Fig. 1

Index of El Ni?o event and its spatial structure. a) Distribution of Ni?o3.4 index. b) Distribution of SSTA in winter (NDJ) of the 2015/2016 event. c) The CTI, EPI and CPI in the CP event. d) The CTI, EPI and CPI in the 1997/1998 event. e) The CTI, EPI and CPI in the 2015/2016 event"

Fig. 2

The pre-condition of the 2015/2016 El Ni?o event. a) NPO index and PMM index in the 2015/2016 event. b, c, d) Distributions of SSTA and wind anomalies in the equatorial Pacific Ocean averaged over Nov and Dec 2014, over Jan and Feb 2015, and over Mar and Apr 2015, respectively"

Fig. 3

Time-longitude sections of SSTA and surface zonal current anomalies. a, b, c) Time-longitude cross sections of SSTA averaged over 2°S-2°N for the CP, 1997/1998 and 2015/2016 events, respectively. The contour interval is 0.5°C. The time interval is one week. d, e, f) Time-longitude cross sections of surface zonal current anomalies averaged over 2°S-2°N for the CP, 1997/1998 and 2015/2016 events, respectively. The contour interval is 0.2 m·s-1. The time interval is one week"

Fig. 4

Time-longitude sections of surface zonal wind anomalies and SSHA. a, b, c) Time-longitude cross sections of surface zonal wind anomalies averaged over 2°S-2°N for the CP, 1997/1998 and 2015/2016 events, respectively. The contour interval is 4 m·s-1. The time interval is one week. d, e, f) Time-longitude cross sections of SSHA averaged over 2°S-2°N for the CP event, 1997/1998 event and 2015/2016 event, respectively. The contour interval is 0.1 m. The time interval is one week"

Fig. 5

Contributions of zonal advection feedback and thermocline feedback for the CP, 1997/1998 and 2015/2016 events, respectively. a) The changes of$-u'{{\bar{T}}_{x}}$ in four phases. b) The changes of$-\bar{w}T_{z}^{'}$ in four phases. The backgrounds of different colors represent different regions; they are Ni?o4 zone, Ni?o3.4 zone, Ni?o3 zone, and Ni?o1+2 zone, respectively. Phase I is the average of Feb and May 2015. Phase II is the average of Jun and Sep 2015. Phase III is the average of Oct 2015 and Jan 2016. Phase IV is the average of Feb and May 2016. The mixed layer depth is 50 m"

Fig. 6

Time-longitude sections of SSHA in the Pacific Ocean during 2015-2016. a, b, c, d) The time-longitude cross sections of SSHA for 5°S, 0°(EQ), 5°N, and 10°N, respectively. The contour interval is 0.1 m. The time interval is one week"

Fig. 7

The changes of warm water volume anomalies in the equatorial Pacific Ocean during 2014-2016. The blue line represents the warm water volume anomalies averaged over 5°S-5°N and 120°E-80°W, the red line represents the warm water volume anomalies averaged over 5°N-20°N and 120°E-80°W, the green line represents the warm water volume anomalies averaged over 5°S-20°S and 120°E-80°W. Calculation formula for warm water volume anomalies is $\iint{\frac{1}{\Delta \rho '\rho }\Delta h\Delta x\Delta y}$, where $\Delta h$ is SSHA, and$\Delta \rho '\rho =0.005$"