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Convective Storms: ASP Colloquium 2006

Convective Storms: ASP Colloquium 2006. Morris Weisman (NCAR/MMM). Archetypes: Building blocks of the observed spectrum Ordinary Cells: short lived (30-60 min), propagate with the mean wind Multicells: long-lived group of ordinary cells

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Convective Storms: ASP Colloquium 2006

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  1. Convective Storms: ASP Colloquium 2006 Morris Weisman (NCAR/MMM)

  2. Archetypes: Building blocks of the observed spectrum Ordinary Cells:short lived (30-60 min), propagate with the mean wind Multicells:long-lived group of ordinary cells Supercells:quasi-steady, rotating, propagate right or left of the vertical wind shear vector

  3. Ordinary Cell:

  4. Multicell:

  5. Multicell evolution

  6. “Backbuilding” multicell

  7. Splitting Supercells, 3 May 1999

  8. Supercell:

  9. Supercell:

  10. Supercell:

  11. Supercells propagate to right and/or left of the mean vertical wind shear vector

  12. So, how well do numerical models reproduce this observed spectrum?? Comet Web Modules: htpp://meted.ucar.edu/topics_convective.php • Convective Storm Matrix • MCS Matrix

  13. Physical processes controlling cell types: • Buoyancy processes: basic updraft/downdraft, (ordinary cells) • Gust front processes: triggering of new cells, upscale growth, (multicells) • Dynamic processes: rotating updraft, dynamic vertical pressure gradient forcing, (supercells)

  14. Buoyant Processes:

  15. 1/2 Wmax = (2 CAPE)

  16. Ordinary Cell Evolution:

  17. Physical processes controlling cell types: • Buoyancy processes: basic updraft/downdraft, (ordinary cells) • Gust front processes: triggering of new cells, upscale growth, (multicells) • Dynamic processes: rotating updraft, dynamic vertical pressure gradient forcing, (supercells)

  18. Density Current: Theoretical speed of propagation:

  19. RKW Theory Rotunno et al. (JAS, 1988) C/∆u > 1 “Optimal”condition for cold pool lifting C/∆u = 1 C/∆u < 1

  20. Physical processes controlling cell types: • Buoyancy processes: basic updraft/downdraft, (ordinary cells) • Gust front processes: triggering of new cells, upscale growth, (multicells) • Dynamic processes: rotating updraft, dynamic vertical pressure gradient forcing, (supercells)

  21. Dynamic Pressure Effects: (take divergence) diagnostic pressure eq. Dynamic pressure Buoyancy pressure Vertical momentum:

  22. Updraft growing in sheared environment:

  23. ~ Updraft growing in sheared environment:

  24. For a wind field in pure rotation: ~

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