East Asia and Western Pacific METEOROLOGY AND CLIMATE

399
THE RELATIONSHIP BETWEEN CURRENTS AND WINDS
NORTHEAST OF TAIWAN
Wen-Ssn Chuang
Institute of Oceanography
National Taiwan University
Taipei, China
ABSTRACT
In the area northeast of Taiwan, the Kuroshio turns as it
encounters the continental shelf of the East China Sea. The turning
also triggers a vigorous exchange of water masses between the open
ocean and the marginal sea, which has been previously identified from
hydrographic surveys and satellite infrared images. Direct evidence
from current measurement, however, was rare. Because of this a
current meter mooring was placed at the shelf break (about 50 km from
the coast of Taiwan at water depth of 500 m) from September 9 to
November 21, 1988. Two current meters were attached to the moorings at
240 and 345 m below the surface.
There were quite significant velocity and temperature variations
in the three months the data covered. In September, the atmospheric
pressure was low, the winds were mild, and the current in both layers
were towards the south-southeast. In other words, there was a
continuous drainage of shelf water to the open ocean in the study
area. In October, the weather condition was characterized by frequent
tropical low (typhoon) passages, the currents fluctuated accordingly.
The dominant flow was still towards the ocean in both layers, but the
magnitude was reduced compared with that of September. The northeast
monsoon season began on November, and the study area was covered by
high pressure system most of the time. The currents at the 240-m depth
showed shoreward flow, while the currents at the 345-m stayed seaward.
Despite the air gradually cooled from September to November, the
water temperature increased during the same period. A sign which
suggests that either the path of the Kuroshio drew near the snelf, or
part of the Kuroshio water was brought to the shelf break. ^The
temperature difference between the 240 and 345-m depth remained
unchanged, in September and October, but increased quite significantly
in November. Together with the information provided by current
records, it is believed that the strength of the outflow from the East
China Sea weakened towards the end of the summer, and the whole
Kuroshio approaches In. In the early winter, the Kuroshio intrusion
occurs in the upper 250 meters or more. Conceivably, these open oceanmarginal
sea exchange processes are seasonally dependent and may be
closely related to the large scale atmospheric conditions.