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The Combined Effects of the Tropical and Extratropical Quasi-biweekly Oscillations on the Record-setting Mei-yu Rainfall in the Summer of 2020
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作者 Zhen HUANG Shuanglin LI +1 位作者 Jianying LI Chao ZHANG 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2023年第4期663-681,I0002-I0014,共32页
During June-July 2020,the strongest recorded mei-yu rainfall occurred in the middle and lower reaches of the Yangtze River.The rainfall processes exhibited an obvious quasi-biweekly(biweekly in brief)variability,and t... During June-July 2020,the strongest recorded mei-yu rainfall occurred in the middle and lower reaches of the Yangtze River.The rainfall processes exhibited an obvious quasi-biweekly(biweekly in brief)variability,and there are altogether five cycles.It is found that the biweekly rainfall cycle mainly arises from the collaborative effects of biweekly variabilities from both the tropics and extratropics.As for the tropics,the biweekly meridional march and retreat of the western Pacific subtropical high(WPSH)is particularly evident.As for the extratropics,geopotential height anomalies near Lake Baikal are active.The former is attributed to the intensified biweekly activity of the southwest-northeast oriented EastAsian Pacific wave train(EAP)originating from the tropical western Pacific,while the latter is associated with the biweekly activities of the eastward propagating Eurasia mid-high latitudinal wave train and the westward propagating North Pacific wave train.Why the biweekly activities of these wave trains intensified is further diagnosed from the perspective of thermodynamical forcing and also from the modulation of interannual background on intraseasonal variability.It is found that the strongest recorded convection anchoring over the tropical western Indian Ocean(IO)triggers anomalous descent over the tropical western Pacific,which modulates the biweekly activity of the EAP.Meanwhile,the anomalous diabatic heating over the IO causes changes of the meridional thermodynamic contrast across the IO to the high latitudes,which modulates the extratropical wave trains.A further diagnosis of barotropic kinetic energy conversion suggests that the active occurrence of two extratropical biweekly wave trains is attributed to the increased efficiency of energy conversion from basic flow.The westward propagation of the extratropical North Pacific wave train is attributed to the weakened and northshifted upper-level westerly,which is caused by the SST warmth near the Kuroshio extension. 展开更多
关键词 strongest recorded mei-yu rainfall in summer 2020 quasi-biweekly variability tropical convection westward propagation of the extratropical North Pacific wave train SSTA in the North Pacific
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Modulation of Tropical Cyclogenesis in the Western North Pacific by the Quasi-Biweekly Oscillation 被引量:4
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作者 Haikun ZHAO Chunzai WANG Ryuji YOSHIDA 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2016年第12期1361-1375,共15页
The quasi-biweekly oscillation (QBWO) is the second most dominant intraseasonal mode over the westem North Pacific (WNP) during boreal summer. In this study, the modulation of WNP tropical cyclogenesis (TCG) by ... The quasi-biweekly oscillation (QBWO) is the second most dominant intraseasonal mode over the westem North Pacific (WNP) during boreal summer. In this study, the modulation of WNP tropical cyclogenesis (TCG) by the QBWO and its association with large-scale patterns are investigated. A strong modulation of WNP TCG events by the QBWO is found. More TCG events occur during the QBWO's convectively active phase. Based on the genesis potential index (GPI), we further evaluate the role of environmental factors in affecting WNP TCG. The positive GPI anomalies associated with the QBWO correspond well with TCG counts and locations. A large positive GPI anomaly is spatially correlated with WNP TCG events during a life cycle of the QBWO. The low-level relative vorticity and mid-level relative humidity appear to be two dominant contributors to the QBWO-composited GPI anomalies during the QBWO's active phase, followed by the nonlinear and potential intensity terms. These positive contributions to the GPI anomalies are partly offset by the negative contribution from the vertical wind shear. During the QBWO's inactive phase, the mid-level relative humidity appears to be the largest contributor, while weak contributions are also made by the nonlinear and low-level relative vorticity terms. Meanwhile, these positive contributions are partly cancelled out by the negative contribution from the potential intensity. The contributions of these environmental factors to the GPI anomalies associated with the QBWO are similar in all five flow patterns--the monsoon shear line, monsoon confluence region, monsoon gyre, easterly wave, and Rossby wave energy dispersion associated with a preexisting TC. Further analyses show that the QBWO strongly modulates the synoptic-scale wave trains (SSWs) over the WNP, with larger amplitude SSWs during the QBWO's active phase. This implies a possible enhanced (weakened) relationship between TCG and SSWs during the active (inactive) phase. This study improves our understanding of the modulation of WNP TCG by the QBWO and thus helps with efforts to improve the intraseasonal prediction of WNP TCG. 展开更多
关键词 tropical cyclogenesis quasi-biweekly oscillation genesis potential index large-scale patterns western NorthPacific
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THE NORTH-SOUTH ANTI-PHASE DISTRIBUTION OF RAINFALL IN MEIYU PERIODS AND ITS RELATIONSHIP WITH QUASI-BIWEEKLY OSCILLATION IN THE ATMOSPHERE 被引量:2
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作者 尹志聪 祝丽娟 袁东敏 《Journal of Tropical Meteorology》 SCIE 2014年第2期154-162,共9页
Based on the daily rainfall datasets from 740 stations in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the relationship between the north-south anti-phase distribution(APD) of rainfall during Meiyu perio... Based on the daily rainfall datasets from 740 stations in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the relationship between the north-south anti-phase distribution(APD) of rainfall during Meiyu periods and the Quasi-Biweekly Oscillation(QBWO) in the atmosphere was analyzed. Diagnostic results are as follows:(1) there was significant north-south oscillation of Meiyu rainfall during the 16 years from 1954 to 2005. Since the 1990 s, the APD enhanced significantly and showed 2- and 4-6-year period. In the region with more rainfall, the QBWO was always more active.(2) The APD of Meiyu and north-south movements of precipitation in eastern China belong to the same phase.(3) The 10-25 day filtered water vapor flux could spread to the area north of 30°N in 1991. The divergence of the water vapor flux which propagated from middle- and higher- latitudes to the of Yangtze-Huaihe River Basins(YHRB) was significant in 1991, but the latitudes that the water vapor flux could reach were further southward and there was no southward propagation of divergence in 1993.(4) The locations of Western Pacific Subtropical High(WPSH) and 10-25 day anti-cyclone, which modulated WPSH's advancement in and out of the South China Sea, were relatively northward in 1991. Furthermore, the vertical circulation showed north-south deviation between 1991 and 1993, just as other elements of the circulation did. 展开更多
关键词 MEIYU anti-phase distribution quasi-biweekly oscillation low frequency oscillation water vapor flux
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Modulation of Tropical Cyclone Activity Over the Northwestern Pacific Through the Quasi-Biweekly Oscillation 被引量:2
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作者 ZHU Li-juan LIN Fei-long LIANG Chu-jin 《Journal of Tropical Meteorology》 SCIE 2021年第2期125-135,共11页
The quasi-biweekly oscillation(QBWO)is the second most dominant intraseasonal mode for circulation over the Northwestern Pacific(WNP)during boreal summer.In this study,we investigated how the QBWO modulates tropical c... The quasi-biweekly oscillation(QBWO)is the second most dominant intraseasonal mode for circulation over the Northwestern Pacific(WNP)during boreal summer.In this study,we investigated how the QBWO modulates tropical cyclone(TC)activities over the WNP from dynamic and thermodynamic perspectives.The propagation of the QBWO can be divided into four phases through empirical orthogonal function analysis of the vorticity at 850 hPa,which was proven to be effective in extracting the QBWO signal.TC generation and landings are significantly enhanced during the active period(phases 1 and 2)relative to the inactive period(phases 3 and 4).Composite analyses show the QBWO could significantly modulate TC activity as it propagates northwestward by changing the atmospheric circulation at both high and low levels.Cumulus convection provides an important link between TCs and the QBWO.The major component of the atmosphere heat source is found to be the latent heat release of convection.The condensation latent heat centers,vertical circulation,and water vapor flux divergence cooperate well during different phases of the QBWO.The vertical profile of the condensation latent heat indicates upper-level heating(cooling)during the active(inactive)phases of the QBWO.Thus,the northwestward propagation of the QBWO can modulate TC activity by affecting the configuration of atmospheric heating over the WNP. 展开更多
关键词 quasi-biweekly oscillation Northwestern Pacific tropical cyclone atmospheric circulation convective condensation heating
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Effect of the westward-propagating zonal wind anomaly on the initial development of quasi-biweekly oscillation over the South China Sea during early summer 被引量:1
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作者 CHEN Guang-Hua WANG Xu 《Atmospheric and Oceanic Science Letters》 CSCD 2017年第1期89-95,共7页
The characteristics of quasi-biweekly oscillation(QBWO) over the South China Sea during early summer are investigated.Composite results demonstrate that QBWO convection and the meridional wind anomaly exhibit local ... The characteristics of quasi-biweekly oscillation(QBWO) over the South China Sea during early summer are investigated.Composite results demonstrate that QBWO convection and the meridional wind anomaly exhibit local variation,while the zonal wind anomaly displays zonal propagation.Besides,emergence of the zonal wind anomaly precedes the enhancement of QBWO convection,suggesting the zonally propagating zonal wind anomaly may play a key role in initiating the development of QBWO convection.Diagnostics of the convergence of moisture flux and divergence tendency indicate that QBWO convection is primarily modulated by eddy divergence.Among the contributing factors in the divergence tendency,the β effect associated with the zonally-propagating zonal wind anomaly makes an appropriate phase difference with the eddy divergence,which can contribute to the convergence tendency in the initial stage of QBWO.As a result,QBWO convection and the meridional wind anomaly are enhanced,thus facilitating the initial development of QBWO convection over the SCS during early summer. 展开更多
关键词 Westward-propagating zonal wind quasi-biweekly oscillation South China Sea early summer
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Modulation of the Intensity of Nascent Tibetan Plateau Vortices by Atmospheric Quasi-Biweekly Oscillation 被引量:1
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作者 Lun LI Renhe ZHANG +1 位作者 Min WEN Jianping DUAN 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2018年第11期1347-1361,共15页
The modulation of the intensity of nascent Tibetan Plateau vortices(ITPV) by atmospheric quasi-biweekly oscillation(QBWO) is investigated based on final operational global analysis data from the National Centers for E... The modulation of the intensity of nascent Tibetan Plateau vortices(ITPV) by atmospheric quasi-biweekly oscillation(QBWO) is investigated based on final operational global analysis data from the National Centers for Environmental Prediction. The spatial and temporal distributions of the ITPV show distinct features of 10–20-day QBWO. The average ITPV is much higher in the positive phases than in the negative phases, and the number of strong TPVs is much larger in the former,with a peak that appears in phase 3. In addition, the maximum centers of the ITPV stretch eastward in the positive phases,indicating periodic variations in the locations where strong TPVs are generated. The large-scale circulations and related thermodynamic fields are discussed to investigate the mechanism by which the 10–20-day QBWO modulates the ITPV. The atmospheric circulations and heating fields of the 10–20-day QBWO have a major impact on the ITPV. In the positive QBWO phases, the anomalous convergence at 500 hPa and divergence at 200 hPa are conducive to ascending motion. In addition, the convergence centers of the water vapor and the atmospheric unstable stratification are found in the positive QBWO phases and move eastward. Correspondingly, condensational latent heat is released and shifts eastward with the heating centers located at 400 hPa, which favors a higher ITPV by depressing the isobaric surface at 500 hPa. All of the dynamic and thermodynamic conditions in the positive QBWO phases are conducive to the generation of stronger TPVs and their eastward expansion. 展开更多
关键词 quasi-biweekly oscillation TIBETAN PLATEAU vortex MODULATION
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Semiannual oscillation,annual oscillation,quasibiennial oscillation,and solar cycle variation of the OH airglow emission in the mesopause region
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作者 Sheng-Yang Gu Dong Wang +3 位作者 YuSong Qin Liang Tang YaFei Wei XianKang Dou 《Earth and Planetary Physics》 EI CAS CSCD 2024年第3期479-496,共18页
The vertically integrated emission rate,centroid altitude,peak emission rate,and peak height of the hydroxyl(OH)airglow were calculated from Thermosphere Ionosphere Mesosphere Energetics and Dynamics(TIMED)/Sounding o... The vertically integrated emission rate,centroid altitude,peak emission rate,and peak height of the hydroxyl(OH)airglow were calculated from Thermosphere Ionosphere Mesosphere Energetics and Dynamics(TIMED)/Sounding of the Atmosphere using Broadband Emission Radiometry(SABER)observations to study the seasonal and interannual variations in the intensity and location of the OH emission.The emission rate is inversely proportional to the height of the emission,with the semiannual oscillation dominating at low latitudes and the annual oscillation dominating at higher latitudes.The OH emission is modulated by the quasibiennial oscillation at the equator,and the quasibiennial oscillation signal is weak at other latitudes.We represented the vertical transport of atomic oxygen by using atomic oxygen concentrations obtained from a global atmospheric model,the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension simulations.Compared with the amplitudes of the migrating diurnal tide(DW1)calculated from temperature data observed by TIMED/SABER,we found that both the vertical transport of atomic oxygen and DW1 amplitudes in the equatorial region exhibit semiannual oscillation and quasibiennial oscillation,which have a strong correlation with the variations in the amplitude and phase of semiannual oscillation and quasibiennial oscillation in OH emission.It is likely that the DW1 affects the vertical transport of atomic oxygen that is involved in the reaction to produce O3,thus affecting the OH emission.We analyzed the relationship between OH emission and solar activity by using the solar radio flux at 10.7 cm as a proxy for solar activity.The results showed that the OH emission is well correlated with solar activity,and the modulation of OH emission by solar activity has a significant latitudinal variation.The small correlation between emission height and solar activity indicates that solar activity modulates OH emission mainly through chemical rather than dynamic processes. 展开更多
关键词 OH airglow semiannual oscillation quasibiennial oscillation solar activity diurnal tide
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Nonlinear Violence in Nonlinear Oscillations at High Energy
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作者 Yair Zarmi 《Applied Mathematics》 2024年第1期65-95,共31页
This paper focuses on the characteristics of solutions of nonlinear oscillatory systems in the limit of very high oscillation energy, E;specifically, systems, in which the nonlinear driving force grows with energy muc... This paper focuses on the characteristics of solutions of nonlinear oscillatory systems in the limit of very high oscillation energy, E;specifically, systems, in which the nonlinear driving force grows with energy much faster for x(t) close to the turning point, a(E), than at any position, x(t), that is not too close to a(E). This behavior dominates important aspects of the solutions. It will be called “nonlinear violence”. In the vicinity of a turning point, the solution of a nonlinear oscillatory systems that is affected by nonlinear violence exhibits the characteristics of boundary-layer behavior (independently of whether the equation of motion of the system can or cannot be cast in the traditional form of a boundary-layer problem.): close to a(E), x(t) varies very rapidly over a short time interval (which vanishes for E → ∞). In traditional boundary layer systems this would be called the “inner” solution. Outside this interval, x(t) soon evolves into a moderate profile (e.g. linear in time, or constant)—the “outer” solution. In (1 + 1)-dimensional nonlinear energy-conserving oscillators, if the solution is reflection-invariant, nonlinear violence determines the characteristics of the whole solution. For large families of nonlinear oscillatory systems, as E → ∞, the solutions for x(t) tend to common, indistinguishable profiles, such as periodic saw-tooth profiles or step-functions. If such profiles are observed experimentally in high-energy oscillations, it may be difficult to decipher the dynamical equations that govern the motion. The solution of motion in a central field with a non-zero angular momentum exhibits extremely fast rotation around a turning point that is affected by nonlinear violence. This provides an example for the possibility of interesting phenomena in (1 + 2)-dimensional oscillatory systems. 展开更多
关键词 High-Energy oscillations Nonlinear Violence Boundary-Layer Characteristics
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Necessary and Sufficient Conditions for Oscillations of the Generalized Liénard Systems
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作者 Hongtao Zhang Xiaolin Liu Ping Yan 《Applied Mathematics》 2024年第6期391-405,共15页
In this paper, we study the second-order nonlinear differential systems of Liénard-type x˙=1a(x)[ h(y)−F(x) ], y˙=−a(x)g(x). Necessary and sufficient conditions to ensure that all nontrivial solutions are oscil... In this paper, we study the second-order nonlinear differential systems of Liénard-type x˙=1a(x)[ h(y)−F(x) ], y˙=−a(x)g(x). Necessary and sufficient conditions to ensure that all nontrivial solutions are oscillatory are established by using a new nonlinear integral inequality. Our results substantially extend and improve previous results known in the literature. 展开更多
关键词 Generalized Liénard System Nonlinear Integral Inequality oscillation
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The de Haas-van Alphen quantum oscillations in the kagome metal RbTi_(3)Bi_(5)
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作者 Zixian Dong Lei Shi +7 位作者 Bin Wang Mengwu Huo Xing Huang Chaoxin Huang Peiyue Ma Yunwei Zhang Bing Shen Meng Wang 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第10期356-361,共6页
The kagome system has attracted great interest in condensed matter physics due to its unique structure that canhost various exotic states such as superconductivity(SC),charge density waves(CDWs)and nontrivial topologi... The kagome system has attracted great interest in condensed matter physics due to its unique structure that canhost various exotic states such as superconductivity(SC),charge density waves(CDWs)and nontrivial topological states.The topological semimetal RbTi_(3)Bi_(5)consisting of a Ti kagome layer shares a similar crystal structure to the topologicalcorrelated materials AV_(3)Sb_(5)(A=K,Rb,Cs)but without the absence of CDW and SC.Systematic de Haas-van Alphenoscillation measurements are performed on single crystals of RbTi_(3)Bi_(5)to pursue nontrivial topological physics and exoticstates.Combining this with theoretical calculations,the detailed Fermi surface topology and band structure are investigated.A two-dimensional Fermi pocket b is revealed with a light effective mass,consistent with the semimetal predictions.TheLandau fan diagram of RbTi_(3)Bi_(5)reveals a zero Berry phase for the b oscillation in contrast to that of CsTi_(3)Bi_(5).Theseresults suggest that kagome RbTi_(3)Bi_(5)is a good candidate for exploring nontrivial topological exotic states and topologicalcorrelated physics. 展开更多
关键词 oscillation Fermi surface band structure
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Influence of the Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation on Antarctic surface air temperature during 1900 to 2015
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作者 Cuijuan Sui Lejiang Yu +2 位作者 Alexey YuKarpechko Licheng Feng Shan Liu 《Acta Oceanologica Sinica》 SCIE CAS CSCD 2024年第3期48-58,共11页
The importance of the Atlantic Multidecadal Oscillation(AMO)and Interdecadal Pacific Oscillation(IPO)in influencing zonally asymmetric changes in Antarctic surface air temperature(SAT)has been established.However,prev... The importance of the Atlantic Multidecadal Oscillation(AMO)and Interdecadal Pacific Oscillation(IPO)in influencing zonally asymmetric changes in Antarctic surface air temperature(SAT)has been established.However,previous studies have primarily concentrated on examining the combined impact of the contrasting phases of the AMO and IPO,which have been dominant since the advent of satellite observations in 1979.This study utilizes long-term reanalysis data to investigate the impact of four combinations of+AMO+IPO,–AMO–IPO,+AMO–IPO,and–AMO+IPO on Antarctic SAT over the past 115 years.The+AMO phase is characterized by a spatial mean temperature amplitude of up to 0.5℃over the North Atlantic Ocean,accompanied by positive sea surface temperature(SST)anomalies in the tropical eastern Pacific and negative SST anomalies in the extratropical-mid-latitude western Pacific,which are indicative of the+IPO phase.The Antarctic SAT exhibits contrasting spatial patterns during the+AMO+IPO and+AMO–IPO periods.However,during the–AMO+IPO period,apart from the Antarctic Peninsula and the vicinity of the Weddell Sea,the entire Antarctic region experiences a warming trend.The most pronounced signal in the SAT anomalies is observed during the austral autumn,whereas the combination of–AMO and–IPO exhibits the smallest magnitude across all the combinations.The wavetrain excited by the SST anomalies associated with the AMO and IPO induces upper-level and surface atmospheric circulation anomalies,which alter the SAT anomalies.Furthermore,downward longwave radiation anomalies related to anomalous cloud cover play a crucial role.In the future,if the phases of AMO and IPO were to reverse(AMO transitioning to a negative phase and IPO transitioning to a positive phase),Antarctica could potentially face more pronounced warming and accelerated melting compared to the current observations. 展开更多
关键词 Atlantic Multidecadal oscillation(AMO) Interdecadal Pacific oscillation(IPO) surface air temperature ANTARCTIC wavetrain Rossby wave source
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Salinity effect-induced ENSO amplitude modulation in association with the interdecadal Pacific Oscillation
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作者 Hai ZHI Xiaokun WANG +2 位作者 Rong-Hua ZHANG Pengfei LIN Jifeng QI 《Journal of Oceanology and Limnology》 SCIE CAS CSCD 2024年第4期1019-1036,共18页
A 110-year ensemble simulation of an ocean general circulation model(OGCM)was analyzed to identify the modulation of salinity interdecadal variability on El Niño-Southern Oscillation(ENSO)amplitude in the tropica... A 110-year ensemble simulation of an ocean general circulation model(OGCM)was analyzed to identify the modulation of salinity interdecadal variability on El Niño-Southern Oscillation(ENSO)amplitude in the tropical Pacific during 1901-2010.The simulating results show that sea surface salinity(SSS)variation in the region exhibits notable and coherent interdecadal variability signal,which is closely associated with the Interdecadal Pacific Oscillation(IPO).As salinity increases or reduces,the SSS modulations on ENSO amplitude during its warm/cold events vary asymmetrically with positive/negative IPO phases.Physically,salinity interdecadal variability can enhance or reduce ENSO-related conditions in upper-ocean stratification,contributing noticeably to ENSO variability.Salinity anomalies associated with the mixed layer depth and barrier layer thickness can modulate ENSO amplitude during positive and negative IPO phases,resulting in the asymmetry of sea surface temperature(SST)anomaly in the tropical Pacific.During positive IPO phases,SSS interdecadal variability contributes positively to El Niño amplitude but negatively to La Niña amplitude by enhancing or reducing SSS interannual variability,and vice versa during negative IPO phases.Quantitatively,the results indicate that the modulation of the ENSO amplitude by the SSS interdecadal variability is 15%-28%during negative IPO phases and 30%-20%during positive IPO phases,respectively.Evidently,the SSS interdecadal variability associated with IPO and its modulation on ENSO amplitude in the tropical Pacific are among factors essentially contributing ENSO diversity. 展开更多
关键词 El Niño-Southern oscillation(ENSO)amplitude Interdecadal Pacific oscillation(IPO) ocean salinity variability tropical Pacific upper-ocean stratification
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Two-dimensional Sb net generated nontrivial topological states in SmAgSb_(2) probed by quantum oscillations
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作者 袁健 石贤彪 +7 位作者 杜红 李田 郗传英 王霞 夏威 王保田 钟瑞丹 郭艳峰 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第7期51-58,共8页
The REAgSb_(2)(RE = rare earth and Y) family has drawn considerable research interest because the two-dimensional Sb net in their crystal structures hosts topological fermions and hence rich topological properties. We... The REAgSb_(2)(RE = rare earth and Y) family has drawn considerable research interest because the two-dimensional Sb net in their crystal structures hosts topological fermions and hence rich topological properties. We report herein the magnetization and magnetotransport measurements of SmAgSb_(2) single crystal, which unveil very large magnetoresistance and high carrier mobility up to 6.2 × 10^(3)% and 5.58 × 10^(3)cm^(2)·V^(-1)·s^(-1), respectively. The analysis of both Shubnikov–de Haas and de Haas–van Alphen quantum oscillations indicates nontrivial Berry phases in the paramagnetic state while trivial Berry curvature in the antiferromagnetic state, indicating a topological phase transition induced by the antiferromagnetic order. It is also supported by the first-principles calculations. The results not only provide a new interesting topological material but also offer valuable insights into the correlation between magnetism and nontrivial topological states. 展开更多
关键词 large magnetoresistance quantum oscillations topological phase transition
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Changes in the Boreal Summer Intraseasonal Oscillation under Global Warming in CMIP6 Models
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作者 Zhefan GAO Chaoxia YUAN 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2024年第10期1984-1998,共15页
Changes in the activities of the Boreal Summer Intraseasonal Oscillation(BSISO)at the end of 21st century under the SSP5-8.5 scenario are assessed by adopting 17 CMIP6 models and the weak-temperature-gradient assumpti... Changes in the activities of the Boreal Summer Intraseasonal Oscillation(BSISO)at the end of 21st century under the SSP5-8.5 scenario are assessed by adopting 17 CMIP6 models and the weak-temperature-gradient assumption.Results show that the intraseasonal variations become more structured.The BSISO-related precipitation anomaly shows a larger zonal scale and propagates further northward.However,there is no broad agreement among models on the changes in the eastward and northward propagation speeds and the frequency of individual phases.In the western North Pacific(WNP),the BSISO precipitation variance is significantly increased,at 4.62%K^(−1),due to the significantly increased efficiency of vertical moisture transport per unit of BSISO apparent heating.The vertical velocity variance is significantly decreased,at−3.51%K^(−1),in the middle troposphere,due to the significantly increased mean-state static stability.Changes in the lower-level zonal wind variance are relatively complex,with a significant increase stretching from the northwestern to southeastern WNP,but the opposite in other regions.This is probably due to the combined impacts of the northeastward shift of the BSISO signals and the reduced BSISO vertical velocity variance under global warming.Changes in strong and normal BSISO events in the WNP are also compared.They show same-signed changes in precipitation and large-scale circulation anomalies but opposite changes in the vertical velocity anomalies.This is probably because the precipitation anomaly of strong(normal)events changes at a rate much larger(smaller)than that of the meanstate static stability,causing enhanced(reduced)vertical motion. 展开更多
关键词 Boreal Summer Intraseasonal oscillation global warming CMIP6 weak-temperature-gradient assumption
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Review of the Analysis and Suppression for High-frequency Oscillations of the Grid-connected Wind Power Generation System
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作者 Bo Pang Qi Si +4 位作者 Pan Jiang Kai Liao Xiaojuan Zhu Jianwei Yang Zhengyou He 《CES Transactions on Electrical Machines and Systems》 EI CSCD 2024年第2期127-142,共16页
High-frequency oscillation(HFO)of gridconnected wind power generation systems(WPGS)is one of the most critical issues in recent years that threaten the safe access of WPGS to the grid.Ensuring the WPGS can damp HFO is... High-frequency oscillation(HFO)of gridconnected wind power generation systems(WPGS)is one of the most critical issues in recent years that threaten the safe access of WPGS to the grid.Ensuring the WPGS can damp HFO is becoming more and more vital for the development of wind power.The HFO phenomenon of wind turbines under different scenarios usually has different mechanisms.Hence,engineers need to acquire the working mechanisms of the different HFO damping technologies and select the appropriate one to ensure the effective implementation of oscillation damping in practical engineering.This paper introduces the general assumptions of WPGS when analyzing HFO,systematically summarizes the reasons for the occurrence of HFO in different scenarios,deeply analyses the key points and difficulties of HFO damping under different scenarios,and then compares the technical performances of various types of HFO suppression methods to provide adequate references for engineers in the application of technology.Finally,this paper discusses possible future research difficulties in the problem of HFO,as well as the possible future trends in the demand for HFO damping. 展开更多
关键词 Damping method High-frequency oscillation STABILITY Wind power generation
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Low-frequency oscillation of train-network system considering traction power supply mode
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作者 Yuchen Liu Xiaoqin Lyu +1 位作者 Mingyuan Chang Qiqi Yang 《Railway Engineering Science》 EI 2024年第2期244-256,共13页
The low-frequency oscillation(LFO)has occurred in the train-network system due to the introduction of the power electronics of the trains.The modeling and analyzing method in current researches based on electrified ra... The low-frequency oscillation(LFO)has occurred in the train-network system due to the introduction of the power electronics of the trains.The modeling and analyzing method in current researches based on electrified railway unilateral power supply system are not suitable for the LFO analysis in a bilateral power supply system,where the trains are supplied by two traction substations.In this work,based on the single-input and single-output impedance model of China CRH5 trains,the node admittance matrices of the train-network system both in unilateral and bilateral power supply modes are established,including three-phase power grid,traction transformers and traction network.Then the modal analysis is used to study the oscillation modes and propagation characteristics of the unilateral and bilateral power supply systems.Moreover,the influence of the equivalent inductance of the power grid,the length of the transmission line,and the length of the traction network are analyzed on the critical oscillation mode of the bilateral power supply system.Finally,the theoretical analysis results are verified by the time-domain simulation model in MATLAB/Simulink. 展开更多
关键词 Low-frequency oscillation Train-network system Modal analysis Bilateral power supply Participation factor
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Detection of Oscillations in Process Control Loops From Visual Image Space Using Deep Convolutional Networks
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作者 Tao Wang Qiming Chen +3 位作者 Xun Lang Lei Xie Peng Li Hongye Su 《IEEE/CAA Journal of Automatica Sinica》 SCIE EI CSCD 2024年第4期982-995,共14页
Oscillation detection has been a hot research topic in industries due to the high incidence of oscillation loops and their negative impact on plant profitability.Although numerous automatic detection techniques have b... Oscillation detection has been a hot research topic in industries due to the high incidence of oscillation loops and their negative impact on plant profitability.Although numerous automatic detection techniques have been proposed,most of them can only address part of the practical difficulties.An oscillation is heuristically defined as a visually apparent periodic variation.However,manual visual inspection is labor-intensive and prone to missed detection.Convolutional neural networks(CNNs),inspired by animal visual systems,have been raised with powerful feature extraction capabilities.In this work,an exploration of the typical CNN models for visual oscillation detection is performed.Specifically,we tested MobileNet-V1,ShuffleNet-V2,Efficient Net-B0,and GhostNet models,and found that such a visual framework is well-suited for oscillation detection.The feasibility and validity of this framework are verified utilizing extensive numerical and industrial cases.Compared with state-of-theart oscillation detectors,the suggested framework is more straightforward and more robust to noise and mean-nonstationarity.In addition,this framework generalizes well and is capable of handling features that are not present in the training data,such as multiple oscillations and outliers. 展开更多
关键词 Convolutional neural networks(CNNs) deep learning image processing oscillation detection process industries
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THE ASYMPTOTIC BEHAVIOR AND OSCILLATION FOR A CLASS OF THIRD-ORDER NONLINEAR DELAY DYNAMIC EQUATIONS
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作者 黄先勇 邓勋环 王其如 《Acta Mathematica Scientia》 SCIE CSCD 2024年第3期925-946,共22页
In this paper,we consider a class of third-order nonlinear delay dynamic equations.First,we establish a Kiguradze-type lemma and some useful estimates.Second,we give a sufficient and necessary condition for the existe... In this paper,we consider a class of third-order nonlinear delay dynamic equations.First,we establish a Kiguradze-type lemma and some useful estimates.Second,we give a sufficient and necessary condition for the existence of eventually positive solutions having upper bounds and tending to zero.Third,we obtain new oscillation criteria by employing the Potzsche chain rule.Then,using the generalized Riccati transformation technique and averaging method,we establish the Philos-type oscillation criteria.Surprisingly,the integral value of the Philos-type oscillation criteria,which guarantees that all unbounded solutions oscillate,is greater than θ_(4)(t_(1),T).The results of Theorem 3.5 and Remark 3.6 are novel.Finally,we offer four examples to illustrate our results. 展开更多
关键词 nonlinear delay dynamic equations NONoscillation asymptotic behavior Philostype oscillation criteria generalized Riccati transformation
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Localization method of subsynchronous oscillation source based on high-resolution time-frequency distribution image and CNN
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作者 Hui Liu Yundan Cheng +3 位作者 Yanhui Xu Guanqun Sun Rusi Chen Xiaodong Yu 《Global Energy Interconnection》 EI CSCD 2024年第1期1-13,共13页
The penetration of new energy sources such as wind power is increasing,which consequently increases the occurrence rate of subsynchronous oscillation events.However,existing subsynchronous oscillation source-identific... The penetration of new energy sources such as wind power is increasing,which consequently increases the occurrence rate of subsynchronous oscillation events.However,existing subsynchronous oscillation source-identification methods primarily analyze fixed-mode oscillations and rarely consider time-varying features,such as frequency drift,caused by the random volatility of wind farms when oscillations occur.This paper proposes a subsynchronous oscillation sourcelocalization method that involves an enhanced short-time Fourier transform and a convolutional neural network(CNN).First,an enhanced STFT is performed to secure high-resolution time-frequency distribution(TFD)images from the measured data of the generation unit ports.Next,these TFD images are amalgamated to form a subsynchronous oscillation feature map that serves as input to the CNN to train the localization model.Ultimately,the trained CNN model realizes the online localization of subsynchronous oscillation sources.The effectiveness and accuracy of the proposed method are validated via multimachine system models simulating forced and natural oscillation events using the Power Systems Computer Aided Design platform.Test results show that the proposed method can localize subsynchronous oscillation sources online while considering unpredictable fluctuations in wind farms,thus providing a foundation for oscillation suppression in practical engineering scenarios. 展开更多
关键词 Subsynchronous oscillation source localization Synchronous squeezing transform Enhanced short-time Fourier transform Convolutional neural networks
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El Niño-Southern Oscillation (ENSO) Variations and Climate Changes Worldwide
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作者 Marilia Hagen Anibal Azevedo 《Atmospheric and Climate Sciences》 2024年第2期233-249,共17页
This investigation aims to study the El-Niño-Southern Oscillation (ENSO) events in these three phases: El Niño, La Niña, and neutral. Warm and cold events relate to the Spring/Summer seasons. This paper... This investigation aims to study the El-Niño-Southern Oscillation (ENSO) events in these three phases: El Niño, La Niña, and neutral. Warm and cold events relate to the Spring/Summer seasons. This paper will search for connections between the ENSO events and climate anomalies worldwide. There is some speculation that those events would be necessary for the climate anomalies observed worldwide. After analyzing the data from the reports to the ENSO, it shows almost periodicity from 1950-2023. We emphasized the occurrence of El Niño two years, when it was most prominent, and the climate anomalies (following NOAA maps), 2015 and 2023. The results indicated that the observed climate anomalies couldn’t be linked to the abnormal events observed. The worldwide temperatures in those years enhanced mostly in 2023. It shows an abnormal behavior compared with all the years scrutinized and analyzed since the records began. Therefore, there must be unknown factors beyond ENSO that rule the worldwide temperatures and the climate anomalies observed. 展开更多
关键词 ENSO Southern oscillation El Niño Climate Anomalies
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