Dynamic height is calculated from XBT and surface salinity data
in the central Pacific using a mean temperature-salinity (T-S)
relation in the usual way below the thermocline but assuming
isohaline water in the upper layer where the temperatures are
isothermal. This scheme produces a better estimate of dynamic
height than the use of a mean T-S relationship alone and produces
significant improvements near the equator where small pressure
gradients imply large geostrophic currents. During the El
Niño of 1982-83, water of very low surface salinity was
observed spanning the equator; this event is attributed both to
extreme local rainfall and anomalous advection from the western
Pacific. Geostrophic transports of the major surface currents are
estimated for the period January 1979 through December 1984. The
North and South Equatorial countercurrents are found to have the
largest annual fluctuations, and the vertical displacements of the
thermocline associated with these fluctuations are qualitatively
consistent with local Ekman pumping. A striking anomaly of the
1982-83 El Niño was a strong peak in North Equatorial
Countercurrent transport in late 1982; at this time surface flow
was eastward from 10°N to 5°S with volume transport on
the order of 60-70 × 10
m
s
. In mid-1983 NECC transport fell to
less than 2 × 10
m
s
.
During the first four months of 1983 strong westerlies extended
from the equator to about 10°S over a broad region in the
central Pacific. The wind curl pattern associated with this
anomaly led to shoaling of the thermocline by 60 m from 5° to
15°S.
Download the paper as it appeared in JPO (pdf, 2.0 Mb)
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Dr. William S. Kessler
NOAA / PMEL / OCRD 7600 Sand Point Way NE Seattle WA 98115 USA |
Tel: 206-526-6221
Fax: 206-526-6744 E-mail: william.s.kessler@noaa.gov |
| See also: | Kessler home page Kessler publications PMEL home page | |