Oceanic Boundary Currents

Measurements of oceanic boundary currents for integral quantities such as heat and freshwater transports are very important for studying their long-term impacts on the global climate. There are a variety of boundary currents, including surface, intermediate and deep boundary currents on both the western and eastern sides of ocean basins. The dynamics and physics of these boundary currents are different, as are the ways of monitoring them. Here, we choose to explore the strategies adopted for observing four representative boundary current systems which have been the subject of detailed studies in recent years: the Kuroshio; the East Australian Current; the Indonesian Throughflow; and the low-latitude boundary current System of the Atlantic. The transport of the Kuroshio south of Japan has been monitored using satellite altimeter data in conjunction with an empirical relation between the transport and sea surface height difference across the stream. Monitoring the transport of the East Australian Current has been achieved by repeated high-resolution expendable bathythermograph (XBT) and/or conductivity-temperature-depth profiler transects maintained at several locations, supplemented with satellite altimeter data. Repeated XBT transects have also been used to monitor transport of the Indonesian Throughflow, in association with current meter and other instrumental estimations of transport through a few major throughflow straits. Finally, the complicated flow field of the low-latitude boundary current system of the Atlantic has been revealed using neutrally buoyant floats, moored current meters and hydrographic observations. The survey will be continued using further advanced observation technologies

The Kuroshio Region off Southwest Japan ASUKA 1993-95 Inverted Echo Sounder Data Report

In order to study the time-varying volume and heat transports of the Kuroshio off southwest Japan, a large number of scientists from Japan and a small number from the U.S.A. formed a group called ASUKA. This group carried out a coordinated investigation which was concentrated in time on the years 1993-95, and in space on a 1,000 km segment of a TOPEX/POSEIDON suborbital track running south-southeast from western Shikoku. This report describes the techniques used to process data collected by ten inverted echo sounders (IES) on this 1,000 km line off Japan, as part of the ASUKA study. The University of Rhode Island (URI) was responsible for all the IES\u27s except IES5 and IES8 which were from the Hydrographic Department of the Japanese Maritime Safety Agency (MSA/HD). The URI IES\u27s were deployed from the Training Vessel Keiten-maru in October 1993 and recovered from the same vessel in November 1995. The MSA/HD IES\u27s were deployed from the Survey Vessel Shoyo in July 1993. IES8 was recovered by Shoyo in May 1994, but unfortunately IES5 was not recovered

A new method for estimating the turbulent heat flux at the bottom of the daily mixed layer

A new method is presented for estimating the vertical turbulent heat flux at the bottom of the daily mixed layer from the temperature data in the mixed layer and net solar irradiance data at the sea surface. We assume that fluctuations in the divergence of advective heat flux have longer than daily time scales. The method is applied to data from the eastern tropical Pacific, where the daily cycle in the temperature field is confined to the upper 10-25 m. The night-to-day difference of the turbulent heat flux calculated from the data obtained during nine daily cycles in November 1984 agrees well on average with the same quantity estimated from microstructure observations. The night-to-day difference of the turbulent heat flux, estimated at several mooring stations near the equator (an average over 100 to 300 daily cycles), varies from 120 to 220 W/m² with larger values on the equator. Equatorial turbulence measurements show that the turbulent heat flux is much larger during nighttime than daytime. Therefore the present estimates give approximately the nighttime average, which is the major part of the turbulent heat flux. From the daytime heat budget we obtain divergence of the low-frequency horizontal heat advection at 1°30’S, 140°W; it is governed by equatorial mesoscale fluctuations having a predominant period of 15-20 days

Fourier Filtering in a Barotropic Polar Ocean Model

A Fourier filtering is examined in a polar ocean model based on the vorticity equation. A circular basin centered at the North Pole is considered. Flows are driven by an inflow and an outflow prescribed at the circumference. Two peninsulas are provided for examination of the filtering effect. In a slip boundary case, longitudinal distribution of the predicted vorticity is expanded in sine series and high wavenumber components are eliminated. The solution obtained with the filtering agrees well with that obtained without filterings. In a viscous boundary case, the vorticity is expanded in cosine series and high wavenumber components are eliminated. The filtering does not affect the general flow pattern, although it slightly affects the local vorticity field near irregular coastal boundaries

Thermal oscillation induced by an interaction between sea ice and ocean in a numerical polar ice-ocean model

A numerical model of simplified Arctic Ocean and Greenland-Norwegian Seas is presented. The essential effects of sea ice, river runoff, surface cooling, and water exchange between the Greenland-Norwegian Seas and the Atlantic Ocean are included. A thermal oscillation occurs due to an interaction between the sea ice and the ocean. The river runoff forms a low-salinity surface layer, which is essential to the oscillation. Parameters governing the time scale of the oscillation are also discussed