ENSO is the strongest interannual signal in the global climate system with worldwide climatic, ecological and societal impacts. Over the past decades, the research about ENSO prediction and predictability has attracted broad attention. With the development of coupled models, the improvement in initialization schemes and the progress in theoretical studies, ENSO has become the most predictable climate mode at the time scales from months to seasons. This paper reviews in detail the progress in ENSO predictions and predictability studies achieved in recent years. An emphasis is placed on two fundamental issues: the improvement in practical prediction skills and progress in the theoretical study of the intrinsic predictability limit. The former includes progress in the couple models, data assimilations, ensemble predictions and so on, and the latter focuses on efforts in the study of the optimal error growth and in the estimate of the intrinsic predictability limit.

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Utilizing improvements in experimental equipment, analytical methods and the initial material, the solubility isotherms of the ternary system MgCl 2 −MgSO 4 −H 2 O were determined in detail at T = (323.15 and 348.15) K using an isothermal method of solid−liquid equilibrium. The results indicate that the solid phases MgSO 4 •nH 2 O (s) (n = 6, 1) and MgCl 2 •6H 2 O (s) are stable and MgSO 4 •nH 2 O (s) (n = 5, 4) are metastable at 323.15 K, which contradicts the results of a previous experimental study 1 in which the phase MgSO 4 •4H 2 O (s) was reported as stable. The liquidus of the four solid phases MgSO 4 •nH 2 O (s) (n = 6, 4, 1) and MgCl 2 •6H 2 O (s) were measured at 348.15 K in this work. The findings indicate that the phases MgSO 4 •H 2 O (s) and MgCl 2 • 6H 2 O (s) are stable and MgSO 4 •6H 2 O (s) and MgSO 4 •4H 2 O (s) are metastable at 348.15 K. Remarkable differences between this work and the literature solubility data for the phase MgSO 4 •H 2 O (s) at 348.15 K are observed. A Pitzer−Simonson−Clegg thermodynamic model was chosen to simulate the properties of the binary systems and to correlate the solubility isotherms of the ternary system at 298.15 K in our previous study and 323.15 K and 348.15 K in this work. Good agreement has been found between the calculated and experimental results. Applying the model parameters and solubility isotherms in the ternary system measured in this work, we obtained the solubility product parameters ln K and chemical potentials for the solid phases MgSO 4 •nH 2 O (s) (n = 6, 5, 4, 1) over a wider temperature range than those for the binary system MgSO 4 −H 2 O.