A Doppler Radar Observation on Wave-like Echoes Generated in a Strong Vertical Shear

Abstract

Wave-like echoes were observed in a weak rain cloud by a Doppler radar on September 6, 1989. The wave-like echoes presented as a series of band echoes with a wavelength of 3.5 km. The wavelike echoes were generated in a strong vertical shear at a height between 3 and 4 km and oriented perpendicular to the shear vector between 3 and 4km. The minimum Richardson number at the shear layer is 0.14. These features are consistent with the condition of Kelvin-Helmholtz (K-H) instability. The vertical cross section of the wave-like echoes were expressed as a series of reflectivity cores and undulation of an isopleth of Doppler velocity. The undulation of Doppler velocity, which is induced by K-H instability, is assumed to cause the horizontal accumulation of precipitation particles and adiabatic heating to form the reflectivity core at the melting level.

Extensive studies of large‐amplitude Kelvin–Helmholtz billows in the lower atmosphere with VHF middle and upper atmosphere radar

“…In the free atmosphere, frontal zones (e.g. Hardy et al, 1973;James and Browning 1981;Takayabu, 1992;Takahashi et al, 1993;Chapman and Browning, 1997) and jet streams (e.g. Klostermeyer and Rüster, 1980;Chilson et al, 1997;Singh et al, 1999;Luce et al, 2008) are the main synoptic environments conducive to KH instability because they are associated with enhanced vertical shear of horizontal wind.…”