86
Michael J. McPhaden
Figure 6.1. Initial design of a TOGA thermal field observing system. Solid lines indicate Ship-ofOpportunity XBT lines, EPOCS Tropic Heat indicates current meter moorings, and IES indicates inverted
echo sounders, which provide a measure of sea level variability. Drifting and moored thermistor chains
are also shown (after U.S. TOGA Project Office, 1988).
technically viable and economically feasible. Sampling characteristics of the proposed
observing system components were viewed as complementary, but each had its limitations. For example, ship-of-opportunity expendable bathythermographs (XBTs), a
proven and reliable technology, could provide good vertical (4 m) and along-track (1
◦ )
horizontal resolution. However, infrequent monthly temporal sampling contaminated
the climate signals of interest with aliased energy from unresolved short-time-scale
fluctuations, particularly near the equator. Also, XBT sampling was confined to fixed
commercial shipping lanes, which left large areas of the ocean unsampled. Drifting
thermistor chains, like those used in FOCAL or in the North Pacific for the 1980–81
Storm Transfer and Response Experiment (STREX) (Large et al., 1986), could provide time series measurements at daily or higher temporal resolution in real time via
Service Argos. However, they were subject to potential spatial sampling biases due
to the effects of converging and diverging upper ocean currents. Moored thermistor
chains, which were still under development, likewise potentially offered the advantage
of high temporal resolution data in real time, but the presumed expense of moorings
would limit their deployment to a few key regions. Thus, both drifting and moored
thermistor chains were primarily viewed as “gap fillers” for the XBT network, which
was considered the principal means of obtaining basin scale coverage for upper ocean
thermal structure.
The AOML workshop recommended that a design study team be commissioned
to systematically evaluate various sampling schemes for upper ocean thermal structure in the Pacific. In response, Bruce Taft and I convened a meeting in Seattle in July
Michael J. McPhaden
Figure 6.1. Initial design of a TOGA thermal field observing system. Solid lines indicate Ship-ofOpportunity XBT lines, EPOCS Tropic Heat indicates current meter moorings, and IES indicates inverted
echo sounders, which provide a measure of sea level variability. Drifting and moored thermistor chains
are also shown (after U.S. TOGA Project Office, 1988).
technically viable and economically feasible. Sampling characteristics of the proposed
observing system components were viewed as complementary, but each had its limitations. For example, ship-of-opportunity expendable bathythermographs (XBTs), a
proven and reliable technology, could provide good vertical (4 m) and along-track (1
◦ )
horizontal resolution. However, infrequent monthly temporal sampling contaminated
the climate signals of interest with aliased energy from unresolved short-time-scale
fluctuations, particularly near the equator. Also, XBT sampling was confined to fixed
commercial shipping lanes, which left large areas of the ocean unsampled. Drifting
thermistor chains, like those used in FOCAL or in the North Pacific for the 1980–81
Storm Transfer and Response Experiment (STREX) (Large et al., 1986), could provide time series measurements at daily or higher temporal resolution in real time via
Service Argos. However, they were subject to potential spatial sampling biases due
to the effects of converging and diverging upper ocean currents. Moored thermistor
chains, which were still under development, likewise potentially offered the advantage
of high temporal resolution data in real time, but the presumed expense of moorings
would limit their deployment to a few key regions. Thus, both drifting and moored
thermistor chains were primarily viewed as “gap fillers” for the XBT network, which
was considered the principal means of obtaining basin scale coverage for upper ocean
thermal structure.
The AOML workshop recommended that a design study team be commissioned
to systematically evaluate various sampling schemes for upper ocean thermal structure in the Pacific. In response, Bruce Taft and I convened a meeting in Seattle in July