Streamwise versus Crosswise Vorticity non-helical cos90 = 0 =0 FRISBEE! crosswise vortcity helical streamwisevortcity Football!
FFD – Forward Flank Downdraft Composite Hodograph (Fig. 8.15 in text) RFD – Rear Flank Downdraft “The storm scale, internally generated horizontal vorticity from the FFD outflow can augment the horizontal vorticity in the ambient environment, leading to larger overall hz. vorticity available for tilting…if the environmental and storm generated hz. vorticity have components in the same direction”
mesocyclone west COLD POOL north
Source of midlevel rotation only 2-3 km? BAMS – VORTEX2 (Wurman et al. 2012)
L w' w' L STRAIGHT LINE SPECTRUM CIRCULAR non-linear/storm splitting linear
pure westerly shear storm-relative winds anti-streamwise streamwise KLEMP FIG 2.6A KLEMP FIG. 2.26 a,b Mesomet Text Fig. 8.40a
Storm Splitt and Lateral Propagation…(straight hodograph) Mesomet Text Fig. 8.35a Mesomet Text Fig. 8.35b
KLEMP FIG 2.6B KLEMP FIG. 2.26 c,d Mesomet Text Fig. 8.40b
pre-split N post-split E aloft sfc midlevels w’z’ < 0 midlevels same hodograph! w’z’ > 0
Important Questions…. What vorticitymechanism(s) are responsible for the low level mesocyclone? What vorticitymechanism(s) are responsible for the w’z’ correlation? What vorticitymechanism(s) are responsible for the mid-level rotation? What dynamics are responsible for storm splitting? What dynamics are responsible for lateral storm propagation? Note that in each case…the ‘WHY’ and ‘HOW’ are also important!!!