Speaker 1 :  Nicholas Pizzo  (Scripps Institution of Oceanography, University of California, San Diego)
    Date & Time : January 21st (Fri.), 2022 / 9:00-9:40AM (Tokyo (JST)) 
                  (--> January 20th (Thu.), 2022 / 4:00-4:40PM (San Diego (PDT)) ) 
    Title : Particle description of the interaction between wave packets and point vortices
    Abstract : 
         This talk explores an idealized model of the ocean surface in which widely separated 
       surface-wave packets and point vortices interact in two horizontal dimensions. We start 
       with a Lagrangian which, in its general form, depends on the fields of wave action, 
       wave phase, stream function and two additional fields that label and track the vertical 
       component of vorticity. By assuming that the wave action and vorticity are confined to 
       infinitesimally small, widely separated regions of the flow, we obtain model equations 
       that are analogous to, but significantly more general than, the familiar system consisting 
       solely of point vortices. We analyse stable and unstable harmonic solutions, solutions in 
       which wave packets eventually coincide with point vortices (violating our assumptions), 
       and solutions in which the wave vector eventually blows up. Additionally, we show that 
       a wave packet induces a net drift on a passive vortex in the direction of wave propagation 
       which is equivalent to Darwin drift. Generalizing our analysis to many wave packets and 
       vortices, we examine the influence of wave packets on an otherwise unstable vortex street 
       and show analytically, according to linear stability analysis, that the wave-packet-induced 
       drift can stabilize the vortex street. The system is then numerically integrated for long 
       times and an example is shown in which the configuration remains stable, which may be 
       particularly relevant for the upper ocean.