Observational Characteristics of Internal Temperature Fluctuations in the Mid-Latitude North Pacific

Abstract

Using the TRANSPAC XBT data at a depth of 300 m, the regional variability of energy, time scales, length scales, and phase propagation of internal temperature fluctuations in the mid-latitude North Pacific is examined. results show that the regional variability in the eastern half of the basin is substantially different from that in the western half. In the eastern North Pacific, the energy of the internal temperature fluctuation is very low and fairly uniformly distributed. Time scales and meridional length scales are distributed over broad ranges, zonal length scales are relatively small, and the direction of phase propagation is almost due west. At the eastern boundary, the opposite tendency in time and length scale distribution holds. In contrast, the energy in the western North Pacific is high, particularly along the main axis of the Kuroshio Extension Current (KEC), and decreases toward the east. It also decreases toward the north and south. Time scales are small near the western boundary and increase eastward. Both zonal and meridional length scales are large near the western boundary and decrease eastward. Phase propagation along the KEC appeared to be eastward, while that in the outer regions north and south of the KEC seemed to be westward with poleward components to the north and south, respectively.