ESC seminar No. 36

Dynamics of the Tsuchiya Jets

Date
April 7 (Mon.) 13:30-14:30
Place
Small meeting room, 2nd floor, conference building, YES
Speaker
Dr. Ryo Furue (IPRC, University of Hawaii)
English
Japanese

Abstract

The Tsuchiya Jets (TJs) are narrow eastward currents, located a few degrees on either side of the equator at depths from 200-500m in the Pacific Ocean. In this study, non-eddy-resolving, oceanic general circulation models (OGCMs) are used to investigate the dynamics of the TJs. Most solutions are found in a rectangular basin, extending 100 degrees zonally and from 40S to 40N. They are forced by a meridional wind representing the southerly winds near the South American coast, by a zonal wind with strong curl north of the equator in the eastern ocean to simulate Ekman suction in the Costa Rica Dome (CRD) region, and by basin-wide easterlies to represent trades. They are also forced by surface heating that warms the ocean in the tropics, and by a prescribed interocean circulation (IOC) that enters the basin through the southern boundary and exits through the western boundary from 2N-6N (the model's Indonesian Passages).

To isolate effects of each forcing, we begin with a solution forced only by the IOC, and then sequentially add forcings by the winds. The last solution in the hierarchy, forced by all the aforementioned processes and with minimal diffusion, resembles the observed flow field in the tropical Pacific. Narrow eastward currents, the model TJs, flow across the basin along the poleward edges of a thick equatorial thermostad, and upwell at the eastern boundary and in the CRD region. Their deeper parts are supplied by water that leaves the western boundary current somewhat poleward of the equator. Their shallower parts originate from water that diverges from the deep portion of the Equatorial Undercurrent (EUC); as a result, the TJ transports increase to the east and the TJs warm as they flow across the basin. The lower part of the northern TJ is found to be driven by eddy form drag due to instability waves generated in the CRD region. When diffusivity is increased to commonly used values, the thermostad is less well defined or even absent and the TJs are weak.

The hierarchy, as well as other properties, indicate that the dynamics of the model's TJs are those of an arrested front, which in a 2 1/2-layer model are generated when characteristics of the flow merge or intersect.

Contact

H. Sasaki
Earth Simulator Center
Tel: 045-778-5843
e-mail: sasaki