtropical and tropical West Africa. Quart. J. Roy. Meteor. Soc.,131, 2337–2365.Knippertz, P., and J. R. Mecikalski, 2004: Re-examining tropical plumes and subtropical jetstreaks. 26 Th Conferences on Hurricanes and TropicalMeteorology. P1.36. doi:, James P., Aylmer H. Thompson, James R. Schaefer, 1988: An Eastern Pacific Tropical Plume. Mon. Wea. Rev., 116, 2505–2521. doi:;2Mcguirk, James P., Aylmer H. Thompson, Neil R. Smith, 1987: Moisture Bursts over the Tropical Pacific Ocean. Mon. Wea. Rev., 115, 787–798. doi:;2Mecikalski, J. R., and G. J. Tripoli, 1998: Inertial available kinetic energy and the dynamics of tropical plume formation. Mon. Wea. Rev., 126, 2200–2216.Tripoli, G. J., 1992: A nonhydrostatic numerical model designed to simulate scale interaction. Mon. Wea. Rev., 120, 1342–1359.

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