Marine Heatwaves (MHWs) have intensified in frequency, duration, and intensity due to global warming, posing profound threats to marine ecosystems. While satellite-derived Sea Surface Temperature (SST) datasets are the cornerstone of MHW detection, their reliability remains a critical concern. Specifically, multi-source Level-4 (L4) analysis datasets may introduce substantial uncertainties in regional MHW assessments, particularly within climatically sensitive hotspots. However, a systematic evaluation of these uncertainties across diverse oceanographic regimes remains lacking. This study systematically evaluates the consistency of three widely used global L4 SST products—NOAA OISST v2.1, REMSS MWIR v5.1, and UKMO OSTIA. The assessment spans two contrasting environments: the Eastern China Marginal Seas (representing complex coastal dynamics) and the Northeastern Pacific (representing open-ocean conditions). Additionally, the 2013–2016 “The Blob” event is analyzed as a benchmark case. Key findings reveal: (1) While the three products show strong consistency in mean-state MHW metrics, they differ noticeably in long-term trend estimates. In regions with weak trend signals, relative deviations can be large, indicating that trend detection in such areas is subject to substantial uncertainty. (2) Intensity-related metrics show significantly higher uncertainty than frequency-related metrics. Notably, in the Bering Sea, different products yield divergent signals regarding MHW occurrence. (3) During “The Blob,” absolute discrepancies in total duration and cumulative intensity reached up to 150 days and 250 ^∘ C· days , respectively. These differences may influence the assessment of ecological stress, although the magnitude of this impact requires further validation. This study suggests that reliance on a single SST product may introduce uncertainty, particularly for regional or event-based assessments, and highlights the potential benefits of incorporating multi-source ensemble approaches in future MHW analyses. The authors state that this study does not involve clinical trials.

Harmful algal blooms (HABs) occur frequently in the coastal waters of the East China Sea and exhibit pronounced spatiotemporal heterogeneity under complex hydrodynamic conditions. However, systematic comparative studies on the driving mechanisms of HABs under different hydrodynamic regimes remain limited. Based on in-situ observations from 2015 to 2020 and a high-resolution coupled physical–ecological model, this study comparatively investigated HAB developmental characteristics and environmental driving mechanisms in two typical coastal regions of the Zhejiang coast: the near-estuary Shengsi area, dominated by Changjiang Diluted Water, and the far-estuary Cangnan area, primarily controlled by coastal current systems. Statistical analyses, Mann–Kendall trend tests, and principal component analysis were applied to identify the dominant environmental controls associated with HAB outbreaks. HABs in Shengsi occurred sporadically from May to September and were mainly characterized by short duration (≤7 days) and small-to-medium spatial scales. In contrast, HAB outbreaks in Cangnan were strongly concentrated in May–June (91% in simulations and 84% in observations), with a higher frequency of large-scale events (duration >20 days; area >400 km²). Mechanistic analyses indicated that HAB dynamics in the nutrient-poor but hydrodynamically stable Cangnan waters were primarily regulated by hydrodynamic processes. An initial increase in current velocity (~0.067 m/s) promoted the transport and accumulation of nutrients (nitrate +0.8 mmol/L; phosphate +0.06 mmol/L), whereas the subsequent rapid weakening of currents, observed in 79.8% of HAB events, enhanced water-column stability and favored algal aggregation. The turning point of current velocity generally preceded the chlorophyll-a peak by approximately one day. Principal component analysis further confirmed the dominant role of physical regulation in Cangnan, where the first principal component explained 56.44% of the total variance. In contrast, Shengsi exhibited sufficient nutrient supply but relatively unstable hydrodynamic conditions due to interactions among multiple water masses. Except for seawater temperature, most environmental variables showed no statistically directed changes before and after HAB outbreaks, with increase–decrease probabilities close to 50%. The first principal component explained only 28.94% of the total variance, indicating a highly multifactor-driven HAB system. This study reveals substantial differences in HAB formation mechanisms between near-estuary and far-estuary systems in the East China Sea. HAB outbreaks in Cangnan are strongly associated with hydrodynamic stability, whereas HABs in Shengsi are jointly regulated by multiple environmental factors. These findings improve the understanding of HAB dynamics under complex coastal hydrodynamic backgrounds and provide a scientific basis for region-specific HAB forecasting and early-warning strategies along the Zhejiang coast.

The offshore transport of coastal water masses in the East China Sea is vital for maintaining ecological stability. Understanding its spatial-temporal pathways helps clarify material transport and ecological responses. This study used total suspended sediment (TSS) data from the Korean Geostationary Ocean Color Imager to analyze TSS distribution and anomalies, combined with satellite-derived surface residual currents. Results show significant seasonal variations: coastal water masses expand to the 50 m isobath in winter and contract to the 20 m isobath in summer. Offshore transport pathways vary spatially, extending to the shelf edge north of 28° N but restricted by the Taiwan Warm Current south of 28° N. A persistent transport pathway near 28° N shifts from northeastward to eastward. Other pathways include one south of Hangzhou Bay (spring and autumn) linked to tidal mixing and another north of the Yangtze River estuary (summer) following the Yangtze River Diluted Water. These findings provide crucial observational insights for modeling material cycling in the East China Sea shelf.

Marine heatwaves (MHWs) pose a serious threat to the marine ecosystems and fishery resources in the East China Sea (ECS). Based on National Oceanic and Atmospheric Administration Optimum Interpolation Sea Surface Temperature High Resolution version 2 data, this study investigated the regional divergence in long-term trends of MHWs in the ECS from 1982 to 2023. The principal findings were as follows. Concerning MHWs, the coastal waters of China from northern Jiangsu coast to northeast of Taiwan Island experienced a relatively high annual average frequency, the longest duration, largest number of total days, strongest intensity, and the most pronounced seasonal signals. Additionally, the areas along the Kuroshio path showed significant levels of frequency, duration, and total days, but with comparatively weak intensity. In the empirical orthogonal function (EOF) analysis, EOF1 of the total days and cumulative intensity exhibited notable variation along the path of the Kuroshio and its offshoots, and in Chinese coastal areas. EOF2 showed significantly more conspicuous variation in areas extending from the Yangtze River Estuary to the northern Jiangsu coast. Furthermore, the MHW indices generally showed a positive trend in the ECS from 1982 to 2023. Importantly, the regions with high annual average MHW indices were also characterized by a significantly positive increasing trend. Moderate (79.10%) and strong (19.94%) events were most prevalent, whereas severe (0.82%) and extreme (0.14%) events occurred infrequently. The enhanced solar radiation and the reduced latent heat loss were the main contributing factors of MHWs in the ECS. These findings provide valuable insights into the ecological environment and resources of the ECS as a marine pastoral area.

It is generally recognised that the north-easterly monsoon leads to greater intrusion of Changjiang Diluted Water (CDW) into Hangzhou Bay in winter than in summer, which strongly influences the hydrography of Hangzhou Bay. However, anomalously lower salinity (<10) and higher dissolved inorganic nitrogen (DIN) concentrations (1.9 mg L- 1) were observed in central Hangzhou Bay in summer (August 2019) than the salinity (>15) and DIN concentrations (1.5 mg L- 1) in winter (March 2022). A high-resolution, well-validated model has further revealed intermittent intrusions of CDW, characterised as intraseasonal (30-120 d) and episodic variations, resulting in a unique low-salinity and high-nutrient water mass in the north-central bay during summer. The intermittent intrusions are driven by the combined effects of the Changjiang discharge, intraseasonal winds, tropical cyclones, and tidal residual currents. The Changjiang discharge amplifies the effect of CDW intrusion on a seasonal scale, which is responsible for the large (>10) decline in summer salinity in the initial intrusion area of the northern bay mouth. The intraseasonal variation in the south-westerly monsoon in summer causes intermittent intrusion of the CDW, accompanied by variations in the Taiwan Warm Current. Intrusion of CDW is greatly enhanced during episodic events of strong northerly winds caused by tropical cyclones. This episodic intrusion can cause a decline in salinity in the initial intrusion area of up to 6 in approximately one week. After the CDW intrudes into the north central bay, the westward tidal residual current along the northern coast continuously transports the CDW toward the head of Hangzhou Bay.

Remote sensing observations reveal strong differences in winter cross-shore movements of the outer salinity fronts between the midfield and far-field regions outside China's Changjiang River plume. However, the characteristics, mechanisms, and associated water exchanges of these outer fronts remain unclear. Based on 7-yr buoy salinity observations and a high-resolution model, we investigate periods of synoptic (;9-13 days) variation and the spring-neap tidal cycle for outer fronts in the midfield and far fi eld. Their cross-shore movements manifest as oscillations in the midfield and an alternation of single and double fronts in the far fi eld. In the midfield, the cross-shore frontal oscillations occur with in-phase salinity variations on opposite sides of the front, indicating a balance between brackish plume water and offshore saline water. The replenishment of low-salinity water from the near fi eld to this region induces significant stratification of seawater, making the entire surface layer highly buoyant and susceptible to modulation by tidal and wind-driven advection. In the far fi eld, the alternations of single and double fronts are accompanied by antiphase salinity variations on opposite sides of the front. During strong downwelling winds, a single front occurs when coastal salinity decreases due to the southward expansion of plume, and offshore salinity increases due to wind-driven onshore transport. During weak downwelling winds, a double front is generated by the combined action of advection and vertical mixing. The salinity in the coastal branch of the double front increases at this time, providing evidence that saline Taiwan warm water can intrude into the coastal area when the offshore branch spreads further offshore.

High-resolution (2 km) high-frequency (hourly) SST data from 2015 to 2021 provided by the Advanced Himawari Imager (AHI) onboard the Japanese Himawari-8 geostationary satellite were used to study spatial and temporal variability of the China Coastal Front (CCF) in the South China Sea. The SST data were processed with the Belkin and O’Reilly (2009) algorithm to generate monthly maps of the CCF’s intensity (defined as SST gradient magnitude GM) and frontal frequency (FF). The horizontal structure of the CCF was investigated from cross-frontal distributions of SST along 11 fixed lines that allowed us to determine inshore and offshore boundaries of the CCF and calculate the CCF’s strength (defined as total cross-frontal step of SST). Combined with the results of Part 1 of this study, where the CCF was documented in the East China Sea, the new results reported in this paper allowed the CCF to be traced from the Yangtze Bank to Hainan Island. The CCF is continuous in winter, when its intensity peaks at 0.15 °C/km (based on monthly data). In summer, when the Guangdong Coastal Current reverses and flows eastward, the CCF’s intensity is reduced to 0.05 °C/km or less, especially off western Guangdong, where the CCF vanishes almost completely. Owing to its breadth (50–100 km, up to 200 km in the Taiwan Strait), the CCF is a very strong front, especially in winter, when the total SST step across the CCF peaks at 9 °C in the Taiwan Strait. The CCF’s strength decreases westward to 6 °C off eastern Guangdong, 5 °C off western Guangdong, and 2 °C off Hainan Island, all in mid-winter.

High-frequency observations of surface current field data over large areas and long time series are imperative for comprehending sea-air interaction and ocean dynamics. Nonetheless, neither in situ observations nor polar-orbiting satellites can fulfill the requirements necessary for such observations. In recent years, geostationary satellite data with ultra-high temporal resolution have been increasingly utilized for the computation of surface flow fields. In this paper, the surface flow field in the East China Sea is estimated using maximum cross-correlation, which is the most widely used flow field computation algorithm, based on the total suspended solids (TSS) data acquired from the Geostationary Ocean Color Imager satellite. The inversion results were compared with the modeled tidal current data and the measured tidal elevation data for verification. The results of the verification demonstrated that the mean deviation of the long semiaxis of the tidal ellipse of the inverted M2 tide is 0.0335 m/s, the mean deviation of the short semiaxis is 0.0276 m/s, and the mean deviation of the tilt angle is 6.89°. Moreover, the spatially averaged flow velocity corresponds with the observed pattern of tidal elevation changes, thus showcasing the field’s significant reliability. Afterward, we calculated the sea surface current fields in the East China Sea for the years 2013 to 2019 and created distribution maps for both climatology and seasonality. The resulting current charts provide an intuitive display of the spatial structure and seasonal variations in the East China Sea circulation. Lastly, we performed a diagnostic analysis on the surface TSS variation mechanism in the frontal zone along the Zhejiang coast, utilizing inverted flow data collected on 3 August 2013, which had a high spatial coverage and complete time series. Our analysis revealed that the intraday variation in TSS in the local surface layer was primarily influenced by tide-induced vertical mixing. The research findings of this article not only provide valuable data support for the study of local ocean dynamics but also verify the reliability of short-period surface flow inversion of high-turbidity waters near the coast using geostationary satellites.

High-resolution (2 km) high-frequency (hourly) SST data from 2015–2020 provided by the Advanced Himawari Imager (AHI) onboard the Japanese Himawari-8 geostationary satellite positioned over 140.7°E were used to study spatial and temporal variability of the China Coastal Front (CCF) in the East China Sea. This dataset was processed with the Belkin and O’Reilly algorithm to generate long-term mean monthly maps of the SST gradient magnitude (GM) and frontal frequency (FF). The horizontal structure of the SST field in the vicinity of the CCF was also investigated from the cross-frontal distributions of SST along eight parallels between 31°N and 24°N. The monthly mean distributions of SST along these 8 parallels were used to determine inshore and offshore boundaries of the CCF and to calculate the CCF strength defined as the total cross-frontal step (range) dSST calculated as the difference between offshore and inshore SST. The CCF emerges in November, fully develops in December, and peaks in strength in January–February. The front’s fragmentation and shrinking/weakening begins in February and March, respectively. In winter (December–February), the front’s strength dSST exceeds 5 °C offshore the Zhejiang-Fujian coast and could be as high as 7.5 °C when nearshore waters cool down to 7 °C. In winter, the front’s strength decreases downstream between 31°N and 24°N. The CCF changes its physical nature as the seasons progress. In winter, the CCF is a water mass front between the cold and fresh water coming from the north and the warm and salty water coming from the south. In summer, the CCF becomes a coastal upwelling front maintained largely by southerly winds. In winter, the CCF’s cross-frontal structure in the SST field is ramp-shaped, with SST increasing monotonously in the offshore direction. In summer, the CCF’s cross-frontal structure in the SST field is V-shaped or U-shaped, featuring a minimum SST formed by cold upwelled water at some distance from the shore. Thus, the summer SST structure effectively consists of two parallel fronts, an inshore one and an offshore one, with a minimum SST in between. Across the inshore/offshore front, the SST decreases/increases in the offshore direction.

The measurement of sea surface temperature (SST) is of utmost importance in the realm of oceanography. The increasing utilization of satellite data in SST research has highlighted the crucial need to compare and evaluate various satellite data sources. Using iQuam2 in situ SST data, this study aims to assess the accuracy of SST datasets obtained from three polar-orbiting satellites (AVHRR, Modis-Aqua, and Modis-Terra) and one geostationary satellite (Himawari-8) in the Bohai-Yellow-East China Sea (BYECS) throughout 2019. The results showed a strong correlation between satellite and in situ data, with R correlation coefficients exceeding 0.99. However, the accuracy of the satellite datasets exhibited some variability, with Himawari-8 showing the highest deviation error and MODIS-Aqua showing the least. Subsequently, the Modis-Aqua data were used as a benchmark to evaluate the SST data of the other three satellites over the previous six years (July 2015–June 2021). The results indicate that, in addition to intricate temporal variations, the deviations of the three satellites from Modis-Aqua also show significant spatial disparities due to the effect of seawater temperature. Compared to Modis-Aqua, the deviation of Himawari-8 generally displayed a negative trend in BYECS and showed pronounced seasonal variation. The deviation of AVHRR showed a negative trend across all regions except for a substantial positive value in the coastal region, with the time variation exhibiting intricate features. The SST values obtained from MODIS-Terra exhibited only marginal disparities from MODIS-Aqua, with positive values during the day and negative values at night. All three satellites showed significantly abnormal bias values after December 2020, indicating that the MODIS-Aqua-derived SST reference dataset may contain outliers beyond this period. In conclusion, the accuracy of the four satellite datasets varies across different regions and time periods. However, they could be effectively utilized and integrated with relevant fusion algorithms to synthesize high-precision datasets in the future.

The fish catch in natural upwelling areas, which accounts for only 0.1% of the ocean surface, accounts for more than 40% of the world’s catch. The Zhoushan fishery, which is the largest fishery in China, is mainly formed by a coastal upwelling that features a low temperature. The upwelling in the study area (29.5–31.5° N, 121.5–123.5° E) is a vital factor affecting the formation of the Zhoushan fishery, and the primary productivity and low temperature that are brought by the rising water are important features of the upwelling. This study used global real-time high-resolution multivariate fused satellite (OSTIA) daily sea surface temperature (SST) data developed by the United Kingdom Meteorological Office that were collected from 1981 to 2020 to explore the spatial and temporal variation of the characteristics of the upwelling phenomenon in the study area. The data were processed by a temperature gradient-based upwelling edge detection algorithm to extract information on the central location of the upwelling, the location clusters in the core area, and the intensity index. The quantities of center and core area clusters were counted for each pixel point, and their corresponding probability values were calculated. The results of the spatial and temporal variation of the characteristics of the upwelling show that the upwelling in the study area was generated in April of each year, increased in intensity, and peaked in August, furthermore, the southern part of the upwelling dissipated in September. The region’s upwelling is spatially oblique and elliptical, with its long axis following the northeast and extending as far as the mouth of the Yangtze River. Its central location and core area were relatively stably existing in Ma’an Archipelago and Zhongjieshan Islands, which was consistent with the location of the two marine pastures in Zhoushan. According to our findings, locations with higher probability values in the upwelling center and core area, where upwelling occurs frequently, are usually accompanied by higher productivity and offer the potential to develop fishing grounds. The insights that were drawn from the study observations can, therefore, provide some reference for future artificial upwelling site selection.

The summer upwelling around the Zhoushan Islands is well-known. The previous concise review of (mostly) observational studies reveals that the present knowledge of the Zhoushan upwelling is unsatisfactory and has focused on seasonal variations. In this study, a sea surface temperature (SST) gradient-based upwelling detection algorithm was used. The Level 3 daily and hourly SST data from the geostationary satellite Himawari-8 were used to explore statistical features, seasonal variations, and short-term variations of the Zhoushan upwelling. Despite the duration period being like in previous studies, there is a new finding that the location of the upwelling center has a significant monthly migration. The statistical results show that the potential upwelling spots are clustered in the location with large topographic gradients and can be divided into four aggregation areas: between Gouqi Island and Lvhua Island, off Shengsi Island, around the Zhongjieshan Islands, and off the Taohua-Liuheng Islands. The core area of the Zhoushan upwelling is located at 122°E–123°E, 29.5°N–31.15°N with an irregular ellipse extending from southwest to northeast. The continuous cloud-free satellite images display that the lifecycle of the short-term variations was about 24 h and included two stages: intensification and decay. Meanwhile, the surface upwelling center has onshore–offshore movement under the advective transport of local tidal currents. A preliminary discussion suggests that the quasi-24 h periodic variations may be caused by the competing effect between tidal mixing and the stratification in the water column.

Modulated by a host of complex processes, suspended sediment fronts (SSFs) on the inner shelf of the East China Sea persist strongly and vary notably. Using hourly suspended sediment concentration data collected by the Geostationary Ocean Color Imager over the period 2011-2021, a gradient-based edge detection algorithm was implemented to extract SSFs; the frontal probability (FP) and seasonal and interannual variability were identified and interpreted. Pronounced frontal activity is principally confined to the nearshore waters within the 60-m isobaths and decreases with increasing offshore distance. Frontogenesis is mainly determined by the bottom topography and tide-induced mixing. Empirical orthogonal function decompositions reveal that the seasonal cycle dominates the variability of SSFs, which responds to the cycles of winds and related changes in coastal currents and upwelling. The highest FPs are identified in winter when wind-induced suspended sediment transport and resuspension reach their annual maxima. In summer, stratification and the intrusion of Kuroshio subsurface water are not conducive to frontogenesis. Furthermore, the discharge of the Yangtze River has a certain influence on the frontal variability in the waters around the Zhoushan Archipelago. Notably, the interannual variability of SSFs is modulated by the El Nino-Southern Oscillation. These findings, based on a comprehensive dataset of SSFs over 10 years, can usefully inform the studies of marine pollutant transport, sedimentary dynamics, fisheries, and wider ecological processes in the study area.

Clouds severely hinder the radiative transmission of visible light; thus, correctly masking cloudy and non-cloudy pixels is a preliminary step in processing ocean color remote sensing data. However, cloud masking over turbid waters is prone to misjudgment, leading to loss of non-cloudy pixel data. This research proposes an improved cloud masking method over turbid water to classify cloudy and non-cloudy pixels based on spectral variability of Rayleigh-corrected reflectance acquired by the Geostationary Ocean Color Imager (GOCI). Compared with other existing cloud masking methods, we demonstrated that this improved method can identify the spatial positions and shapes of clouds more realistically, and more accurate pixels of turbid waters were retained. This improved method can be effectively applied in typical turbid coastal waters. It has potential to be used in cloud masking procedures of spaceborne ocean color sensors without short-wave infrared bands.

IN this paper we use MIKE21 to simulate and verify the tidal, currents and sediments of the waters near the Zhoushan Liuheng Xiaoguo Juwei reclamation project, and based on that, we calculate the hydrodynamic force and sediment erosion and sedimentation of the sea area near the project. The results show that the scope of hydrodynamic impact of the slag disposal project on the surrounding sea area is only very small, and it will have little impact on the hydrodynamic environment of the surrounding sea area. For the surrounding sea topography and silting environmental impact range is limited to the vicinity of the perimeter, will not affect the surrounding large-scale sea silting situation.

Compared to the traditional polar-orbit satellite, the geostationary satellites with high temporal-spatial resolution are uniquely capable of monitoring short-term and regional oceanic phenomena. In this chapter, we will give two cases to illustrate the great potential of geostationary satellites in observing the short-term process in the ocean and coastal dynamic environment. The first case is using the geostationary ocean color satellite to explore the complete evolutionary process of submesoscale frontal waves off the southeast coast of China. While this evolutionary process has been generated using numerical simulations, it has never previously been reported from actual observations. The second case is using the geostationary meteorological satellite to explore the whole short-term variation in the surface upwelling off northeastern Taiwan. This upwelling is an important pathway for cross-shelf exchanges between the East China Sea and the Kuroshio Current. Therefore, this study will improve the current knowledge of the cross-shelf exchange process.

在分析和总结河南中牟含气页岩层电阻率等物理性征基础上,将广域电磁法勘探技术用于南华盆地低阻覆盖区页岩气探测,获得工作区地下5 km内地层电阻率分布规律和特征,查明了工作区的构造展布,同时揭示了以二叠系太原组、山西组以及上、下石盒子组为主要目的层的含气页岩发育特征.此次探测工作表明,在低阻覆盖区广域电磁法是获取南华盆地深部含气页岩埋深和分布范围的有效探测手段,可为后期有利区带评价、区块优选页岩气层提供地球物理参数.

文章基于广域电磁法(WFEM)的基本理论,结合当前资源勘查所面临的问题及航空物探的发展现状,主要从基本理论、装备研究、应用测试3个主要方面对航空广域电磁法进行了初步探索.通过探索我们认识到,航空广域电磁数据采集质量易受飞机飞行姿态及飞机本体噪声的影响,但是大于100 Hz的高频段具有更好的数据质量和实际工程应用的可行性.

深海溶解甲烷浓度数据连续获取的方法技术,对于海洋环境和天然气水合物开发过程中甲烷扩散作用及通量的动态监测,具有重要的科学意义和实际应用价值.本文较详细地介绍了依据“海水脱气、气体样品定量输入、电化学高精度检测”技术思路,采用“增压排液整机系统控制的海水循环、减压稳流、气液分离、烃类组分高精度检测技术改进”方法,研发“深海甲烷电化学原位长期监测技术”的关键环节和技术方法.结合原位传感器在胶州湾港口为期94天底水长期监测实验获取的数据成果,对原位传感器的技术性能、数据质量、地质效果进行了研究评价.结果 表明:①原位传感器量程甲烷指标达到0.01～ 10000 nmol/L,灵敏度达到0.01 nmol/L,对烃类组分检测具有较好的稳定性和选择性;②监测水域溶解甲烷数值范围19.01～106.87 nmol/L,正常甲烷背景32.41 nmol/L,局部异常甲烷背景80.60 nmol/L,资料显示异常与污水排放过程对海水环境污染有关;③实测甲烷数据成果地球化学特征与胶州湾海域海水环境以往调查研究成果符合,证明了实测数据的客观性和科学性;④海试监测试验成果证明,原位传感器测试性能可靠、结构设计合理、设计思路科学,基本具备了海洋科学调查中对海水甲烷浓度数据获取的能力,在未来海洋天然气水合物开发过程中对甲烷扩散作用的动态监测及深海甲烷浓度通量的长期监测中,具有实际应用价值和科学意义.

Short-term biweekly variations in the surface upwelling off northeastern Taiwan are well documented. However, due to limitations in the spatiotemporal resolution and coverage of the observed data, the lifecycle and associated dynamics are poorly understood. In this study, a gradient-based edge detection algorithm is proposed to detect the surface upwelling. The sea surface temperature data of geostationary satellite Himawari-8 were used to explore a complete short-term process as a case study. The evolution was analyzed in terms of an upwelling index measured via the temperature difference between upwelled and surrounding water and the area and shape of the surface upwelling. The process lasted approximately 17days as the upwelling moved northeastward under the advection of the Kuroshio Current and included two stages: intensification and decay. The last 8years (2010-2017) of multisatellite combined sea surface temperature data were examined to verify the results obtained in the case study. A statistical analysis shows that most of the short-term processes occur in the summer with an average lifecycle of approximately 155days. The trajectories of the upwelling center can be grouped into three types: quasi-stationary near the shelf break, moving northward across the shelf break, and moving northeastward along the shelf break. A preliminary discussion suggests that the observed variations may be caused by the collective effects of multiple dynamical mechanisms, such as fluctuations in the Kuroshio Current, surface wind curl, and typhoons. This study furthers our knowledge of the surface upwelling off northeastern Taiwan and provides constraints for numerical simulations. Plain Language Summary The upwelling off northeastern Taiwan is an important pathway for shelf-ocean exchanges between the East China Sea and the Kuroshio Current. In this study, we used two satellite data of sea surface temperature to explore the short-term variations of surface upwelling off northeastern Taiwan. In order to quantify the process, we proposed a gradient-based edge detection algorithm to detect the surface upwelling. The results show that the short-term variations are ubiquitous and primarily occur in the summer. The lifecycle lasts about 155days and can be divided into two stages: intensification and decay. The trajectories of the upwelling center over the process can be classified into three types: quasi-stationary, cross-shelf northward, and along the Kuroshio Current northeastward. The latter two types reveal to us a new route of water exchange between the upwelled subsurface Kuroshio waters and the East China Sea shelf waters. A preliminary examination suggests that the observed variations are likely caused by the collective effects of multiple dynamical mechanisms such as fluctuations in the Kuroshio Current, surface wind curl, and typhoons. This study will strengthen our understanding of surface upwelling variations and improve current knowledge on the cross-shelf exchange process of upwelled Kuroshio subsurface waters.