POSSIBLE MECHANISMS OF CLEAR-AIR TURBULENCE IN STRONGLY ANTICYCLONIC FLOWS

The forecasting of clear-air turbulence (CAT) continues to be a challe nging problem despite progress made in the understanding of vertical s hear (Kelvin-Helmholtz) instabilities. The possible connections betwee n horizontal anticyclonic flows and CAT are addressed. Analytical expr essions are derived to show that current CAT diagnostics do not correc tly account for the dynamics of strongly anticyclonic situations. In g radient-balanced anticyclonic flows, nonfrontogenetical enhancement of vertical shear may lead to CAT. A review of observations, theory, and modeling is presented to support the claim that strong anticyclonic r elative vorticity can also lead to CAT through the generation of gravi ty wave activity by geostrophic adjustment and inertial instability. C AT diagnostics are then discussed in light of these claims. Observatio nal work is in progress to investigate the possibility of inertial ins tability-triggered CAT.