The transport and accumulation of moisture played an essential role in the extremely heavy rainfall of July 2020 in Japan. To better understand this event in terms of moisture sources and transport routes, backward particle trajectory analysis was conducted. We found two major moisture sources: transport from the tropics and uptake from the subtropics. A narrow moisture channel was found along the edge of the western Pacific Subtropical High (WPSH), transporting the moisture to the Baiu front. However, most moisture from the tropics was lost due to precipitation, and their contributions were reduced to about 15%. In contrast, the subtropical regions contributed over 80% moisture via evaporation and lower tropospheric convection. Among those regions, the western Pacific contributed the most (>33%). This study highlights the role of WPSH in moisture transport and demonstrated the importance of moisture uptake during transport.
The features of coastal upwelling in the southwestern Yellow Sea were investigated based on oceanology data from a research cruise and a regional circulation model. The observation data suggest that a relatively colder and saltier water core exists from the deeper layer to the surface, off the Subei Bank. The concentrations of nutrients also suggest that coastal upwelling is beneficial for nutrient enrichment in the upper layer. The numerical simulations are in good agreement with oceanology observations. Furthermore, sensitivity experiments indicate that, in addition to the tidal-induced upwelling and tidal mixing proposed in previous studies, the summer monsoon is also critical to vertical circulation in the southwestern Yellow Sea. The southwesterly wind stress and positive wind stress curl make considerable contributions to upwelling off the Subei coast compared with tidal motions. Moreover, this study also proposes that changes in the summer monsoon and its curl may have been helpful to the formation of upwelling during the past decade, which may have provided a favorable marine environment for the frequent occurrence of green tides. This study provides a theoretical basis for the mechanisms of coastal upwelling and the nitrogen cycle in the Yellow Sea.
The radial sand ridges consist of more than 70 sand ridges that are spread out radially on the continental shelf of the South Yellow Sea. As a unique geomorphological feature in the world, its evolution process and characteristics are crucial to marine resource management and ecological protection. Based on the multi-source remote sensing image data from 1979 to 2019, three types of geomorphic feature lines, artificial coastlines, waterlines, and sand ridge lines were extracted. Using the GIS sequence analysis method (Digital Shoreline Analysis System (DSAS), spatial overlay analysis, standard deviational ellipse method), the evolution characteristics of the shoreline, exposed tidal flats, and underwater sand ridges from land to sea were interpreted. The results demonstrate that: (1) The coastline has been advancing towards the sea with a maximum advance rate of 348.76 m/a from Wanggang estuary to Xiaoyangkou Port. (2) The exposed tidal flats have decreased by 1484 km2 including the reclaimed area of 1414 km2 and showed a trend of erosion in the north around Xiyang channel and deposition in the southeast around the Gaoni and Jiangjiasha areas. (3) The overall sand ridge lines showed a trend of gradually moving southeast (135°), and the moving distance is nearly 4 km in the past 40 years. In particular, the sand ridge of Tiaozini has moved 11 km southward, while distances of 8 km for Liangyuesha and 5 km for Lengjiasha were also observed. For the first time, this study quantified the overall migration trend of the RSRs. The imbalance of the regional tidal wave system may be one of the main factors leading to the overall southeastward shift of the radiation sandbanks.
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