image: N-year return significant wave height of wind-wave in East China Sea. Left panels are results computed from TP satellite data, middle panels are from ERA reanalysis data, and right panels are computed from WW3 model hindcast. view more
Credit: ©Science China Press
Wind-wave maps are preliminary knowledge for marginal sea. From the scientific aspect, wind-wave modifies the vertical structure of atmospheric wind and oceanic current thus plays an important role in air-sea interaction. From the practical viewpoint, wind-wave in the coastal region is responsible for the sediment migration and coastal line change, and it is a main factor of coastal and offshore engineering, harbor management and marine safety. It is also mentioned wind-wave is a new kind of energy for humanity. However, the wind-wave maps in East China Sea are still not at-hand for these multiple purpose.
Obtaining regional wind-wave climate and extrema is quit challengeable for requiring long-term time series. The most reliable method of data collecting relies on in-situ buoy observation. However, in-situ buoy-based observation is high cost on both economic and human resources, and therefore it is very rare in East China Sea. Nevertheless, the significant wave height, which is an important parameter of wind-wave, is provided by satellite altimeter for more than 20 years. Meanwhile, the atmospheric reanalysis data which assimilate the satellite product has several updates in history. Hence there are some fundamental datasets for performing analysis on wind-wave climate and extrema.
But the research bottlenecks of marginal seas are still obvious, especially for East China Sea. For instance, the cross-track resolution of satellite altimeter is too coarse to describe the wind-wave in marginal sea, therefore the quality of satellite altimeter and related atmospheric reanalysis data should be carefully evaluated. In comparative view, the satellite-retrieved wind product has relative high horizontal resolution, which could be used to directly drive numerical wave model for obtaining long-term wind-wave results, and this method is sufficient based on the present numerical skill. For East China Sea, the comprehensive studies on satellite altimeter, atmospheric reanalysis, and stand-alone model output have not been reported before.
A recent study published in Science China Earth Sciences uses third-generation wave model to perform numerical simulation of wind-wave in North Pacific from 1988 to 2002, and analyses the output in East China Sea, and compares a variety of datasets for the first time. The results show the deficiency of satellite altimeter data in describing marginal-sea wind-waves, prove the consistency between satellite altimeter data and atmospheric reanalysis data on long-term wave statistics, and discover the pattern difference between model output and atmospheric reanalysis (or satellite altimeter) on extrema of wind-wave (Figure 1).
In detail, the results supply clear wind-wave maps of multi-year averaged wave parameters in specific region. The spatial distributions of wave height and wave period are emerged on the sense of wave climate. The climatological results are applausive for the similarity among multiple data sources. The results seems deterministic that the climatological wind-wave follow the pattern of bathymetry pattern, as surface waves are high and long in open ocean but low and short in continental area.
For the extrema, or N-year return extreme value, the results emphasis the single peak pattern from the stand-alone model output, where the model forcing field contains multi-core in horizontal structure. The results imply the coupling of wind and wave is not so close to be feasible of direct wave parameterization only by wind.
The first author of paper, Hailun He, from Second Institute of Oceanography, State Oceanic Administration, China, suggested, the stand-alone numerical model outputs deserve attentions from both scientific researchers and engineering practitioners, for its considerable differences with the atmospheric reanalysis on the N-year return extreme value. Furthermore, atmospheric reanalysis also based on the third-generation wave model but assimilate the satellite altimeter data, which make the atmospheric reanalysis resembles the satellite altimeter data. However, the satellite altimeter is not accurate enough, the necessary of assimilating satellite altimeter in numerical wave model still leaves in-debate.
The study give more insight into the wind-wave study in East China Sea. The results is not only valuable for regional wind-wave study and its forecasting, but also for the environmental protect and resource development of regional ocean, such as hazard defense, engineering design, ocean navigation, wind-wave energy, etc.
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This research was funded by National Natural Science Foundation of China (Grant Nos. 41476021, 41576013 & 41321004), National High Technology Research and Development Program of China (Grant No. 2013AA122803), National Program on Global Change and Air-Sea Interaction (Grant No. GASI-IPOVAI-04).
See the article:
He H L, Song J B, Bai Y F, Xu Y, Wang J J, Bi F. 2018. Climate and extrema of ocean waves in the East China Sea. Science China Earth Sciences, 61,
https://doi.org/10.1007/s11430-017-9156-7
http://engine.scichina.com/publisher/scp/journal/SCES/doi/10.1007/s11430-017-9156-7?slug=abstract
https://link.springer.com/article/10.1007%2Fs11430-017-9156-7