The Interaction Between Mesoscale Eddy And Low-frequency Oceanic Current In The Kuroshio Extension Region

In this paper, SODA data and OFES data are used to study the interactionbetween mesoscale eddy and low-frequency oceanic current in the KuroshioExtension region (KE). A positive feedback, which plays an important role in theinteraction between atmospheric synoptic eddies and low-frequency flows in the extratropics, is investigated by discussing the relationship between annual average eddyvorticity flux anomalies and low-frequency currents, and the effect on low-frequencycurrent by the eddy forcing in KE.Mesoscale eddy fields and low-frequency currents are obtained by filtering andtime-mean methodology. Using correlation analysis of the eddy vorticity flux andlow-frequency current, the result from SODA data is same as that from OFES data.The correlation coefficient between meridional (zonal) eddy vorticity flux and zonal(meridional) low-frequency current is very fragmented, which doesn’t show a positivefeedback with high positive (negative) correlation value. Calculating angles betweenthe eddy vorticity fluxes and anomalous low-frequency currents, the probability, morethan0.5, indicating the anomalous eddy vorticity fluxes tends to be directedpreferentially to the left-hand side of the anomalous annual average currents, isn’t big.Classifying the angles into12groups with30interval, the distribution is random andthe probability of each group is nearly one-twelfth. The left-hand rule isn’t at work,suggesting that positive feedback for mesoscale eddies on low-frequency currents isn’tobvious in KE.A scatter distribution of annual average meridional shear of zonal currents andthe convergency of eddy vorticity fluxes (VFC) is examined and a cyclonic(anticyclonic) shear doesn’t lead to a positive (negative) VFC because of the randomdistribution. The linear tendency is negative, but the value is small, which shows thatthe result was not significant. Using one-point covariance statistics of mesoscale eddy fields to reconstruct the mesoscale eddy structures, it is found that the amplitude ofthe wave-packet-like structure of mesoscale eddy field naturally decays as thedistance from the base point increases, and it exhibits slightly tilted and stretched.However, the packet broadly distributes along the path of the KE jet while the eddyforcing corresponding to the eddy structure change is patchy.Although projecting the time-varying eddy forcing field upon the meanstream-function to the normalized time series of the eddy kinetic energy level, aspatial pattern is gained and appears somewhat patchy. Along the path of themeandering KE jet, there is a general tendency for a cyclonic (anticyclonic) forcing inthe trough (ridge) of the KE’s quasi-stationary meanders. Dynamically, this impliesthat the KE’s quasi-stationary meanders are being sustained against dissipation by theeddy forcing.In spite of mesoscale eddies supporting the climatological mean current by theeddy forcing along the KE jet, the positive feedback for mesoscale eddy onlow-frequency flow is very weak. It isn’t one of the most important mechanisms of theinteraction between mesoscale eddy and low-frequency current.