Rapid Local Changes in Helicity and Vertical Wind Shear Associated with the Passage of Ducted Gravity Waves

Ducted gravity waves are associated with potentially large perturbations in horizontal winds. It may be shown, neglecting friction, that these perturbations are maximized at the surface and minimized at the top of the wave duct, producing perturbation vertical wind shear as well. The magnitude of this shear is maximized in the wave ridge and the wave trough. The perturbation shear may be significant, on the order of 10 -2 s -1 . It is also shown that the perturbation vertical shear associated with the passage of a ducted gravity wave may significantly increase or decrease the storm-relative helicity over 30-60 minute time periods in the environment of a supercell storm. This could result in a source of transient horizontal vorticity which may be tilted into the vertical by a storm updraft.