Expendable current profiler (XCP) section across the North Pacific at 25°N

Abstract

In mid-1985,201 expendable current profiler (XCP) probes were deployed along a track which crossed the North Pacific mostly along latitude 24°15′. About three quarters of the probes provided good data on relative horizontal velocity and temperature. Small vertical scale features in velocity show different characteristics in the California Current, the eastern Pacific and the western Pacific. Spectral energy of the small vertical scale features (WKB stretched wavelength of 20–150 m) increases to the west in rather discrete “jumps” at 153°W, 173°E and 132°E. A simple power law model of spectral energy of this band reveals that the steeper the spectral slope, the larger its amplitude; 20 m wavelength band energy is quite uniform across the ocean. The 150 m vertical-average and horizontal eddy-scale (30–80 km) velocity is nearly geostrophic because the estimated geostrophic currents from the accompanying CTD survey agree very well with XCP currents. The characteristics of eddies in the eastern Pacific are similar to the variability described by Niiler and Hall: (1988, Journal of Physical Oceanography, 18, 1670–1685) from moored current meters. The eddy energy also increases to the west. The most surprising finding in these measurements is the strong (order of 10–15 cm s−1) large horizontal scale eastward flow in both the eastern Pacific and the western Pacific. This strong eastward flow has a zonal extent of 1200 km. Other data suggest a meridional extent of 300–400 km.