82
Michael J. McPhaden
by the 1976–77 El Ni˜ no, which was linked to the extreme winter weather across the
eastern half of the United States (Canby, 1977).
NORPAX AND EPOCS
The North Pacific Experiment (NORPAX) was established in the late-1960s with support from the U.S. National Science Foundation (NSF) and Office of Naval Research
(ONR) to look for North Pacific influences on North American climate, building
on ideas developed by Jerome Namais (1969). However, finding little convincing
evidence from observations or atmospheric modeling studies that the North Pacific
Ocean forced the overlying atmosphere to significantly affect seasonal climate variability over the United States (Chervin et al., 1976; Davis, 1978), NORPAX looked
south toward the equator to test oceanic aspects of Bjerknes’s hypothesis for El
Ni˜ no. A centerpiece of the NORPAX experiment was the Hawaii-to-Tahiti Shuttle
Experiment, a sustained effort to study oceanic variability over a 16-month period
during 1979–80 in the central Pacific between 152
◦ W and 158
◦ W (Wyrtki et al.,
1981).
The late 1970s also saw the establishment of NOAA’s Equatorial Pacific Ocean
Climate Studies (EPOCS) program to study El Ni˜ no and its climatic impacts over
North America. EPOCS concentrated its activities in the eastern Pacific between
95
◦ W and 140
◦ W, a region where El Ni˜ no SST, thermocline depth, and sea level
variations were large. An important oceanographic contribution of EPOCS was the
establishment of long-term current meter mooring sites along the equator in the eastern
Pacific to study changes in ocean circulation related to El Ni˜ no (Halpern, 1996).
First attempts by the Woods Hole Oceanographic Institution to anchor surface
current meter moorings on the equator met with only limited success presumably
because drag exerted by the strong vertically sheared South Equatorial Current and
Equatorial Undercurrent parted mooring lines or submerged surface buoys (Taft et
al., 1974). In an effort to design a surface mooring that could survive in this severe
environment, Hugh Milburn of NOAA’s Pacific Marine Environmental Laboratory
(PMEL) performed computer model experiments of taut line mooring dynamics in
equatorial flow regimes to evaluate details of line lengths, system weights, and drag
coefficients. These experiments led to a mooring design that incorporated plastic
clip-on airfoil-shaped fairings to reduce drag in the areas of high current. PMEL successfully deployed one of these newly designed moorings on the equator at 0
◦ , 150
◦ W
for 35 days in August–September 1976 (Halpern et al., 1976) and a second mooring
for almost 100 days in April–July 1977 at 0
◦ , 125
◦ W (Halpern, 1977). The success of
these deployments demonstrated the feasibility of maintaining current meter moorings for long-term measurements along the equator where currents routinely exceeded
100 cm s
−1 in the upper 200 m. Subsequent deployments during EPOCS established
a 6-month design lifetime for equatorial moorings, after which mechanical wear and
biofouling of the current meters became limiting factors.
Michael J. McPhaden
by the 1976–77 El Ni˜ no, which was linked to the extreme winter weather across the
eastern half of the United States (Canby, 1977).
NORPAX AND EPOCS
The North Pacific Experiment (NORPAX) was established in the late-1960s with support from the U.S. National Science Foundation (NSF) and Office of Naval Research
(ONR) to look for North Pacific influences on North American climate, building
on ideas developed by Jerome Namais (1969). However, finding little convincing
evidence from observations or atmospheric modeling studies that the North Pacific
Ocean forced the overlying atmosphere to significantly affect seasonal climate variability over the United States (Chervin et al., 1976; Davis, 1978), NORPAX looked
south toward the equator to test oceanic aspects of Bjerknes’s hypothesis for El
Ni˜ no. A centerpiece of the NORPAX experiment was the Hawaii-to-Tahiti Shuttle
Experiment, a sustained effort to study oceanic variability over a 16-month period
during 1979–80 in the central Pacific between 152
◦ W and 158
◦ W (Wyrtki et al.,
1981).
The late 1970s also saw the establishment of NOAA’s Equatorial Pacific Ocean
Climate Studies (EPOCS) program to study El Ni˜ no and its climatic impacts over
North America. EPOCS concentrated its activities in the eastern Pacific between
95
◦ W and 140
◦ W, a region where El Ni˜ no SST, thermocline depth, and sea level
variations were large. An important oceanographic contribution of EPOCS was the
establishment of long-term current meter mooring sites along the equator in the eastern
Pacific to study changes in ocean circulation related to El Ni˜ no (Halpern, 1996).
First attempts by the Woods Hole Oceanographic Institution to anchor surface
current meter moorings on the equator met with only limited success presumably
because drag exerted by the strong vertically sheared South Equatorial Current and
Equatorial Undercurrent parted mooring lines or submerged surface buoys (Taft et
al., 1974). In an effort to design a surface mooring that could survive in this severe
environment, Hugh Milburn of NOAA’s Pacific Marine Environmental Laboratory
(PMEL) performed computer model experiments of taut line mooring dynamics in
equatorial flow regimes to evaluate details of line lengths, system weights, and drag
coefficients. These experiments led to a mooring design that incorporated plastic
clip-on airfoil-shaped fairings to reduce drag in the areas of high current. PMEL successfully deployed one of these newly designed moorings on the equator at 0
◦ , 150
◦ W
for 35 days in August–September 1976 (Halpern et al., 1976) and a second mooring
for almost 100 days in April–July 1977 at 0
◦ , 125
◦ W (Halpern, 1977). The success of
these deployments demonstrated the feasibility of maintaining current meter moorings for long-term measurements along the equator where currents routinely exceeded
100 cm s
−1 in the upper 200 m. Subsequent deployments during EPOCS established
a 6-month design lifetime for equatorial moorings, after which mechanical wear and
biofouling of the current meters became limiting factors.