China's Ocean and Climate Prediction Scheme Released via a UN Platform

On September 27, 2023, the DCC-OCC International Launching Conference commenced in Qingdao. Endorsed by the Intergovernmental Oceanographic Commission of United Nations Educational, Scientific and Cultural Organization (IOC/UNESCO), the Best Practice Recommendations on the BV Theory – Improving the Performance of Ocean and Climate Models was launched. The scheme represents a premium public service offering from the Decade Collaborative Center on Ocean-Climate Nexus and Coordination Amongst Decade Implementing Partners in P.R. China (DCC-OCC), in collaboration with the Ocean Decade Programme "Ocean to Climate Seamless Forecasting System" (OSF) coordinated by it for the Ocean Decade. It has delivered a robust scientific and technological boost towards realizing a predicted ocean, one of the seven expected outcomes under the Ocean Decade.

In the 1960s, American oceanographer Kirk Bryan, in collaboration with colleagues, developed the world's first ocean general circulation model. Over the past five decades, such models have evolved into ultra-high degree-of-freedom numerical frameworks with a faster computing speed, a higher temporal-spatial resolution, and a more complete physical process. During this time, the development of ocean general circulation models featured two distinct characteristics. First, the core R&D technologies were controlled by countries with advanced capabilities in this field, such as European countries and the United States. Developing countries only acted as users of such technologies or simply improved some physical processes within the models. Second, even with significant strides forward, there are still huge deviations in the simulation of ocean general circulation models. A prime concern stems from an insufficient ability to stimulate upper ocean processes, which manifest in issues like a higher summer sea surface temperature, a lower subsurface layer temperature, and a smaller mixed layer depth. The deviation in ocean simulations will make it harder to accurately predict ocean conditions. Meanwhile, as an underlying surface of atmospheric processes, a small deviation will be transmitted and amplified through the air-sea interaction, thereby directly impacting the accuracy of weather forecast and climate prediction. Thus, minimizing the deviation in upper ocean simulations of ocean general circulation models represents a critical challenge at the forefront of international scientific research as well as a long-term technological difficulty for accurate ocean and climate prediction.

The fundamental reason for inaccurate upper ocean simulations stems from the limited ability of ocean general circulation models to precisely describe oceanic turbulence. Nobel laureate in physics Richard Feynman once described turbulence as "the most important unsolved problem of classical physics". In the field of oceanic turbulence, domestic and international scientists have had a limited understanding of the energy source that drives the generation of upper ocean turbulence. Waves are dynamic entities carrying the most energy. Conventionally, for the sake of simplifying the analysis, waves are presumed to be irrotational. This standard assumption implies that waves cannot give rise to turbulence due to the nature of irrotational motion. Consequently, there has been a longstanding misconception that waves do not generate turbulence before breaking.

However, the essence of waves is fundamentally rooted in rotational motion. To address the issue of oceanic turbulence, Researcher QIAO Fangli from FIO and his team shifted away from the traditional view that assumes waves are irrotational and developed an analysis that treats non-breaking wave-induced mixing as a function of wave number spectrum. They introduced an innovative concept known as the surface wave-induced mixing or BV theory, which reveals that the rotational motion of non-breaking waves generates turbulence through the wave-turbulence interaction, playing a leading role in upper ocean mixing. Subsequently, the team designed a marine scientific experiment which, for the first time, unveiled through observational data a mechanism by which waves interact with turbulence to amplify it. This discovery provides solid evidence for the surface wave-induced mixing theory. So far, scientists from many countries have verified the correctness of the theory via laboratory experiments and field observations at sea. Due to a succession of original innovations in marine science and technology, QIAO Fangli was elected as a member of Academia Europaea.

The application of this theory in ocean general circulation models demonstrates that it can substantially enhance the simulation effect of the upper ocean, reducing the deviation in simulations of such models by over 80%. Numerous ocean general circulation model R&D institutions in countries, such as the United States, Sweden, Germany, France, Australia, and China, have adopted this theory, resulting in a significant decrease in model errors. In addition, the surface wave-induced mixing theory has the potential to notably improve the simulation effect of earth system models as the air-sea interaction can impact the atmosphere. For example, the introduction of wave-induced mixing processes in an earth system model can dramatically decrease the deviation in the simulation of the equatorial Pacific cold tongue and monsoon.

At the Conference, the IOC/UNESCO and DCC-OCC jointly released the Best Practice Recommendations on the BV Theory for global users. Meanwhile, relevant testing procedures were also published and shared. The scheme is among the best practices under the Ocean Decade. It aims to provide scientific reference and guidance for actions related to the "Ocean Decade" in pertinent domains. It is noteworthy that this occasion marks the inaugural presentation of a numerical model scheme developed by China to the global community in the form of a UN report. This significant milestone emphasizes China's substantial scientific and technological advances in the R&D of ocean and climate models. Furthermore, it underscores China's evolution from being a participant to assuming a leadership position in the pivotal scientific and technological domain of global ocean governance.

In the process of deeply engaging in the UN Ocean Decade, Chinese scientists set their sights on and even spearhead the international frontier of marine science and technology through extensive and in-depth international cooperation in marine science and technology. Their expertise enables them to deliver high-standard public service products for stakeholders worldwide, which embodies China's significant contribution to the international arena of marine science and technology. As the Ocean Decade advances into its third year, China's involvement in the initiative is gaining momentum. We are assured that in the coming years, Chinese marine researchers will contribute more Chinese wisdom and solutions to global marine governance, spearheading a new era of international marine cooperation through independent and original innovation in marine science and technology.