![]() The enhanced surface chlorophyll signals observed along the spiral bands are likely caused by vortex Rossby waves embedded in the ocean eddies. ![]() These features are also identified in the atmospheric spiral rain bands of tropical cyclones, which are induced by vortex Rossby waves and can cause strong vertical motions. ![]() The spiral's azimuthal moving velocity is substantially smaller than the eddy's rotational velocity and the spiral tends to move outward from eddy center to eddy edge. In this study, we combine global satellite ocean-color data, ocean surface drifter measurements, and satellite altimeter data to demonstrate that the spiral bands are footprints of wave motions embedded in oceanic eddies, rather than simple tracer lines elongated by the straining flow field. This submesoscale process serves as an important upwelling mechanism to close the upper ocean nutrient budget and sustain the primary production of phytoplankton in euphotic layer, but their dynamical origin is not fully understood so far. Spiral band (with scales ~1–10 km and approximately days) is a common submesoscale feature of mesoscale eddies, characterized by enhanced surface chlorophyll concentrations. Oceanic mesoscale eddies are energetic vortices with radius ranging from tens to hundreds of kilometers. As vortex Rossby waves are closely related to eddy evolution under background deformation, further observational analysis indicates that an intense eddy energy variation and a strong background deformation field constitute the favorable conditions for the emergence of the spiral chlorophyll bands. By combining satellite ocean-color, satellite-altimetry, and surface drifter data, we find that the oceanic spiral chlorophyll bands emerge globally and share a series of structural and kinematic features with atmospheric spiral rain bands of tropical cyclones, which indicate that they are footprints of the vertical motions induced by vortex Rossby waves embedded in eddies. Spiral band is one of the most typical submesoscale structures of mesoscale eddies, characterized with enhancement of surface chlorophyll concentration. Oceanic submesoscale processes (with scales ~1–10 km and approximately days) have been progressively recognized as an important upwelling mechanism to close the upper ocean nutrient budget and sustain the primary production in euphotic layer.
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