Picture (above): Ocean storm at sunset. Credit: Joe Desousa (Unsplash)
Climate models have problems in simulating El Nino correctly. This is partly because most climate models underestimate two important feedback mechanisms operating in the El Niño/Southern Oscillation (ENSO),
- the positive (amplifying) zonal surface wind feedback and
- negative (damping) surface-heat flux feedback.
These are two of the most important atmospheric processes controlling the evolution of El Nino.
A new study by CLEX researchers and colleagues shows that CMIP5 models as a group underestimate the feedbacks by on average by 54% when simulating the sea surface temperatures by themselves. However, if they are forced by observed sea-surface temperatures they only underestimate these atmospheric feedbacks on average by 23%.
This underestimate can be linked to the wrong location at which climate models simulate the most important tropical circulation, called the Walker circulation. The Walker circulation in most climate models is located too far to the west.
By highlighting the biases created by seas surface temperatures and the mean state of the Pacific Walker Circulation, this study can help climate modellers improve climate model simulations of natural climate variability and climate change.
- Paper: Bayr, T., Dommenget, D. & Latif, M. Walker circulation controls ENSO atmospheric feedbacks in uncoupled and coupled climate model simulations. Clim Dyn54, 2831–2846 (2020). https://doi.org/10.1007/s00382-020-05152-2