Mesoscale Thermohaline, Sound Velocity and Baroclinic Flow Structure of the Pacific Subtropical Front During the Winter of 1980

Abstract

The three-dimensional thermohaline. sound velocity and baroclinic flow structure of the. pacific sub-tropical front during January and February 1990 are discussed. The front is meander-like, with a wavelength of 180 km, a wave amplitude of 55 km, and is centered around latitude 30°N. On 37 km spatial and 10-day time scales the front barely moves, but its intensity increases due to an intrusion of cold and low-salinity water from the north. The front is nearly vertical in the upper 130 m and slopes southward below. The strongest cross-frontal differences are 1.7°C for temperature, 0.6? for salinity. 0.4 kg m?3 for density and 13 m s?1 for sound velocity and occur beneath the base of the mixed Layer. The baroclinic flow field indicates a meandering current with maximum speeds of 0.3 m s?1. Cyclonic eddies occur north and anti-cyclonic eddies occur south of the front. Satellite-tracked drifters confirm these patterns. Vertical shear of the baroclinic flow in the frontal region varies between 10?4 and 10?3 s?1 and is strongest below the base of the mixed layer. The principle of conservation of potential vorticity is applied to fronts and compared to observations.