The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind,ultimately being vital in controlling sola...The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind,ultimately being vital in controlling solar activities and driving space weather.Despite numerous efforts to explore these regions,to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane,leaving their behavior and evolution poorly understood.This observation gap has left three top-level scientific questions unanswered:How does the solar dynamo work and drive the solar magnetic cycle?What drives the fast solar wind?How do space weather processes globally originate from the Sun and propagate throughout the solar system?The Solar Polarorbit Observatory(SPO)mission,a solar polar exploration spacecraft,is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes.In order to achieve its scientific goals,SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere,to observe the Sun in the extreme ultraviolet,X-ray,and radio wavelengths,to image the corona and the heliosphere up to 45 R_(s),and to perform in-situ detection of magnetic fields,and low-and high-energy particles in the solar wind.The SPO mission is capable of providing critical vector magnetic fields and Doppler velocities of the polar regions to advance our understanding of the origin of the solar magnetic cycle,providing unprecedented imaging observations of the solar poles alongside in-situ measurements of charged particles and magnetic fields from high heliolatitudes to unveil the mass and energy supply that drive the fast solar wind,and providing observational constraints for improving our ability to model and predict the three-dimensional(3D)structures and propagation of space weather events.展开更多
A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar ...A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier (GLM). Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang's MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.展开更多
A new hybrid numerical scheme of combining an E-CUSP(Energy-Convective Upwind and Split Pressure) method for the fluid part and the Constrained Transport(CT) for the magnetic induction part is proposed.In order to avo...A new hybrid numerical scheme of combining an E-CUSP(Energy-Convective Upwind and Split Pressure) method for the fluid part and the Constrained Transport(CT) for the magnetic induction part is proposed.In order to avoid the occurrence of negative pressure in the reconstructed profiles and its updated value,a positivity preserving method is provided.Furthermore,the MHD equations are solved at each physical time step by advancing in pseudo time.The use of dual time stepping is beneficial in the computation since the use of dual time stepping allows the physical time step not to be limited by the corresponding values in the smallest cell and to be selected based on the numerical accuracy criterion.This newly established hybrid scheme combined with positivity preserving method and dual time technique has demonstrated the accurateness and robustness through numerical experiments of benchmark problems such as the 2D Orszag-Tang vortex problem and the3 D shock-cloud interaction problem.展开更多
The Arbitrary accuracy Derivatives Riemann problem method(ADER) scheme is a new high order numerical scheme based on the concept of finite volume integration,and it is very easy to be extended up to any order of space...The Arbitrary accuracy Derivatives Riemann problem method(ADER) scheme is a new high order numerical scheme based on the concept of finite volume integration,and it is very easy to be extended up to any order of space and time accuracy by using a Taylor time expansion at the cell interface position.So far the approach has been applied successfully to flow mechanics problems.Our objective here is to carry out the extension of multidimensional ADER schemes to multidimensional MHD systems of conservation laws by calculating several MHD problems in one and two dimensions: (ⅰ) Brio-Wu shock tube problem,(ⅱ) Dai-Woodward shock tube problem,(ⅲ) Orszag-Tang MHD vortex problem.The numerical results prove that the ADER scheme possesses the ability to solve MHD problem,remains high order accuracy both in space and time,keeps precise in capturing the shock.Meanwhile,the compared tests show that the ADER scheme can restrain the oscillation and obtain the high order non-oscillatory result.展开更多
Using 86 CME-interplanetary shock events,the correlation between the peak values of (a) the solar wind parameters(B_z,E_y,P_(dyn)) and the geomagnetic indices(SYM-H,ASY-H,Kp), (b) the coupling functions(Borovsky,Akaso...Using 86 CME-interplanetary shock events,the correlation between the peak values of (a) the solar wind parameters(B_z,E_y,P_(dyn)) and the geomagnetic indices(SYM-H,ASY-H,Kp), (b) the coupling functions(Borovsky,Akasofu,Newell) and the geomagnetic indices,(c) the solar wind parameters/coupling functions/geomagnetic indices and the ionospheric parameter(Δf_0F_(2min)), are investigated.The statistical results show that in group(a),B_(z min) and SYM-H_(min) have the best correlation,that in group(b),the best correlation is between the peak values of Akasofu function (A_(min)) and SYM-H_(min),and that in group(c),the best correlation is between K_(pmax) andΔf_0F_(2min). Based on the statistical results,a method for predicting f_0F_2 of a single station is attempted to be set up.The input is modified B_(z min) and the outputs are SYM-H_(min) andΔf_0F_(2min).Then 25 CME-IPS events that caused geomagnetic storms in 1998 and 2009 are used to check the prediction method. The results show that our method can be used to predict SYM-H_(min) andΔf_0F_(2min).展开更多
This is an overview of progresses in heliospheric physics made in China in the period of June, 2000 to May, 2002. The report is focused on theoretical studies,modelling and observational analysis of interplanetary phy...This is an overview of progresses in heliospheric physics made in China in the period of June, 2000 to May, 2002. The report is focused on theoretical studies,modelling and observational analysis of interplanetary physical phenomena, and consists of five sections: the acceleration and heating of the solar wind, corona structures, coronal mass ejections, magnetic reconnection phenomena, and in terplanetary transient phenomena. The main achievements made recently by Chinese scientists in related areas are simply listed in corresponding sections without any priority, only certain editorial consideration.展开更多
An asynchronous and parallel time-marching method for three-dimensional (3D) time-dependent magnetohydrodynamic (MHD) simulation is used for large-scale solar wind simulation. It uses different local time steps in the...An asynchronous and parallel time-marching method for three-dimensional (3D) time-dependent magnetohydrodynamic (MHD) simulation is used for large-scale solar wind simulation. It uses different local time steps in the corona and the heliosphere according to the local Courant-Friedrichs-Levy (CFL) conditions. The solar wind background with observed solar photospheric magnetic field as input is first presented. The simulation time for the background solar wind by using the asynchronous method is <1/6 of that by using the normal synchronous time-marching method with the same computation precision. Then, we choose the coronal mass ejection (CME) event of 13 November, 2003 as a test case. The time-dependent variations of the pressure and the velocity configured from a CME model at the inner boundary are applied to generate transient structures in order to study the dynamical interaction of a CME with the background solar wind flow between 1 and 230 Rs. This time-marching method is very effective in terms of computation time for large-scale 3D time-dependent numerical MHD problem. In this validation study, we find that this 3D MHD model, with the asynchronous and parallel time-marching method, provides a relatively satisfactory comparison with the ACE spacecraft obser- vations at L1 point.展开更多
High-performance computational models are required to make the real-time or faster than rea^-time numerical prediction of adverse space weather events and their influence on the geospace environment. The main objectiv...High-performance computational models are required to make the real-time or faster than rea^-time numerical prediction of adverse space weather events and their influence on the geospace environment. The main objective in this article is to explore the application of programmable graphic processing units （GPUs） to the numerical space weather modeling for the study of solar wind background that is a crucial part in the numerical space weather modeling. GPU programming is realized for our Solar-Interplanetary-CESE MHD model （SIP-CESE MHD model） by numerically studying the solar corona/interplanetary so- lar wind. The global solar wind structures are obtained by the established GPU model with the magnetic field synoptic data as input. Meanwhile, the time-dependent solar surface boundary conditions derived from the method of characteristics and the mass flux limit are incorporated to couple the observation and the three-dimensional （3D） MHD model. The simulated evolu- tion of the global structures for two Carrington rotations 2058 and 2062 is compared with solar observations and solar wind measurements t^om spacecraft near the Earth. The MHD model is also validated by comparison with the standard potential field source surface （PFSS） model. Comparisons show that the MHD results are in good overall agreement with coronal and interplanetary structures, including the size and distribution of coronal holes, the position and shape of the streamer belts, and the transition of the solar wind speeds and magnetic field polarities.展开更多
During Ulysses’first rapid pole-to-pole transit from September 1994 to June 1995,its observations showed that middle-or high-speed solar winds covered all latitudes except those between?20°and+20°near the e...During Ulysses’first rapid pole-to-pole transit from September 1994 to June 1995,its observations showed that middle-or high-speed solar winds covered all latitudes except those between?20°and+20°near the ecliptic plane,where the velocity was 300―450 km/s.At poleward 40°,however,only fast solar winds at the speed of 700―870 km/s were observed.In addition,the transitions from low-speed wind to high-speed wind or vice versa were abrupt.In this paper,the large-scale structure of solar wind observed by Ulysses near solar minimum is simulated by using the three-dimensional numerical MHD model.The model com-bines TVD Lax-Friedrich scheme and MacCormack II scheme and decomposes the calculation region into two re-gions:one from 1 to 22 Rs and the other from 18 Rs to 1 AU.Based on the observations of the solar photospheric magnetic field and an addition of the volumetric heating to MHD equations,the large-scale solar wind structure mentioned above is reproduced by using the three-dimensional MHD model and the numerical results are roughly consistent with Ulysses’observations.Our simulation shows that the initial magnetic field topology and the addition of volume heating may govern the bimodal structure of solar wind observed by Ulysses and also demonstrates that the three-dimensional MHD numerical model used here is efficient in modeling the large-scale solar wind structure.展开更多
A 1D-HD shock propagation model is established to predict the arrival time of interplanetary shocks at 1 AU. Applying this model to 68 solar events during the period of February 1997 to October 2000, it is found that ...A 1D-HD shock propagation model is established to predict the arrival time of interplanetary shocks at 1 AU. Applying this model to 68 solar events during the period of February 1997 to October 2000, it is found that our model could be practically equivalent to the STOA, ISPM and HAFv.2 models in forecasting the shock arrival time. The absolute error in the transit time from our model is not larger than those of the other three models for the same sample events. Also, the prediction test shows that the relative error of our model is ≤10% for 31% of all events, ≤30% for 75%, and ≤50% for 84%, which is comparable to the relative errors of the other mod- els. These results might demonstrate a potential capability of our model in terms of real-time forecasting.展开更多
Using 80 CME-ICME events during 1997.1―2002.9,based on the eruptive source locations of CMEs and solar magnetic field observation at the photosphere,a current sheet magnetic coordinate(CMC)system is established in or...Using 80 CME-ICME events during 1997.1―2002.9,based on the eruptive source locations of CMEs and solar magnetic field observation at the photosphere,a current sheet magnetic coordinate(CMC)system is established in order to study the propagation of CME and its geoeffectiveness.In context of this coordinate system,the effect of the eruptive source location and the form of heliospheric current sheet(HCS)at the eruptive time of CME on the geomagnetic storm intensity caused by CME and the CME’s transit time at the Earth is investigated in detail.Our preliminary conclusions are:1)The geomagnetic disturbances caused by CMEs tend to have the so-called“same side-opposite side effect”,i.e.CMEs erupt from the same side of the HCS as the earth would be more likely to arrive at the earth and the geomagnetic disturbances associated with them tend to be of larger magnitude,while CMEs erupting from the opposite side would arrive at the earth with less probability and the corresponding geomagnetic disturbance magnitudes would be relatively weaker.2)The angular separation between the earth and the HCS affect the corresponding disturbance intensity.That is,when our earth is located near the HCS,adverse space weather events occur most probably.3)The erupting location of the CME and its nearby form of HCS will also affect its arrival time at the earth.According to these conclusions,in this context of CMC coordinate we arrive at new prediction method for estimating the geomagnetic storm intensity(Dstmin)caused by CMEs and their transit times.The application of the empirical model for 80 CME-ICME events shows that the relative error of Dst is within 30%for 59%events with Dstmin≤?50 nT,while the averaged absolute error of transit time is lower than 10 h for all events.展开更多
Aiming at two intense shock events on October 28 and 29,2003,this paper presents a two-step method,which combines synoptic analysis of space weather——“observing”and quantitative prediction——“palpating”,and the...Aiming at two intense shock events on October 28 and 29,2003,this paper presents a two-step method,which combines synoptic analysis of space weather——“observing”and quantitative prediction——“palpating”,and then uses it to test predictions.In the first step of“observing”,on the basis of observations of the solar source surface magnetic field,interplanetary scintillation(IPS)and ACE spacecraft,we find that the propagation of the shocks is asymmetric relative to the normal direction of their solar sources,and the Earth is located near the direction of the fastest speed and the greatest energy of the shocks.As the two fast ejection shock events,the fast explosion of coronal mass of the extremely high temperature,the strong magnetic field,and the high speed background solar wind are also helpful to their rapid propagation.In the second step of“palpating”,we adopt a new membership function of the fast shock events for the ISF method.The predicted results show that for the onset time of the geomagnetic disturbance,the relative errors between the observational and the predicted results are 1.8%and 6.7%;and for the magnetic disturbance magnitude,the relative errors are 4.1%and 3.1%,re-spectively.Furthermore,the comparison among the predicted results of our two-step method with those of five other prevailing methods shows that the two-step method is advantageous.The results tell us that understanding the physical features of shock propagation thoroughly is of great importance in improving the prediction precision.展开更多
Two interplanetary shocks are examined to determine the responses of the magnetic field and plasma in the plasma sheet upon the shock impacts by using TC-1 observational data.The two shocks are observed by WIND on Nov...Two interplanetary shocks are examined to determine the responses of the magnetic field and plasma in the plasma sheet upon the shock impacts by using TC-1 observational data.The two shocks are observed by WIND on November 7,2004.Prior to and after the shock,the IMF is either weakly southward or northward.The responses of the plasma sheet to the two shocks are intense and much similar.When the shock interacts with the magnetosphere,the magnetic field impulsively increases 1-2 min after the geomagnetic field sudden impulse (SI) judged from the Sym-H index change,and the magnetic field line is stretched.On the other hand,all of the ion density,the ion temperature,and the velocity of ion flow in the plasma sheet increase.Interestingly,quasi-periodical oscillations of the ion flow are suddenly enhanced,and the plasma flow is basically perpendicular to the local magnetic field.The responses of the magnetic field and the plasma are nearly simultaneous.The responses in the plasma sheet are probably caused by the lateral compression due to the dynamic pressure enhancement downstream the shock when the shock propagates antisunward in the magnetosheath.展开更多
In this paper,we report two MC events observed by WIND spacecraft with good examples of fieldaligned residual flow inside the MC structure. For both events,the co-moving frames are determined through the deHoffman-Tel...In this paper,we report two MC events observed by WIND spacecraft with good examples of fieldaligned residual flow inside the MC structure. For both events,the co-moving frames are determined through the deHoffman-Teller (HT) analysis and the axial orientations are inferred by the newly developed minimal residue (MR) method. The nature coordinate system for both events are constructed with velocity of the HT frame and the inferred MC axis,the field and flow remaining in the HT frame are analyzed at this coordinate system. As a result,we find that the residual flows in the co-moving HT frame of the two MC events are almost anti-parallel to the helical magnetic field. We speculate that the field-aligned residual flows are large scale coherent hydrodynamic vortices co-moving with the MCs at the supersonic speed near 1 AU. Data analyses show that the event in slow ambient solar wind is expanding at 1 AU and another one in fast solar wind does not show apparent expansion. Proton behaviors for both events are quasi-isothermal. Accelerated HT analysis shows that both events have no suitable HT frame with constant accelerations,which suggests that both events may be moving at the constant speed near 1 AU under the assumptions of the HT analysis. For both events,the ratio of the dynamic pressure to the magnetic pressure is larger than that of the thermal pressure to magnetic pressure,which suggests that the dynamic effects due to the plasma flows remaining in the co-moving HT frame are more important than the thermal effects in the study of MC evolution and propagation.展开更多
Based on the WIND observational data for the plasma waves from thermal noise receptor (TNR) working on the frequency 4―256 kHz and the solar wind and the magnetic fields, we analyze the plasma wave activities in the ...Based on the WIND observational data for the plasma waves from thermal noise receptor (TNR) working on the frequency 4―256 kHz and the solar wind and the magnetic fields, we analyze the plasma wave activities in the 60 magnetic cloud’s boundary layers (BLs) and find that there are often various plasma wave activities in the BLs, which are different from those in the adjacent solar wind (SW) and the magnetic clouds (MC). The basic characteris-tics are that: (1) the enhancement of the Langmuir wave near the electronic plasma frequency (fpe) is a dominant wave ac-tivity, which occupies 75% investigated samples; (2) the events enhanced both in the langmuir and ion acustic (f < fpe) waves are about 60% of investigated samples; (3) broadband, continuous enhancement events in the plasma wave activities were observed in the whole frequency band of TNR, and about 30% of the 60 samples, however, were not observed in the SW and the MC investigated events; (4) although the ratio of the temperatures between the electon and proton, Te/Tp≤1, the ion caustic wave enhancement activities are still often observed in the BLs, which makes it difficult to ex- plain them by the traditional plasma theory. New results reported in this paper further show that the magnetic cloud’s BL is an important dynamic structure, which could provide useful diagnosis for understanding the cloud’s BL physics and could expand a space developing space plasma wave theory.展开更多
We present the solar-terrestrial transit process of three successive coronal mass ejections(CMEs)of November 4―5,1998 originating from active region 8375 by using a time-dependent three-dimensional magnetohydrodynami...We present the solar-terrestrial transit process of three successive coronal mass ejections(CMEs)of November 4―5,1998 originating from active region 8375 by using a time-dependent three-dimensional magnetohydrodynamics(MHD)simula-tion.These CMEs interacted with each other while they were propagating in inter-planetary space and finally formed a"complex ejecta".A newly developed SIP-CESE MHD model was applied to solve MHD equations numerically.The quiet solar wind was started from Parker-like 1D solar wind solution and the magnetic field map was calculated from the solar photospheric magnetic field data.In our simulation,the ejections were initiated using pulse in the real active region 8375.The interplanetary disturbance parameters,such as speed,direction and angular size of the expanding CME,were determined from the SOHO/LASCO data with the cone-model.We discussed the three-dimensional aspects of the propagation,in-teraction and merging of the three ejections.The simulated interplanetary shocks were compared with the nearby-Earth measurement.The results showed that our simulation could reproduce and explain some of the general features observed by satellite for the"complex ejecta".展开更多
文摘The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind,ultimately being vital in controlling solar activities and driving space weather.Despite numerous efforts to explore these regions,to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane,leaving their behavior and evolution poorly understood.This observation gap has left three top-level scientific questions unanswered:How does the solar dynamo work and drive the solar magnetic cycle?What drives the fast solar wind?How do space weather processes globally originate from the Sun and propagate throughout the solar system?The Solar Polarorbit Observatory(SPO)mission,a solar polar exploration spacecraft,is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes.In order to achieve its scientific goals,SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere,to observe the Sun in the extreme ultraviolet,X-ray,and radio wavelengths,to image the corona and the heliosphere up to 45 R_(s),and to perform in-situ detection of magnetic fields,and low-and high-energy particles in the solar wind.The SPO mission is capable of providing critical vector magnetic fields and Doppler velocities of the polar regions to advance our understanding of the origin of the solar magnetic cycle,providing unprecedented imaging observations of the solar poles alongside in-situ measurements of charged particles and magnetic fields from high heliolatitudes to unveil the mass and energy supply that drive the fast solar wind,and providing observational constraints for improving our ability to model and predict the three-dimensional(3D)structures and propagation of space weather events.
基金Supported by the National Natural Science Foundation of China (40374056, 40536029, 40574068)the International Collaboration Research Team Program of the Chinese Academy of Sciences
文摘A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier (GLM). Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang's MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.
基金Supported by the National Basic Research Program of China(2012CB825601)the National Natural Science Foundationof China(41031066,41231068,41274192,41074121,41204127)+1 种基金the Knowledge Innovation Program of the ChineseAcademy of Sciences(KZZD-EW-01-4)the Specialized Research Fund for State Key Laboratories
文摘A new hybrid numerical scheme of combining an E-CUSP(Energy-Convective Upwind and Split Pressure) method for the fluid part and the Constrained Transport(CT) for the magnetic induction part is proposed.In order to avoid the occurrence of negative pressure in the reconstructed profiles and its updated value,a positivity preserving method is provided.Furthermore,the MHD equations are solved at each physical time step by advancing in pseudo time.The use of dual time stepping is beneficial in the computation since the use of dual time stepping allows the physical time step not to be limited by the corresponding values in the smallest cell and to be selected based on the numerical accuracy criterion.This newly established hybrid scheme combined with positivity preserving method and dual time technique has demonstrated the accurateness and robustness through numerical experiments of benchmark problems such as the 2D Orszag-Tang vortex problem and the3 D shock-cloud interaction problem.
基金Supported by the National Natural Science Foundation of China(40904050,40874077)the Specialized Research Fund for State Key Laboratories
文摘The Arbitrary accuracy Derivatives Riemann problem method(ADER) scheme is a new high order numerical scheme based on the concept of finite volume integration,and it is very easy to be extended up to any order of space and time accuracy by using a Taylor time expansion at the cell interface position.So far the approach has been applied successfully to flow mechanics problems.Our objective here is to carry out the extension of multidimensional ADER schemes to multidimensional MHD systems of conservation laws by calculating several MHD problems in one and two dimensions: (ⅰ) Brio-Wu shock tube problem,(ⅱ) Dai-Woodward shock tube problem,(ⅲ) Orszag-Tang MHD vortex problem.The numerical results prove that the ADER scheme possesses the ability to solve MHD problem,remains high order accuracy both in space and time,keeps precise in capturing the shock.Meanwhile,the compared tests show that the ADER scheme can restrain the oscillation and obtain the high order non-oscillatory result.
基金Supported by the National Natural Science Foundation of China(40890162,40704030,40674084)the Specialized Research Fund for State Key Laboratories
文摘Using 86 CME-interplanetary shock events,the correlation between the peak values of (a) the solar wind parameters(B_z,E_y,P_(dyn)) and the geomagnetic indices(SYM-H,ASY-H,Kp), (b) the coupling functions(Borovsky,Akasofu,Newell) and the geomagnetic indices,(c) the solar wind parameters/coupling functions/geomagnetic indices and the ionospheric parameter(Δf_0F_(2min)), are investigated.The statistical results show that in group(a),B_(z min) and SYM-H_(min) have the best correlation,that in group(b),the best correlation is between the peak values of Akasofu function (A_(min)) and SYM-H_(min),and that in group(c),the best correlation is between K_(pmax) andΔf_0F_(2min). Based on the statistical results,a method for predicting f_0F_2 of a single station is attempted to be set up.The input is modified B_(z min) and the outputs are SYM-H_(min) andΔf_0F_(2min).Then 25 CME-IPS events that caused geomagnetic storms in 1998 and 2009 are used to check the prediction method. The results show that our method can be used to predict SYM-H_(min) andΔf_0F_(2min).
基金Supported by the National Natural Science Foundation of China through grant No.49925412 and 49990450
文摘This is an overview of progresses in heliospheric physics made in China in the period of June, 2000 to May, 2002. The report is focused on theoretical studies,modelling and observational analysis of interplanetary physical phenomena, and consists of five sections: the acceleration and heating of the solar wind, corona structures, coronal mass ejections, magnetic reconnection phenomena, and in terplanetary transient phenomena. The main achievements made recently by Chinese scientists in related areas are simply listed in corresponding sections without any priority, only certain editorial consideration.
基金Supported by the National Natural Science Foundation of China (Grant No. 40874077, 40621003, 40874091, 40536029, 40523006 and 40604019)the National Basic Research Program of China ("973" Project) (Grant No. 2006CB806304)the Specialized Research Fund for State Key Laboratorie
文摘An asynchronous and parallel time-marching method for three-dimensional (3D) time-dependent magnetohydrodynamic (MHD) simulation is used for large-scale solar wind simulation. It uses different local time steps in the corona and the heliosphere according to the local Courant-Friedrichs-Levy (CFL) conditions. The solar wind background with observed solar photospheric magnetic field as input is first presented. The simulation time for the background solar wind by using the asynchronous method is <1/6 of that by using the normal synchronous time-marching method with the same computation precision. Then, we choose the coronal mass ejection (CME) event of 13 November, 2003 as a test case. The time-dependent variations of the pressure and the velocity configured from a CME model at the inner boundary are applied to generate transient structures in order to study the dynamical interaction of a CME with the background solar wind flow between 1 and 230 Rs. This time-marching method is very effective in terms of computation time for large-scale 3D time-dependent numerical MHD problem. In this validation study, we find that this 3D MHD model, with the asynchronous and parallel time-marching method, provides a relatively satisfactory comparison with the ACE spacecraft obser- vations at L1 point.
基金supported by the National Natural Science Foundation of China(Grant Nos.41031066,41231068,41274192,41074121&41074122)the National Basic Research Program of China(Grant No.2012CB825601)+1 种基金the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZZD-EW-01-4)the Specialized Research Fund for State Key Laboratories
文摘High-performance computational models are required to make the real-time or faster than rea^-time numerical prediction of adverse space weather events and their influence on the geospace environment. The main objective in this article is to explore the application of programmable graphic processing units （GPUs） to the numerical space weather modeling for the study of solar wind background that is a crucial part in the numerical space weather modeling. GPU programming is realized for our Solar-Interplanetary-CESE MHD model （SIP-CESE MHD model） by numerically studying the solar corona/interplanetary so- lar wind. The global solar wind structures are obtained by the established GPU model with the magnetic field synoptic data as input. Meanwhile, the time-dependent solar surface boundary conditions derived from the method of characteristics and the mass flux limit are incorporated to couple the observation and the three-dimensional （3D） MHD model. The simulated evolu- tion of the global structures for two Carrington rotations 2058 and 2062 is compared with solar observations and solar wind measurements t^om spacecraft near the Earth. The MHD model is also validated by comparison with the standard potential field source surface （PFSS） model. Comparisons show that the MHD results are in good overall agreement with coronal and interplanetary structures, including the size and distribution of coronal holes, the position and shape of the streamer belts, and the transition of the solar wind speeds and magnetic field polarities.
基金jointly supported by the National Natural Science Foundation of China(Grant Nos.40204010,40374056,40336053 and 49925412)973 Project(Grant No.G2000078405)One-Hundred Talent Project of CAS.
文摘During Ulysses’first rapid pole-to-pole transit from September 1994 to June 1995,its observations showed that middle-or high-speed solar winds covered all latitudes except those between?20°and+20°near the ecliptic plane,where the velocity was 300―450 km/s.At poleward 40°,however,only fast solar winds at the speed of 700―870 km/s were observed.In addition,the transitions from low-speed wind to high-speed wind or vice versa were abrupt.In this paper,the large-scale structure of solar wind observed by Ulysses near solar minimum is simulated by using the three-dimensional numerical MHD model.The model com-bines TVD Lax-Friedrich scheme and MacCormack II scheme and decomposes the calculation region into two re-gions:one from 1 to 22 Rs and the other from 18 Rs to 1 AU.Based on the observations of the solar photospheric magnetic field and an addition of the volumetric heating to MHD equations,the large-scale solar wind structure mentioned above is reproduced by using the three-dimensional MHD model and the numerical results are roughly consistent with Ulysses’observations.Our simulation shows that the initial magnetic field topology and the addition of volume heating may govern the bimodal structure of solar wind observed by Ulysses and also demonstrates that the three-dimensional MHD numerical model used here is efficient in modeling the large-scale solar wind structure.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40890162 40874078+2 种基金 40536029 and 40523006)Na-tional Basic Research Program of China (Grant No. 2006CB806304)Specialized Research Fund for State Key Laboratories and Special Fund for Public Welfare Industry (Meteorology) (Contract GYHY200806024)
文摘A 1D-HD shock propagation model is established to predict the arrival time of interplanetary shocks at 1 AU. Applying this model to 68 solar events during the period of February 1997 to October 2000, it is found that our model could be practically equivalent to the STOA, ISPM and HAFv.2 models in forecasting the shock arrival time. The absolute error in the transit time from our model is not larger than those of the other three models for the same sample events. Also, the prediction test shows that the relative error of our model is ≤10% for 31% of all events, ≤30% for 75%, and ≤50% for 84%, which is comparable to the relative errors of the other mod- els. These results might demonstrate a potential capability of our model in terms of real-time forecasting.
基金This work was jointly supported by the National Natural Science Foundation of China(Grant Nos.40374056,40336053)the One-hundred Talent Program of the Chinese Academy of Sciences and the National Key Basic Research Science Foundation(Grant No.G200078405)by the International Collaboration Research Team Program of the ChineseAcademy of Sciences.
文摘Using 80 CME-ICME events during 1997.1―2002.9,based on the eruptive source locations of CMEs and solar magnetic field observation at the photosphere,a current sheet magnetic coordinate(CMC)system is established in order to study the propagation of CME and its geoeffectiveness.In context of this coordinate system,the effect of the eruptive source location and the form of heliospheric current sheet(HCS)at the eruptive time of CME on the geomagnetic storm intensity caused by CME and the CME’s transit time at the Earth is investigated in detail.Our preliminary conclusions are:1)The geomagnetic disturbances caused by CMEs tend to have the so-called“same side-opposite side effect”,i.e.CMEs erupt from the same side of the HCS as the earth would be more likely to arrive at the earth and the geomagnetic disturbances associated with them tend to be of larger magnitude,while CMEs erupting from the opposite side would arrive at the earth with less probability and the corresponding geomagnetic disturbance magnitudes would be relatively weaker.2)The angular separation between the earth and the HCS affect the corresponding disturbance intensity.That is,when our earth is located near the HCS,adverse space weather events occur most probably.3)The erupting location of the CME and its nearby form of HCS will also affect its arrival time at the earth.According to these conclusions,in this context of CMC coordinate we arrive at new prediction method for estimating the geomagnetic storm intensity(Dstmin)caused by CMEs and their transit times.The application of the empirical model for 80 CME-ICME events shows that the relative error of Dst is within 30%for 59%events with Dstmin≤?50 nT,while the averaged absolute error of transit time is lower than 10 h for all events.
基金jointly supported by the National Natural Science Foundation of China(Grant Nos.40536029,40336053 and 40374056)the International Collaboration Research Team Program of the Chinese Academy of Sciences.
文摘Aiming at two intense shock events on October 28 and 29,2003,this paper presents a two-step method,which combines synoptic analysis of space weather——“observing”and quantitative prediction——“palpating”,and then uses it to test predictions.In the first step of“observing”,on the basis of observations of the solar source surface magnetic field,interplanetary scintillation(IPS)and ACE spacecraft,we find that the propagation of the shocks is asymmetric relative to the normal direction of their solar sources,and the Earth is located near the direction of the fastest speed and the greatest energy of the shocks.As the two fast ejection shock events,the fast explosion of coronal mass of the extremely high temperature,the strong magnetic field,and the high speed background solar wind are also helpful to their rapid propagation.In the second step of“palpating”,we adopt a new membership function of the fast shock events for the ISF method.The predicted results show that for the onset time of the geomagnetic disturbance,the relative errors between the observational and the predicted results are 1.8%and 6.7%;and for the magnetic disturbance magnitude,the relative errors are 4.1%and 3.1%,re-spectively.Furthermore,the comparison among the predicted results of our two-step method with those of five other prevailing methods shows that the two-step method is advantageous.The results tell us that understanding the physical features of shock propagation thoroughly is of great importance in improving the prediction precision.
基金supported by the National Natural Science Foundation of China (Grant Nos.40804046,40890160 and 40731054)National Basic Research Program of China (Grant No.2006CB806304)the Specialized Research Fund for State Key Laboratories
文摘Two interplanetary shocks are examined to determine the responses of the magnetic field and plasma in the plasma sheet upon the shock impacts by using TC-1 observational data.The two shocks are observed by WIND on November 7,2004.Prior to and after the shock,the IMF is either weakly southward or northward.The responses of the plasma sheet to the two shocks are intense and much similar.When the shock interacts with the magnetosphere,the magnetic field impulsively increases 1-2 min after the geomagnetic field sudden impulse (SI) judged from the Sym-H index change,and the magnetic field line is stretched.On the other hand,all of the ion density,the ion temperature,and the velocity of ion flow in the plasma sheet increase.Interestingly,quasi-periodical oscillations of the ion flow are suddenly enhanced,and the plasma flow is basically perpendicular to the local magnetic field.The responses of the magnetic field and the plasma are nearly simultaneous.The responses in the plasma sheet are probably caused by the lateral compression due to the dynamic pressure enhancement downstream the shock when the shock propagates antisunward in the magnetosheath.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40621003, 40804046, 40536029, 40674084 and 40523006)the National Basic Re-search Program of China ("973" Project) (Grant No. 4902006CB806304)+1 种基金the Spe-cialized Research Fund for State Key Laboratoriesthe Open Research Program of the State Key Laboratory of Space Weather, Chinese Academy of Sciences
文摘In this paper,we report two MC events observed by WIND spacecraft with good examples of fieldaligned residual flow inside the MC structure. For both events,the co-moving frames are determined through the deHoffman-Teller (HT) analysis and the axial orientations are inferred by the newly developed minimal residue (MR) method. The nature coordinate system for both events are constructed with velocity of the HT frame and the inferred MC axis,the field and flow remaining in the HT frame are analyzed at this coordinate system. As a result,we find that the residual flows in the co-moving HT frame of the two MC events are almost anti-parallel to the helical magnetic field. We speculate that the field-aligned residual flows are large scale coherent hydrodynamic vortices co-moving with the MCs at the supersonic speed near 1 AU. Data analyses show that the event in slow ambient solar wind is expanding at 1 AU and another one in fast solar wind does not show apparent expansion. Proton behaviors for both events are quasi-isothermal. Accelerated HT analysis shows that both events have no suitable HT frame with constant accelerations,which suggests that both events may be moving at the constant speed near 1 AU under the assumptions of the HT analysis. For both events,the ratio of the dynamic pressure to the magnetic pressure is larger than that of the thermal pressure to magnetic pressure,which suggests that the dynamic effects due to the plasma flows remaining in the co-moving HT frame are more important than the thermal effects in the study of MC evolution and propagation.
基金supported by the National Natural Science Foundation of China(Grant Nos.G200078405,40336053,40274052).
文摘Based on the WIND observational data for the plasma waves from thermal noise receptor (TNR) working on the frequency 4―256 kHz and the solar wind and the magnetic fields, we analyze the plasma wave activities in the 60 magnetic cloud’s boundary layers (BLs) and find that there are often various plasma wave activities in the BLs, which are different from those in the adjacent solar wind (SW) and the magnetic clouds (MC). The basic characteris-tics are that: (1) the enhancement of the Langmuir wave near the electronic plasma frequency (fpe) is a dominant wave ac-tivity, which occupies 75% investigated samples; (2) the events enhanced both in the langmuir and ion acustic (f < fpe) waves are about 60% of investigated samples; (3) broadband, continuous enhancement events in the plasma wave activities were observed in the whole frequency band of TNR, and about 30% of the 60 samples, however, were not observed in the SW and the MC investigated events; (4) although the ratio of the temperatures between the electon and proton, Te/Tp≤1, the ion caustic wave enhancement activities are still often observed in the BLs, which makes it difficult to ex- plain them by the traditional plasma theory. New results reported in this paper further show that the magnetic cloud’s BL is an important dynamic structure, which could provide useful diagnosis for understanding the cloud’s BL physics and could expand a space developing space plasma wave theory.
基金the National Natural Science Foundation of China(Grant Nos.40536029,40621003,40504020 and 40523006)the National Basic Research Program of China("973")(Grant No.2006CB806304)the CAS International Partnership Program for Creative Research Teams
文摘We present the solar-terrestrial transit process of three successive coronal mass ejections(CMEs)of November 4―5,1998 originating from active region 8375 by using a time-dependent three-dimensional magnetohydrodynamics(MHD)simula-tion.These CMEs interacted with each other while they were propagating in inter-planetary space and finally formed a"complex ejecta".A newly developed SIP-CESE MHD model was applied to solve MHD equations numerically.The quiet solar wind was started from Parker-like 1D solar wind solution and the magnetic field map was calculated from the solar photospheric magnetic field data.In our simulation,the ejections were initiated using pulse in the real active region 8375.The interplanetary disturbance parameters,such as speed,direction and angular size of the expanding CME,were determined from the SOHO/LASCO data with the cone-model.We discussed the three-dimensional aspects of the propagation,in-teraction and merging of the three ejections.The simulated interplanetary shocks were compared with the nearby-Earth measurement.The results showed that our simulation could reproduce and explain some of the general features observed by satellite for the"complex ejecta".
