In this paper,the relationship between a pair of low-frequency vortexes over the equatorial Indian Ocean and the South China Sea(SCS) summer monsoon onset is studied based on a multi-year(1980-2003) analysis.A pair of...In this paper,the relationship between a pair of low-frequency vortexes over the equatorial Indian Ocean and the South China Sea(SCS) summer monsoon onset is studied based on a multi-year(1980-2003) analysis.A pair of vortexes symmetric about the equator is an important feature prior to the SCS summer monsoon onset.A composite analysis shows that the life cycle of the pair of vortexes is closely associated with the SCS summer monsoon onset.The westerly between the twin cyclones is an important factor to the SCS summer monsoon onset process.展开更多
The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to...The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to train safety,significantly lowering the critical wind velocity.Therefore,developing strategies to enhance crosswind stability is essential.This study focuses on the leeward region adjacent to the train body,where separated flows with large vortices generate significant negative surface pressure.Enhancing this negative pressure distribution is proposed as a potential method to improve a train’s resistance to overturning.To achieve this,winglets are installed on the leeward side as a flow control measure,and their effects at different deflection angles are evaluated.The influence of five deflection angles on the leeward-side flow field and aerodynamic loads is analyzed,considering the head,middle,and tail cars.Results indicate that a deflection angle of 90°optimally reduces the overall overturning moment by 27.6%compared to the baseline model in a three-car configuration.These findings highlight that optimizing the winglet deflection angle to approximately 90°can significantly enhance a train’s resistance to overturning,offering valuable insights for aerodynamic optimization in strong wind conditions.展开更多
In recent years,train-tail swaying of 160 km/h electric multiple units(EMUs)inside single-line tunnels has been heavily researched,because the issue needs to be solved urgently.In this paper,a co-simulation model of v...In recent years,train-tail swaying of 160 km/h electric multiple units(EMUs)inside single-line tunnels has been heavily researched,because the issue needs to be solved urgently.In this paper,a co-simulation model of vortex-induced vibration(VIV)of the tail car body is established,and the aerodynamics of train-tail swaying is studied.The simulation results were confirmed through a field test of operating EMUs.Furthermore,the influence mechanism of train-tail swaying on the wake flow field is studied in detail through a wind-tunnel experiment and a simulation of a reduced-scaled train model.The results demonstrate that the aerodynamic force frequency(i.e.,vortex-induced frequency)of the train tail increases linearly with train speed.When the train runs at 130 km/h,with a small amplitude of train-tail swaying(within 10 mm),the vortex-induced frequency is 1.7 Hz,which primarily depends on the nose shape of the train tail.After the tail car body nose is extended,the vortex-induced frequency is decreased.As the swaying amplitude of the train tail increases(exceeding 25 mm),the separation point of the high-intensity vortex in the train wake shifts downstream to the nose tip,and the vortex-induced frequency shifts from 1.7 Hz to the nearby car body hunting(i.e.,the primary hunting)frequency of 1.3 Hz,which leads to the frequency-locking phenomenon of VIV,and the resonance intensifies train-tail swaying.For the motor vehicle of the train tail,optimization of the yaw damper to improve its primary hunting stability can effectively alleviate train-tail swaying inside single-line tunnels.Optimization of the tail car body nose shape reduces the amplitude of the vortex-induced force,thereby weakening the aerodynamic effect and solving the problem of train-tail swaying inside the single-line tunnels.展开更多
The Northeast China cold vortex(NCCV)is the most important midlatitude synoptic system for weather and climate anomalies in Northeast China in the warm season.Many previous studies have focused on its synoptic and cli...The Northeast China cold vortex(NCCV)is the most important midlatitude synoptic system for weather and climate anomalies in Northeast China in the warm season.Many previous studies have focused on its synoptic and climatic variability.However,little is known about the variability of the NCCV on subseasonal timescales.In this study,we investigate the subseasonal variability of the NCCV in the warm season(May to August)and its impact based on the NCEP–NCAR reanalysis dataset and observational climate data from 1981 to 2020.Results show that the NCCV frequency exhibits a significant quasi-biweekly oscillation(QBWO,10–25 days).In 32 out of 40 years,there is at least one significant period between 10 and 25 days.Our result provides the first direct evidence for a significant QBWO signal in the NCCV frequency.The QBWO circulation on NCCV days features a cold low-pressure anomaly surrounded by warm high-pressure anomalies from northwest to southeast in a clockwise direction,which is related to an upstream wave train propagating southeastward from the Ural Mountains into Northeast China and a downstream blocking high to the northeast.The NCCV QBWO causes more rainfall,with a quadrature phase shift as rainfall leading the NCCV for approximately three days,and synchronized reduced surface air temperature in Northeast China.展开更多
With the increasing demand of higher travelling speed,a new streamlined high-speed maglev train has been designed to reach a speed of 600 km/h.To better capture the flow field structures around the maglev train,an imp...With the increasing demand of higher travelling speed,a new streamlined high-speed maglev train has been designed to reach a speed of 600 km/h.To better capture the flow field structures around the maglev train,an improved delayed detached eddy simulation(IDDES)is adopted to model the turbulence.Results show that the new maglev train has good aerodynamic load performance such as small drag coefficient contributing to energy conservation.The main frequencies of aerodynamic forces for each car have a scattered distribution.There are two pairs of counter-rotating large vortices in the non-streamlined part of the train that make the boundary layer thicker.Many high-intensity vortices are distributed in the narrow space between skirt plates or train floor and track.In the gap between the train floor and track(except near the tail car nose),the main frequency of vortex shedding remains constant and its strength increases exponentially in the streamwise direction.In the wake,the counter-rotating vortices gradually expand and reproduce some small vortices that move downward.The vortex has quite random and complex frequencydomain distribution characteristics in the wake.The maximum time-averaged velocity of the slipstream occurs near the nose of the head car,based on which,the track-side safety domain is divided.展开更多
According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was ...According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was studied and eight types of flow regions were proposed. They are high pressure with air stagnant region, pressure decreasing with air accelerating region, low pressure with high air flow velocity region I, turbulent region, steady flow region, low pressure with high air flow velocity region II,pressure increasing with air decelerating region and wake region. The analysis of the vortex structure around the train shows that the vortex is mainly induced by structures with complex mutation and large curvature change. The head and rear of train, the underbody structure, the carriage connection section and the wake region are the main vortex generating sources while the train body with even cross-section has rare vortexes. The wake structure development law studied lays foundation for the train drag reduction.展开更多
This study uses NCEP/NCAR daily reanalysis data,NOAA outgoing long-wave radiation(OLR) data,the real-time multivariate MJO(RMM) index from the Australian Bureau of Meteorology and Tibetan Plateau vortex(TPV)data from ...This study uses NCEP/NCAR daily reanalysis data,NOAA outgoing long-wave radiation(OLR) data,the real-time multivariate MJO(RMM) index from the Australian Bureau of Meteorology and Tibetan Plateau vortex(TPV)data from the Chengdu Institute of Plateau Meteorology to discuss modulation of the Madden-Julian Oscillation(MJO)on the Tibetan Plateau Vortex(TPV).Wavelet and composite analysis are used.Results show that the MJO plays an important role in the occurrence of the TPV that the number of TPVs generated within an active period of the MJO is three times as much as that during an inactive period.In addition,during the active period,the number of the TPVs generated in phases 1 and 2 is larger than that in phases 3 and 7.After compositing phases 1 and 7 separately,all meteorological elements in phase 1 are apparently conducive to the generation of the TPV,whereas those in phase 7 are somewhat constrained.With its eastward propagation process,the MJO convection centre spreads eastward,and the vertical circulation within the tropical atmosphere changes.Due to the interaction between the mid-latitude and low-latitude atmosphere,changes occur in the baroclinic characteristics of the atmosphere,the available potential energy and eddy available potential energy of the atmosphere,and the circulation structures of the atmosphere over the Tibetan Plateau(TP) and surrounding areas.This results in significantly different water vapour transportation and latent heat distribution.Advantageous and disadvantageous conditions therefore alternate,leading to a significant difference among the numbers of plateau vortex in different phases.展开更多
This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The im...This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The impact of the VGs is assessed through the improved delayed detached eddy simulations(IDDES)after validating predictions against previous experimental measurements and other numerical predictions for the base case.The simulations indicate that strategically installed VGs can reduce the average slipstream velocity(U slipstream)and the upper limit of slipstream velocity(U_(slipstream,max))by~17%and~15%,respectively,as well as moving the peaks downstream by approximately train height,thus reducing the danger posed by slipstream to waiting passengers and trackside workers.Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake.It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs.These latter vortices prevent the merging of vortical airflow around the trailing nose tip,which is otherwise induced by the longitudinal vortex of the train.They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream,limiting outwards advection through interaction with the image pair,and contributing to a decrease in the peak slipstream value.The method proposed offers a simple approach to wake control leading to significant slipstream benefits.展开更多
2016年7月1日安徽境内出现了一次造成严重洪涝灾害的强梅雨锋暴雨过程,主要由两个中尺度低涡活动引发,暴雨中心桐城出现“列车效应”,次中心巢湖出现“列车带效应”。本文基于常规观测、地面加密自动观测、多普勒天气雷达和欧洲中期天...2016年7月1日安徽境内出现了一次造成严重洪涝灾害的强梅雨锋暴雨过程,主要由两个中尺度低涡活动引发,暴雨中心桐城出现“列车效应”,次中心巢湖出现“列车带效应”。本文基于常规观测、地面加密自动观测、多普勒天气雷达和欧洲中期天气预报中心(European Center for Medium-range Weather Forecasts,ECMWF)0.25°×0.25°的ERA5再分析资料,分析了两地对流的发生发展及其与中尺度低涡活动的关系。结果表明:这次暴雨发生在双阻型、高空有冷涡、副热带高压稳定维持的背景下,两个中尺度低涡活动引发强降水。多条强对流短雨带在高空气流引导下自西向东移动依次经过巢湖,形成巢湖“列车带效应”。不断触发的新风暴沿西南-东北向雨带依次经过桐城,形成桐城“列车效应”。影响巢湖和桐城的风暴均呈低质心结构,风暴合并后降水明显增强。巢湖“列车带效应”位于中尺度低涡C1西南象限的冷式切变线右侧,动力不稳定较明显,既有低涡后部冷空气入侵南部暖湿空气触发对流风暴后由西北向东南方向依次经过巢湖,也有南部超低空急流触发对流风暴后由西南向东北方向依次经过巢湖,形成强降水。桐城“列车效应”处于中尺度低涡C2的东南象限,热力不稳定相对较强,低层冷空气不明显,深厚低空急流与边界层气旋式辐合作用,后向传播的风暴自西南向东北移动经过桐城,造成极端降水。展开更多
Persistent(5-day or longer)extreme cold events(ECEs)over northeastern China during the boreal winter of 1979–2020 are investigated using daily minimum temperature(Tmin)from the China Meteorological Data Network.The e...Persistent(5-day or longer)extreme cold events(ECEs)over northeastern China during the boreal winter of 1979–2020 are investigated using daily minimum temperature(Tmin)from the China Meteorological Data Network.The extreme cooling area and intensity indices associated with the ECEs exhibit a dominant 10–40-day periodicity,indicating a close link with atmospheric intraseasonal oscillations(ISOs).The ECEs are categorized into W-and N-type.In the former,the low-frequency cooling associated with the ISO first penetrates into the western boundary of the northeastern China domain and later occupies the entire domain at its peak phase.The upper-tropospheric circulation associated with this type is characterized by a northwest–southeast-oriented Rossby wave train,expanding from the Ural Mountains to the western Pacific Ocean.In the latter,the cooling invades the northern boundary first and then penetrates into the entire domain.The upper tropospheric precursory signal associated with this type is a zonally oriented negative geopotential height anomaly,which slowly moves southward.A downward-propagating signal is observed in the stratospheric potential vorticity field prior to the peak cooling,implying a possible stratospheric impact.In addition to the W-and N-types,ECEs can also occur in a localized region near either at the northern or southern boundary of the domain.展开更多
Spatiotemporal vector and phase properties of interference field of low-frequency signalling tone between three local vortices in a real shallow sea wave-guide have been studied.It has been demonstrated that in the fi...Spatiotemporal vector and phase properties of interference field of low-frequency signalling tone between three local vortices in a real shallow sea wave-guide have been studied.It has been demonstrated that in the field of constructive interference,components of particle velocity field and acoustic pressure are coherent.As a consequence the transfer of signal energy alog the axis of a shallow sea wave-guide is accomplished with plane wave.Physical objects are detected in the field of destructive interference,which,according to known deterministic signs,can be defined as local vortices of the intensity vector.A large-scale vorticity with acoustic intensity vector curl,components different from zero originates in the vicinity of local vortices.Regular particle displacements of local vortices have been detected against combined receiving device phase centre along the axis of a wave-guide.It has been demonstrated that the structure of vortices depends on signal/noise ratio.Local vortices and vorticity form vortex structure of vector acoustic field.Signalling tone with frequency of 88 ± 1 Hz from near-surface moving sound source was taken into consideration.Introduced results of full-scale experiment expand our concepts of real fundamental properties of shallow sea acoustic field and are to be considered in theoretical models.展开更多
基金financed by the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No. KZCX2-YW-Q11-03)the National Basic Research Program of China(Grant No.2010CB950401)
文摘In this paper,the relationship between a pair of low-frequency vortexes over the equatorial Indian Ocean and the South China Sea(SCS) summer monsoon onset is studied based on a multi-year(1980-2003) analysis.A pair of vortexes symmetric about the equator is an important feature prior to the SCS summer monsoon onset.A composite analysis shows that the life cycle of the pair of vortexes is closely associated with the SCS summer monsoon onset.The westerly between the twin cyclones is an important factor to the SCS summer monsoon onset process.
基金Project(2020YFA0710903)supported by the National Key Research and Development Program of ChinaProject(2025ZZTS0623)supported by the Graduate Student Independent Innovation Project of Central South University,ChinaProject(202406370145)supported by the China Scholarship Council。
文摘The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to train safety,significantly lowering the critical wind velocity.Therefore,developing strategies to enhance crosswind stability is essential.This study focuses on the leeward region adjacent to the train body,where separated flows with large vortices generate significant negative surface pressure.Enhancing this negative pressure distribution is proposed as a potential method to improve a train’s resistance to overturning.To achieve this,winglets are installed on the leeward side as a flow control measure,and their effects at different deflection angles are evaluated.The influence of five deflection angles on the leeward-side flow field and aerodynamic loads is analyzed,considering the head,middle,and tail cars.Results indicate that a deflection angle of 90°optimally reduces the overall overturning moment by 27.6%compared to the baseline model in a three-car configuration.These findings highlight that optimizing the winglet deflection angle to approximately 90°can significantly enhance a train’s resistance to overturning,offering valuable insights for aerodynamic optimization in strong wind conditions.
基金supported by the National Natural Science Foundation of China(Nos.52372403 and U2268211)the Natural Science Foundation of Sichuan Province(No.2022NSFSC0034),China+1 种基金the National Railway Group Science and Technology Program(No.2023J071)the Traction Power State Key Laboratory of the Independent Research and Development Projects(No.2022TPL-T02),China.
文摘In recent years,train-tail swaying of 160 km/h electric multiple units(EMUs)inside single-line tunnels has been heavily researched,because the issue needs to be solved urgently.In this paper,a co-simulation model of vortex-induced vibration(VIV)of the tail car body is established,and the aerodynamics of train-tail swaying is studied.The simulation results were confirmed through a field test of operating EMUs.Furthermore,the influence mechanism of train-tail swaying on the wake flow field is studied in detail through a wind-tunnel experiment and a simulation of a reduced-scaled train model.The results demonstrate that the aerodynamic force frequency(i.e.,vortex-induced frequency)of the train tail increases linearly with train speed.When the train runs at 130 km/h,with a small amplitude of train-tail swaying(within 10 mm),the vortex-induced frequency is 1.7 Hz,which primarily depends on the nose shape of the train tail.After the tail car body nose is extended,the vortex-induced frequency is decreased.As the swaying amplitude of the train tail increases(exceeding 25 mm),the separation point of the high-intensity vortex in the train wake shifts downstream to the nose tip,and the vortex-induced frequency shifts from 1.7 Hz to the nearby car body hunting(i.e.,the primary hunting)frequency of 1.3 Hz,which leads to the frequency-locking phenomenon of VIV,and the resonance intensifies train-tail swaying.For the motor vehicle of the train tail,optimization of the yaw damper to improve its primary hunting stability can effectively alleviate train-tail swaying inside single-line tunnels.Optimization of the tail car body nose shape reduces the amplitude of the vortex-induced force,thereby weakening the aerodynamic effect and solving the problem of train-tail swaying inside the single-line tunnels.
基金funded by the National Key R&D Program of China(Grant Nos.2023YFC3007700 and 2023YFC3007701)。
文摘The Northeast China cold vortex(NCCV)is the most important midlatitude synoptic system for weather and climate anomalies in Northeast China in the warm season.Many previous studies have focused on its synoptic and climatic variability.However,little is known about the variability of the NCCV on subseasonal timescales.In this study,we investigate the subseasonal variability of the NCCV in the warm season(May to August)and its impact based on the NCEP–NCAR reanalysis dataset and observational climate data from 1981 to 2020.Results show that the NCCV frequency exhibits a significant quasi-biweekly oscillation(QBWO,10–25 days).In 32 out of 40 years,there is at least one significant period between 10 and 25 days.Our result provides the first direct evidence for a significant QBWO signal in the NCCV frequency.The QBWO circulation on NCCV days features a cold low-pressure anomaly surrounded by warm high-pressure anomalies from northwest to southeast in a clockwise direction,which is related to an upstream wave train propagating southeastward from the Ural Mountains into Northeast China and a downstream blocking high to the northeast.The NCCV QBWO causes more rainfall,with a quadrature phase shift as rainfall leading the NCCV for approximately three days,and synchronized reduced surface air temperature in Northeast China.
基金Project supported by the National Natural Science Foundation of China(No.51605397)the National Key R&D Program of China(No.2016YFB1200602-15)the Sichuan Provincial Science and Technology Support Program(No.2019YJ0227),China。
文摘With the increasing demand of higher travelling speed,a new streamlined high-speed maglev train has been designed to reach a speed of 600 km/h.To better capture the flow field structures around the maglev train,an improved delayed detached eddy simulation(IDDES)is adopted to model the turbulence.Results show that the new maglev train has good aerodynamic load performance such as small drag coefficient contributing to energy conservation.The main frequencies of aerodynamic forces for each car have a scattered distribution.There are two pairs of counter-rotating large vortices in the non-streamlined part of the train that make the boundary layer thicker.Many high-intensity vortices are distributed in the narrow space between skirt plates or train floor and track.In the gap between the train floor and track(except near the tail car nose),the main frequency of vortex shedding remains constant and its strength increases exponentially in the streamwise direction.In the wake,the counter-rotating vortices gradually expand and reproduce some small vortices that move downward.The vortex has quite random and complex frequencydomain distribution characteristics in the wake.The maximum time-averaged velocity of the slipstream occurs near the nose of the head car,based on which,the track-side safety domain is divided.
基金Project(U1134203)supported by the National Natural Science Foundation of China
文摘According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was studied and eight types of flow regions were proposed. They are high pressure with air stagnant region, pressure decreasing with air accelerating region, low pressure with high air flow velocity region I, turbulent region, steady flow region, low pressure with high air flow velocity region II,pressure increasing with air decelerating region and wake region. The analysis of the vortex structure around the train shows that the vortex is mainly induced by structures with complex mutation and large curvature change. The head and rear of train, the underbody structure, the carriage connection section and the wake region are the main vortex generating sources while the train body with even cross-section has rare vortexes. The wake structure development law studied lays foundation for the train drag reduction.
基金National Basic Research Program of China(2012CB417202)National Natural Science Foundation of China(41175045,91337215,Ul 133603)Special Fund for Meteorological Research in the Public Interest(GYHY201206042)
文摘This study uses NCEP/NCAR daily reanalysis data,NOAA outgoing long-wave radiation(OLR) data,the real-time multivariate MJO(RMM) index from the Australian Bureau of Meteorology and Tibetan Plateau vortex(TPV)data from the Chengdu Institute of Plateau Meteorology to discuss modulation of the Madden-Julian Oscillation(MJO)on the Tibetan Plateau Vortex(TPV).Wavelet and composite analysis are used.Results show that the MJO plays an important role in the occurrence of the TPV that the number of TPVs generated within an active period of the MJO is three times as much as that during an inactive period.In addition,during the active period,the number of the TPVs generated in phases 1 and 2 is larger than that in phases 3 and 7.After compositing phases 1 and 7 separately,all meteorological elements in phase 1 are apparently conducive to the generation of the TPV,whereas those in phase 7 are somewhat constrained.With its eastward propagation process,the MJO convection centre spreads eastward,and the vertical circulation within the tropical atmosphere changes.Due to the interaction between the mid-latitude and low-latitude atmosphere,changes occur in the baroclinic characteristics of the atmosphere,the available potential energy and eddy available potential energy of the atmosphere,and the circulation structures of the atmosphere over the Tibetan Plateau(TP) and surrounding areas.This results in significantly different water vapour transportation and latent heat distribution.Advantageous and disadvantageous conditions therefore alternate,leading to a significant difference among the numbers of plateau vortex in different phases.
基金Project(52372370)supported by the National Natural Science Foundation of ChinaProject(2023ZZTS0379)supported by the Graduate Student Independent Innovation Project of Central South University,ChinaProject(202206370058)supported by the China Scholarship Council。
文摘This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The impact of the VGs is assessed through the improved delayed detached eddy simulations(IDDES)after validating predictions against previous experimental measurements and other numerical predictions for the base case.The simulations indicate that strategically installed VGs can reduce the average slipstream velocity(U slipstream)and the upper limit of slipstream velocity(U_(slipstream,max))by~17%and~15%,respectively,as well as moving the peaks downstream by approximately train height,thus reducing the danger posed by slipstream to waiting passengers and trackside workers.Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake.It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs.These latter vortices prevent the merging of vortical airflow around the trailing nose tip,which is otherwise induced by the longitudinal vortex of the train.They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream,limiting outwards advection through interaction with the image pair,and contributing to a decrease in the peak slipstream value.The method proposed offers a simple approach to wake control leading to significant slipstream benefits.
文摘2016年7月1日安徽境内出现了一次造成严重洪涝灾害的强梅雨锋暴雨过程,主要由两个中尺度低涡活动引发,暴雨中心桐城出现“列车效应”,次中心巢湖出现“列车带效应”。本文基于常规观测、地面加密自动观测、多普勒天气雷达和欧洲中期天气预报中心(European Center for Medium-range Weather Forecasts,ECMWF)0.25°×0.25°的ERA5再分析资料,分析了两地对流的发生发展及其与中尺度低涡活动的关系。结果表明:这次暴雨发生在双阻型、高空有冷涡、副热带高压稳定维持的背景下,两个中尺度低涡活动引发强降水。多条强对流短雨带在高空气流引导下自西向东移动依次经过巢湖,形成巢湖“列车带效应”。不断触发的新风暴沿西南-东北向雨带依次经过桐城,形成桐城“列车效应”。影响巢湖和桐城的风暴均呈低质心结构,风暴合并后降水明显增强。巢湖“列车带效应”位于中尺度低涡C1西南象限的冷式切变线右侧,动力不稳定较明显,既有低涡后部冷空气入侵南部暖湿空气触发对流风暴后由西北向东南方向依次经过巢湖,也有南部超低空急流触发对流风暴后由西南向东北方向依次经过巢湖,形成强降水。桐城“列车效应”处于中尺度低涡C2的东南象限,热力不稳定相对较强,低层冷空气不明显,深厚低空急流与边界层气旋式辐合作用,后向传播的风暴自西南向东北移动经过桐城,造成极端降水。
基金supported by the National Natural Science Foundation of China(Grant Nos.42088101 and 42075032).
文摘Persistent(5-day or longer)extreme cold events(ECEs)over northeastern China during the boreal winter of 1979–2020 are investigated using daily minimum temperature(Tmin)from the China Meteorological Data Network.The extreme cooling area and intensity indices associated with the ECEs exhibit a dominant 10–40-day periodicity,indicating a close link with atmospheric intraseasonal oscillations(ISOs).The ECEs are categorized into W-and N-type.In the former,the low-frequency cooling associated with the ISO first penetrates into the western boundary of the northeastern China domain and later occupies the entire domain at its peak phase.The upper-tropospheric circulation associated with this type is characterized by a northwest–southeast-oriented Rossby wave train,expanding from the Ural Mountains to the western Pacific Ocean.In the latter,the cooling invades the northern boundary first and then penetrates into the entire domain.The upper tropospheric precursory signal associated with this type is a zonally oriented negative geopotential height anomaly,which slowly moves southward.A downward-propagating signal is observed in the stratospheric potential vorticity field prior to the peak cooling,implying a possible stratospheric impact.In addition to the W-and N-types,ECEs can also occur in a localized region near either at the northern or southern boundary of the domain.
文摘Spatiotemporal vector and phase properties of interference field of low-frequency signalling tone between three local vortices in a real shallow sea wave-guide have been studied.It has been demonstrated that in the field of constructive interference,components of particle velocity field and acoustic pressure are coherent.As a consequence the transfer of signal energy alog the axis of a shallow sea wave-guide is accomplished with plane wave.Physical objects are detected in the field of destructive interference,which,according to known deterministic signs,can be defined as local vortices of the intensity vector.A large-scale vorticity with acoustic intensity vector curl,components different from zero originates in the vicinity of local vortices.Regular particle displacements of local vortices have been detected against combined receiving device phase centre along the axis of a wave-guide.It has been demonstrated that the structure of vortices depends on signal/noise ratio.Local vortices and vorticity form vortex structure of vector acoustic field.Signalling tone with frequency of 88 ± 1 Hz from near-surface moving sound source was taken into consideration.Introduced results of full-scale experiment expand our concepts of real fundamental properties of shallow sea acoustic field and are to be considered in theoretical models.
