Symmetric, 2-D Squall Line

1. Symmetric, 2-D Squall Line

2. Johnson and Hamilton (1988)

3. Houze et al. (BAMS, 1989)

4. Basic Equations: 2D Squall Line ⁄ *Also, no vortex tilting or stretching -- Or, more simply, consider the 2D horizontal vorticity equation: where

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

7. 2D Convective System Evolution: C/∆u << 1 C/∆u ~ 1 C/∆u > 1 Weak shear, strong cold pool: rapid evolution Strong shear, weak cold pool: slow evolution

41. 2D Convective System Evolution: C/∆u << 1 C/∆u ~ 1 C/∆u > 1 Weak shear, strong cold pool: rapid evolution Strong shear, weak cold pool: slow evolution

42. Mature System: C/∆u > 1

43. Lafore and Moncrieff (1989)

45. Rear-inflow jet intensity increases with increasing CAPE!

47. 2D Convective System Evolution: C/∆u << 1 C/∆u ~ 1 C/∆u > 1 Weak shear, strong cold pool: rapid evolution Strong shear, weak cold pool: slow evolution

48. RKW Theory: all other things being equal (e.g., same external forcing), squall line strength/longevity is “optimized” when the circulation associated with the system-generated cold pool remains “in balance” with the circulation associated with the low-level vertical wind shear. Issue: Squall-lines are observed to be strong and long-lived for a wider range of environments than suggested by the models (e.g., weaker shears, deeper shears,….). So, what is the utility of RKW theory?

49. Thorpe et al. (1982) (2D) Squall Lines steadiest when shear confined to low-levels!

50. Fovell (1988) (2D)