Fig. 1

The first two modes of the Joint empirical orthogonal functions (EOF) of boreal spring (March—April—May) mean precipitation rate (shaded, mm·month-1) and sea surface temperature (contours, ℃) in the global tropical ocean and the corresponding time series. (a) the first mode; (b) the second mode; (c) the corresponding time series (PC1 and PC2). Short dashed lines indicate the value of one standard deviation, the dotted line indicates the zero. The gray bars in c indicate the three-month mean Nino3.4 index in November—next January (NDJ)"

Fig. 2

Lead and lag correlation coefficient between the Noni 3.4 index and PC1, and PC2, respectively. (a) PC1 and Niño3.4 index; (b) PC2 and Niño3.4 index. Dashed lines indicate the threshold value of 95% confidence level of Student’s t-test, the grey rectangles mark the mature phase of the first and second modes, the lead and lag indicate the Nino3.4 index leads and lags the first and second modes"

Fig. 3

Anomalies of precipitation (Precip, mm·month-1), sea surface temperature (SST, ℃), sea level pressure (Slp, hPa), and 10 m wind (m·s-1) in the tropical Atlantic Ocean obtained by regressing to the PC1, respectively. (a, c, e) precipitation (shaded) and SST (contours); (b, d, f) Slp (shaded) and winds (vectors); (a, b) the last December to January; (c, d) February—March; (e, f) April—May. The regressed results exceeding 95% confidence level of Student’s t-test are shown"

Fig. 4

Anomalies of precipitation (Precip, mm·month-1), sea surface temperature (SST, ℃), sea level pressure (Slp, hPa), and 10 m wind (m·s-1) in the tropical Indian Ocean obtained by regressing to the PC1, respectively. (a, c, e, g) precipitation (shaded) and SST (contours); (b, d, f) Slp (shaded) and winds (vectors); (a, b) the last October to November; (c, d) December to January; (e, f) February—March; (g, h) April—May. The regressed results exceeding 95% confidence level of Student’s t-test are shown."

Fig. 5

Longitude-time diagram of the meridional averaged anomalies of sea surface height (SSH, shaded, cm), and 10 m wind curl (contours, s-1) in the south tropical Indian Ocean between 12°—8°S obtained by regressing to the PC1, respectively. The regressed results exceeding 95% confidence level of Student’s t-test are shown"

Fig. 6

Latitude-time diagram of the zonal averaged anomalies of precipitation (mm·month-1), sea surface temperature (℃), sea level pressure (hPa), and 10 m wind (m·s-1) in the tropical Indian Ocean, the Atlantic Ocean and the Pacific Oceans obtained by regressing to the PC1 and PC2, respectively, and the climatological mean precipitation and wind. The regressed results exceeding 95% confidence level of Student’s t-test are shown. (a, d, g) Indian Ocean (50°—90°E); (b, e, h) Atlantic Ocean (60°W—20°E); (c, f, i) Pacific (140°E—80°W); (a, b, c) regressions of precipitation (shading) and SST (contours); (d, e, f) regressions of sea level pressure (shaded), and 10 m wind (vectors); (g, h, i) climatological mean precipitation (shaded) and wind (vectors). White bold contours in e and f labels the heavy precipitation centers with precipitation rate larger than 130 mm·month-1. The anomalies in the tropical Indian Ocean and the Atlantic Ocean are regressed to the PC1; the anomalies in the Pacific ocean are regressed to the PC2"

Fig. 7

Anomalies of precipitation (mm·month-1) and sea surface temperature (℃) in the tropical Pacific Ocean obtained by regressing to the PC2, respectively. The regressed results exceeding 95% confidence level of Student’s t-test are shown. (a) spring (March—April—May, MAM); (b) summer (June—July—August, JJA); (c) fall (September—October—November, SON); (d) winter (December—January—February, DJF)"