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EASTERLY WAVE STRUCTURAL EVOLUTION OVER WEST AFRICA AND THE EAST ATLANTIC

5D.6. EASTERLY WAVE STRUCTURAL EVOLUTION OVER WEST AFRICA AND THE EAST ATLANTIC . Matthew A. Janiga Department of Atmospheric and Environmental Sciences, University at Albany Albany, NY. 29 th AMS Conference on Hurricanes and Tropical Meteorology May 14, 2010 Tucson, AZ.

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EASTERLY WAVE STRUCTURAL EVOLUTION OVER WEST AFRICA AND THE EAST ATLANTIC

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  1. 5D.6 EASTERLY WAVE STRUCTURAL EVOLUTION OVER WEST AFRICA AND THE EAST ATLANTIC Matthew A. Janiga Department of Atmospheric and Environmental Sciences, University at Albany Albany, NY • 29th AMS Conference on Hurricanes and Tropical Meteorology • May 14, 2010 Tucson, AZ Supported by NSF grant ATM0507976

  2. Outline • Introduction and motivation. • Composite methodology. • Evolution of kinematic structure. • Synoptic forcing for moist convection. • Conclusions and Open Questions.

  3. 700 hPa Potential Vorticity and Zonal Wind • Reversal of mid-level PV strip allows for barotropic growth. • Strong low-level temperature gradient allows for baroclinic growth. • Large change in basic state at West Coast. PV [PVU, shaded], U [ms-1, contours] • 925 hPa Potential Temp. and Wind θ [K, shaded], Wind [ms-1, vectors]

  4. Motivation and Scientific Issues • Composite study evaluation of intense AEW case studies. • How does the AEW respond to changes in the zonal basic state? • How does the AEW influence the development of moist convection using a convective ingredients approach?

  5. 700 hPa Relative Vorticity • 2 day low-pass vorticity averaged over a 4.5° radius at each grid point. • Maxima exceeding 1 x 10-5 s-1 are tracked by finding maxima closest to extrapolated positions. • Keep those tracks that maintain westward velocity > 2 ms-1 between at least 7.5°E-22.5°E. 2004 Frances Ivan Karl Lisa • Relative Vorticity [shaded, x 10-5 s-1] • thick (thin) = composited (excluded) track • solid (dashed) = composited (excluded) portion

  6. Track Age • 64 tracks identified for compositing over the period JAS 1989-2005. • Composites produced for 5° width bins centered every 5° from 5°E to 20°W. • ECMWF Interim Reanalysis grids and Cloud User Archive Service (CLAUS) brightness temperature composited relative to the 700 hPa vortices. • Track Zonal Velocity

  7. 700 hPa Potential Vorticity and Stream Function 20°W 5°E • PV [PVU, shaded], Stream function [x 106 m2s-1, solid contours]

  8. Evolution of the Northern Vortex • 925 hPa 2-10 day filtered height and wind • 925 hPa θ and 2-10 day filtered θ 5°E 5°E W H L C H • θ [K, contours], θ’ [K, shaded] • Height’ [m, shaded], Wind’ [ms-1, vectors]

  9. Evolution of the Northern Vortex • 925 hPa 2-10 day filtered height and wind • 925 hPa θ and 2-10 day filtered θ 0° 0° W H L C H • θ [K, contours], θ’ [K, shaded] • Height’ [m, shaded], Wind’ [ms-1, vectors]

  10. Evolution of the Northern Vortex • 925 hPa 2-10 day filtered height and wind • 925 hPa θ and 2-10 day filtered θ 5°W 5°W W L H C H • θ [K, contours], θ’ [K, shaded] • Height’ [m, shaded], Wind’ [ms-1, vectors]

  11. Evolution of the Northern Vortex • 925 hPa 2-10 day filtered height and wind • 925 hPa θ and 2-10 day filtered θ 10°W 10°W W L C H H • θ [K, contours], θ’ [K, shaded] • Height’ [m, shaded], Wind’ [ms-1, vectors]

  12. Evolution of the Northern Vortex • 925 hPa 2-10 day filtered height and wind • 925 hPa θ and 2-10 day filtered θ 15°W 15°W W H C H • θ [K, contours], θ’ [K, shaded] • Height’ [m, shaded], Wind’ [ms-1, vectors]

  13. Evolution of the Northern Vortex • 925 hPa 2-10 day filtered height and wind • 925 hPa θ and 2-10 day filtered θ 20°W 20°W W H C • No more baroclinic growth • θ [K, contours], θ’ [K, shaded] • Height’ [m, shaded], Wind’ [ms-1, vectors]

  14. Convection and and Q-Vectors • 700 hPa Stream function and • % times IR cooler than 220K • 900-700 hPa Q Convergence and Q 5°E 5°E • QConv [x 10-19 Pa-1s-3, shaded], • Q [x 10-14 mPa-1s-3, vectors] • SF [x 106 m2s-1, contours], • IR [% exceedance, shaded]

  15. Convection and and Q-Vectors • 700 hPa Stream function and • % times IR cooler than 220K • 900-700 hPa Q Convergence and Q 0° 0° • QConv [x 10-19 Pa-1s-3, shaded], • Q [x 10-14 mPa-1s-3, vectors] • SF [x 106 m2s-1, contours], • IR [% exceedance, shaded]

  16. Convection and and Q-Vectors • 700 hPa Stream function and • % times IR cooler than 220K • 900-700 hPa Q Convergence and Q 5°W 5°W • QConv [x 10-19 Pa-1s-3, shaded], • Q [x 10-14 mPa-1s-3, vectors] • SF [x 106 m2s-1, contours], • IR [% exceedance, shaded]

  17. Convection and and Q-Vectors • 700 hPa Stream function and • % times IR cooler than 220K • 900-700 hPa Q Convergence and Q 10°W 10°W 10°W • QConv [x 10-19 Pa-1s-3, shaded], • Q [x 10-14 mPa-1s-3, vectors] • SF [x 106 m2s-1, contours], • IR [% exceedance, shaded]

  18. Convection and and Q-Vectors • 700 hPa Stream function and • % times IR cooler than 220K • 900-700 hPa Q Convergence and Q 15°W 15°W • QConv [x 10-19 Pa-1s-3, shaded], • Q [x 10-14 mPa-1s-3, vectors] • SF [x 106 m2s-1, contours], • IR [% exceedance, shaded]

  19. Convection and Q-Vectors • 700 hPa Stream function and • % times IR cooler than 220K • 900-700 hPa Q Convergence and Q 20°W 20°W 20°W • QConv [x 10-19 Pa-1s-3, shaded], • Q [x 10-14 mPa-1s-3, vectors] • SF [x 106 m2s-1, contours], • IR [% exceedance, shaded]

  20. CAPE and CIN • CAPE and CIN • CAPE is enhanced by mid-level northerlies and reduced in the southerlies. • CIN is reduced by low-level southerlies and enhanced in the northerlies. • In the area of greatest convection (northerlies) CIN is enhanced but still “low enough” 25-75 Jkg-1. 10°W • CAPE [J kg-1, shaded], • CIN [J kg-1, contours]

  21. Developing (East of 5°E) +θ θ -θ • Start with a disturbance on the PV strip. • Strong baroclinic and barotropic tilts. • Convection ahead of trough. Baroclinic Growth (0°-10°W) • Intensification of baroclinic wave. • Enhancement (suppression) of convection in northerlies (southerlies) increases. +θ -θ΄ θ +θ΄ -θ West Coast Transition (10-20°W) • Cessation of baroclinic growth. • Mid-level vortex becomes more important. • Convection moves into the trough. -θ΄ +θ΄ θ

  22. Open Questions / Future Work • Mesoscale Issues • How is the low-level flow modified by complex terrain such as the Air Mountains and Guinea Highlands? • What is the mesoscale structure of the northern vortex and perturbations to the ITD? • More complete diagnosis of balanced vertical motion. • What is the spectrum of AEW disturbances: structure, origins, impacts?

  23. Thanks you for your time!

  24. Frontal Wave • 925 hPa θ (K, contours), 2-10 day filtered θ (K, shaded), vector wind (kts, barbs) • average composite position (star)

  25. Perturbation Low-level Flow • 925 hPa height (m, contours) • 2-10 day filtered height (m, shaded)

  26. Q-Vectors & Q-Vector Convergence • 925-700 hPa mean-layer Q conv. (x 10-19 Pa-1 s-3, shaded), Q vector (x 10-13 Pa-1 s-3, vectors) • average composite position (star)

  27. Forcing for Vertical Motion PV in West African Shear • If the potential vorticity is steady the isentropic upglide represents the adiabatic vertical motion from a Lagrangian perspective. • In reality the shear deforms the PV lifting isentropic surfaces. θ Easterly Jet z Monsoon x With Baroclinicity θ z y Adapted from Raymond and Jiang (1990)

  28. Unfiltered and 2-10 day filtered parcel buoyancy LFC • Pb’ [K, shaded], • Pb [K, contours]

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