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The Influence of Typhoon'Hongxia'on the Intrusion of the Kuroshio Current into the South China Sea

Journal of Ocean University of China 2023年第2期22卷 297-312页

作者： GAO Shumin HAN Shuzong WANG Shicheng wu Dexing WANG Mingjie wu kejian LIU Lili College of Oceanic and Atmospheric Sciences Ocean University of ChinaQingdao 266100China Physical Oceanography Laboratory Ocean University of ChinaQingdao 266100China Tianjin Key Laboratory for Oceanic Meteorology Tianjin 300074China Tianjin Institute of Meteorological Science Tianjin 300074China

This paper uses the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)model to analyze the impact of typhoon‘Hongxia’on the velocity and position movement of the Kuroshio axis,the impact of typhoons on the Kuroshio intrusion into South China Sea(SCS),the corresponding water,heat,and salt fluxes,and the impact of Kuroshio water in the northeastern SCS.When typhoon‘Hongxia’passed,the Kuroshio intrusion into the SCS was the most significant at 21?N latitude.In the vertical direction,the Kuroshio intrusion was strongest in the subsurface layer,leading to the most significant changes in temperature and salinity in the northeastern part of the SCS in the subsurface layer.Under the influence of the southeastern monsoon in summer,a large amount of low-salinity water accumulates at the surface of the northeastern part of the SCS,and Kuroshio intrusive water remains in the bottom and middle portions of the subsurface layer.The westward deviation of the Kuroshio axis caused by the typhoon displays a certain lag compared with the hot and salty water intrusion into the SCS approximately 7 d later.The impact of the typhoon on the Kuroshio intrusion into the SCS lasts for 20 d.The typhoon caused increases in the water,heat,and salt fluxes associated with the Kuroshio intrusion into the SCS,and the contribution of the typhoon to these fluxes was as high as 40%.Under typhoon conditions,the maximum Kuroshio intrusion flux reached more than twice that before the typhoon.

关键词： typhoon Kuroshio intrusion South China Sea COAWST coupling model flux

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A new control design for a morphing UAV based on disturbance observer and command filtered backstepping techniques

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Science China(Technological Sciences) 2019年第10期62卷 1845-1853页

作者： wu kejian ZHANG PeiXi wu Hao School of Instrumentation Science and Opto-Electronics Engineering Beihang UniversityBeijing100191China The9th Designing of China Aerospace Science Industry Corporation Wuhan430040China School of Automation Science and Electrical Engineering Beihang UniversityBeijing100191China

Morphing unmanned aerial vehicle(UAV) can manipulate its shape for excellent flight performance under different conditions.The most research of the morphing UAV focuses on modeling. However, the issues including nonlinear characteristics, strong couplings, and mismatched disturbances are inevitable, which can lead to a great challenge in controller design. In this paper,a composite anti-disturbance controller is developed for morphing UAV to achieve enhanced flight performance under multiple sources of disturbances. In the inner loop, a nonlinear disturbance observer(DO) is constructed to estimate the inertial forces and moment;while in the outer loop, the command filtered backstepping(CFBS) method is adopted to guarantee the stability of the closed-loop system. The system outputs can promptly track reference signals in the morphing process of the UAV. The novelty is that the disturbance estimations are added into the control laws to compensate the mismatched disturbances. When comparing to the previous methods, the control scheme presented in this study can significantly improve the performance of anti-disturbance.Finally, the effectiveness of the proposed method is illustrated by numerical simulations.

关键词： morphing UAV longitudinal altitude disturbance observer command filtered backstepping

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Investigation of the Heat Budget of the Tropical Indian Ocean During Indian Ocean Dipole Events Occurring After ENSO

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Journal of Ocean University of China 2020年第3期19卷 525-535页

作者： XIA Haofeng wu kejian College of Oceanic and Atmospheric Science Ocean University of ChinaQingdao 266100China

The Indian Ocean Dipole(IOD) is an important natural mode of the tropical Indian Ocean(TIO). Sea surface temperature anomaly(SSTA) variations in the TIO are an essential focus of the study of the IOD. Monthly variations of air-sea heat flux, rate of change of heat content and oceanic thermal advection in positive/negative IOD events(pIODs/nIODs) occurring after El Nino/La Nina were investigated, using long-series authoritative data, including sea surface wind, sea surface flux, ocean current, etc. It was found that the zonal wind anomaly induced by the initial SSTA gradient is the main trigger of IODs occurring after ENSOs. In pIODs, SSTA evolution in the TIO is primarily determined by the local surface heat flux anomaly, while in nIODs, it is controlled by anomalous oceanic thermal advection. The anomalous southwestern anticyclonic circulation in pIODs enhances regional differences in evaporative capacity and latent heat, and in nIODs, it augments the east-west difference in the advective thermal budget. Further, the meridional anomaly mechanism is also non-negligible during the development of nIODs. As the SWA moves eastward, the meridional SWA prevails near 60°E and the corresponding meridional anomalous current appears. The corresponding maximum meridional thermal advection anomaly reaches 200 Wm^-2 in September.

关键词： IODs after ENSO SSTA air-sea heat flux oceanic thermal advection

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Influence of the Physical Environment on the Migration and Distribution of Nibea albiflora in the Yellow Sea

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Journal of Ocean University of China 2017年第1期16卷 87-92页

作者： ZHU Xianye wu kejian wu Lunyu Physical Oceanography Laboratory Ocean University of China First Institute of Oceanography State Oceanic Administration

This study investigates the migration and distribution of the warm-temperate fish Nibea albiflora. Their spawning migration and wintering migratory routes within in the Yellow Sea are described in detail. Considering the main physical features and environment of the Yellow Sea, it appears to be have one wintering ground and three migratory routes from the wintering ground to the spawning grounds. The fish begin to migrate from the wintering ground to the spawning grounds in the northwest region of the Yellow Sea in late March. The Yellow Sea has three spawning grounds. The first is located near the Yalu River on the Liaodong Peninsula and the second one is located in Rushan Bay of Shandong Peninsula. The third spawning ground is located in Haizhou Bay in the southern region of the Yellow Sea. This study found that the temperature of the Yellow Sea influences the migration of N. albiflora, and that the migratory routes coincide with the thermal fronts in the sea. Nutrients for juvenile fish are taken from the coastal upwelling area. Chlorophyll is a good environmental indicator of phytoplankton biomass and thereby provides the status of biological resources. Different types of sediment in near-shore zones are also of practical significance for the growth of fish. The study of the effects of marine environments on the migration of various fishes is not only significant to the fishing industry, but can also provide a scientific basis for the understanding of the ecological implications of the relevant physical processes.

关键词： Nibea albiflora migration temperature chlorophyll sediments

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Wave Effect on the Ocean Circulations Through Mass Transport and Wave-Induced Pumping

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Journal of Ocean University of China 2014年第2期13卷 175-182页

作者： BI Fan wu kejian Physical Oceanography Laboratory Ocean University of China

The wave Coriolis-Stokes-Force-modified ocean momentum equations are reviewed in this paper and the wave Stokes transport is pointed out to be part of the ocean circulations. Using the European Centre for Medium-Range Weather Forecasts 40-year reanalysis data(ERA-40 data) and the Simple Ocean Data Assimilation(SODA) version 2.2.4 data, the magnitude of this transport is compared with that of wind-driven Sverdrup transport and a 5-to-10-precent contribution by the wave Stokes transport is found. Both transports are stronger in boreal winter than in summers. The wave effect can be either contribution or cancellation in different seasons. Examination with Kuroshio transport verifies similar seasonal variations. The clarification of the efficient wave boundary condition helps to understand the role of waves in mass transport. It acts as surface wind stress and can be functional down to the bottom of the ageostrophic layer. The pumping velocities resulting from wave-induced stress are zonally distributed and are significant in relatively high latitudes. Further work will focus on the model performance of the wave-stress-changed-boundary and the role of swells in the eastern part of the oceans.

关键词：海洋环流运输大众季节性变化流通数值天气预报波浪作用再分析资料

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The effect of Stokes drift on Ekman transport in the open sea

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Acta Oceanologica Sinica 2012年第6期31卷 12-18页

作者： BI Fan wu kejian ZHANG Yuming Physical Oceanography Laboratory Ocean University of ChinaQingdao 266100China

By introducing the wave-induced Coriolis-Stokes forcing into ageostrophic motion equation, th1 Eulerian transport is modified by the wave-induced Stokes drift. The long-term mean contributions of the Stokes transport with remotely generated swells being included to the ageostrophic transport are analyzed using the ECMWF （European Centre for Medium-Range X,Veather Forecasts） reanalysis data. The ratio of Stokes transport to Ekman transport in north-south （N-S） direction can reach maximum of over 50% in the subtropical region. The preliminary influence of the Stokes transport on the North Pacific gyre is all year persistent, while the effect on the North Atlantic gyre is only obvious in boreal winter and early spring.

关键词： Stokes transport Ekman transport ocean swell ocean gyres

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时-空-谱融合自动纯化生成样本的农作物遥感分类

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农业工程学报 2024年第10期40卷 157-167页

作者：刘修宇张锦水吴俊旭申克建北京师范大学遥感科学国家重点实验室北京100875 北京师范大学地理科学学部遥感科学与工程研究院北京100875 农业农村部大数据发展中心北京100125

准确及时地获取农作物种植面积是粮食估产的重要基础,对稳定市场和粮食安全至关重要。随着卫星遥感技术的发展和农作物识别算法的成熟,遥感在农业领域得到了广泛深入的应用,但农作物自动化识别普遍受到缺乏足够代表性训练样本数据的制... 详细信息

准确及时地获取农作物种植面积是粮食估产的重要基础,对稳定市场和粮食安全至关重要。随着卫星遥感技术的发展和农作物识别算法的成熟,遥感在农业领域得到了广泛深入的应用,但农作物自动化识别普遍受到缺乏足够代表性训练样本数据的制约。该研究提出了一种多阶段样本纯化策略,综合考虑时间、空间、光谱和物候信息,基于历史作物空间分布图和当季遥感影像自动生成高质量的训练样本,以支持农作物的自动化识别。利用谷歌地球引擎(google earth engine,GEE)云平台及Sentinel-2数据,采用随机森林算法对浙江省两个地区的水稻进行自动化识别。研究结果表明,该方法能够利用历史专题数据和当季遥感影像生成最新且充足的训练样本,样本点精度高达98.5%。样本点数量和影像特征对分类结果影响的定量分析结果表明,作物识别的精度超过96%,Kappa系数超过0.93。此外,所提算法对含有误差的历史分类数据表现出较好的鲁棒性。研究结果可为区域级农作物识别提供一种可靠的样本自动化生成方法,在大尺度自动化作物制图中具有广泛的应用潜力。

关键词：遥感农作物分类随机森林样本自动生成 Sentinel-2

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Tidal energy budget in the Zhujiang(Pearl River) Estuary

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Acta Oceanologica Sinica 2016年第5期35卷 54-65页

作者： BAI Peng GU Yanzhen LI Peiliang wu kejian Physical Oceanography Laboratory Ocean University of China College of Information Science and Engineering Ocean University of China

Tidal energy budget in the Zhujiang（Pearl River） Estuary（ZE） is evaluated by employing high-resolution baroclinic regional ocean modeling system（ROMS）. The results obtained via applying the least square method on the model elevations are compared against the tidal harmonic constants at 18 tide stations along the ZE and its adjacent coast. The mean absolute errors between the simulation and the observation of M_2, S_2, K_1 and O_1 are 4.6, 2.8, 3.2 and 2.8 cm in amplitudes and 9.8°, 15.0°, 4.6° and 4.6° in phase-lags, respectively. The comparisons between the simulated and observed sea level heights at 11 tide gauge stations also suggest good model performance. The total tidal energy flux incoming the ZE is estimated to be 343.49 MW in the dry season and larger than 336.18 MW in the wet season, which should due to higher mean sea level height and heavier density in the dry season. M_2, K_1, S_2, O_1 and N_2, the top five barotropic tidal energy flux contributors for the ZE,import 242.23（236.79）, 52.97（52.08）, 24.49（23.96）, 16.22（15.91） and 7.10（6.97） MW energy flux into the ZE in dry（wet） season, successively and respectively. The enhanced turbulent mixing induced by eddies around isolated islands and sharp headlands dominated by bottom friction, interaction between tidal currents and sill topography or constricted narrow waterways together account for the five energy dissipation hotspots, which add up to about 38% of the total energy dissipation inside the ZE.

关键词： tidal energy flux energy dissipation Zhujiang Estuary regional ocean modeling system

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The low-frequency variance of the ocean surface wave field in the area of the Antarctic Circumpolar Current

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Acta Oceanologica Sinica 2013年第5期32卷 15-21页

作者： ZHANG Xiaoshuang wu kejian WANG Bin WANG Zhifeng Ocean University of China Key Laboratory of Marine Environmental Information Technology National Marine Data and Information ServiceState Oceanic Administration Physical Oceanography Laboratory Ocean University of China

The low-frequency variance of the surface wave in the area of the Antarctic Circumpolar Current （ACC） and its correlation with the antarctic circumpolar wave （ACW） are focused on. The analysis of the series of 44 a significant wave height （SWH） interannual anomalies reveals that the SWH anomalies have a strong periodicity of about 4-5 a and this signal propagates eastward obviously from 1985 to 1995, which needs about 8 a to complete a mimacircle around the earth. The method of empirical orthogonal function （EOF） is used to analyze the filtered monthly SWH anomalies to study the spatio-temporal distributions and the propagation characteristics of the low-frequency signals in the wave field. Both the dominant wavenumber- 2 pattern in space and the propagation feature in the south Pacific, the south Atlantic and the south Indian ocean show strong consistency with the ACW. So it is reasonable to conclude that the ACW signal also exists in the wave field. The ACW is important for the climate in the Southern Ocean, so it is worth to pay more attention to the large- scale effect of the surface wave, which may also be important for climate studies.

关键词： significant wave height antarctic circumpolar wave empirical orthogonal function low-frequ-ency variance

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Evaluation of the simulation capability of the Wavewatch Ⅲ model for Pacific Ocean wave

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Acta Oceanologica Sinica 2015年第9期34卷 43-57页

作者： BI Fan SONG Jinbao wu kejian XU Yao Key Laboratory of Ocean Circulation and Waves Institute of OceanologyChinese Academy of Sciences College of Physical and Environmental Oceanography Ocean University of China Ocean College Zhejiang University Key Laboratory of Physical Oceanography (Ocean University of China) Ministry of Education

Wave climate analysis and other applications for the Pacific Ocean require a reliable wave hindcast. Five source and sink term packages in the Wavewatch III model （v3.14 and v4.18） are compared and assessed in this study through comprehensive observations, including altimeter significant wave height, advanced synthetic aperture radar swell, and buoy wave parameters and spectrum. In addition to the evaluation of typically used integral parameters, the spectra partitioning method contributes to the detailed wave system and wave maturity validation. The modified performance evaluation method （PS） effectively reduces attribute numbers and facilitates the overall assessment. To avoid possible misleading results in the root mean square error-based validations, another indicator called HH （indicating the two authors） is also calculated to guarantee the consistency of the results. The widely used Tolman and Chalikov （TC） package is still generally efficient in determining the integral properties of wave spectra but is physically deficient in explaining the dissipation processes. The ST4 package performs well in overall wave parameters and significantly improves the accuracy of wave systems in the open ocean. Meanwhile, the newly published ST6 package is slightly better in determining swell energy variations. The two packages （ACC350 and BIA） obtained from Wavewatch III v3.14 exhibit large scatters at different sea states. The three most ideal packages are further examined in terms of reproducing wave- induced momentum flux from the perspective of transport. Stokes transport analysis indicates that ST4 is the closest to the NDBC-buoy-spectrum-based transport values, and TC and ST6 tend to overestimate and underestimate the transport magnitude, respectively, in swell mixed areas. This difference must be considered, particularly in air-wave-current coupling research and upper ocean analysis. The assessment results provide guidance for the selection of ST4 for use in a background Pacific Ocean hindcast for high wave climate

关键词： Wavewatch III evaluation Pacific Ocean source and sink term packages wave-induced flux Stokes transport

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