Vertical Velocities and Transports in the Equatorial Pacific during 1993–99*

Abstract

Geostrophic and Ekman transports calculated from observations of subsurface thermal structure and surface winds are used to determine vertical velocities and transports as a function of time, depth, and longitude in the equatorial Pacific within 5°S–5°N, 165°E–95°W during 1993–99 via a box volume balance. The vertical transports are determined in boxes of 10° of latitude by generally 15° in longitude. The corresponding vertical velocities represent a spatial average over these regions. Both the total vertical velocity and the cross-isopycnal component of the vertical velocity (approximated by the cross-isothermal component) are calculated on seasonal and interannual timescales. For the eastern equatorial Pacific (5°S–5°N, 155°–95°W) the mean vertical transport across 50 m is (24 ± 3) × 106 m3 s−1. Variability in the vertical velocity is large relative to the mean. On interannual timescales this variability is well correlated with the local winds in the western portion of the study area, while the correspondence is weaker in the east where wind variability is much smaller. At seasonal timescales there is good correspondence between the vertical velocity and the local winds throughout the study region. The cross-isothermal vertical velocity is significantly smaller than the total vertical velocity, and the means of both compare well with the few historical estimates available.