El Ni ˜
no and Ocean Observations
87
1984 specifically to review relevant scientific issues, sampling requirements, existing
methodologies, and next steps toward implementation of a basin scale thermal field
observing system for TOGA (McPhaden and Taft, 1984). By this time, Stan Hayes had
successfully advanced the development of a prototype moored thermistor chain and
had scheduled deployment of a first mooring in the eastern equatorial Pacific for late
1984. Peter Niiler reported on a pilot deployment in the tropical Pacific of two drifting
buoys with thermistor chains and five drifters with dummy chains of varying lengths
to determine the effects of chain length on buoy motion. The workshop recommended
that these efforts continue and expand as a complement to XBT sampling. In particular, the workshop concluded that, “Ultimately, we can anticipate deployments of
about 10–12 moored thermistor chains . . . ” and “ . . . annual deployments of about
30 uniformly spaced drifters drogued with thermistor chains . . . ” as part of the TOGA
effort to routinely observe variations in thermal structure of the upper Pacific Ocean.
DRIFTING THERMISTOR CHAINS, PART II
In April 1985, Bill Large, Jim McWilliams, Peter Niiler, Bruce Taft, and I submitted a
proposal jointly to NSF and the U.S. TOGA Project Office to support the development
of a drifting thermistor chain project as part of the TOGA Observing System (the
name ultimately given to the totality of systematic in situ and satellite measurement
techniques used during TOGA). Large, McWilliams, and Niiler had previously carried
out drifter thermistor chain measurements during STREX. Peter Niiler had already
conducted initial engineering tests of drifting thermistor chains in the tropical Pacific.
Bruce Taft was a longtime veteran of Pacific field programs and would coordinate
logistics, deployments, and initial data processing from PMEL. I was on the research
faculty at the University of Washington by this time (after sharing an office with Bill
Large for awhile as a postdoc at NCAR) and had experience with the FOCAL drifting
thermistor chain project. The proposal was for 3 years initially (1986–88) with the
expectation that we would continue and expand if initial efforts were successful.
Our proposal reviewed well and we were awarded funds for an initial purchase
of 10 drifters. We ordered from the same vendor that produced the STREX drifters,
with a few modifications to the STREX design. One was that we required a 300-mlong thermistor chain rather than the 120-m-long thermistor chain used in STREX to
ensure sufficient depth range to sample the upper thermocline throughout the tropical
Pacific. Another was that we wanted the 12 subsurface thermistors on the chain
multiplexed on three independent wire buses to mitigate data loss due to fish bite,
which was a severe problem with the FOCAL drifters. In principle, neither of these
modifications should have involved significant engineering challenges. In practice,
though, they proved to be the Achilles heel of the project.
We had specified a design lifetime for the drifters of 1 year. However, our first
installment of 10 drifters was poorly fabricated and delivered with software and hardware design flaws. A trial deployment of two drifters in the California Current in
no and Ocean Observations
87
1984 specifically to review relevant scientific issues, sampling requirements, existing
methodologies, and next steps toward implementation of a basin scale thermal field
observing system for TOGA (McPhaden and Taft, 1984). By this time, Stan Hayes had
successfully advanced the development of a prototype moored thermistor chain and
had scheduled deployment of a first mooring in the eastern equatorial Pacific for late
1984. Peter Niiler reported on a pilot deployment in the tropical Pacific of two drifting
buoys with thermistor chains and five drifters with dummy chains of varying lengths
to determine the effects of chain length on buoy motion. The workshop recommended
that these efforts continue and expand as a complement to XBT sampling. In particular, the workshop concluded that, “Ultimately, we can anticipate deployments of
about 10–12 moored thermistor chains . . . ” and “ . . . annual deployments of about
30 uniformly spaced drifters drogued with thermistor chains . . . ” as part of the TOGA
effort to routinely observe variations in thermal structure of the upper Pacific Ocean.
DRIFTING THERMISTOR CHAINS, PART II
In April 1985, Bill Large, Jim McWilliams, Peter Niiler, Bruce Taft, and I submitted a
proposal jointly to NSF and the U.S. TOGA Project Office to support the development
of a drifting thermistor chain project as part of the TOGA Observing System (the
name ultimately given to the totality of systematic in situ and satellite measurement
techniques used during TOGA). Large, McWilliams, and Niiler had previously carried
out drifter thermistor chain measurements during STREX. Peter Niiler had already
conducted initial engineering tests of drifting thermistor chains in the tropical Pacific.
Bruce Taft was a longtime veteran of Pacific field programs and would coordinate
logistics, deployments, and initial data processing from PMEL. I was on the research
faculty at the University of Washington by this time (after sharing an office with Bill
Large for awhile as a postdoc at NCAR) and had experience with the FOCAL drifting
thermistor chain project. The proposal was for 3 years initially (1986–88) with the
expectation that we would continue and expand if initial efforts were successful.
Our proposal reviewed well and we were awarded funds for an initial purchase
of 10 drifters. We ordered from the same vendor that produced the STREX drifters,
with a few modifications to the STREX design. One was that we required a 300-mlong thermistor chain rather than the 120-m-long thermistor chain used in STREX to
ensure sufficient depth range to sample the upper thermocline throughout the tropical
Pacific. Another was that we wanted the 12 subsurface thermistors on the chain
multiplexed on three independent wire buses to mitigate data loss due to fish bite,
which was a severe problem with the FOCAL drifters. In principle, neither of these
modifications should have involved significant engineering challenges. In practice,
though, they proved to be the Achilles heel of the project.
We had specified a design lifetime for the drifters of 1 year. However, our first
installment of 10 drifters was poorly fabricated and delivered with software and hardware design flaws. A trial deployment of two drifters in the California Current in