Figure 3

Average sub-thermocline temperature in the southern Indian Ocean.

Mean sub-thermocline temperature across the southern tropical and subtropical IO from: (a) observations, (b) CMIP5 historical and RCP experiments ensembles, (c) individual forcing experiment ensembles from runs that contain external forcings other than anthropogenic aerosols and (d) individual forcing experiment ensembles from runs that contain anthropogenic aerosols, including the RCP4.5 and 8.5 experiments. The number of models used in each MME is shown in the brackets of the figure legend. The models selected to show the RCP changes in (d) are the CMIP5 models that have individual forcing experiments. The region averaged for the observations is 40°E–110°E, 10°S–30°S, 300–900 m (except for Levitus09 which is 300–700 m) and for simulations is 40°E–110°E, 15°S–35°S, 300–900 m. As the models simulate the cooling further south, the latitudinal extent of the simulations is extended 5° polewards. A time series of the PDO⁵⁹, with a 144-month low-pass filter, is shown in (b). The observational estimate average is based on four observed products: Levitus09 (1955–2009), Ishii09 (1945–2011), Argo⁵⁸ (2005–2012) and SODA-POP V2.2.4 (1955–2010). All time series have been low-pass filtered using an 11-year running mean, except for the Argo measurements which show the interannual variability. The dotted lines in (a) indicates the error estimate of the observational average based on the one-standard deviation of the Argo measurements (considered true observations).