Solar wind charge exchange produces emissions in the soft X-ray energy range which can enable the study of near-Earth space regions such as the magnetopause,the magnetosheath and the polar cusps by remote sensing tech...Solar wind charge exchange produces emissions in the soft X-ray energy range which can enable the study of near-Earth space regions such as the magnetopause,the magnetosheath and the polar cusps by remote sensing techniques.The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)and Lunar Environment heliospheric X-ray Imager(LEXI)missions aim to obtain soft Xray images of near-Earth space thanks to their Soft X-ray Imager(SXI)instruments.While earlier modeling works have already simulated soft X-ray images as might be obtained by SMILE SXI during its mission,the numerical models used so far are all based on the magnetohydrodynamics description of the space plasma.To investigate the possible signatures of ion-kinetic-scale processes in soft Xray images,we use for the first time a global hybrid-Vlasov simulation of the geospace from the Vlasiator model.The simulation is driven by fast and tenuous solar wind conditions and purely southward interplanetary magnetic field.We first produce global X-ray images of the dayside near-Earth space by placing a virtual imaging satellite at two different locations,providing meridional and equatorial views.We then analyze regional features present in the images and show that they correspond to signatures in soft X-ray emissions of mirrormode wave structures in the magnetosheath and flux transfer events(FTEs)at the magnetopause.Our results suggest that,although the time scales associated with the motion of those transient phenomena will likely be significantly smaller than the integration time of the SMILE and LEXI imagers,mirror-mode structures and FTEs can cumulatively produce detectable signatures in the soft X-ray images.For instance,a local increase by 30%in the proton density at the dayside magnetopause resulting from the transit of multiple FTEs leads to a 12%enhancement in the line-of-sight-and time-integrated soft X-ray emissivity originating from this region.Likewise,a proton density increase by 14%in the magnetosheath associated with mirror-mode structures can resu展开更多
The energy transfer between ions （protons） and low frequency waves （LFWs） in the frequency range f1 from 0.3 to 10 Hz is observed by Cluster crossing the high-altitude polar cusp. The energy transfer between low f...The energy transfer between ions （protons） and low frequency waves （LFWs） in the frequency range f1 from 0.3 to 10 Hz is observed by Cluster crossing the high-altitude polar cusp. The energy transfer between low frequency waves and ions has two means. One is that the energy is transferred from low frequency waves to ions and ions energy increases, The other is that the energy is transferred from ions to low frequency waves and the ion energy decreases. lon gyratory motion plays an important role in the energy transfer processes. The electromagnetic field of f1 LFWs can accelerate or decelerate protons along the direction of ambient magnetic field and warm or refrigerate protons in the parallel and perpendicular directions of ambient magnetic field, The peak values of proton number densities have the corresponding peak values of electromagnetic energy of low-frequency waves. This implies that the kinetic Alfven waves and solitary kinetic Alfven waves possibly exist in the high-altitude cusp region.展开更多
Cusp spot,High Latitude Dayside aurora(HiLDA),‘space hurricane’,and 15MLT-PCA(Polar Cap Arc observed around 15:00 Magnetic Local Time)are mesoscale auroral structures observed in the polar cap region.They share many...Cusp spot,High Latitude Dayside aurora(HiLDA),‘space hurricane’,and 15MLT-PCA(Polar Cap Arc observed around 15:00 Magnetic Local Time)are mesoscale auroral structures observed in the polar cap region.They share many common properties and,at the same time,have notable differences.A 15MLT-PCA is a polar cap arc connected to the auroral oval,but the others are auroral spots detached from the oval.A cusp spot differs from a HiLDA in local time location.A space hurricane differs from a HiLDA in having spiral-arm structures.Until now,relationships among these auroras have not been depicted clearly.Here we propose a unified model,based on lobe reconnection,that encompasses their similarities and differences.We then provide critical supporting evidence for the model.The model suggests that different reconnection sites under different IMF conditions result in these differently-appearing auroral forms.The model explains all the characteristic features of these auroras and has implications for understanding the dawn/dusk and inter-hemispheric asymmetries observed in their occurrence patterns.We anticipate confirmation of the model by observations to be made during the Solar wind-Magnetosphere-Ionosphere Link Explorer(SMILE)mission.Moreover,since the model indicates that these auroras appear on the footprint of the poleward cusp boundary,we expect data from the SMILE mission to make it possible to estimate the approximate shape of the cusp.展开更多
基金the European Research Council for starting grant 200141-QuESpace,with which the Vlasiator model was developedconsolidator grant 682068-PRESTISSIMO awarded for further development of Vlasiator and its use in scientific investigations+4 种基金Academy of Finland grant numbers 338629-AERGELC’H,339756-KIMCHI,336805-FORESAIL,and 335554-ICT-SUNVACThe Academy of Finland also supported this work through the PROFI4 grant(grant number 3189131)support from the NASA grants,80NSSC20K1670 and 80MSFC20C0019the NASA GSFC FY23 IRADHIF funds。
文摘Solar wind charge exchange produces emissions in the soft X-ray energy range which can enable the study of near-Earth space regions such as the magnetopause,the magnetosheath and the polar cusps by remote sensing techniques.The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)and Lunar Environment heliospheric X-ray Imager(LEXI)missions aim to obtain soft Xray images of near-Earth space thanks to their Soft X-ray Imager(SXI)instruments.While earlier modeling works have already simulated soft X-ray images as might be obtained by SMILE SXI during its mission,the numerical models used so far are all based on the magnetohydrodynamics description of the space plasma.To investigate the possible signatures of ion-kinetic-scale processes in soft Xray images,we use for the first time a global hybrid-Vlasov simulation of the geospace from the Vlasiator model.The simulation is driven by fast and tenuous solar wind conditions and purely southward interplanetary magnetic field.We first produce global X-ray images of the dayside near-Earth space by placing a virtual imaging satellite at two different locations,providing meridional and equatorial views.We then analyze regional features present in the images and show that they correspond to signatures in soft X-ray emissions of mirrormode wave structures in the magnetosheath and flux transfer events(FTEs)at the magnetopause.Our results suggest that,although the time scales associated with the motion of those transient phenomena will likely be significantly smaller than the integration time of the SMILE and LEXI imagers,mirror-mode structures and FTEs can cumulatively produce detectable signatures in the soft X-ray images.For instance,a local increase by 30%in the proton density at the dayside magnetopause resulting from the transit of multiple FTEs leads to a 12%enhancement in the line-of-sight-and time-integrated soft X-ray emissivity originating from this region.Likewise,a proton density increase by 14%in the magnetosheath associated with mirror-mode structures can resu
基金Supported by the National Natural Science Foundation of China under Grant No 40390150, and the Postdoctoral Science Foundation of High Education of China.
文摘The energy transfer between ions （protons） and low frequency waves （LFWs） in the frequency range f1 from 0.3 to 10 Hz is observed by Cluster crossing the high-altitude polar cusp. The energy transfer between low frequency waves and ions has two means. One is that the energy is transferred from low frequency waves to ions and ions energy increases, The other is that the energy is transferred from ions to low frequency waves and the ion energy decreases. lon gyratory motion plays an important role in the energy transfer processes. The electromagnetic field of f1 LFWs can accelerate or decelerate protons along the direction of ambient magnetic field and warm or refrigerate protons in the parallel and perpendicular directions of ambient magnetic field, The peak values of proton number densities have the corresponding peak values of electromagnetic energy of low-frequency waves. This implies that the kinetic Alfven waves and solitary kinetic Alfven waves possibly exist in the high-altitude cusp region.
基金the National Natural Science Foundation of China(42030101,41974185,41774174)the Shanghai Science and Technology Innovation Action Plan(No.21DZ1206102).
文摘Cusp spot,High Latitude Dayside aurora(HiLDA),‘space hurricane’,and 15MLT-PCA(Polar Cap Arc observed around 15:00 Magnetic Local Time)are mesoscale auroral structures observed in the polar cap region.They share many common properties and,at the same time,have notable differences.A 15MLT-PCA is a polar cap arc connected to the auroral oval,but the others are auroral spots detached from the oval.A cusp spot differs from a HiLDA in local time location.A space hurricane differs from a HiLDA in having spiral-arm structures.Until now,relationships among these auroras have not been depicted clearly.Here we propose a unified model,based on lobe reconnection,that encompasses their similarities and differences.We then provide critical supporting evidence for the model.The model suggests that different reconnection sites under different IMF conditions result in these differently-appearing auroral forms.The model explains all the characteristic features of these auroras and has implications for understanding the dawn/dusk and inter-hemispheric asymmetries observed in their occurrence patterns.We anticipate confirmation of the model by observations to be made during the Solar wind-Magnetosphere-Ionosphere Link Explorer(SMILE)mission.Moreover,since the model indicates that these auroras appear on the footprint of the poleward cusp boundary,we expect data from the SMILE mission to make it possible to estimate the approximate shape of the cusp.
