Fig. 1

Schematic diagram of heat content diagnostic analysis areas and cross-sections. ① represents the meridional section from point (5°N, 118°E) to point (5°S, 118°E); ②represents the zonal section from point (5°S, 118°E) to point (5°S, 148°E). Red line represents western boundary"

Fig. 2

Seasonal change of heat content (a), seasonal averages of heat content in August (b) and November (c) in the equatorial Pacific box (118°E-75°W, 5°S-5°N, 0-300m). Units: ℃"

Fig. 3

Seasonal balance in the equatorial Pacific box. a) The mean (bar) and standard deviation (error bar) of the terms in the heat content equation in the equatorial Pacific box (118°E-75°W, 5°S-5°N, 0-300 m). b) Seasonal evolution of the terms in the heat content equation. c) Decomposition of heat transport using the modified boundary flux form. Positive means the term will increase the heat content in the box."

Fig. 4

Relationship between Niño 3.4 index and heat content anomaly in the equatorial Pacific box. a) Niño 3.4 index (red curve, right Y axis) and the equatorial Pacific box (118°E-75°W, 5°S-5°N, 0-300 m) heat content anomaly (blue bar, left Y axis). b) The lead-lag correlation coefficients of the two time series in Fig. 4a"

Fig. 5

Time integral of anomaly terms in the heat content equation in the equatorial Pacific box (118°E-75°W, 5°S-5°N, 0-300 m). a) Overall balance of terms; b) decomposition of total heat transport using the modified boundary flux form ; c) heat transport in three directions. The dashed circles represent five El Niño events"

Fig. 6

Time integral of anomaly terms in the heat content equation in the Niño 3.4 box (170°W-120°W, 5°S-5°N, 0-80 m). a) Overall balance of terms; b) heat transport in three directions using the modified boundary flux form. The dashed circles represent five El Niño events"

Fig. 7

The reason that the heat content anomaly in the equatorial Pacific box leads the Niño 3.4 index. a) Time integral of meridional heat transport anomaly in the equatorial Pacific box (blue bar, left Y axis) and time integral of vertical heat transport anomaly in the Niño 3.4 box (red curve, right axis). b) Time integral of heat transport anomaly in the equatorial Pacific box (blue bar, left Y axis) and Niño 3.4 box (red curve, right axis). c) Time integral of surface heat flux anomaly in the equatorial Pacific box (blue bar, left Y axis) and Niño 3.4 box (red curve, right Y axis). d) Sum of the time integral of surface heat flux anomaly and the time integral of heat transport anomaly in the two boxes"

Fig. 8

Composite analysis of main terms in the heat content equation in the equatorial Pacific box (118°E-75°W, 5°S-5°N, 0-300m) during eastern Pacific El Niño event (a) and central Pacific El Niño event (b)"

Fig. 9

Composite analysis of main terms in the heat content equation in the Niño 3.4 box (170°W-120°W, 5°S-5°N, 0-80 m) during eastern Pacific El Niño event (a) and central Pacific El Niño event (b)"