Fig. 1.
Time series (1955–2012) of yearly, ocean heat content (1022 J) for the 0–700-m layer of the Indian Ocean (thick solid curves). One standard deviation errors (thin vertical lines) and linear trends (dotted lines) are shown in each panel. Data provided by Dr. John Antonov and replotted after Levitus et al. (2009).
Fig. SB1.
Schematic diagram of the Indo-Pacific Walker circulation. The ascending branch over warm water is associated with low surface pressure and the descending branches over cold water are associated with high surface pressure.
Fig. 2.
(a) January and (b) July monthly SST climatology (color) and surface wind stress (arrows) from HadISST (Rayner et al. 2006) and ECMWF operational analysis/reanalysis winds (Balmaseda et al. 2008) for the 1960–2009 period; (c) January and (d) July depth of 20°C isotherm (D20; color) averaged for 2001–12 period based on in situ temperature data (Hosoda et al. 2008) and surface currents from Ocean Surface Current Analyses Real-Time (OSCAR) data (arrows; Bonjean and Lagerloef 2002) averaged for 1992–2012. Large bulk arrows identify the Leeuwin Current, Agulhas Current, ITF, SEC, and Somali Currents. The black boxes show the thermocline ridge region.
Fig. 3.
Schematic diagram showing the zonal- and time-mean meridional overturning circulation of the upper Indian Ocean that consists of a STC and CEC. Adapted from Lee (2004).
Fig. 4.
(left) September, October, and November mean SSTA for the 1997 IOD event, based on the detrended and demeaned SST from 1920 to 2011; (right) dipole mode index (DMI; black) for each year, which is defined as the September, October, and November mean SSTA difference between the western pole (10°S–10°N, 50°–70°E) and eastern pole (10°S–0°, 90°–110°E); the red curve is 8-yr low-passed DMI, which shows decadal variability. The red dashed vertical line marks the 1997 IOD.
Fig. 5.
(a) Linear trend of HadISST (Rayner et al. 2006) from 1950 to 2010; color (white) shading shows values that are above (below) 95% significance; (b)–(d) As in (a), but for SST from Hurrell et al. (2008), Kaplan et al. (1998), and Smith and Reynolds (2004) extended reconstructed (ER) data, respectively. The two horizontal lines show 15°S and 15°N latitudes. The tropical Indian Ocean warms faster than most regions of the tropical Pacific and Atlantic, except for a local area in the eastern Pacific south of the equator. This trend pattern also holds for median Hadley Centre Sea Surface Temperature dataset version 3 (HadSST3) data (Kennedy et al. 2011a,b) for the period of 1958–2006, even though the warming rate over the Indo-Pacific warm pool is slower (not shown). HadSST3 data are available until 2006 and have too many missing values in the tropical Pacific from 1950–57.
Fig. 6.
Linear trend of zonal-mean temperature across the Indian Ocean in the upper 1500 m from 1955 to 2003. The contour interval is 0.05°C decade−1, and the dark solid lines are zero contours. Pink shading indicates values ≥ 0.025°C decade−1 and blue shading indicates values ≤ −0.025°C decade−1. Adapted from Bindoff et al. (2007).
Fig. 7.
(a) The 1950–2000 climatological-mean surface salinity. Contours every 0.5 on the practical salinity scale (PSS) are plotted in black. (b) The 50-yr linear surface salinity trend [PSS (50 yr) −1]. Contours every 0.2 are plotted in white. Regions where the resolved linear trend is not significant at the 99% confidence level are stippled in gray. Adapted from Durack and Wijffels (2010).
Fig. 8.
Regional sea level trends for 1961–2001 computed from (a) the Church et al. (2004) reconstructed data, (b) the Hamlington et al. (2011) reconstructed data, and (c) a Hybrid Coordinate Ocean Model (HYCOM) simulation. Adapted from Hamlington et al. (2011).
Fig. 9.
(a) Linear trend of SSH anomaly (SSHA) from multisatellite merged French Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) data (Ducet et al. 2000) for the 1993–2000 period; values exceeding 95% significance are shown; (b) As in (a), but for 2000–07. Units are centimeters per year. The horizontal line marks the latitude of 15°S.
Fig. 10.
Linear trends in SSHA for the period 1993–2000 for (a) HYCOM experiment with full forcing in both the Indian and Pacific Oceans (referred to as INDOPAC), (b) HYCOM experiment with variability of the Pacific forcing excluded (referred to as IND), and (c) DIFF = (INDOPAC – IND), which assesses the effect of Pacific forcing via the Indonesian Archipelago and also includes oceanic internal variability effect; (d)–(f) As in (a)–(c), but for the period of 2000–07. Values exceeding 95% significance are shown. Units are centimeters per year. Adapted from Trenary and Han (2013).
Fig. 11.
The first two EOF patterns of steric sea level anomalies over the (left) Indo-Pacific sector and (right) their corresponding normalized PCs at decadal (7-yr low-passed) time scales from an OGCM experiment. Arrows are the wind stress components regressed onto each normalized PC. The percentage explained by each EOF is shown in parentheses. Adapted from Nidheesh et al. (2013).
Fig. 12.
(a),(c) PCs and (b),(d) spatial amplitudes of the first and second EOF modes of the simulated decadal (9–35-yr bandpass) SSTA by a global coupled model control run. (e)–(h) As in (a)–(d), but for the observed decadal (9–35-yr bandpass) SSTA from extended reconstructed data of Smith and Reynolds (2004). Contour interval is 0.01°C and negative anomalies are shaded for the spatial amplitude (from Tozuka et al. 2007).
Fig. 13.
(a) The leading EOF of SST for the Indian Ocean, based on 8-yr low-pass filtered monthly HadISST from 1900 to 2008, which explains 54% variance. The monthly SST data from 1870 to 2012 are first detrended and demeaned and then the Lanczos low-pass filter with half power point placed at 8-yr period is applied. The filtered SST from 1900 to 2008 is chosen to perform the EOF analysis. (b) As in (a), but for the Pacific SST, which represents the IPO spatial pattern and explains 35% variance. (c) The leading PC (PC1) of 8-yr low-passed SST for the Pacific (black curve) and Indian Ocean (red). Adapted from Han et al. (2014).
