Progress and perspective on interactions between ocean and typhoon

Abstract

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 typhoons 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.