[AOS15-P05] Detailed water properties of mesoscale vortex pairs in the Sea of Japan: direct observations using an underwater glider
Keywords:underwater glider, vortex pairs, spatiotemporal change, subpolar front
We successfully completed for the first time a spatially high-resolution survey with an underwater glider (Seaglider, Kongsberg Underwater Technology Inc.) along a Jason-2 satellite altimeter track #86 off Sado Island from 20 April through 2 June 2016. The Seaglider repeatedly profiled temperature and salinity from the ocean surface to roughly 900 m depth with an along-track profile separation 2–3 km, which is sufficient to resolve the mesoscale structures. A total of 257 profiles were obtained during a two-round-trip observation (four transects; referred to as “Transects 1–4”).
We applied principal component analysis using a time series of the absolute sea surface height (SSH) from 1993 to 2015 by AVISO and a correlation matrix method. Horizontal distribution of SSH of the first principal component are approximately in phase over the interested study domain with intraseasonal variations, whereas that of the second principal component (PC2) shows the existence of a vortex pair off Sado Island with primarily interannual variation.
A large variability of mesoscale frontal/eddy structures and water properties was revealed by the glider observations; Transects 1 to 4 were respectively characterized by a cyclonic eddy, a vortex pair, an anticyclonic eddy, and baroclinic jets (no eddies). We detected the vortex pair consisting of northern anticyclonic eddy and southern cyclonic eddy along Transect 2, almost corresponding to that of PC2. The paired anticyclonic and cyclonic eddies have distinct water properties and spatial structures. The anticyclonic eddy had a diffusive-convection favorable vertical structure near the surface layer (< 50 m depth) characterized by water being colder and fresher than those at the underlying subsurface layer. The counterpart of the cyclonic eddy was salt-fingering favorable which is warmer and more saline at the surface layer. In the cyclonic eddy, horizontal interleaving structures were also observed. With the horizontally high-resolution data obtained by the glider observations we will investigate the mixing processes and their spatial/temporal variability within the vortex pair system from statistical and quantitative approaches.