State-of-the-art Climate Models Overestimate the Coupling between the Subsurface and Surface Indian Ocean Dipoles
The Indian Ocean Dipole (IOD) is a climatic feature of the tropical Indian Ocean (TIO) involving an oscillation of sea surface temperatures between the western and eastern parts of the basin. Recent evidence has highlighted the contribution of an existing east–west oscillation of subsurface temperature in the TIO (Sub-IOD) to the development of the surface IOD. Interestingly, both the IOD and Sub-IOD are known to be modulated by the El Nino–Southern Oscillation (ENSO)—a recurring climate pattern involving changes in sea surface temperatures in the central and eastern tropical Pacific Ocean. Therefore, with the continual development of climate models and reanalysis datasets (products that provide numerical descriptions of the climate by combining models with observations), the mutual linkages among the Sub-IOD, IOD, and ENSO, can and should be further investigated on an ongoing basis.
Recently, a paper published in
Advances in Atmospheric Sciences has revealed that most state-of-the-art climate models tend to overestimate the amplitude and dominant period of the Sub-IOD. By assessing the historical simulations of 31 such models, the researchers also found that the coupling between the Sub-IOD and surface IOD is overly strong owing to a biased much steeper thermocline tilt in most of the models compared with reanalysis data. Moreover, in terms of the different types or "flavors" of ENSO that we now know exist, most models show a much tighter association of the Sub-IOD and IOD with the canonical ENSO (i.e., the classical ENSO type in which the maximum temperature anomalies are found in the eastern Pacific). Plus, the linkage between the more westward-centered Central Pacific type of ENSO and the Sub-IOD that occurs in winter to spring, independent of the IOD, is also well reproduced.
"Our results can potentially lead to more reliable predictions and future projections of regional and global climate," says SONG Ge, from the Institute of Atmospheric Physics at the Chinese Academy of Sciences and lead author of the study.
Lead–lag correlations between the indices of the IOD and Sub-IOD in 31 state-of-the-art climate models and in reanalysis data (ORAS4). Darker colors represent a stronger coupling between the IOD and Sub-IOD (image by SONG Ge).
Reference: Citation: Ge, S., and R. C. Ren, 2023: Subsurface and surface Indian Ocean Dipole and their association with ENSO in CMIP6 models. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-022-2086-2 .
