(1) The JES circulation was simulated in this study by the POM model under the seasonal surface flux forcing. The northern JES (i.e., the Japan Basin) is occupied by a cyclonic gyre (called the JB gyre) and the southern JES is characterized as a multi-eddy structure. The volume transport streamfunction has a double-gyre structure with negative values (cyclonic) in the northern JES and positive values (anticyclonic) in the southern JES. The simulated JB gyre is the strongest and recirculates 8 Sv in the winter. It weakens and retreats northward in the spring and summer. In the fall, the cyclonic JB gyre disappears and weak multi-anticyclonic eddies appear.
(2) The current systems such as the LCC, EKWC, NKCC, and JNB are simulated reasonably well. The simulated LCC has a maximum southward component (0.21 m/s), occurring near the surface in the winter with a width of 100 km and extending to a depth of 800 m. It weakens to a minimum of 0.15 m/s in the summer and fall, and shrinks in size to a width of 60 km and depth of 400 m.
The simulated EKWC varies from 0.42 m/s (summer) to 0.30 m/s (winter). The
width of the EKWC is around 60 km all year round. However, the depth is around
1,400 m in the summer and 800 m in the winter. The (northward) overshot EKWC
leaves the Korean coast moving northward and converges with the southward
flowing NKCC, at 40
N, 130E, and forms a current meandering
toward east along the SPF.
The simulated JNB has a maximum eastward component of 0.24 m/s in the winter and weakens to 0.09 m/s in the summer. This is consistent with the earlier observational study. The effect of coastal geometry, such as the Noto Peninsula on the JNB, is also simulated.
The simulated UTB warm-core anticyclonic eddy has a western branch of the TWC
(i.e., EKWC) which moves northward along the southern part of the Korean coast
and separates from the coast after approaching the East Korean Bay. It keeps
its northward motion until meeting the NKCC near 40N, meanders
southeastward, and forms a warm-core anticyclonic eddy. This eddy is strongest
in the summer and its center is located at 38.5N 130E. The
size of the eddy is around 150 km. The tangential velocity is around 0.4 m/s.
(3) The nonlinear advection does not affect the general circulation pattern evidently, but does affect the formation of the mesoscale eddies, and especially the UTB eddy (all seasons) and the JB cyclonic gyre (spring).
(4) The model wind effects on the JES circulation are more pervasive than those of non-linear dynamic effects. The winter winds cause a strong basin-wide JES cyclonic gyre with 8 Sv recirculation in the northern JES and the summer winds drive a weak nearly basin-wide JES anticyclonic gyre. Thus, the wind forcing is the most important fact (80%) for the generation of the JB cyclonic gyre. Besides, the winds also influence the surface circulation such as driving the LCC (winter), damping the EKWC (winter), generating the UTB eddy (all seasons), and generating eddies along the JNB (all seasons). The wind has almost no effect on the occurrence of the JNB for all seasons.
(5) The model boundary-forcing enhances (weakens) the JES volume transport in
the summer (winter). It has very weak effects on the occurrence of the LCC
except in the winter, when the boundary-forcing accounts for 30% of the LCC
at 46N. It weakens the JB cyclonic gyre by 2 Sv (25%) in the
winter. Besides, the boundary forcing also influences the surface circulation
such as driving the UTB eddy in all the seasons (50% in the winter),
generating the EKWC (50-100%) in the winter and 21% in the summer), and
generating the JNB and eddies along the JNB.
(6) Future studies should concentrate on less simplistic scenarios. Realistic lateral transport should be included and the use of extrapolated climatological winds needs to be upgraded to incorporate synoptic winds to improve realism. Finally, the assumption of quasi-linearity that allowed us to use simple differences to quantify the effect of external forcing needs to be rigorously tested. It is very important to develop a thorough methodology to perform sensitivity studies under the highly non-linear conditions that may exist in the littoral environment.