A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to ...A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to understand the source of fast-flowing plasmas, many questions remain unanswered about the mechanisms that produce high-speed flows and the effects they have on magnetospheric disturbances, especially their contributions to magnetospheric convection and substorms. In this paper, we discuss briefly the history of high-speed flows and review the proposed mechanisms, signatures of high-speed flows in auroras and their interaction with the background plasma. We then summarize the relationships between high-speed flows and magnetic structures, discuss questions associated with substorms, and finally pose several important scientific questions that need to be addressed.展开更多
It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma f...It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma flow (up to 2 km/s) in the polar cap ionosphere and large cross-polar cap potential (CPCP) during a period of horizontal IMF (|BZ| < 2 nT) observed by both ACE (at the L1 point) and Geotail (on the dusk flank of the magnetosheath).The CPCP is even higher than that under preceding BZ ≈-23 nT.Furthermore,GOES8 observed that the magnetosheath field turns northward as the anti-sunward plasma flow and CPCP start to increase,which implies that the magnetosheath field interacting with the Earth's magnetopause has significantly rotated and differs from the IMF observed by ACE and Geotail.In accordance with previous theoretical work,we suggest that the magnetic field line draping produces a southward magnetosheath field and enhances anti-sunward plasma flow and the CPCP.展开更多
Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moo...Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moon’s interaction with the sun mission during 13:00–15:00 UT on July 3,2012,were studied.The morphologies of the flux ropes were studied in detail based on Grad-Shfranov reconstruction method and electronic pitch angle distribution data.It is found that(1)the flux rope cross-sectional dimensions are 1.0 Re×0.78 Re,1.3 Re×0.78 Re,and 2.5 Re×1.25 Re,respectively.The magnetic field lines were asymmetric about the center with field line compression on both sides of the current sheet at the leading region;(2)the electron energy flux data presented asymmetry with larger electron flux and lower temperature in the precursor region.The flux ropes were blocked by the resistance of compressed particle density in the front central plasma sheet and the enhanced magnetic field on its sides;and(3)it is found that the flux rope has a layered structure.From inside out,event 1 can be divided into three regions,namely electronic depletion core region,closed field line region,and the caudal area possible with fields connected with the ionosphere.It suggests that the flux ropes cannot merge with the tail magnetic field lines near the lunar orbit.Especially,the flux rope asymmetrical shape reflects the different reconnection processes that caused it on both sides of the magnetic structure.The events shown in this paper support the multiple X-line magnetic reconnection model for flux ropes with in situ observations.展开更多
We studied the compressional wave event in Pc5 frequency range observed in the dawn-side magnetic equator on 9 March 1998 by Grad-Shafranov(GS) reconstruction method for the first time. To test the effectiveness of ap...We studied the compressional wave event in Pc5 frequency range observed in the dawn-side magnetic equator on 9 March 1998 by Grad-Shafranov(GS) reconstruction method for the first time. To test the effectiveness of application of GS method on Pc5 compressional wave, we benchmarked our procedure by applying it to a one-dimensional current sheet model first. Excluding the left-hand corners, the average error magnitude was less than 10%. The reconstruction of actual data showed that we obtained the 2-D map of compressional wave without suffering model constraints for the first time. The magnetic filed lines density cyclical changed, and the wavelength was about 2-4 times earth radius. The reconstructed magnetic topology had a shape very similar to the empirical 2-dimensional standing wave model proposed by the former workers. Besides, we also recovered the plasma thermal pressure and current density of the wave quantitatively.展开更多
We identified 28 discrete electron events(DEEs) with enhanced fluxes at ~50-200 keV in the high-altitude cusp/polar cap/lobe,using the electron measurements by the BeiDa Image Electron Spectrometer(BD-IES) instrument ...We identified 28 discrete electron events(DEEs) with enhanced fluxes at ~50-200 keV in the high-altitude cusp/polar cap/lobe,using the electron measurements by the BeiDa Image Electron Spectrometer(BD-IES) instrument onboard an inclined(55°)geosynchronous orbit(IGSO) satellite from October 2015 to January 2016. We find that among the 28 DEEs, 22 occur in the nightside and mostly in the northern cusp/polar cap/lobe, while 6 occur in the dayside and all in the southern cusp; 24 events correspond to an average interplanetary magnetic field(IMF) component B_z>0, 3 correspond to an average IMF B_z<0, and 1 has no OMNI IMF data. In these DEEs, the observed average omnidirectional electron differential flux generally fits well to a power-law spectrum, J^E^(-γ), with the spectral index y ranging from 2.6 to 4.6, while the average electron flux varies over three orders of magnitude from event to event. The spectral index of these cusp DEEs are(strongly) larger than the spectral index of solar wind superhalo electrons(radiation belt electrons) observed by the WIND 3 D Plasma & Energetic Particle instrument(the BD-IES). At^110 keV,the electron flux of DEEs in the cusp/polar cap/lobe shows a weak positive correlation with the solar wind superhalo electron flux but no obvious correlation with the radiation belt electron flux. These results suggest that these DEEs probably originate from transient processes acting on the solar wind superhalo electrons, e.g., the mid/high-latitude reconnection.展开更多
Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely ...Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely on near-Earth satellite data. The model of the bow shock in the distant magnetotail and other factors that affect the bow shock, such as the interplanetary magnetic field(IMF) B_y, remain unclear. Here, based on the bow shock crossings of ARTEMIS from January 2011 to January 2015, new coefficients of the tail-flaring angle a of the Chao model(one of the most accurate models currently available) were obtained by fitting data from the middle-distance magnetotail(near-lunar orbit, geocentric distance -20R_E>X>-50R_E). In addition, the effects of the IMF B_y on the flaring angle a were analyzed. Our results showed that:(1) the new fitting coefficients of the Chao model in the middle-distance magnetotail are more consistent with the observed results;(2) the tail-flaring angle a of the bow shock increases as the absolute value of the IMF B_y increases. Moreover, positive IMF B_y has a greater effect than negative IMF B_y on flaring angle. These results provide a reference for bow shock modeling that includes the IMF B_y.展开更多
It is important to determine the dimensionality and velocity information in the study of spatial magnetic structures. Many data analysis theories/techniques are based on the assumption of one or two dimensions. For ex...It is important to determine the dimensionality and velocity information in the study of spatial magnetic structures. Many data analysis theories/techniques are based on the assumption of one or two dimensions. For example, the Grad-Shafranov(GS)reconstruction method assumes a dimensionality of two or less. The Minimum Direction Derivative(MDD) method provides an indication of the dimensionality. For the structure velocity, the components in each dimensionality can be calculated by SpatioTemporal Difference analysis(STD). In order to improve the convenience of use of MDD method, a new parameter Dm quantifying the dimensionality based on MDD eigenvalues is introduced in this paper. The influences of noise/turbulence,separation distance and tetrahedron configuration on MDD and the evaluation of Dmare systematically tested using two analytical models for magnetic structures, representing a magnetic mirror and magnetic flux rope. We tested and gave the threshold values of three quality indicators for MDD results using the flux rope model. We also show that the error induced by turbulence is comparable to that of random noise when the turbulence scales are less than the spacecraft separation. Besides, the accuracy of STD velocity estimation will also be influenced by turbulence for cases with excessively high data time resolution.By using Dm, we show that an ideal model of a mirror-like structure can be divided into one dimension(1-D) and three dimension(3-D) regions. This restricts the applicability of the GS method in mirror-like structures. For example, in a given reconstruction range, the GS error increased from less than 7% to more than 15% by using the data along trajectories in 1-D and 3-D regions as predicated by Dm. Thus, it is important to estimate the structure dimensionality, which can be further used to estimate the reliability of the GS reconstruction map.展开更多
Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region.They are characterized by a simultaneous depression of magnetic field magnitude and plasma density,which are bounded with enhance...Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region.They are characterized by a simultaneous depression of magnetic field magnitude and plasma density,which are bounded with enhancements of these two parameters and surrounded by ultralow frequency(ULF)waves.Previous studies focused on the interplanetary magnetic field(IMF)conditions,solar wind(SW)conditions,and the growth of the foreshock waves related to the generation of foreshock cavitons.Previously,a multipoint spacecraft analysis method using Cluster data was applied to analyze only two foreshock cavitons,and this method did not consider uncertainties.In this study,multipoint spacecraft analysis methods,including the timing method,the minimum directional derivative(MDD)method,and the spatiotemporal difference(STD)method are applied to determine the velocity in both spacecraft and solar wind frames.The propagation properties show good agreement with previous results from simulations and observations that most cavitons move sunward in the solar wind frame,with the velocities larger than the Alfvén speed.The propagation properties of foreshock cavitons support the formation mechanism of cavitons in previous simulations,which suggested that cavitons are formed due to the nonlinear evolution of compressive ULF waves.We find that there is clear decreasing trend between the size of cavitons and their velocity in the solar wind frame.In addition,the timing method considering errors has been applied to study the evolution properties by comparing the velocities with errors of the leading and trailing edges,and we identify three stable cavitons and one contracting caviton,which has not been studied before.Most cavitons should remain stable when they travel toward the Earth’s bow shock.The relationship between the size of foreshock cavitons and their distance from the bow shock is also discussed.展开更多
基金supported by the National Natural Science Foundation of China (40874086 and 41031065)the Specialized Research Fund for State Key Laboratories (08262DAA4S)
文摘A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to understand the source of fast-flowing plasmas, many questions remain unanswered about the mechanisms that produce high-speed flows and the effects they have on magnetospheric disturbances, especially their contributions to magnetospheric convection and substorms. In this paper, we discuss briefly the history of high-speed flows and review the proposed mechanisms, signatures of high-speed flows in auroras and their interaction with the background plasma. We then summarize the relationships between high-speed flows and magnetic structures, discuss questions associated with substorms, and finally pose several important scientific questions that need to be addressed.
基金supported by the KIP Pilot Project of the Chinese Academy of Scineces(KZCX2-YW-123)the National Natural Science Foundation of China (41004072,41031065,41074106,41074117,40974090,40874088 and 40831061)the National Basic Research Program of China(2011CB811405)
文摘It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma flow (up to 2 km/s) in the polar cap ionosphere and large cross-polar cap potential (CPCP) during a period of horizontal IMF (|BZ| < 2 nT) observed by both ACE (at the L1 point) and Geotail (on the dusk flank of the magnetosheath).The CPCP is even higher than that under preceding BZ ≈-23 nT.Furthermore,GOES8 observed that the magnetosheath field turns northward as the anti-sunward plasma flow and CPCP start to increase,which implies that the magnetosheath field interacting with the Earth's magnetopause has significantly rotated and differs from the IMF observed by ACE and Geotail.In accordance with previous theoretical work,we suggest that the magnetic field line draping produces a southward magnetosheath field and enhances anti-sunward plasma flow and the CPCP.
基金supported by the Specialized Research Fund for State Key Laboratoriesthe scientific research foundation of Shandong province Outstanding Young Scientist Award(Grant No.2013BSE27132)+2 种基金the National Natural Science Foundation of China(Grant Nos.4103106541322031)the Shandong Natural Science Foundation(Grant No.JQ201112)
文摘Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moon’s interaction with the sun mission during 13:00–15:00 UT on July 3,2012,were studied.The morphologies of the flux ropes were studied in detail based on Grad-Shfranov reconstruction method and electronic pitch angle distribution data.It is found that(1)the flux rope cross-sectional dimensions are 1.0 Re×0.78 Re,1.3 Re×0.78 Re,and 2.5 Re×1.25 Re,respectively.The magnetic field lines were asymmetric about the center with field line compression on both sides of the current sheet at the leading region;(2)the electron energy flux data presented asymmetry with larger electron flux and lower temperature in the precursor region.The flux ropes were blocked by the resistance of compressed particle density in the front central plasma sheet and the enhanced magnetic field on its sides;and(3)it is found that the flux rope has a layered structure.From inside out,event 1 can be divided into three regions,namely electronic depletion core region,closed field line region,and the caudal area possible with fields connected with the ionosphere.It suggests that the flux ropes cannot merge with the tail magnetic field lines near the lunar orbit.Especially,the flux rope asymmetrical shape reflects the different reconnection processes that caused it on both sides of the magnetic structure.The events shown in this paper support the multiple X-line magnetic reconnection model for flux ropes with in situ observations.
文摘We studied the compressional wave event in Pc5 frequency range observed in the dawn-side magnetic equator on 9 March 1998 by Grad-Shafranov(GS) reconstruction method for the first time. To test the effectiveness of application of GS method on Pc5 compressional wave, we benchmarked our procedure by applying it to a one-dimensional current sheet model first. Excluding the left-hand corners, the average error magnitude was less than 10%. The reconstruction of actual data showed that we obtained the 2-D map of compressional wave without suffering model constraints for the first time. The magnetic filed lines density cyclical changed, and the wavelength was about 2-4 times earth radius. The reconstructed magnetic topology had a shape very similar to the empirical 2-dimensional standing wave model proposed by the former workers. Besides, we also recovered the plasma thermal pressure and current density of the wave quantitatively.
基金supported by the National Natural Science Foundation of China(Grant Nos.41421003,41474148,41774183&41374167)Major Project of Chinese National Programs for Fundamental Research and Development(Grant No.2012CB825603)
文摘We identified 28 discrete electron events(DEEs) with enhanced fluxes at ~50-200 keV in the high-altitude cusp/polar cap/lobe,using the electron measurements by the BeiDa Image Electron Spectrometer(BD-IES) instrument onboard an inclined(55°)geosynchronous orbit(IGSO) satellite from October 2015 to January 2016. We find that among the 28 DEEs, 22 occur in the nightside and mostly in the northern cusp/polar cap/lobe, while 6 occur in the dayside and all in the southern cusp; 24 events correspond to an average interplanetary magnetic field(IMF) component B_z>0, 3 correspond to an average IMF B_z<0, and 1 has no OMNI IMF data. In these DEEs, the observed average omnidirectional electron differential flux generally fits well to a power-law spectrum, J^E^(-γ), with the spectral index y ranging from 2.6 to 4.6, while the average electron flux varies over three orders of magnitude from event to event. The spectral index of these cusp DEEs are(strongly) larger than the spectral index of solar wind superhalo electrons(radiation belt electrons) observed by the WIND 3 D Plasma & Energetic Particle instrument(the BD-IES). At^110 keV,the electron flux of DEEs in the cusp/polar cap/lobe shows a weak positive correlation with the solar wind superhalo electron flux but no obvious correlation with the radiation belt electron flux. These results suggest that these DEEs probably originate from transient processes acting on the solar wind superhalo electrons, e.g., the mid/high-latitude reconnection.
基金supported by the National Natural Science Foundation of China(Grant Nos.41322031,41404131,41574157,41031065&41304129)the Specialized Research Fund for State Key Laboratoriesthe Shandong Natural Science Foundation(Grant Nos.2013BSE27132,BS2013HZ001)
文摘Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely on near-Earth satellite data. The model of the bow shock in the distant magnetotail and other factors that affect the bow shock, such as the interplanetary magnetic field(IMF) B_y, remain unclear. Here, based on the bow shock crossings of ARTEMIS from January 2011 to January 2015, new coefficients of the tail-flaring angle a of the Chao model(one of the most accurate models currently available) were obtained by fitting data from the middle-distance magnetotail(near-lunar orbit, geocentric distance -20R_E>X>-50R_E). In addition, the effects of the IMF B_y on the flaring angle a were analyzed. Our results showed that:(1) the new fitting coefficients of the Chao model in the middle-distance magnetotail are more consistent with the observed results;(2) the tail-flaring angle a of the bow shock increases as the absolute value of the IMF B_y increases. Moreover, positive IMF B_y has a greater effect than negative IMF B_y on flaring angle. These results provide a reference for bow shock modeling that includes the IMF B_y.
基金supported by the Shandong University(Weihai)Future Plan for Young Scholar(Grant No.2017WHWLJH08)Specialized Research Fund for State Key Laboratoriesthe Scientific Research Foundation of Shandong Province Outstanding Young Scientist Award(Grant No.BS2013HZ001)
文摘It is important to determine the dimensionality and velocity information in the study of spatial magnetic structures. Many data analysis theories/techniques are based on the assumption of one or two dimensions. For example, the Grad-Shafranov(GS)reconstruction method assumes a dimensionality of two or less. The Minimum Direction Derivative(MDD) method provides an indication of the dimensionality. For the structure velocity, the components in each dimensionality can be calculated by SpatioTemporal Difference analysis(STD). In order to improve the convenience of use of MDD method, a new parameter Dm quantifying the dimensionality based on MDD eigenvalues is introduced in this paper. The influences of noise/turbulence,separation distance and tetrahedron configuration on MDD and the evaluation of Dmare systematically tested using two analytical models for magnetic structures, representing a magnetic mirror and magnetic flux rope. We tested and gave the threshold values of three quality indicators for MDD results using the flux rope model. We also show that the error induced by turbulence is comparable to that of random noise when the turbulence scales are less than the spacecraft separation. Besides, the accuracy of STD velocity estimation will also be influenced by turbulence for cases with excessively high data time resolution.By using Dm, we show that an ideal model of a mirror-like structure can be divided into one dimension(1-D) and three dimension(3-D) regions. This restricts the applicability of the GS method in mirror-like structures. For example, in a given reconstruction range, the GS error increased from less than 7% to more than 15% by using the data along trajectories in 1-D and 3-D regions as predicated by Dm. Thus, it is important to estimate the structure dimensionality, which can be further used to estimate the reliability of the GS reconstruction map.
基金supported by the National Natural Science Foundation of China(Grant Nos.41574157,41628402&41774153)partially supported by National Science Foundation(Grant No.AGS-1352669)+1 种基金the International Space Science Institute-Beijing for supporting the international team “Dayside Transient Phenomena and Their Impact on the Magnetosphere-Ionosphere”supported by the specialized research fund for State Key Laboratories
文摘Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region.They are characterized by a simultaneous depression of magnetic field magnitude and plasma density,which are bounded with enhancements of these two parameters and surrounded by ultralow frequency(ULF)waves.Previous studies focused on the interplanetary magnetic field(IMF)conditions,solar wind(SW)conditions,and the growth of the foreshock waves related to the generation of foreshock cavitons.Previously,a multipoint spacecraft analysis method using Cluster data was applied to analyze only two foreshock cavitons,and this method did not consider uncertainties.In this study,multipoint spacecraft analysis methods,including the timing method,the minimum directional derivative(MDD)method,and the spatiotemporal difference(STD)method are applied to determine the velocity in both spacecraft and solar wind frames.The propagation properties show good agreement with previous results from simulations and observations that most cavitons move sunward in the solar wind frame,with the velocities larger than the Alfvén speed.The propagation properties of foreshock cavitons support the formation mechanism of cavitons in previous simulations,which suggested that cavitons are formed due to the nonlinear evolution of compressive ULF waves.We find that there is clear decreasing trend between the size of cavitons and their velocity in the solar wind frame.In addition,the timing method considering errors has been applied to study the evolution properties by comparing the velocities with errors of the leading and trailing edges,and we identify three stable cavitons and one contracting caviton,which has not been studied before.Most cavitons should remain stable when they travel toward the Earth’s bow shock.The relationship between the size of foreshock cavitons and their distance from the bow shock is also discussed.