The El Niño and Southern Oscillation (ENSO) in the tropical Pacific Ocean is one of the most significant interannual variations in the global ocean-atmospheric system, together with its counterpart La Niña, strongly influencing the climate of the Asia-Pacific region via inducing extreme events such as flooding and drought. It is crucial to understand the underlying dynamics and predicting the happening of this phenomenon.
However, in the 21st century, the prediction skill has waned, which is associated with more signals happening in the central Pacific, rather in the eastern Pacific as it did before this century. The former type is usually called CP ENSO while the latter is called EP ENSO.
To overcome these challenges, the research team led by Prof. WANG Fan from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) and their collaborators tried to understand from a new perspective - the subsurface ocean mixing's effect on ENSO.
The study was published in Nature Communications on March 8.
The researchers successfully invented an estimation method, which utilizes wide-coverage, long-term Argo profile data, and for the first time produced abundant of mixing data (>4,0000) in the equatorial Pacific region. They revealed the important effect of ocean subsurface mixing on the growth of both El Niño and La Niña of the CP type.
"It is a positive feedback loop, the CP ENSO associated wind and ocean state lead to variations in occurrence rate and strength of ocean subsurface mixing, in turn, the later enhances the growth of CP ENSO, with an efficiency larger than other mechanisms," said Dr. LIU Chuanyu, the first author of the study. "This loop does not stop until other negative feedback mechanisms become stronger than the positive feedbacks."
This study provides a new perspective to understand the ENSO dynamics, because it is a diabatic mechanism, while the previous proposed mechanisms, of either positive or negative feedback, are all adiabatic essentially.
"It is hopefully this mechanism is well represented in the prediction models of ENSO, so that to improve prediction skills," added Prof. WANG, one of the corresponding authors.
Photographic image of the proposed diabatic CP ENSO positive feedback. (Image by IOCAS)
（Text by Dr. LIU Chuanyu）
Media Contact:
ZHANG Yiyi
Institute of Oceanology
E-mail: zhangyiyi@qdio.ac.cn
(Editor: ZHANG Yiyi)