On the Origin of TPOS and the First Observation of an Equatorial Ocean Kelvin Wave

Jacob Bjerknes's pioneering studies in the 1960s of global atmospheric response to equatorial sea surface temperature (SST) perturbations set the stage for two major tropical ocean-atmosphere observational programs in the 1970s. The North Pacific Experiment (NORPAX) and Equatorial Pacific Ocean Climate Studies (EPOCS) were built around the question: How did equatorial ocean circulation contribute to SST perturbations in the central (NORPAX region) and eastern (EPOCS region) equatorial Pacific? The answer required long-period time series measurements of surface wind and upper-ocean currents and temperature recorded on the Pacific equator where water depths were more than 5,000 m. Compounding the logistical challenge of remoteness were strong currents greater than 0.5 m s^-1 towards the west at the surface and 1.5 m s^-1 towards the east at 100 m. In 5 August – 9 September 1976, I tested a moored observational system to record time series measurements of surface wind and currents at 2 depths in the upper ocean at 0°, 140°W. I incorporated fairings in the upper 300 m of the mooring to reduce current drag. Since this was my first equatorial taut-line surface mooring (called EQUA-1), I intended the research vessel to remain near the mooring in case a problem occurred, which was a best practice in 1974 when the Soviet Union deployed surface moorings in the equatorial Atlantic for time intervals up to 3 weeks. Ten days after the EQUA-1 deployment, I made a high-risk decision to leave EQUA-1 on station when the ship made a medical emergency transit to Honolulu. The success of EQUA-1 was followed with EQUA-2 at 0°, 125°W from 4 April – 11 July 1977. EQUA-2 had a full complement of instrumentation, including current meters at 10, 50, 100, 150, and 200 m. The start time of EQUA-2 was very fortuitous. The very large pulse of eastward transport per unit width on 10-30 April 1977 represented the first observation of the annual April appearance of an equatorial Kelvin wave. The successes of EQUA-1 and EQUA-2 led, in January 1979, to continuous monitoring of surface winds and upper ocean currents and temperature at several sites along the equator. Real-time transmission of measurements began in 1983. In the mid 1980s the moored current meter array provided engineering knowledge for the development of the TAO monitoring system. TPOS subsumed TAO.