1. Supercells: Theory Richard Rotunno
National Center for Atmospheric Research, USA
Photo by Morris Weisman

2. Ordinary Cell Review

3. Mesoscale Convective System Review
Lower Level Wind Shear: Multi-Cells
Wind Shear

4. Mesoscale Convective System Review
Mature System

5. Supercells

7. Tuscaloosa-Birmingham Storm, 27 April 2011

8. Physical Processes Depend on Buoyancy and Vertical Wind Shear
Ordinary Cells  Occur in weak shear & have a min life cycle.
Multicells (MCSs)  Long-lived group of ordinary cells organized by the vertical wind shear to produce mesoscale convective systems.
Supercells  quasi-steady, rotating, propagate to the right or left of the vertical wind shear vector

9. Hodograph

10. Vertical Wind Shear Affects Updrafts

11. Splitting Supercells, 3 May 1999

12. Supercell Across-Shear Propagation
updraft
shear vector
cell motion
updraft

13. Divergence of Momentum Equation

14. Divergence of Momentum Equation
Does not produce propagation

15. Divergence of Momentum Equation
Updraft in Shear
Splat Spin
Davies-Jones (2002 J Atmos Sci)

16. Divergence of Momentum Equation
Spin
Low pressure  Rotation

17. Horizontal vorticity associated with ambient vertical wind shear

18. Vortex Lines

19. Rotunno (1981 Mon Wea Rev)

25. Breaking of Left-Right Symmetry

27. Breaking of Left-Right Symmetry
Updraft in Shear
Splat Spin

28. 2D Updraft in Sheared Environment
Rotunno and Klemp (1982 Mon Wea Rev)

32. Supercell Thunderstorm with Tornado
Adapted from Klemp (1987, Ann. Rev. Fluid Mech.)

34. Summary of Supercells Buoyancy and Vertical Wind Shear
Ordinary Cells  Occur in weak shear & have a min life cycle.
Multicells (MCSs)  Long-lived group of ordinary cells organized by the vertical wind shear to produce mesoscale convective systems.
Supercells  quasi-steady, rotating, propagate to the right or left of the vertical wind shear vector.
Tomorrow:
Tornadoes  Sources of rotation in supercells,
tornado dynamics based on laboratory analogues