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magnetopause properties at the dusk magnetospheric flank from global magnetohydrodynamic simulations,the kinetic Vlasov equilibrium,and in situ observations--Potential implications for SMILE

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Earth and Planetary Physics 2024年第1期8卷 222-233页

作者： Marius Echim Costel Munteanu Gabriel Voitcu Eliza Teodorescu Institute of Space Science Măgurele 077125Romania Royal Belgian Institute for Space Aeronomy 1180 BrusselsBelgium Solar-Terrestrial Centre of Excellence(STCE) 1180 BrusselsBelgium

We derived the properties of the terrestrial magnetopause(MP)from two modeling approaches,one global–fluid,the other local–kinetic,and compared the results with data collected in situ by the Magnetospheric Multiscale 2(MMS2)spacecraft.We used global magnetohydrodynamic(MHD)simulations of the Earth’s magnetosphere(publicly available from the NASA-CCMC[National Aeronautics and Space Administration–Community Coordinated Modeling Center])and local Vlasov equilibrium models(based on kinetic models for tangential discontinuities)to extract spatial profiles of the plasma and field variables at the Earth’s MP.The global MHD simulations used initial solar wind conditions extracted from the OMNI database at the time epoch when the MMS2 observes the MP.The kinetic Vlasov model used asymptotic boundary conditions derived from the same in situ MMS measurements upstream or downstream of the MP.The global MHD simulations provide a three-dimensional image of the magnetosphere at the time when the MMS2 crosses the MP.The Vlasov model provides a one-dimensional local view of the MP derived from first principles of kinetic theory.The MMS2 experimental data also serve as a reference for comparing and validating the numerical simulations and modeling.We found that the MP transition layer formed in global MHD simulations was generally localized closer to the Earth(roughly by one Earth radius)from the position of the real MP observed by the MMS.We also found that the global MHD simulations overestimated the thickness of the MP transition by one order of magnitude for three analyzed variables:magnetic field,density,and tangential speed.The MP thickness derived from the local Vlasov equilibrium was consistent with observations for all three of these variables.The overestimation of density in the Vlasov equilibrium was reduced compared with the global MHD solutions.We discuss our results in the context of future SMILE(Solar wind Magnetosphere Ionosphere Link Explorer)campaigns for observing the Earth’s MP.

关键词： magnetopause magnetohydrodynamic numerical simulations Vlasov equilibrium Magnetospheric Multiscale observations

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Using restored two-dimensional X-ray images to reconstruct the three-dimensional magnetopause

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Earth and Planetary Physics 2024年第1期8卷 133-154页

作者： RongCong Wang JiaQi Wang DaLin Li TianRan Sun XiaoDong Peng YiHong Guo National Space Science Center Chinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing100049China Aerospace Information Research Institute Chinese Academy of SciencesBeijing 100094China

Astronomical imaging technologies are basic tools for the exploration of the universe,providing basic data for the research of astronomy and space physics.The Soft X-ray Imager(SXI)carried by the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)aims to capture two-dimensional(2-D)images of the Earth’s magnetosheath by using soft X-ray imaging.However,the observed 2-D images are affected by many noise factors,destroying the contained information,which is not conducive to the subsequent reconstruction of the three-dimensional(3-D)structure of the magnetopause.The analysis of SXI-simulated observation images shows that such damage cannot be evaluated with traditional restoration models.This makes it difficult to establish the mapping relationship between SXIsimulated observation images and target images by using mathematical models.We propose an image restoration algorithm for SXIsimulated observation images that can recover large-scale structure information on the magnetosphere.The idea is to train a patch estimator by selecting noise–clean patch pairs with the same distribution through the Classification–Expectation Maximization algorithm to achieve the restoration estimation of the SXI-simulated observation image,whose mapping relationship with the target image is established by the patch estimator.The Classification–Expectation Maximization algorithm is used to select multiple patch clusters with the same distribution and then train different patch estimators so as to improve the accuracy of the estimator.Experimental results showed that our image restoration algorithm is superior to other classical image restoration algorithms in the SXI-simulated observation image restoration task,according to the peak signal-to-noise ratio and structural similarity.The restoration results of SXI-simulated observation images are used in the tangent fitting approach and the computed tomography approach toward magnetospheric reconstruction techniques,significantly improving the reconstruction results.Hence,the proposed te

关键词： Solar wind Magnetosphere Ionosphere Link Explorer(SMILE) soft X-ray imager magnetopause image restoration

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On the apparent line-of-sight alignment of the peak X-ray intensity of the magnetosheath and the tangent to the magnetopause,as viewed by SMILE-SXI

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Earth and Planetary Physics 2024年第1期8卷 155-172页

作者： Andrew Read Department of Physics&Astronomy University of LeicesterLeicesterLE17RHUK

The Soft X-ray Imager(SXI)on board the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)spacecraft will be able to view the Earth’s magnetosheath in soft X-rays.Simulated images of the X-ray emission visible from the position of SMILE are created for a range of solar wind densities by using 3 years of the SMILE mission orbit,together with models of the expected X-ray emissivity from the Earth’s magnetosheath.Results from global magnetohydrodynamic simulations and a simple model for exospheric neutral densities are used to compare the locations of the lines of sight along which integrated soft X-ray intensities peak with the lines of sight lying tangent to surfaces(defined here to be the magnetopause)along which local soft X-ray intensities peak or exhibit their strongest gradients,or both,for strongly southward interplanetary magnetic field conditions when no depletion or low-latitude boundary layers are expected.Where,in the parameter space of the various times and seasons,orbital phases,solar wind conditions,and magnetopause models,the alignment of the X-ray emission peak with the magnetopause tangent is good,or is not,is presented.The main results are as follows.The spacecraft needs to be positioned well outside the magnetopause;low-altitude times near perigee are not good.In addition,there are seasonal aspects:dayside-apogee orbits are generally very good because the spacecraft travels out sunward at high altitude,but nightside-apogee orbits,behind the Earth,are bad because the spacecraft only rarely leaves the magnetopause.Dusk-apogee and dawnapogee orbits are intermediate.Dayside-apogee orbits worsen slightly over the first three mission years,whereas nightside-apogee orbits improve slightly.Additionally,many more times of good agreement with the peak-to-tangent hypothesis occur when the solar wind is in a high-density state,as opposed to a low-density state.In a high-density state,the magnetopause is compressed,and the spacecraft is more often a good distance outside the magnetopause.

关键词： X-rays magnetosphere magnetosheath magnetopause Solar wind Magnetosphere Ionosphere Link Explorer(SMILE) Earth solar wind charge exchange

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Finding the magnetopause location using soft X-ray observations and a statistical inverse method

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Earth and Planetary Physics 2024年第1期8卷 184-203页

作者： Gonzalo Cucho-Padin Hyunju Connor Jaewoong Jung Brian Walsh David G.Sibeck Space Weather Laboratory NASA Goddard Space Flight CenterGreenbeltMDUSA Department of Physics The Catholic University of AmericaWashingtonDCUSA Geospace Physics Laboratory NASA Goddard Space Flight CenterGreenbeltMDUSA Astronomy Department University of Maryland College ParkCollege ParkMDUSA Center for Space Physics Department of Mechanical EngineeringBoston UniversityBostonMAUSA

Variability in the location and shape of the dayside magnetopause is attributed to magnetic reconnection,a fundamental process that enables the transfer of mass,energy,and momentum from the solar wind into the magnetosphere.The spatial and temporal properties of the magnetopause,under varying solar and magnetospheric conditions,remain largely unknown because empirical studies using in-situ observations are challenging to interpret.Global wide field-of-view(FOV)imaging is the only means to simultaneously observe the spatial distribution of the plasma properties over the vast dayside magnetospheric region and,subsequently,quantify the energy transport from the interplanetary medium into the terrestrial magnetosphere.Two upcoming missions,ESA/CAS SMILE and NASA’s LEXI will provide wide-field imagery of the dayside magnetosheath in soft X-rays,an emission generated by charge exchange interactions between high charge-state heavy ions of solar wind origin and exospheric neutral atoms.High-cadence two-dimensional observations of the magnetosheath will allow the estimation of dynamic properties of its inner boundary,the magnetopause,and enable studies of its response to changes in the solar wind dynamic pressure and interplanetary magnetic field orientation.This work introduces a statistically-based estimation approach based on inverse theory to estimate the spatial distribution of magnetosheath soft X-ray emissivities and,with this,identify the location of the magnetopause over the Sun−Earth line.To do so,we simulate the magnetosheath structure using the MHD-based OpenGGCM model and generate synthetic soft X-ray images using LEXI’s orbit and attitude information.Our results show that 3-D estimations using the described statistically-based technique are robust against Poisson-distributed shot noise inherent to soft X-ray images.Also,our proposed methodology shows that the accuracy of both three-dimensional(3-D)estimation and the magnetopause standoff distance calculation highly depends on the observational point.

关键词： magnetopause soft X-ray tomography

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Estimating the subsolar magnetopause position from soft X-ray images using a low-pass image filter

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Earth and Planetary Physics 2024年第1期8卷 173-183页

作者： Hyangpyo Kim Hyunju K.Connor Jaewoong Jung Brian M.Walsh David Sibeck Kip D.Kuntz Frederick S.Porter Catriana K.Paw U Rousseau A.Nutter Ramiz Qudsi Rumi Nakamura Michael Collier Space Research Institute Austrian Academy of Sciences8042 GrazAustria Geophysical Institute University of Alaska FairbanksFairbanksAlaska 99775USA National Aeronautics and Space Administration(NASA)Goddard Space Flight Center GreenbeltMaryland 20771USA Astronomy Department University of Maryland College ParkCollege ParkMaryland 20742USA Center for Space Physics Boston UniversityBostonMassachusetts 02215USA Department of Physics and Astronomy Johns Hopkins UniversityBaltimoreMaryland 21218USA Howard University WashingtonDC 20059USA

The Lunar Environment heliospheric X-ray Imager(LEXI)and Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)missions will image the Earth’s dayside magneto pause and cusps in soft X-rays after their respective launches in the near future,to specify glo bal magnetic reconnection modes for varying solar wind conditions.To suppo rt the success of these scientific missions,it is critical to develop techniques that extract the magnetopause locations from the observed soft X-ray images.In this research,we introduce a new geometric equation that calculates the subsolar magnetopause position(RS)from a satellite position,the look direction of the instrument,and the angle at which the X-ray emission is maximized.Two assumptions are used in this method:(1)The look direction where soft X-ray emissions are maximized lies tangent to the magnetopause,and(2)the magnetopause surface near the subsolar point is almost spherical and thus RSis nea rly equal to the radius of the magneto pause curvature.We create synthetic soft X-ray images by using the Open Geospace General Circulation Model(OpenGGCM)global magnetohydrodynamic model,the galactic background,the instrument point spread function,and Poisson noise.We then apply the fast Fourier transform and Gaussian low-pass filte rs to the synthetic images to re move noise and obtain accurate look angles for the soft X-ray pea ks.From the filte red images,we calculate RS and its accuracy for different LEXI locations,look directions,and solar wind densities by using the OpenGGCM subsolar magnetopause location as ground truth.Our method estimates RS with an accuracy of10 cm-3.The accuracy improves for greater solar wind densities and during southward interplanetary magnetic fields.The method ca ptures the magnetopause motion during southwa rd interplaneta ry magnetic field turnings.Consequently,the technique will enable quantitative analysis of the magnetopause motion and help reveal the dayside reconnection modes for dynamic solar wind con

关键词： soft X-ray magnetopause reconnection low-pass filter LEXI SMILE

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Simulation of the SMILE Soft X-ray Imager response to a southward interplanetary magnetic field turning

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Earth and Planetary Physics 2024年第1期8卷 39-46页

作者： Andrey Samsonov Graziella Branduardi-Raymont Steven Sembay Andrew Read David Sibeck Lutz Rastaetter Mullard Space Science Laboratory University College LondonDorking RH56NTUK Leicester University Leicester LE17RHUK Goddard Space Flight Center National Aeronautics and Space AdministrationGreenbeltMD 20771USA

The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)Soft X-ray Imager(SXI)will shine a spotlight on magnetopause dynamics during magnetic reconnection.We simulate an event with a southward interplanetary magnetic field turning and produce SXI count maps with a 5-minute integration time.By making assumptions about the magnetopause shape,we find the magnetopause standoff distance from the count maps and compare it with the one obtained directly from the magnetohydrodynamic(MHD)simulation.The root mean square deviations between the reconstructed and MHD standoff distances do not exceed 0.2 RE(Earth radius)and the maximal difference equals 0.24 RE during the 25-minute interval around the southward turning.

关键词： magnetopause magnetic reconnection solar wind charge exchange southward interplanetary magnetic field numerical modeling Solar wind Magnetosphere Ionosphere Link Explorer(SMILE) Soft X-ray Imager

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Global hybrid simulations of soft X-ray emissions in the Earth’s magnetosheath

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Earth and Planetary Physics 2024年第1期8卷 47-58页

作者： Jin Guo TianRan Sun San Lu QuanMing Lu Yu Lin XueYi Wang Chi Wang RongSheng Wang Kai Huang School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China CAS Center for Excellence in Comparative Planetology/CAS Key Lab of Geospace Environment University of Science and Technology of ChinaHefei 230026China Collaborative Innovation Center of Astronautical Science and Technology Harbin 150001China National Space Science Center Chinese Academy of SciencesBeijing 100190China Physics Department Auburn UniversityAuburnALUSA

Earth’s magnetopause is a thin boundary separating the shocked solar wind plasma from the magnetospheric plasmas,and it is also the boundary of the solar wind energy transport to the magnetosphere.Soft X-ray imaging allows investigation of the large-scale magnetopause by providing a two-dimensional(2-D)global view from a satellite.By performing 3-D global hybrid-particle-in-cell(hybrid-PIC)simulations,we obtain soft X-ray images of Earth’s magnetopause under different solar wind conditions,such as different plasma densities and directions of the southward interplanetary magnetic field.In all cases,magnetic reconnection occurs at low latitude magnetopause.The soft X-ray images observed by a hypothetical satellite are shown,with all of the following identified:the boundary of the magnetopause,the cusps,and the magnetosheath.Local X-ray emissivity in the magnetosheath is characterized by large amplitude fluctuations(up to 160%);however,the maximum line-of-sight-integrated X-ray intensity matches the tangent directions of the magnetopause well,indicating that these fluctuations have limited impact on identifying the magnetopause boundary in the X-ray images.Moreover,the magnetopause boundary can be identified using multiple viewing geometries.We also find that solar wind conditions have little effect on the magnetopause identification.The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission will provide X-ray images of the magnetopause for the first time,and our global hybrid-PIC simulation results can help better understand the 2-D X-ray images of the magnetopause from a 3-D perspective,with particle kinetic effects considered.

关键词： magnetopause X-ray emissivity X-ray imaging SMILE global hybrid-PIC simulation

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Observations of the step-like accelerating processes of cold ions in the reconnection layer at the dayside magnetopause

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Science Bulletin 2018年第1期63卷 31-37页

作者： Qinghe Zhang Michael Lockwood John C.Foster Qiugang Zong Malcolm W.Dunlop Shunrong Zhang Joran Moen Beichen Zhang Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment Institute of Space SciencesShandong UniversityWeihai 264209China Department of Meteorology University of ReadingReading RG6 6BBUK MIT Haystack Observatory WestfordMA 01886USA School of Earth and Space Sciences Peking UniversityBeijing 100087China Space Sciences Division SSTDRutherford Appleton LaboratoryDidcot OX11 OQXUK Department of Physics University of OsloBlindern 0316OsloNorway SOA Key Laboratory for Polar Science Polar Research Institute of ChinaShanghai 200136China

Cold ions of plasmaspheric origin have been observed to abundantly appear in the magnetospheric side of the Earth's magnetopause. These cold ions could affect the magnetic reconnection processes at the magnetopause by changing the Alfvén velocity and the reconnection rate, while they could also be heated in the reconnection layer during the ongoing reconnections. We report in situ observations from a partially crossing of a reconnection layer near the subsolar magnetopause. During this crossing, step-like accelerating processes of the cold ions were clearly observed, suggesting that the inflow cold ions may be separately accelerated by the rotation discontinuity and slow shock inside the reconnection layer.

关键词： Cold ions Magnetic reconnection Ion accelerations magnetopause

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Ionospheric polarization electric field guiding magnetopause reconnection: A conceptual model of throat aurora

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Science China Earth Sciences 2019年第12期62卷 2099-2105页

作者： Desheng HAN State Key Laboratory of Marine Geology School of Ocean and Earth Science Tongji University

Frequently observed throat auroras have been suggested to be correspondent to indentations on the subsolar magnetopause,but how these indentations can be generated is unknown yet.Based on analyzing the detailed observational features of throat aurora,a conceptual model for generation of throat aurora is proposed.This model suggests that precipitation of a north-south aligned stripy diffuse aurora can lead to an ionospheric conductivity enhancement and thus produce a polarization electric field in dusk-to-dawn direction in the ionosphere.After mapping to the magnetosphere along closed field lines,this electric field can guide a magnetopause reconnection to develop inward the magnetosphere and result in a throat aurora.Because this model can comprehensively explain all the observational results that have been presented up to now,we argue that the assumption of ionospheric polarization electric field affecting magnetopause reconnection should be true and be worthy of further investigations.

关键词： Throat aurora Ionospheric polarization electric field magnetopause reconnection Magnetosphere-ionosphere coupling Cusp ionosphere

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Equilibrium structure of low latitude magnetopause

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Science China Mathematics 1995年第4期38卷 481-489页

作者：于大海周国成 Center for Space Science and Applied Research Chinese Academy of Sciences Beijing 100080 China

A new magnetopause model is proposed based on observation results, in which the magnetic-field includes one constant component and one monotomcally increasing component, so that magnetic field shear exists during the intervals when the interplanetary magnetic field has a northward component. Under this model, a completely analytical self-consistent equilibrium distribution function is derived based on the Vlasov-Maxwell equations. Through the analysis of this distribution function and its moments, the following can be concluded: (i) The equilibrium distribution function consists of a homogeneous Maxwellian distribution and two inhomogeneous shifted-Maxwellian distributions. There are "hole" and "bump" structures which have different cross-field drift velocities in the velocity distribution, (ii) The density decreases monotonously from the outside of the magneto-pause to the inside, (iii) The electrical current distribution is a typical current sheet structure, (iv) Under a certain condition of

关键词： low latitude magnetopause magnetic field shear eqailibrium distribution function hole and bump structures.

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