Radar observations of wind‐shear splitting within evolving atmospheric kelvin‐helmholtz billows

The high‐resolution radar at Chilbolton was used to measure the velocity structure of large‐amplitude Kelvin‐Helmholtz billows within a precipitating warm‐frontal zone. A deep layer of frontal shear was observed to split into thin layers of more concentrated shear displaying the characteristic braided structure previously reported within clear‐air radar reflectivity patterns and attributed to a splitting of the thermal stratification. the billows were situated within a region of strong wind veer with height and they were orientated at right angles to the mean flow such that air parcels within them were tending to follow helical trajectories up the inclined frontal zone. Radar scans normal to the axes of the billows at different distances from their origin, close to the position of the surface warm front, provided an indication of the evolution of the split‐shear structure.