Dynamical Effects of Storm Generated Mesoscale Processes and Pressure perturbations Terrance Seddon

Over view Dynamical effects Generation of Mesoscale Pressure fields Evolution of supercells to the tornadic phase Cold pool interactions Pressure perturbation

Generation of Mesoscale Pressure fields Dynamic effects of lifting, such as lifting pressure gradients on the flanks of updrafts, contribute to the splitting of storms Dynamic lowering of midlevel pressures induces updraft growth on both signs of the updraft, P’NL=-ζ2

Illustration for signs on updraft

Illustration for non-linear hodographs

Evolution of storms into Tornadic phase This evolution is not completely understood, but some things are known about what is needed to cause it. They must injest streamwise vorticity into updrafts Baroclinic vorticities must generate along forward-flank downdrafts Mesoscale Vortex breakdown The final ingredient can also happen to the tornado vorticity itself, resulting in smaller scale suction vorticities

Cold pool interactions Cold pools are responsible for new convective development. With a proper balance between cold pools and low level shear, continual regeneration of storms is possible, but not required for long lived storms. This balance is usually complicated by other sources of vorcitiy

Cold pool and wind shear interactions Top pictures show a zero shear environment, with wind speeds the same all the way up Lower pictures show an environment where the wind speeds are faster near the surface and decrease as they go up.

Proposed events leading to Mesoscale influences Steps Referenced figures Initial updraft leans down shear due to ambient shear (a) Cold pool develops and counteracts the down shear tilt. (b) Cold pool overwhelms the updraft and creates a rear-inflow jet. (c)

Divergence of the horizontal momentum equation

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