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The Island Rule with lateral and bottom friction

Acta Oceanologica Sinica 2019年第4期38卷 146-153页

作者： Yanzhao Yang Zexun Wei Guanlin Wang Zhan Lian Liwei Wang College of Meteorology and Oceanography National University of Defense Technology College of Mathematical Science and Physics Qingdao University of Science and Technology Key Laboratory of Marine Science and Numerical Modeling First Institute of OceanographyMinistry of Natural Resources Laboratory for Regional Oceanography and Numerical Modeling Pilot National Laboratory for Marine Science and Technology (Qingdao)

The Island Rule, derived from the Sverdrup theory, is widely used to estimate and analyze water transport through a strait. Previous studies presented single-or multi-island rules with either lateral or bottom friction. In this paper,an analytical model of wind-driven circulation is assumed based on linear dynamics. Considering both lateral and bottom friction, the analytic solutions of the transport streamfunction around the islands are derived and the volume transport through the channel is presented. The results are similar to those of Wajsowicz, but the frictional constants represent different values. The analytic solution shows that the relationship between the lateral frictional and bottom frictional dissipation is complex in terms of the frictional constants. To understand the interaction between the two friction types, lateral and bottom friction values were randomly chosen on a barotropic beta plane. The result shows an approximately linear relationship between the lateral and bottom friction in consisting of the combined frictional constants. We studied the effect of the channel width on the transport through the channel. The results show that the friction enhances the flow under some widths, which is similar to the flow behavior when only the lateral friction is considered. We also compared the transport through the channel at different depths and founded that the deeper the water, the smaller the transport reduction ratio when the horizontal eddy viscosity coefficient and the bottom drag coefficient remained constants. To further present the combined role of lateral frictional and bottom frictional dissipation, we compared our model with the model of Wajsowicz for two islands, where only the lateral or bottom friction were considered, with different channel widths. The results showed that the effect of the lateral friction is greater than the bottom friction when the channel is narrow, especially in the Munk boundary layer thickness. When the channel is

关键词： Island Rule lateral friction bottom friction transport streamfunction

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The role of plasma beta in global coronal models: Bringing balance back to the force

arXiv

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arXiv 2023年

作者： Brchnelova, Michaela Kuźma, Blażej Zhang, Fan Lani, Andrea Poedts, Stefaan Centre for Mathematical Plasma Astrophysics KU Leuven Celestijnenlaan 200B Leuven3001 Belgium Shenzhen Key Laboratory of Numerical Prediction for Space Storm Institute of Space Science and Applied Technology Harbin Institute of Technology Shenzhen518055 China Key Laboratory of Solar Activity and Space Weather National Space Science Center Chinese Academy of Sciences Beijing100190 China Institute of Physics University of Maria Curie-Sklodowska ul. Radziszewskiego 10 Lublin20-031 Poland

Context. COolfluid COrona uNstrUcTured (COCONUT) is a global coronal magnetohydrodynamic (MHD) model that has been recently developed and will soon be integrated into the ESA Virtual Space Weather Modelling Centre (VSWMC). In order to achieve robustness and fast convergence to steady-state for numerical simulations with COCONUT, several assumptions and simplifications have been made during its development, such as prescribing filtered photospheric magnetic maps for representing the magnetic field conditions in the lower corona. This filtering leads to smoothing and lower magnetic field values at the inner boundary (i.e., the solar surface), resulting in an unrealistically high plasma β (more than 1 in a large portion of the domain). Aims. In this paper, we examine the effects of prescribing such filtered/smoothed magnetograms in global coronal simulations and formulate a method for achieving more realistic plasma β values and improving the resolution of electromagnetic features without losing computational performance. Methods. We make use of the newly developed COCONUT solver to demonstrate the effects of the highly pre-processed magnetic maps set at the inner boundary and the resulting high plasma β on the features in the computational domain. Then, in our new approach, we shift the inner boundary to 2 R☉ from the original 1.01 R☉ and preserve the prescribed highly filtered magnetic map. With the shifted boundary, naturally, the boundary density and pressure are also adjusted to better represent the considered physical location. This effectively reduces the prescribed plasma β and leads to a more realistic setup. The method is applied on a magnetic dipole, a minimum (2008) and a maximum (2012) solar activity case, to demonstrate its effects. Results. The results obtained with the proposed approach show significant improvements in the resolved density and radial velocity profiles, and far more realistic values of the plasma β at the boundary and inside the computat

关键词： Magnetohydrodynamics

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The Predictability of Ocean Environments that Contributed to the 2020/21 Extreme Cold Events in China:2020/21 La Niña and 2020 Arctic Sea Ice Loss

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Advances in Atmospheric sciences 2022年第4期39卷 658-675页

作者： Fei ZHENG Ji-Ping LIU Xiang-Hui FANG Mi-Rong SONG Chao-Yuan YANG Yuan YUAN Ke-Xin LI Ji WANG Jiang ZHU International Center for Climate and Environment Science(ICCES) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science&TechnologyNanjing 210044China Department of Atmospheric and Environmental Sciences University at Albany State University of New YorkAlbanyNY 12222USA Department of Atmospheric and Oceanic Sciences&Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China School of Atmospheric Sciences Sun Yat-sen UniversityZhuhai 519082China National Climate Center Beijing 100081China University of Chinese Academy of Sciences Beijing 100049China Beijing Municipal Climate Center Beijing 100089China

Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many *** to make accurate climate predictions of extreme cold events is still an urgent *** synergistic effect of the warm Arctic and cold tropical Pacific has been demonstrated to intensify the intrusions of cold air from polar regions into middle-high latitudes,further influencing the cold conditions in ***,climate models failed to predict these two ocean environments at expected lead *** seasonal climate forecasts only predicted the 2020/21 La Niña after the signal had already become apparent and significantly underestimated the observed Arctic sea ice loss in autumn 2020 with a 1-2 month *** this work,the corresponding physical factors that may help improve the accuracy of seasonal climate predictions are further *** the 2020/21 La Niña prediction,through sensitivity experiments involving different atmospheric-oceanic initial conditions,the predominant southeasterly wind anomalies over the equatorial Pacific in spring of 2020 are diagnosed to play an irreplaceable role in triggering this cold event.A reasonable inclusion of atmospheric surface winds into the initialization will help the model predict La Niña development from the early spring of *** predicting the Arctic sea ice loss in autumn 2020,an anomalously cyclonic circulation from the central Arctic Ocean predicted by the model,which swept abnormally hot air over Siberia into the Arctic Ocean,is recognized as an important contributor to successfully predicting the minimum Arctic sea ice extent.

关键词： extreme cold event predictability La Niña Arctic sea ice loss

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An Ultra Wideband FSS Operating at Ka Band 5

An Ultra Wideband FSS Operating at Ka Band

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5th IEEE International Conference on Computational Electromagnetics, ICCEM 2019

作者： Xu, Yinfang Zhang, Shengjun National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing Institute of Space Long March Vehicle Beijing China

ISBN: (纸本)9781538671115

An Ultra Wideband frequency selective surface (FSS) with forth-order bandpass responses operating at Ka band is proposed in the paper. To improve the performance of the FSS especially in angular stability, the coupling of capacitive surface and inductive surface is employed to realize the miniaturization of the structural unit around 0.26λ. Furthermore, to enhance the passband and to suppress sharply the bandstop edge of the FSS, a multi-layer FSS structure is adopted to form a forth-order filter. In addition, the FSS working at the Ka band frequency with a low-profile broadband and a high rejection stopband is designed. The proposed FSS can provide sharp frequency selectivity and stable frequency responses as functions of angle and polarization of incidence of the EM wave. Principles of operation, detailed design, and simulated results of the fabricated prototypes are presented and discussed in this paper. © 2019 IEEE.

关键词： Frequency selective surfaces

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An Improved Adaptive Pulse Compression Algorithm Based on Linear Frequency Modulation Signal

An Improved Adaptive Pulse Compression Algorithm Based on Li...

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2019 IEEE International Conference on Signal, Information and Data Processing, ICSIDP 2019

作者： Bai, Jinliang Qin, Peng Li, Hu Zhang, Ran Zhang, Xinyu National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing Institute of Space Long March Vehicle Beijing China

ISBN: (纸本)9781728123455

In this paper, the radar signal is optimized based on the pulse compression repair (PCR) algorithm, which mainly reduces the computational amount to makes it more advantageous to achieve. The main idea is to implement PCR in a parallel way. The method of implementing parallelism is well known, that is, the signal is segmented, and different segmentation methods can be adopted according to different signal models. In this paper, the chirp signal is mainly processed by decimation and segmentation, and some intrinsic benefits of the performance and computational balance of the proposed method are discussed. © 2019 IEEE.

关键词： Frequency modulation

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Pressure level of maximum radiative heating enhancement in response to increasing CO_(2) over the global monsoon area

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Atmospheric and Oceanic science Letters 2021年第3期14卷 19-24页

作者： Xia Qu Gang Huang Xiaocong Wang Center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina Laboratory for Regional Oceanography and Numerical Modeling Qingdao National Laboratory for Marine Science and TechnologyQingdaoChina University of Chinese Academy of Sciences BeijingChina

Based on the 1%CO_(2) experiment of CMIP6,in response to increasing CO_(2),the summer-mean radiative heating(RH)over the global monsoon area(MA)generally features an increasing response in the mid-troposphere and a decreasing response in the lower and upper *** pressure level of the maximum RH increase over the Asian MA is the highest and largest in range(500–775 hPa);the maximum increases over the North African,South American,and Australian MA are at 550–600 hPa;throughout the North American MA,the maximum heating increase is at 600 hPa;and the levels of the maximum over South Africa are 600 and 775 *** most of the global MA,the maximum enhancement of RH is at 500,550,and 600 *** is mainly led by the increase in cloud water at and above the maximum level and the decrease in cloud water below,which leads to similar changes in total cloud *** of the longwave heating(cooling)effect at the cloud base(top),the RH enhancements peak at those *** the northeast part of the Asian MA and southeast part of the South African MA,RH enhancement peaks at 700 and 775 hPa,mainly attributable to the cloud water reduction *** reduction leads to similar changes in total *** to the longwave cooling effect at the cloud top,the reduction contributes to the RH enhancement at the corresponding maximum levels.

关键词： Radiative heating Increasing CO_(2) Global monsoon area Cloud

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Adaptive feed-forward control for seeker based on the disturbance observer 4

Adaptive feed-forward control for seeker based on the distur...

引用

4th IEEE Advanced Information technology, Electronic and Automation Control Conference, IAEAC 2019

作者： Liu, Xin Niu, Zhenhong Shu, Yi Xue, Lian Zhu, Mingchao National Key Laboratory of Science and Technology on Test Physics Numerical Mathematics China Chinese Academy of Sciences Changchun Institute of Optics Mechanics and Physics China

ISBN: (纸本)9781728119076

In order to improve the tracking and stabilization performance, a control method combining disturbance observer and adaptive feed-forward control using parameterization is proposed for seeker stabilized platforms. The system identification algorithm is used to identify dynamic model of the true plant. Then the discrete-time disturbance observer is designed. The feedback loop controller is designed using pole-placement techniques. The recursive least square (RLS) adaptive filter is used to build the inverse model of the feedback control loop and in this way, the feed-forward control is constructed. The adaptive filter and the feedback loop constitute a control scheme with two degrees-of-freedom (DOF). Tracking experiments conducted on velocity command inputs verify the validity of the adaptive feed-forward controller. Experimental results show that this method responses quickly to commands. For a sinusoidal signal at the frequency of 30Hz, the adaptive feed-forward controller can obtain an amplitude response without attenuation and the phase lag is reduced to 11° in contrast with the feedback control whose phase lag is 60°. This method significantly improves the transient performance and is superior to the feedback control alone. © 2019 IEEE.

关键词： Adaptive filters

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Impact analysis of CFAR detection for false targets generated by the phase-switched screen

Impact analysis of CFAR detection for false targets generate...

引用

2019 IEEE International Conference on Signal, Information and Data Processing, ICSIDP 2019

作者： Zheng, Ran Chen, Yuan S Zhang, Yu X Guo, Lei Bai, Liang J Zhang, Ping L Zhang, Ran National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing Institute of Space Long March Vehicle Beijing China National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing Institute of Space Long March Vehicle No. 1 Nanda Hongmen Road of Fengtai District Beijing China

ISBN: (纸本)9781728123455

The phase-switched screen (PSS) has been proved effective in the application of shielding a target or deceiving the radar system when the modulation frequency of it is set greater or smaller than the signal bandwidth. This paper analyses impacts of false targets generated by PSS (PSS-decoys) echoes on radar constant false alarm rate detection. The generation principle of PSS-decoys and the key factors that influence the signatures of PSS-decoys are introduced briefly at first. On base of it, the detection cost caused by the false alarm and false dismissal in a search period of radar is chosen as the criteria of detection performance. The detection costs of CA-CFAR, OS-CFAR, CMLD-CFAR detectors under multiple decoys jamming environment are analysed. Specially, we investigate the influence of the PSS key factors on detection costs from the perspective of simulation. The results show that detection costs will increase remarkably due to false targets existing and it is sensitive to the switching frequency, and the relationship to the duty ratio is tightly relevant to SNR. Among three detectors, the detection costs of CMLD-CFAR detector are higher than that of adopting CA-CFAR and that of adopting OS-CFAR. © 2019 IEEE.

关键词： Signal detection

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A Direct Position Determination Method for Four-station TDOA Location System

A Direct Position Determination Method for Four-station TDOA...

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2019 IEEE International Conference on Signal, Information and Data Processing, ICSIDP 2019

作者： Qi, Sun-Rui Yuan, Chen-Shun Liang, Bai-Jin Gao-Lu Li-Hu Sun-Heng BEIJING INSTITUTE of SPACE LONG MARCH VEHICLE National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing100076 China

ISBN: (纸本)9781728123455

Aiming at the four-station networked TDOA (Time Difference of Arrival) localization system, a direct location method based on electronic elevation map search is proposed, the Geometric Dilution Precision (GDOP) is derived, and the factors affecting the location accuracy are analyzed. The location method under real conditions is also simulated, and its feasibility is demonstrated, which provides a new engineering method for networked TDOA location. © 2019 IEEE.

关键词： Time difference of arrival

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A Physical Layer key Generation method with Reliable Negotiation

A Physical Layer Key Generation method with Reliable Negotia...

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2019 IEEE International Conference on Signal, Information and Data Processing, ICSIDP 2019

作者： Wang, Yuchen Wu, Xuanli Xu, Zhicong Wu, Wei Li, Hu Zhang, Ran School of Electronics and Information Engineering Harbin Institude of Technology Harbin China National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing China

ISBN: (纸本)9781728123455

There is a risk of information leakage in the process of wireless communication. The introduction of key generation in the physical layer can effectively improve the security of wireless communication. This paper proposes a new physical layer key generation method in the TDD (time division duplex) communication system. Assume that the uplink and downlink channels are reciprocal. Through LDPC (Low Density Parity Check)channel coding and negotiation algorithm, the inconsistency rate of key generation between Alice and Bob is reduced. Simulation and analysis results show that the method improves the key generation rate and reduces the key inconsistency rate. © 2019 IEEE.

关键词： Hash functions

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