Spatial and temporal variability of heat content above the thermocline in the tropical Pacific Ocean

Heat content of the upper layer above the 20℃ isotherm in the tropical Pacific Ocean is estimated by using the sea temperature data set with a resolution 2°latitude×5°longitude (1980~1993) for the water depths (every 10 m) from 0 m to 400 m, and its temporal and spatial variabilities are analyzed. (1) The temporal variability indicates that the total heat in the upper layer of the equatorial Pacific Ocean is charcterized by the interannual variability. The time series of the equatorial heat anomaly 5 months lead that of the El Nino index at the best positive lag correlation between the two, and the former 13 months lag behind the latter at their best negative lag correlation. Therefore the equatorial heat content can be used as a better predictor than the El Nino index for a warm or cold event. In addition, it is also found that less heat anomaly in the equator corresponds to the stronger warm events in the period (1980~1993) and much more heat was accumulated in the 4 years including 1992/11993 ENSO (1989~1993) than the 4 years including 1982/1983 ENSO (1980~1983); (2) The spatial variability indicates that the area with the highest lag correlation among the grids moves in an anti-clockwise circle in the northern tropical Pacific Ocean within 4 years period and in a clockwise circle in the southern tropical Pacific Ocean. This result provides scientific evidence for the quasi-cycle theory of El Nino events.