Seasonal Variation in Transport of the Pacific North Equatorial Current Relative to the Wind Field

Abstract

Geostrophic transports in the upper 300 m relative to 1000 db are computed from observations along four meridional sections occupied monthly during the Trade Wind Zone Oceanography Study, February 1964 to June 1965. Transports varied from a minimum of about 11×10⁶ m³ s⁻¹ in February of both 1964 and 1965 to a maximum of 23×10⁶ m³ s⁻¹ in September 1964. The ridge in the thermocline at the southern edge of the current rose or fell simultaneously as the transport increased or decreased. Theoretical vertical displacements were computed from the wind stress curl using a formula derived by Yoshida and Mao. The observed vertical displacements of the thermocline are similar to the computed displacements. Thus, the observations of the Trade Wind Zone Oceanography Study are in agreement with the simple model of variation in the strength of equatorial currents that was developed by Yoshida and by Fedorov. According to the model, the divergence of Ekman transports cause variation in the meridional slope of the thermocline and in the geostrophic current speed.