1 / 80

Deep Moist Convection (DMC) Part 2 – Modes of Isolated Organization

Deep Moist Convection (DMC) Part 2 – Modes of Isolated Organization. AOS 453 – Spring 2014 4/3/ 2014. Structure Of DMC Lectures This Week. Tuesday DMC (Convective/Convection) Initiation Chapter 7 in MR09 Isolated DMC Organization (Part 1) Chapter 8 in MR09 SPC Mesoanalysis Introduction

dewei
Télécharger la présentation

Deep Moist Convection (DMC) Part 2 – Modes of Isolated Organization

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Deep Moist Convection (DMC)Part 2 – Modes of Isolated Organization AOS 453 – Spring 2014 4/3/2014

  2. Structure Of DMC Lectures This Week • Tuesday • DMC (Convective/Convection) Initiation • Chapter 7 in MR09 • Isolated DMC Organization (Part 1) • Chapter 8 in MR09 • SPC Mesoanalysis Introduction • Thursday • Isolated DMC Organization (Part 2) • Chapter 8 in MR09 • Diagnostic Indices and Variables for Isolated DMC • SPC Mesoanalysis Continued

  3. Tuesday Recap • What is DMC? • Troporpheric Overturning • Parcels lifted to LFC and freely convect throughout significant portion of troposphere • How does DMC get initiated? • Need to reach LFC by either: • Mechanically Lifting Parcels • Air mass boundaries (including density current/outflow boundaries) • Orographic Lifting • Decrease pre-existing CIN to make it easier to overcome (takes a long time) • Via large scale processes • Synoptic UVM • Differential moisture advection • Surface heating • Via manipulating lapse rate (lapse rate tendency) • DMC initiation is a complex problem • Driven largely by mesoscale processes, but can be helped by synoptic scale • Need to account for entrainment. • Drier mid-troposheric air will decrease buoyancy of plumes • Vertical wind shear will increase turbulent mixing across periphery of plumes increasing entrainment and decreasing the buoyancy of plumes

  4. Tuesday Recap • Isolated DMC Organization (part 1) • The role of vertical wind shear • Vertical wind shear is vertical gradient of horizontal wind component • Often represented as wind vector difference between two layers • Can plot wind shear using a hodograph • Wind shear alone prevents initiation, but wind shear + buoyancy (CAPE) promotes organization • Bulk Richardson Number • Wind shears role in organization is twofold: 1.) Displaces precipitation away from updraft 2.) Induces a dynamic pressure gradient

  5. Structure Of DMC Lectures This Week • Tuesday • DMC (Convective/Convection) Initiation • Chapter 7 in MR09 • Isolated DMC Organization (Part 1) • Chapter 8 in MR09 • SPC Mesoanalysis Introduction • Thursday • Isolated DMC Organization (Part 2) • Chapter 8 in MR09 • Diagnostic Indices and Variables for Isolated DMC • SPC Mesoanalysis Continued

  6. Modes of Organization – And their relationship to wind shear

  7. Modes of Organization – And their relationship to wind shear

  8. Modes of Organization – And their relationship to wind shear

  9. Modes of Organization – And their relationship to wind shear

  10. Modes of Organization – And their relationship to wind shear

  11. Modes of Organization – And their relationship to wind shear

  12. Ordinary/Single Cell Convection

  13. Single-Cell Convection(Ordinary Thunderstorms) • Think one updraft • Driven by buoyancy • No organized, initiated convection from its outflow • Gust front lifting in associated (weak shear) environments is weak and shallow (no dynamic PGF!) • Usually initiated in concert with several other single cells (usually there is a field of deep convection on satellite imagery) • COLLIDING outflow (not necessarily individual outflow) is often associated with new convection initiation • Not to be confused as “organized” or “multicell” convection. We’ll see the difference soon…

  14. Ordinary/Single Cell Convection- 3 Stages In Life Cycle

  15. Ordinary/Single Cell Convection- 3 Stages In Life Cycle

  16. Ordinary/Single Cell Convection- 3 Stages In Life Cycle Ordinary/Single Cell Lifetime (τ)

  17. Ordinary/Single Cell Convection- Like The Mayfly • Can come up with approximate quantitative relationship for lifecycle time, τ • Function of depth of convection: H • Speed of updraft : wup • Speed of precip (terminal velocity): vt

  18. Ordinary/Single Cell Convection- Like The Mayfly If H = 10km If H = 10km wup = 5 m s-1 wup = 10 m s-1 vt = 5 m s-1 vt = 10 m s-1 τ ≈ 1 hrτ ≈ 30 min

  19. Multicell Thunderstorms

  20. Multicell Thunderstorms • ♬ Just a spoon-full of wind shear helps the thunderstorm live long…the thunderstorm live long…the thunderstorm live long ♬

  21. Multicell Thunderstorms • 0-6km wind shear ~ 10-20 m s-1 • So there is environmental HORIZONTAL vorticity (prove it to yourself) • NOT just one individual updraft (so last slide’s little song number was a little deceiving) • Multiple ordinary/single cells going through life cycle one after the other • Driven by cold pool propagation • Organized initiation of new cells along leading edge outflow boundary • New cells initiate along the downshear outflow boundary or gust front • Can think of collective low-level outflow (cold pool) as a thunderstorm “machine” or “conveyor belt”

  22. Why Does Wind Shear Matter? • How come the same organization doesn’t occur in ordinary/single cell convection? • Multicell convection is composed of a bunch of ordinary/single cells that have same life cycle, so why in ordinary/single cell case do we not see the same organization?

  23. First Need To Discuss Baroclinically Generated Vorticity and Vortex Rings WARM / LESS DENSE WARM / LESS DENSE COLD / DENSE WARM / LESS DENSE WARM / LESS DENSE

  24. First Need To Discuss Baroclinically Generated Vorticity and Vortex Rings WARM / LESS DENSE WARM / LESS DENSE COLD / DENSE WARM / LESS DENSE WARM / LESS DENSE

  25. First Need To Discuss Baroclinically Generated Vorticity and Vortex Rings WARM / LESS DENSE WARM / LESS DENSE COLD / DENSE WARM / LESS DENSE WARM / LESS DENSE

  26. Once It Hits The Ground…

  27. Once It Hits The Ground…

  28. It Spreads Radially Away From Center Of Maximum Pressure (directly beneath the downdraft) H

  29. It Spreads Radially Away From Center Of Maximum Pressure (directly beneath the downdraft)

  30. Who cares? • Interaction with environmental wind shear promotes enhanced vertical lifting along downshear outflow boundary! • Compared to ordinary/single cell case • Better/more-likely for lifting to lift air to LFC and initiate new DMC

  31. Who cares about the wind shear? • Taller downshear outflow boundary • More mechanical lifting • Cooperative horizontal vorticity between baroclinically generated vortex ring and environmental shear

  32. WHAT DIRECTION IS THE SHEAR VECTOR?

More Related