Fig. 1

a: Standard deviation of SLA during 1993-2017. The black box1 and box2 indicate two regions with strong SLA variability. The black box3 denotes the area where the CEOF is applied for the intra-seasonal SLA in section 3. b-c: Power spectral analysis for SLA in box1 and box2. Blue dotted line denotes the 95% confidence line, and the red vertical lines indicate the cutoff periods (30-120 day) for intra-seasonal signals, the x-axis is log10 coordinates"

Fig. 2

Multiyear mean surface geostrophic current anomaly and standard deviation (a-c), variance contribution (d-f), mean EKE(log10) of 30~120 day filtered SLA during 1993-2017(g-i). The left, middle and right columns are for all, summer (April-September) and Winter (October-March)"

Fig. 3

Spatial amplitude (shading; cm) and phase (contour; interval = 30°) corresponding to CEOF1(a) and CEOF2 (b) of the 30-120 day filtered SLA. Time series for CEOF1 (c) and CEOF2 (d)"

Fig. 4

Same as Fig. 3, except calculated from the 30~120 day bandpass filtered SLA from April to September"

Fig. 5

Same as Fig. 3, except calculated from the 30~120 day bandpass filtered SLA from October to March"

Tab. 1

Variance of the first three leading CEOF modes"

Fig. 6

Temporal evolution of an anticyclonic eddy detected by altimeter SLA, and geostrophic current anomalies from November 2016 to June 2017. Enclosed white contour and white dot denote eddy boundary and eddy core, respectively"

Fig. 7

Properties of the anticyclonic eddy detected by altimeter SLA from November 2016 to June 2017: EKE (a), radius (b), and propagation speed (c)"

Fig. 8

Geographic distributions of eddy occurrence (units in times). The upper row is for the whole year, the middle row is for winter (October to March) and the lower row is for summer (April to September) at each 0.5°×0.5° pixel in the NSCS between January 1993 and January 2017. The eddy occurrence denotes all detected eddy snapshots. The left, middle and right columns are for all eddies, anticyclonic eddies and cyclonic eddies, respectively"

Fig. 9

Geographic distributions of eddy propagation speeds (units: cm·s-1). The upper row is for the whole year, the middle row is for winter (October to March) and the lower row is for summer (April to September) at each 0.5°×0.5° pixel in the NSCS between January 1993 and January 2017. The left, middle and right columns are for all eddies, anticyclonic eddies and cyclonic eddies, respectively"