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Study of Beam Scan with Variable Linear Polarisation Directions of Antenna Arrays Using MMIC T/R Modules
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作者 李镇 邓次平 《Journal of Beijing Institute of Technology》 EI CAS 1992年第1期24-30,共7页
The beam scan with variable linear polarization directions of antenna arrays using MM/C transmit-receive (T/R) modules is explored. It is shown that the beam scan and the polarizations of electric fields can be contro... The beam scan with variable linear polarization directions of antenna arrays using MM/C transmit-receive (T/R) modules is explored. It is shown that the beam scan and the polarizations of electric fields can be controlled simultaneously if the forms of module arrangement are chosen properly and the amplitudes and the phases of array excitation are determined by the method presented in this article. Moreover, the calculations of the amplitudes and the phases of array excitation are simplified greatly while using the bounded conditions properly, and the desired beam sweep rate is achieved. 展开更多
关键词 millimeter waves antenna array scanning antenna/variable polarization
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Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints 被引量:13
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作者 丁吉坤 王东坡 +1 位作者 王颖 杜辉 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2014年第5期1307-1316,共10页
AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas (VPTIG) welding process and the effects of post weld heat treatment (PWHT) on the tensile properties, microstructure and fatigu... AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas (VPTIG) welding process and the effects of post weld heat treatment (PWHT) on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded (AW) sample and PWHT sample. The PWHT method used on the samples was solution treatment (535 ℃, 30 rain), water quenching and artificial aging (175 ℃, 12 h). The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively. 展开更多
关键词 AA2219 aluminium alloy variable polarity TIG post weld heat treatment mechanical properties MICROSTRUCTURE fatigue behaviour
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Characteristics of arc in variable polarity plasma arc welding of aluminum alloy 被引量:6
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作者 洪海涛 韩永全 +1 位作者 杜茂华 吴永军 《China Welding》 EI CAS 2014年第3期73-77,共5页
A double invert variable polarity plasma arc (VPPA) power source based on 16-bit MCU applied for aluminum alloys was developed. Mechanics, electrical and the produced heat mechanism of VPPAW arc were tested and anal... A double invert variable polarity plasma arc (VPPA) power source based on 16-bit MCU applied for aluminum alloys was developed. Mechanics, electrical and the produced heat mechanism of VPPAW arc were tested and analyzed. Results indicate that during the VPPA welding procedure of aluminum alloy, the arc of electrode negative (EN) has more effect on force, whereas the arc of electrode positive ( EP ) has more effect on heat. It should be noted that keeping the balance of the force and heat is the critical element of VPPAW. This power source had been successfully used to weld aluminum alloy with a 15 mm thickness in vertical welding. The conclusions are applicable to the variable polarity plasma arc welding technique used in the aerospace industry. 展开更多
关键词 variable polarity plasma arc arc pressure aluminum alloy
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A novel variable polarity welding power based on high-frequency pulse modulation 被引量:3
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作者 邱灵 杨春利 +2 位作者 范成磊 林三宝 伍昀 《China Welding》 EI CAS 2006年第3期11-15,共5页
A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative (DCEN), which can i... A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative (DCEN), which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor (DSP) is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition. 展开更多
关键词 variable polarity welding digital signal processor DSP) high-frequency pulse current pulse current welding
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Experimental Analysis on the Variable Polarity Plasma Arc Pressure 被引量:1
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作者 JIANG Yi XU Binshi +2 位作者 LUE Yaohui LIU Cunlong LIU Ming 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2011年第4期607-611,共5页
Arc pressure is one of the key factors for variable polarity plasma arc(VPPA) and welding pool formation. In this paper, VPPA pressure is measured by pressure transducer and U-tube barometer methods, and advantages ... Arc pressure is one of the key factors for variable polarity plasma arc(VPPA) and welding pool formation. In this paper, VPPA pressure is measured by pressure transducer and U-tube barometer methods, and advantages and disadvantages of the two methods are compared. The effects of welding parameters, including with straight polarity(SP) current, reverse polarity(RP) current, time ratio of SP to RP, plasma gas flow rate, on VPPA pressure are investigated by using an orthogonal design. The experimental results indicate that the influencing degree of the welding parameters are in the order of plasma gas flow rate, SP current, time ratio of SP to RP, RP current. These results are important to researches of VPPA welding process and its mechanism. The physics behavior of VPPA is taken into account when the above influence mechanisms are analyzed. Firstly, according to the mechanism of the cooling compression to the arc, the compression to VPPA is enhanced with the increase of plasma gas flow, so the VPPA pressure would increase obviously. Secondly, although the temperature of VPPA is as a function of the welding current, the radius of VPPA is also enhanced. So the effects of SP current on VPPA pressure are inferior to the effects of plasma gas flow. Thirdly, VPPA pressure increases as a function of time ratio of SP to RP because the frequency of welding current influences the arc pressure to the some degree; Finally, the RP intervals are farther less than the SP intervals, so the influence to the pressure is minimal. 展开更多
关键词 variable polarity plasma arc arc pressure orthogonal experiment
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Study on the measureto improve the arcstabilization in smaller current welding for the variable polarity GTAW powersource 被引量:2
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作者 张广军 耿正 +1 位作者 吴林 殷树言 《China Welding》 EI CAS 2000年第1期78-82,共5页
The variable polarity power source which incorporates a constant current power and a secondary inverter does not need special apparatus for stabilizing arc. The pulse for stabilizing arc is created by the circuit stru... The variable polarity power source which incorporates a constant current power and a secondary inverter does not need special apparatus for stabilizing arc. The pulse for stabilizing arc is created by the circuit structure itself. The paper analyzes the principle of acquiring the pulse, provides the better method to improve the arc stabilization under smaller welding current. Test shows the arc is highly stable , and the process has no high frequency electromagnetic interference, which is suitable for automatic welding case. 展开更多
关键词 variable polarity power source stabilizing arc aluminum GTAW
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Formative mechanism of the undercut defect in horizontal variable polarity plasma arc welding 被引量:1
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作者 张勤练 杨春利 +1 位作者 林三宝 范成磊 《China Welding》 EI CAS 2014年第3期1-8,共8页
Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. T... Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. The characteristic of welding defects was introduced. Preliminary experiments indicated that the undercut defect could not be eliminated easily. The relationship between welding parameters and the undercut defect showed that this deject could be lessened by using higher heat input. The fluid flow of weld pool was observed by a high speed camera. The fluid flow in weld pool was not symmetric and much of molten metal gathered in the lower part. The fluid flow velocity in the lower part was bigger than that in the upper part. To this end, the formative mechanism of the undercut defect was proposed. The flowability of the molten metal was an influential factor for the undercut defect. A preheating method was designed to verify the formative mechanism. 展开更多
关键词 horizontal welding variable polarity plasma arc aluminum alloy undercut defect
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Complex variable approach in studying modified polarization saturation model in two-dimensional semipermeable piezoelectric media 被引量:1
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作者 S. SINGH K. SHARMA R. R. BHARGAVA 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI CSCD 2017年第11期1517-1532,共16页
A modified polarization saturation model is proposed and addressed math- ematically using a complex variable approach in two-dimensional (2D) semipermeable piezoelectric media. In this model, an existing polarizatio... A modified polarization saturation model is proposed and addressed math- ematically using a complex variable approach in two-dimensional (2D) semipermeable piezoelectric media. In this model, an existing polarization saturation (PS) model in 2D piezoelectric media is modified by considering a linearly varying saturated normal electric displacement load in place of a constant normal electric displacement load, applied on a saturated electric zone. A centre cracked infinite 2D piezoelectric domain subject to an arbitrary poling direction and in-plane electromechanical loadings is considered for the analytical and numerical studies. Here, the problem is mathematically modeled as a non-homogeneous Riemann-Hilbert problem in terms of unknown complex potential functions representing electric displacement and stress components. Having solved the Hilbert problem, the solutions to the saturated zone length, the crack opening displace- ment (COD), the crack opening potential (COP), and the local stress intensity factors (SIFs) are obtained in explicit forms. A numerical study is also presented for the proposed modified model, showing the effects of the saturation condition on the applied electrical loading, the saturation zone length, and the COP. The results of fracture parameters obtained from the proposed model are compared with the existing PS model subject to electrical loading, crack face conditions, and polarization angles. 展开更多
关键词 complex variable fracture parameter local stress intensity factor (SIF) piezoelectric polarization saturation (PS) model
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Visual sensing of weld pool in variable polarity TIG welding of aluminium alloy 被引量:4
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作者 张广军 闫志鸿 吴林 《中国有色金属学会会刊:英文版》 EI CSCD 2006年第3期522-526,共5页
The passive visual sensing method was successfully applied to monitor the weld pool in TIG welding of aluminium alloy. In order to reduce the disturbance from the arc and acquire clear image, two techniques were used:... The passive visual sensing method was successfully applied to monitor the weld pool in TIG welding of aluminium alloy. In order to reduce the disturbance from the arc and acquire clear image, two techniques were used: one was the own-developed computer-controlled variable polarity power(VPP), the other was the composite filter technology. The VPP source did not have high-frequency electromagnetic interference from arc stabilizer in traditional AC welding power, and its output current wave was controlled by computer, so the imaging current and the imaging time could be adjusted easily. Filter spectral window was identified at 650 nm by analyzing the measured arc light spectral distribution. At the end, the high quality and clear images of welding pool of aluminium alloy were successfully acquired at low imaging current. 展开更多
关键词 铝合金 TIG焊接 视觉传感 滤谱器 焊接熔池
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Simultaneous Determination of Fluorescein, Rhodamine 6G and Rhodamine B in Turbid Solution by Polarization Variable-Angle Synchronous Fluorescence Spectrometry 被引量:2
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作者 Yao Qun LI Fang QIAN Xian Zhi HUANG(Department of Chemistry and Key Laboratory of Analytical Sciences of the Ministry of Education,Xiamen University, Xiamen 361005) 《Chinese Chemical Letters》 SCIE CAS CSCD 2000年第7期613-614,共2页
Polarization variable-angle synchronous fluorescence spectrometry was proposed to determine samples in turbid solution. A mixture of fluorescein, rhodamine 6G and rhodamine B was used to evaluate the technique. The ba... Polarization variable-angle synchronous fluorescence spectrometry was proposed to determine samples in turbid solution. A mixture of fluorescein, rhodamine 6G and rhodamine B was used to evaluate the technique. The background caused by scattering light was decreased remarkably. The limits of detection were 0.6 ng/ml for fluorescein, 2.3 ng/ml for rhodamine 6G and 4.1 ng/ml for rhodamine B, respectively. 展开更多
关键词 variable-angle synchronous fluorescence polarIZATION FLUORESCEIN rhodamine 6G rhodamine B
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Mechanical properties of welded joints in vertical-up variable polarity plasma arc welding of 2219 aluminum alloy
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作者 杨春利 郭立杰 +1 位作者 林三宝 沈鸿源 《中国有色金属学会会刊:英文版》 CSCD 2005年第S2期83-86,共4页
The mechanical properties of the 2219 aluminum alloy welded joints by vertical-up variant polarity plasma arc welding (VPPAW) with keyhole were analyzed. The tensile strength of welded joints can reach 55% of that of ... The mechanical properties of the 2219 aluminum alloy welded joints by vertical-up variant polarity plasma arc welding (VPPAW) with keyhole were analyzed. The tensile strength of welded joints can reach 55% of that of base metal. The microstructure of weld joints was studied to explain the mechanical properties of the weld. The results show that the intensity of weld center is less than that of HAZ, and the intensity of weld center is the worst. So an advanced welding procedures is presented to reduce the heat input and increase the welding speed. The results in this procedures show that the tensile strength of welded joints reaches more than 60% of that of the parent metal, and the specific elongation does not descend. 展开更多
关键词 2219 aluminum alloy variable polarity plasma ARC WELDING MECHANICAL PROPERTY microstructure
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Beam pointing correction of variable polarization MMW/IR combined detection
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作者 刘建勋 张伟 +2 位作者 邓洪 孙厚军 吕昕 《Journal of Beijing Institute of Technology》 EI CAS 2012年第1期96-100,共5页
A kind of beam-scanning algorithm of variable polarization millimeter array antenna based on the phased array technology is put forward in this paper. The algorithm can be successfully applied to deal with beam direct... A kind of beam-scanning algorithm of variable polarization millimeter array antenna based on the phased array technology is put forward in this paper. The algorithm can be successfully applied to deal with beam directivities inconsistency of millimeter wave/infrared( MMW/IR ) multimode detector, it can keep electric axis and optical axis coincident. Accordingly, this method can decrease the data fusion difficulty and improve the accuracy of angle measurement. Simulation results show that variable polarization millimeter array antenna has flexible beam-scanning abibility within ±0.5° after the algorithm was adopted, simultaneously, antenna polarization purity is better than 20 dB within the half power beamwidth, sidelobe imbalance keeps high available and antenna gain of the sum beam is over 26.8 dB. 展开更多
关键词 phased array digital beamforming variable polarization combined detection
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Cathodic cleaning in variable polarity plasma arc welding of aluminum alloys
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作者 陈克选 李鹤岐 李春旭 《China Welding》 EI CAS 2003年第2期168-170,共3页
Variable polarity plasma arc welding (VPPAW) is one of the most excellent processes used for welding aluminum alloys recently. It combines the advantages of variable polarity welding and plasma arc welding, and can ac... Variable polarity plasma arc welding (VPPAW) is one of the most excellent processes used for welding aluminum alloys recently. It combines the advantages of variable polarity welding and plasma arc welding, and can achieve the most rational heat distribution and cathodic cleaning. With the VPPAW equipment developed by authors, the cathodic cleaning regularity that is one of the most important problems in VPPAW is investigated in this paper. The results will be helpful in realizing the real cleaning mechanism. 展开更多
关键词 variable polarity plasma arc welding aluminum alloys cathodic cleaning
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Effect of variable polarity frequency on 2A14-T6 aluminum alloy welds using HPVP-GTAW process
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作者 李玉龙 从保强 +2 位作者 齐铂金 刘方军 杨明轩 《China Welding》 EI CAS 2014年第1期40-45,共6页
Hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) for 2A14-T6 high strength aluminum alloy was carried out and the effects of variable polarity frequency with constant pulse cur... Hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) for 2A14-T6 high strength aluminum alloy was carried out and the effects of variable polarity frequency with constant pulse current frequency 40 kHz on weld bead geometry, microstrueture and microhardness were analyzed. Experimental results indicate that, compared to that of the conventional VP-GTAW process, the weld depth and ratio of weld depth to width are improved significantly by the variable polarity frequency in the HPVP-GTAW process, which the ratio of weld depth to width is improved by 36% at equal variable polarity frequency of 100 Hz, and improved by 55% with that of 200 Hz. Weld microstructure and microhardness distribution are changed obviously with the increase of variable polarity frequency. In the conventional VP-GTA W process, the grains in weld central zone are coarser, and the microhardness in weld central zone and fusion zone is about 95 HV and the lowest 82 HV, respectively. The microhardness is enhanced to a certain extent both in the weld central zone and fusion zone with the variation of variable polarity frequency in the HPVP-GTAW process due to the refinement and uniformity of weld microstructure. With the variable polarity frequency of 600 Hz, the microhardness in weld central zone and fusion zone reaches nearly 110 HV and 97 HV, respectively. 展开更多
关键词 high strength aluminum alloy variable polarity frequency gas tungsten arc welding weld bead geometry
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A numerical model of wire melting rate in variable-polarity submerged arc welding
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作者 程方杰 武云龙 +2 位作者 王颖 张建优 王东坡 《China Welding》 EI CAS 2013年第3期36-41,共6页
Based on the pre-existing wire melting rate model of direct-current submerged arc welding ( DC-SAW) , a new numerical model of wire melting rate was developed for variable-polarity submerged are welding (VP-SAW) b... Based on the pre-existing wire melting rate model of direct-current submerged arc welding ( DC-SAW) , a new numerical model of wire melting rate was developed for variable-polarity submerged are welding (VP-SAW) by accounting for the combined effects of duty cycle β and offset α. The experimental measurements are in a good agreement with the results calculated by this new wire melting rate model, with the maximum discrepancy being less than 10%. Therefore it is evident that this new numerical model can successfully describe the dependence of wire melting rate on the duty cycle β and offset α. 展开更多
关键词 wire melting rate duty cycle OFFSET variable-polarity welding
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Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors 被引量:1
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作者 代由勇 颜世申 +3 位作者 田玉峰 陈延学 刘国磊 梅良模 《Chinese Physics B》 SCIE EI CAS CSCD 2010年第3期477-481,共5页
This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high trans... This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the 'hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained. 展开更多
关键词 variable range hopping ferromagnetic semiconductors electrical transport spin polar-ization
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Radio-frequency design of a new C-band variable power splitter
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作者 Zong-Bin Li Alexej Grudiev +2 位作者 Wen-Cheng Fang Qiang Gu Zhen-Tang Zhao 《Nuclear Science and Techniques》 SCIE CAS CSCD 2019年第6期122-128,共7页
A novel variable C-band radio-frequency (RF) power splitter was designed at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Using three RF impedance combiners, an H-bend, and an RF polarizer, this ... A novel variable C-band radio-frequency (RF) power splitter was designed at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Using three RF impedance combiners, an H-bend, and an RF polarizer, this new power splitter is much more compact than a traditionally designed splitter, which comprises three 3-dB hybrids. The parameters were optimized to achieve good matching and minimize reflection. Here, the RF design of the new C-band variable power splitter is presented. 展开更多
关键词 Power SPLITTER variable polarizer COMPACT
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物联网通信中的Polar信道编码技术优化研究
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作者 李真真 黄钧露 《通信电源技术》 2024年第16期143-145,共3页
文章针对物联网通信中的Polar码研究了一种可变步长的编码方法,并探讨了固定码长与可变码长两种不同编码方法的性能比较。通过对比两种方法在不同信噪比条件下的误码率表现,结果显示可变码长Polar码在各个信噪比条件下均优于固定码长Po... 文章针对物联网通信中的Polar码研究了一种可变步长的编码方法,并探讨了固定码长与可变码长两种不同编码方法的性能比较。通过对比两种方法在不同信噪比条件下的误码率表现,结果显示可变码长Polar码在各个信噪比条件下均优于固定码长Polar码。这一研究为极化码在通信系统中的应用提供了重要参考,对于提高通信系统的可靠性和性能具有一定的指导意义。 展开更多
关键词 信道编码 polar 可变步长 信道状态
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A Preliminary Study on the Polar Climate Predictability 被引量:2
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作者 王会军 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 1999年第3期361-366,共6页
Studies have revealed that predictability of the atmospheric general circulation is generally high in the tropics throughout the year and that there is some predictability in the Northern extra-tropical winter atmosph... Studies have revealed that predictability of the atmospheric general circulation is generally high in the tropics throughout the year and that there is some predictability in the Northern extra-tropical winter atmospheric circulation through some patterns of tele connection. Predictability of the general circulation at the polar regions has still remained as a ‘ cold’ topic and little has been known about this question. Based on a preliminary study on the predictability by using the Institute of Atmospheric Physics (IAP) general circulation model, it is found that the SST-related predictability of the Southern winter lower atmospheric circulation in Antarctica is reasonably high and that there is some predictability in the 500 hPa and 200 hPa geopotential height fields over Europe and the Okhotsk Sea region during the Northern winter. It is suggested that more researches on this issue based on data analysis and model simulations are needed to obtain better understanding. 展开更多
关键词 polar climate predictability El Nino Climate variability
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Sub seasonal variations of weak stratospheric polar vortex in December and its impact on Eurasian air temperature 被引量:1
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作者 PENG Cheng FAN Ke DAI Haixia 《Atmospheric and Oceanic Science Letters》 CSCD 2019年第5期369-375,共7页
Weak stratospheric polar vortex(WPV)events during winter months were investigated.WPV events were identified as being weakest in December,accompanied by the most dramatic increase in geopotential height over the polar... Weak stratospheric polar vortex(WPV)events during winter months were investigated.WPV events were identified as being weakest in December,accompanied by the most dramatic increase in geopotential height over the polar region.After the onset of a December WPV event,the dynamic processes influencing Eurasian temperature can be split into two separate periods.Period I(lag of 0-25 days)is referred to as the stratosphere-troposphere interactions period,as it is mainly characterized by stratospheric signals propagating downwards.In Period I,a stratospheric negative Northern Annular Mode(NAM)pattern associated with the WPV propagates downwards,inducing a negative NAM in the troposphere.The anomalous low centers over the Mediterranean and North Pacific bring cold advection to northern Eurasia,resulting in a north-cold-south-warm dipole pattern over Eurasia.The zero line between negative and positive temperature anomalies moves southwards during days 5-20.Stratospheric cold anomalies at midlatitudes propagate downwards to high latitudes in the troposphere and contribute to the dipole structure.During PeriodⅡ(lag of 25-40 days),as downward signals from the stratosphere have vanished,the dynamic processes mainly take place within the troposphere.Specifically,a wave train is initiated from the North Atlantic region to northern Europe.The propagation of wave activity flux intensifies a cyclonic anomaly over northern Europe,which brings cold advection to Scandinavia and warm advection to central Asia.Therefore,a northwest-cold-southeast-warm dipole structure occupies Eurasia and migrates southeastwards during this period. 展开更多
关键词 Stratospheric polar vortex weak stratospheric polar vortex events in December subseasonal variability stratosphere-troposphere interaction winter Eurasian air temperature(0-40 days)
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