Title

Kuroshio variability at 24 degrees N on mesoscale, seasonal, and decadal time scales

Date of Award

1999

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Meteorology and Physical Oceanography

First Committee Member

Thomas N. Lee, Committee Chair

Second Committee Member

William E. Johns, Committee Member

Abstract

The 24°N section crosses the North Pacific Subtropical Gyre, with the intensified Kuroshio on the western boundary confined by the East Taiwan Channel (ETC). As part of the World Ocean Circulation Experiment (WOCE), the PCM-1 moored current meter array was deployed in the ETC to monitor the Kuroshio transport and structure from September 1994 to May 1996. In this study, the moored measurement of the Kuroshio is combined with historical data, both long-term sea level records and basinwide hydrographic surveys, in addition to modern satellite observations and numerical model results, to investigate the Kuroshio variability and its role in the North Pacific climate system.Approximately 60% of the subinertial velocity and temperature variance in the Kuroshio east of Taiwan is associated with two modes revealed from empirical orthogonal function (EOF) analysis. The 'transport' mode is dominated by a 100-day peak, while the most coherent energetic 'meandering' signals are found in four limited frequency bands centered near periods of 100 days, 40 days, 18 days, and 10 days.On the 100-day time scale, the Kuroshio transport entering the East China Sea is strongly related to meandering of the current caused by westward-propagating anticyclonic eddies from the interior ocean. During low transport events, the Kuroshio meanders off-shore and partially bypasses the East Taiwan Channel to flow east of the Ryukyu islands.The improved estimate of Kuroshio transport and its seasonal variation from continuous measurements by the PCM-1 array and sea level difference (SLD) are used to determine the trans-Pacific heat flux and its seasonal cycle across 24°N. With 0.55 PW annual mean and an uncertainty of 0.2 PW, the heat flux has a minimum value of -0.07 PW in January and February but becomes stronger in the second half of the year with a maximum of 1.01 PW in July and a secondary maximum of 0.9 PW in November.The PCM-1 records, hydrographic sections, and SLD across the Kuroshio over the last 30 years consistently suggest a transport increase in 1975 and a decrease in 1989. This decadal transport variation is found to result from the subtropical gyre adjustment to wind curl anomalies along 24°N and in the southern part of the gyre. EOF analysis of the North Pacific SST from 1960--1998 reveals two primary SST patterns confined along the Subtropical Front Zone (STFZ) and Subarctic Front Zone (SAFZ) respectively. The temporal variation of the STFZ mode shows no relationship with the Kuroshio transport but a significant anticorrelation with the central Equatorial Pacific SST anomaly. (Abstract shortened by UMI.)

Keywords

Physical Oceanography; Physics, Atmospheric Science

Link to Full Text

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