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Abstract

Beta-plumes and origin of striated patterns in the ocean

Dr Nikolai MAXIMENKO(1), Dr Oleg MELNICHENKO(1), Pr Emanuele DI LORENZO(2), Dr Ali BELMADANI(1), Pr Niklas SCHNEIDER(1)

(1) IPRC/SOEST, University of Hawaii, United States
(2) Georgia Institute of Technology, United States

Session theme: Others (Posters only)

  • poster

    Abstract

    Dynamics of \"striations\", quasi-zonal jet-like features seen on maps of multi-year mean geostrophic velocity (see Figure), is analyzed in the framework of beta-plumes, ocean circulations generated by localized sources of vorticity. Beta-plumes are exemplified in the ocean by the Azores Current induced by the outflow of Mediterranean water from Gibraltar, the Hawaiian Lee Countercurrent generated by the orographic wind stress curl in the lee of Big Island of Hawai\'i, and features off of the California coast resulting from nonlinear interaction between baroclinic meander of the California Current and Ekman flow. Experiments with the idealized ROMS model demonstrate formation of the system of jets west from the source area in linear regime and of system of eddy trains in nonlinear regime. In the presence of the background meridional flow, common in the regions populated by striations, beta-plumes change in two ways: orientation and generation of eddies. Axes of beta-plumes are tilted by the large-scale advection in the same manner both in linear and non-linear regimes. In linear case, tilted axes allow trapped Rossby waves to propagate meridionally against the flow. In nonlinear case, the tilt is achieved by a superposition of westward drift of eddies and their meridional advection by the flow. Due to instability of meridional flow, new eddies are generated not only in the beta-plume vorticity source but also along the jets west from the source area. Both the tilt of striations, consistent with the direction of the large-scale flow, and formation of eddies away from eastern boundaries are confirmed using altimetric maps of the sea level anomaly. New eddies are shown to form preferentially on crests and troughs of pre-existing striations. This complex organization of eddies is also confirmed by the structure of space correlation functions of geostrophic velocity and vorticity. The functions combine \"eddy\" correlations, suspiciously coinciding with the AVISO mapping functions, and long-rage correlations extending up to 2000 km in the zonal direction and including a set of crests in the meridional direction. This study demonstrates how originally simple physic of a beta-plume, when placed into realistic conditions of unstable ocean gyres, develops complex organization of mesoscale eddies, which both results from and visualizes the striated pattern of the plume.

    This paper was also accepted for oral presentation at the \"20 years of progress in radar altimetry\" conference.

     
    Corresponding author:

      Dr Nikolai Maximenko
      IPRC/SOEST, University of Hawaii
      1680 East West Road, POST #401
      96822 Honolulu
      United States
      E-mail:
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