实验室中研究大尺度涡气旋反气旋对称性
We performed an experimental study of large-scale wakes in a rotating shallow-water layer.Standard particle image velocimetry was used to measure the horizontal velocity field, while alaser-induced fluorescence technique was used to measure the geopotential deviation i.e., theinterface deviation. According to these measurements, we were able to quantify the dynamics in awide region of parameter space beyond the quasi-geostrophic regime. For obstacles larger than thedeformation radius and with small Rossby numbers, a significant asymmetry occurs in the wakebetween cyclonic and anticyclonic vortices. These parameters correspond to a frontal geostrophicregime with the relative interface deviation being larger than 0.1–0.2. In this case, anticyclonesremain coherent and circular, whereas cyclones tend to be elongated and distorted. Moresurprisingly, for some extreme cases, coherent cyclones do not emerge at all, and only ananticyclonic vortex street appears several diameters behind the obstacle. The transition from aquasi-geostrophic to a frontal geostrophic regime is characterized by a strong increase in theStrouhal number, which can reach a value up to 0.6. Hence, we found that a large-scale wake coulddiffer strongly from the classical Karman street when the relative geopotential deviation becomeslarger than the Rossby number.