Characteristics and generations of internal wave in the Sulu Sea inferred from optical satellite images
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Characteristics and generations of internal wave in the Sulu Sea inferred from optical satellite images* ZHANG Xudong1, LI Xiaofeng1, **, ZHANG Tao1, 2 1
CAS Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences and Center for
2
College of Geomatics, Shandong University of Science and Technology, Qingdao 266071, China
Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
Received Jan. 19, 2020; accepted in principle Mar. 8, 2020; accepted for publication Jun. 19, 2020 © Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Characteristics and generation of internal waves (IWs) in the Sulu Sea are studied using Moderate-Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) images taken from October 2016 to September 2019. Satellite observations show that IWs in the Sulu Sea mainly located in the shallower western areas with occasional observations in the deeper eastern regions. The dominant length of wave crest (LWC) of IWs is between 50 and 150 km with the largest LWC reaching over 300 km. The analysis of temporal distributions of IWs shows that March has the most IWs and July has the least. Further analysis shows that the seasonal variation is mainly due to the cloud contamination of optical satellite images. New generation sites of IWs are analyzed using satellite images. Six possible generation sites for IWs in the western Sulu Sea and one generation site for IWs in the eastern Sulu Sea are found using the ray-tracing method. Multi IW sources in the same strait are found, which may be due to the seawater flow over the strait in different directions. The analysis shows that IWs with long wave crest in the Sulu Sea is a combined effort of all straits between small islands in the Sulu Archipelago. Remote generated IWs with long wave crest in the eastern Sulu Sea are studied, which are generated at the straits around (121.5°E, 6°N) by the nonlinear evolution of internal tide originated from the Sulu Archipelago. Keyword: internal waves (IWs); Sulu Sea; Moderate-Resolution Imaging Spectroradiometer (MODIS); Suomi National Polar-Orbiting Partnership (NPP)
1 INTRODUCTION Internal waves (IWs) with large amplitude and long wave crests are observed frequently in the global oceans (Jackson, 2007; Zhao et al., 2014), such as the South China Sea (Liu and Hsu, 2004), East China Sea (Nam et al., 2018), Andaman Sea (Sun et al., 2019), Black Sea (Lavrova et al., 2014), Red Sea (da Silva et al., 2012) and White Sea (Kozlov et al., 2014). The propagation and dissipation of IWs have significant impacts on the distributions of plankton and chlorophyll (Vázquez et al., 2009), ocean mixing (Villamaña et al., 2017), and sediment resuspension (Jia et al., 2019). Large-amplitude IWs can travel several thousand kilometers with a strong shear force and hence play an essential role in affecting the ocean environment (Lü et al., 2016). Properties of IWs hav
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