Changes in Thermal Structure of the Equatorial Pacific during the 1972 El Niño as Revealed by Bathythermograph Observations

Abstract

Abstract Bathythermograph data from the equatorial Pacific are used to study changes in upper ocean thermal structure during the period 1971–73 using data averaged over 2- or 3-month segments. This gives reasonable descriptions of the changes in two regions—the central Pacific (particularly in a section crossing the equator at 170–160°W) and along the eastern boundary. The behavior in the two regions is quite distinct, e.g., in the central Pacific, thermocline depth anomalies do not correlate well with surface temperature anomalies, but they do along the eastern boundary. The first baroclinic mode can be used to describe changes in vertical structure in the central Pacific, but the major changes near the eastern boundary are much more like those associated with the second baroclinic mode. Subsurface changes along the eastern boundary are extremely large, e.g., the 14°C isotherm at the equator plunged from the 100 m level in January–February 1972 to the 250 m level in May–June. It did not get back to the 1...