Figure  1.  ETOPO1 depth of the eastern tropical Pacific Ocean, position of the mooring site (red triangle) and the section in c (a); depth around the mooring site (b); climatologic temperature (from World Ocean Atlas 2009) at a meridional section of 154°W (0°−20°N) and the observation range of current metres (red line represents the observation range of 75-kHz ADCPs at upper layers and the red dots below 1 200 m represent the location of Aquadopp current meters) (c).

Figure  2.  Time series of 3-d averaged flow vectors after 3-d low-pass filtering at different depths.

Figure  3.  Kinetic energy of intra-seasonal variability (ISV), low-frequency variability and their ratio. The blue circle line represents kinetic energy of low-frequency variability (Ke-low); the blue asterick line represents kinetic energy of ISV (Ke-isv); the red triangle line represents the ratio of Ke-isv and Ke-low.

Figure  4.  Power spectral density (PSD) of the velocity in zonal (a) and meridional (b) currents.

Figure  5.  Standard deviations (Std) of the meridional and zonal velocities at the intra-seasonal time scale.

Figure  6.  Continuous wavelet transform of meridional velocity at surface current (a) and currents at 50−100 m (b), 450−500 m (c), 900−1 000 m (d), 1 854 m (e) , 4 616 m (f). The colour filled maps represent the wavelet power spectrum (WPS), and the curves on the right represent the global wavelet spectrum (GWS). In the colour maps, the thick black contours denote the 5% significance level against red noise. The cone of influence where edge effects might distort the picture is shown in lighter shades.

Figure  7.  Cross spectrum analysis between the surface meridional current (OSCAR) and those at other depths. a. Cross power spectral density; b. cross power spectral phase lag; c. magnitude-squared coherence. The cpd means counts per day.

Figure  8.  Time series of 3-d averaged flow vectors after 20−40 d bandpass filtering.

Figure  9.  Comparison of meridional velocity at 4 616 m from observations and reanalysis products. a. Time series; b. squared wavelet coherence; c. power spectral density (PSD) of the meridional velocity at the mooring site, from reanalysis data.

Figure  10.  Spatial amplitude (a), spatial phase (b), spatial reconstruction (c), temporal amplitude (d), temporal phase (e), frequency-spectra density (f) of the first complex empirical orthogonal function (CEOF) mode of meridional velocity at 4 000 m. The mooring site is marked with a triangle in a, b and c. The cpd means counts per day.

Figure  11.  The first three empirical orthogonal function modes of sea level anomaly at the intra-seasonal time scale.

Figure  12.  Continuous wavelet transform of the time series of the first three empirical orthogonal function modes of sea level anomaly. WPS: wavelet power spectrum; GWS: global wavelet spectrum.

Figure  13.  Time series of the first empirical orthogonal function (EOF) mode of sea level anomaly (SLA) and meridional velocity at 4 616 m (a); cross wavelet transform (b) and squared wavelet coherence (c) between the time series of the first EOF mode of SLA and meridional velocity at 4 616 m.

Figure  14.  Spatial patterns of 35 m (a) and 4 000 m (b) meridional velocity; homogeneous (c) and heterogeneous (d) correlation map for the 4 000 m velocity, the 95% significance level is shown as red contours; time evolution of the expansion coefficients of 35 m and 4 000 m meridional velocity (e). All is for the first leading SVD mode. The mooring site is marked with a red triangle in a and b. SVD: Singular Value Decomposition; SCF: Squared Covariance Fraction (measuring the amount of squared covariance for which each mode accounts).