Deep currents obtained from Argo float trajectories in the Japan/East Sea

Abstract

The deep currents at 700–800m depths from Argo float trajectories (including pre-Argo floats) have been compiled from 1999 to 2010 in the Japan/East Sea (JES). More than 14,000 velocities from the dataset provides the first view of interbasin-scale dependency in deep currents of the JES, such as mean circulation and eddy variability, especially with an emphasis on their topographic steering characteristics. The observational findings in this study are (1) The Argo observation exhibits dominance of cyclonic mean circulation in the entire JES yet with a distinct interbasin variability of its magnitude. The mean circulation is strongest in the eastern Japan Basin (JB), while overall currents in the Ulleung Basin (UB) are weaker than that in the eastern Japan Basin and western Yamato Basin (YB) by a factor of two to three. (2) The eddy kinetic energy (EKE) is maximum in the western Japan Basin where strong dipole structure of wind-stress curl in winter is located. The interior of each basin (the eastern JB, UB, and YB) has local maxima of the EKE a factor of four to five smaller than that in the western JB. (3) Cyclonic bottom following characteristics prevail in the bin-averaged velocities. However, the individual deep flows presumably containing temporal variability have a preference to follow topography not only with cyclonic flows (shallow depth to the right), but also anticyclonic flows (shallow depth to the left), especially when flows are highly energetic. Occurrence of anticyclonic flows is proportional to the local EKE level relative to mean kinetic energy, implying that such flows could exist only in a transient manner such as topographic Rossby waves. The Argo observations may demonstrate an asymmetry of stable cyclonic and unstable anticyclonic circulation in the marginal seas of the northern hemisphere as the previous theoretical modeling studies suggested.