5:15 PM - 7:15 PM
[ACG47-P08] Water Mass Structures of the Nonlinear Cold Eddy in the South of the Kuroshio Extension Region
Nonlinear eddies (U/c > 1) dominate ocean regions outside the tropical band (Chelton et al., 2011). In
these eddies, the vorticity properties (U) dominate over wave properties (c), suggesting they can trap and
transport water mass properties while propagating. However, there have been few discussions
about water mass changes in nonlinear eddies based on observations.This study demonstrates
water mass trapping by nonlinear eddies using ARMOR3D.
On December 11, 2005, the Shoyo Maru (operated by the Fisheries Agency) traversed the center of a
cold eddy south of the Kuroshio Extension Region. This eddy was selected as our target for analysis. The
eddy’s area was determined using the Q parameter (Isern-Fontanet et al., 2003), with the eddy center
defined as the point of minimum sea level within the Q-defined area. The eddy’s nonlinearity (U/c)
was calculated using the average geostrophic current (U) within the Q-defined area and the propagation
speed (c) determined from the eddy center positions at times t1 and t2.
The target eddy showed strong nonlinearity with U/c > 5. Time series analysis of potential temperature
at the eddy center revealed relatively stable conditions on isopycnal surfaces between 22.0σθ and
26.8σθ. However, significant variations were observed between 27.0σθ and 27.5σθ. Time derivatives of
potential temperature at the eddy center across isopycnal surfaces confirmed substantially larger changes
in the 27.0σθ–27.5σθ range compared to 22.0σθ–26.8σθ.
These results suggest that while the eddy effectively trapped water masses in the upper layers (22.0σθ–
26.8σθ), the deeper layer (27.0σθ–27.5σθ) experienced external water mass advection rather than trapping.
these eddies, the vorticity properties (U) dominate over wave properties (c), suggesting they can trap and
transport water mass properties while propagating. However, there have been few discussions
about water mass changes in nonlinear eddies based on observations.This study demonstrates
water mass trapping by nonlinear eddies using ARMOR3D.
On December 11, 2005, the Shoyo Maru (operated by the Fisheries Agency) traversed the center of a
cold eddy south of the Kuroshio Extension Region. This eddy was selected as our target for analysis. The
eddy’s area was determined using the Q parameter (Isern-Fontanet et al., 2003), with the eddy center
defined as the point of minimum sea level within the Q-defined area. The eddy’s nonlinearity (U/c)
was calculated using the average geostrophic current (U) within the Q-defined area and the propagation
speed (c) determined from the eddy center positions at times t1 and t2.
The target eddy showed strong nonlinearity with U/c > 5. Time series analysis of potential temperature
at the eddy center revealed relatively stable conditions on isopycnal surfaces between 22.0σθ and
26.8σθ. However, significant variations were observed between 27.0σθ and 27.5σθ. Time derivatives of
potential temperature at the eddy center across isopycnal surfaces confirmed substantially larger changes
in the 27.0σθ–27.5σθ range compared to 22.0σθ–26.8σθ.
These results suggest that while the eddy effectively trapped water masses in the upper layers (22.0σθ–
26.8σθ), the deeper layer (27.0σθ–27.5σθ) experienced external water mass advection rather than trapping.