Fig. 1

Anomalous Ni?o 3.4 (170°-120°W, 5°S-5°N) index (dotted line, left axis), anomalous North Atlantic tripole mode index (solid line, right axis) evolution during El Ni?o events of 1997-1998 (a) and 2015-2016 (b). The number 0 represents a developing year, and 1 represents a decaying year"

Fig. 2

SSTA (shading) and anomalous wind vector at 850 hPa (arrow) during the developing phase in June-August (a, b) and September-November (c, d), the peak phase in December-February (e, f), and the El Ni?o decaying phase in March-May (g, h) and June-August (i, j) for 1997-1998 (left panels) and 2015-2016 ( right panels)"

Fig. 3

Ocean dynamic process (green) and thermal process (orange) contributions for the change of regionally-averaged ocean mixed layer SSTA (gray) in the tropical North Atlantic (50°-15°W, 10°-25°N) in January-March of 1998 and 2016"

Fig. 4

All terms contributions of 1998 (blue) and 2016 (orange) for the change of regional-average ocean mixed layer SSTA in the tropical North Atlantic (50°-15°W, 10°-25°N) from January to March"

Fig. 5

Meridional time section structure of the tropical North Atlantic surface wind anomaly (arrow; units: m·s-1), latent heat flux anomaly (contour; units: W·M-2, downward is positive), SSTA (shading; units: ℃) from September in El Ni?o developing phase to August in El Ni?o decaying phase. All data are regionally-averaged in the tropical North Atlantic (50°-15°W). The solid line is positive and the dashed line is negative. a) 1997-1998; b) 2015-2016"

Fig. 6

Spatial distributions of tropical North Atlantic surface latent heat flux anomaly (a, b; units: W·M-2), net surface shortwave radiation anomaly (c, d; units: W·M-2) in February and the anomalous total cloud cover (c, d; shading, units: % ) in January-March in El Ni?o developing years. The solid line is positive and the dashed line is negative, Contour lines range from -60 to 60 with an interval of 10 (a, b) and range from -16 to 16 with an interval of 4 (c, d); Boxes are tropical diagnostic area. (a, c) are for 1998, and (b, d) are for 2016"

Fig. 7

Spatial distributions of Pacific and Atlantic anomalous geopotential height at 500 hPa (contour; units: gpm), anomalous tropospheric temperature (shading; units: ℃) and anomalous wind vector at 850 hPa (arrow; unit:s m·s-1) in Jannuary-March in El Ni?o developing years. The solid line is positive and the dashed line is negative. a) 1998; b) 2016"

Fig. 8

Spatial distributions of Pacific and Atlantic anomalous zonal wind at 300 hPa (shading; units: m·s-1) and climatology (contour; units: m·s-1) in Jannuary-March in El Ni?o developing years. a) 1998; b) 2016"

Fig. 9

Meridional vertical section structure of Hadley circulation anomalies in the Atlantic (between 80°W and 0°) by averaging anomalous longitudinal divergent wind (a, b; units: m·s-1) and anomalous vertical velocity, zonal vertical section structure of Walker circulation anomalies (between 5°S and 5°N) by averaging anomalous latitudinal divergent wind (units: m·s-1) and anomalous vertical velocity (c, d; units: 10-2 mb·s-1) during El Ni?o developing phase in January-March. (a, c) 1998; (b, d) 2016"