Theory and application of spontaneous imbalance to clear-air turbulence

A new method of clear-air turbulence (CAT) forecasting based on the Lighthill-Ford theory of spontaneous imbalance and emission of inertia-gravity waves has been derived and applied on episodic and seasonal timescales. A scale analysis of this theory for mid-latitude synoptic-scale flows identifies advection of relative vorticity as the leading-order source term. Examination of leading- and second-order terms is used to elucidate previous theory and practice of CAT forecasting. Application of the Lighthill-Ford theory on a variety of timescales leads to superior forecasts compared to the the most skillful operational CAT forecasting methods currently in existence. Our results suggest that spontaneous balance theory could lead to major advances in operational CAT forecasting.