海洋与台风相互作用研究进展

Progress and perspective on interactions between ocean and typhoon

台风灾害是全球最主要的气象灾害之一.到目前为止,人们已经从大气科学的角度对台风进行了长期系统并且卓有成效的研究.但人们对台风过程中海洋的剧烈变化及其对台风的反馈仍然缺乏足够的认识,这也成为限制台风研究和预报水平的一个瓶颈问题.因此,海洋与台风在各种时空尺度上的相互作用机理及其对台风预报和短期气候趋势预测的贡献是当前国际海洋与大气科学研究的重大前沿课题.本文基于国家重点基础研究发展计划,总结了海洋与台风相互作用的最新研究成果,重点梳理了海洋中尺度过程对台风的影响与反馈、海洋与台风的低频相互作用及其对短期气候变化趋势的影响、台风过程中的海洋多源资料同化及利用海气耦合模式进行台风预报等若干方面的研究进展.最后,提出了今后在海洋与台风相互作用研究中需要关注和重点解决的若干关键科学问题.

Typhoon is one of the most destructive natural disasters on the earth. A lot of fruitful research has been conducted, especially from the perspective of atmospheric sciences. During a typhoon, the ocean also undergoes dramatic variabilities, which can have significant feedbacks to the atmosphere and typhoon. Generally, the sea surface temperatures(SST) decrease and inertial oscillations are greatly enhanced. The fingerprints of typhoon on the ocean are not constrained to the local sea surface, but can be extended to the ocean interior and remote areas, which play an important role in the climate change on a much longer and larger spatiotemporal scales. In addition, the mesoscale eddy accounts for a large amount of kinetic energy in the ocean. Much progress has been achieved on the responses and feedbacks of ocean eddy to typhoon, but it remains a large uncertainty for the ocean-typhoon interaction. Particularly, the three-dimensional structure of ocean eddy during typhoon is unclear due to the lack of observations. Overall, so far, there have been no comprehensive understandings of the ocean-typhoon interactions, which are believed to be a bottleneck for improving the typhoon prediction. Therefore, the mechanisms of ocean-typhoon interactions at various spatiotemporal scales, as well as their contributions to the short-term and long-term typhoon forecast, have become a hot and challenging topic for both the oceanic and the atmospheric sciences. In this paper, recent progress in the ocean-typhoon interactions is reviewed, based on several collaborative projects in China. The foci are on the local responses and feedbacks between mesoscale variabilities in the upper ocean and typhoon, the ocean-typhoon interactions at low frequency and the impacts on global climate, data assimilation during typhoon, and typhoon forecast in the ocean-atmosphere coupled framework. The major challenge to the ocean-typhoon interactions resides in the lack of persistent and reliable observations, especially the synchronized observations in both the ocean and the atmosphere. Some valuable experiments have been conducted recently and are summarized in this study. For example, mooring/buoy arrays are carefully designed and deployed in the northern South China Sea consecutively from 2014 up to now. The monitoring for a long period accumulates very useful in-situ data for the study on the ocean-typhoon interactions. In addition, several novel technics are also proposed and tested recently, such as the one using rocket-deployed dropsondes to obtain vertical profiles in the atmosphere within a typhoon, and the Iridium Argo the sampling frequency of which can be remotely and manually increased when a typhoon is coming. On the mechanisms of ocean-typhoon interaction, a hypothesis of "cold suction" in the ocean is proposed and examined, which is another avenue for the typhoon’s impacts on the subsurface in the ocean, except for the traditional concept of "heat pump". Evidence for "cold suction" is found in in-situ observations. The new concept makes the theory for ocean-typhoon interactions more comprehensive. For the practical application, the improvement of typhoon prediction is the golden goal. A lot of efforts have been put into the data assimilation, which synthesizes data from different resources, such as the remote sensing data of the sea surface properties and the Argo data for the ocean interior. Improved data assimilation methods are proposed to facilitate the extreme conditions during typhoon. Until now, most operational typhoon forecast still rely on the atmosphere-only model. Nevertheless, the atmosphere-ocean-wave coupled systems have been established and evaluated. Some improvement has been shown for the operational typhoon forecast. Finally, some key scientific problems and technical challenges are raised in this paper, which are expected to shed light on the future studies on the ocean-typhoon interaction.