Dr. Ryo Furue

Japan Agency for Marine-Earth Science and Technology

University of Hawaii

Email: furue@hawaii.edu

Research Interests: The coastal currents along the western and southern coasts of Australia, developing an analytic layer model that potentially explains the existence of the Leeuwin Current, a shallow poleward current along the west coast of Australia, and its connection with the interior southeastern Indian Ocean. He then developed a novel technique to reconstruct the three-dimensional geostrophic velocity field from a gridded hydrographic dataset. He also has been studying the deep, mesoscale zonal jets, a series of eastward and westward alternating, semi-stationary zonal flows prominent below the main pycnocline in GCMs.

How deterministic are the deep zonal jets in the Pacific?

Abstract

Eddy-resolving oceanic general circulation models (OGCMs) often show eastward and westward alternating flows below the main thermocline in the velocity field averaged over one year or longer. Their existence has been confirmed in observations. Several mechanisms have been proposed to explain these deep jets, some of them suggesting that the positions of the jets are determined by external forcing (“deterministic”) and others, that they are only statistically determined. In this study we focus on the North Pacific around 140°W.

To determine how deterministic the deep jets are, we use a 10-member ensemble of runs of an eddy-resolving, semi-global OGCM. Its surface forcing is based on atmospheric conditions derived from a reanalysis product. The ensemble runs are started from the beginning of 1965 and extended to the end of 2016; their difference comes solely from slight differences in their initial conditions. Poleward of the equatorial currents, the tropical jets show some tendency to migrate poleward at decadal timescales and their positions appear deterministic, suggesting that they are controlled

by external forcing. Further poleward, the subtropical jets systematically migrate equatorward at a period of ~5 years, as indicated by a previous study. Their positions are not deterministic. Further poleward, there are several jets which are fixed in time and space and whose positions are deterministic, suggesting that they are controlled by topographic features. Near the American continent, the jets have shorter meridional wavelengths, their positions move in non-systematic ways and their positions are not deterministic.