Magnetosonic waves are an important medium for energy transfer in collisionless space plasma.Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars.These waves are believed to origin...Magnetosonic waves are an important medium for energy transfer in collisionless space plasma.Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars.These waves are believed to originate from pickup ions or reflected particles.By utilizing MAVEN spacecraft data,we have observed the occurrence of quasi-perpendicularly propagating magnetosonic emissions near the proton gyrofrequency in the Martian magnetotail region.These plasma waves are associated with a significant enhancement of proton and oxygen flux.The excited magnetosonic waves could possibly heat the protons through resonance and facilitate the ionospheric plasma escape.Our results could be helpful to better understand the Mars’magnetospheric dynamics and offer insights into possible energy redistribution between waves and plasma in the Martian nightside magnetosphere.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
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 observ...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.展开更多
Throat aurora was defined based on the ground observations near local noon and has been suggested to be the ground signature of an indentation on the subsolar magnetopause.A global view of the auroral oval with throat...Throat aurora was defined based on the ground observations near local noon and has been suggested to be the ground signature of an indentation on the subsolar magnetopause.A global view of the auroral oval with throat aurora will be critical for inferring global processes at the magnetopause,but it has never been achieved.Using imaging spectrograph observations from Defense Meteorological Satellite Program satellites,for the first time,here we show typical throat auroras in a global view and reveal some important observational facts as follows.(1)The throat auroras can be as long as^8 degrees in latitudinal direction,which is hardly to be fully seen in the ground-based camera.(2)The plasma flows and field aligned currents associated with throat aurora show consistences with previous radar observations,which have been suggested to be the observational evidence of magnetopause reconnection.(3)Most importantly,we confirmed that the electron and ion precipitations associated with throat aurora are always spatially separated,i.e.,electrons in the east and ions in the west.The observational results not only establish a new picture of the aurora oval near local noon,but also provide important support to a conceptual model of throat aurora.展开更多
基金the National Natural Science Foundation of China(42030101,42204158)Shanghai Pujiang Program(No.21PJD078)+1 种基金Shanghai Science and Technology Innovation Action Plan(No.21DZ1206100)the Fundamental Research Funds for the Central Universities.
文摘Magnetosonic waves are an important medium for energy transfer in collisionless space plasma.Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars.These waves are believed to originate from pickup ions or reflected particles.By utilizing MAVEN spacecraft data,we have observed the occurrence of quasi-perpendicularly propagating magnetosonic emissions near the proton gyrofrequency in the Martian magnetotail region.These plasma waves are associated with a significant enhancement of proton and oxygen flux.The excited magnetosonic waves could possibly heat the protons through resonance and facilitate the ionospheric plasma escape.Our results could be helpful to better understand the Mars’magnetospheric dynamics and offer insights into possible energy redistribution between waves and plasma in the Martian nightside magnetosphere.
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.
基金supported by the National Key R & D Program of China (Grant No. 2018YFC1407303)the National Natural Science Foundation of China (Grant Nos. 41774174, 41704159, 41831072 & 41431072)
文摘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.
基金supported by the National Key R&D Program of China(Grant No.2018YFC1407303)the National Natural Science Foundation of China(Grant Nos.41774174,41831072,41904139)the Department of Education of Guizhou Province(Grant No.QJHKYZ[2019]064)。
文摘Throat aurora was defined based on the ground observations near local noon and has been suggested to be the ground signature of an indentation on the subsolar magnetopause.A global view of the auroral oval with throat aurora will be critical for inferring global processes at the magnetopause,but it has never been achieved.Using imaging spectrograph observations from Defense Meteorological Satellite Program satellites,for the first time,here we show typical throat auroras in a global view and reveal some important observational facts as follows.(1)The throat auroras can be as long as^8 degrees in latitudinal direction,which is hardly to be fully seen in the ground-based camera.(2)The plasma flows and field aligned currents associated with throat aurora show consistences with previous radar observations,which have been suggested to be the observational evidence of magnetopause reconnection.(3)Most importantly,we confirmed that the electron and ion precipitations associated with throat aurora are always spatially separated,i.e.,electrons in the east and ions in the west.The observational results not only establish a new picture of the aurora oval near local noon,but also provide important support to a conceptual model of throat aurora.
