Abstract
Parameter dependence of gravity-wave radiation from an unstable jet is investigated using a two-layer, f-plane shallow-water model. The sweeping parameters are the Rossby number Ro and the Froude number Fr. If Ro/Fr ≳ 0.6, the barotropic instability dominates and gravity waves that are almost independent of the longitudinal direction and have latitudinal wavelengths longer than the jet width are radiated. The radiation occurs when the jet develops into cyclonic and anticyclonic vortex trains. The amplitude of the radiated waves increases monotonically with Ro and Fr. If Ro/Fr ≲ 0.6, the baroclinic instability dominates and gravity waves the latitudinal wavelengths of which are shorter than or the same order of length as the jet width are radiated from cyclonic vortices dominating in the jet region. In this regime, the amplitude of the radiated waves increases with Fr, whereas it decreases with Ro. To understand the different dependences of the wave amplitude on Ro, we adopt the Lagrangian Rossby number RLG, and show that the amplitude increases with RLG.
