The recently deployed Transition Region Explorer(TREx)-RGB(red-green-blue)all-sky imager(ASI)is designed to capture“true color”images of the aurora and airglow.Because the 557.7 nm green line is usually the brightes...The recently deployed Transition Region Explorer(TREx)-RGB(red-green-blue)all-sky imager(ASI)is designed to capture“true color”images of the aurora and airglow.Because the 557.7 nm green line is usually the brightest emission line in visible auroras,the green channel of a TREx-RGB camera is usually dominated by the 557.7 nm emission.Under this rationale,the TREx mission does not include a specific 557.7 nm imager and is designed to use the RGB green-channel data as a proxy for the 557.7 nm aurora.In this study,we present an initial effort to establish the conversion ratio or formula linking the RGB green-channel data to the absolute intensity of 557.7 nm auroras,which is crucial for quantitative uses of the RGB data.We illustrate two approaches:(1)through a comparison with the collocated measurement of green-line auroras from the TREx spectrograph,and(2)through a comparison with the modeled green-line intensity according to realistic electron precipitation flux measurements from low-Earth-orbit satellites,with the aid of an auroral transport model.We demonstrate the procedures and provide initial results for the TREx-RGB ASIs at the Rabbit Lake and Lucky Lake stations.The RGB response is found to be nonlinear.Empirical conversion ratios or formulas between RGB green-channel data and the green-line auroral intensity are given and can be applied immediately by TREx-RGB data users.The methodology established in this study will also be applicable to the upcoming SMILE ASI mission,which will adopt a similar RGB camera system in its deployment.展开更多
Global images of auroras obtained by cameras on spacecraft are a key tool for studying the near-Earth environment.However,the cameras are sensitive not only to auroral emissions produced by precipitating particles,but...Global images of auroras obtained by cameras on spacecraft are a key tool for studying the near-Earth environment.However,the cameras are sensitive not only to auroral emissions produced by precipitating particles,but also to dayglow emissions produced by photoelectrons induced by sunlight.Nightglow emissions and scattered sunlight can contribute to the background signal.To fully utilize such images in space science,background contamination must be removed to isolate the auroral signal.Here we outline a data-driven approach to modeling the background intensity in multiple images by formulating linear inverse problems based on B-splines and spherical harmonics.The approach is robust,flexible,and iteratively deselects outliers,such as auroral emissions.The final model is smooth across the terminator and accounts for slow temporal variations and large-scale asymmetries in the dayglow.We demonstrate the model by using the three far ultraviolet cameras on the Imager for Magnetopause-to-Aurora Global Exploration(IMAGE)mission.The method can be applied to historical missions and is relevant for upcoming missions,such as the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission.展开更多
The dune aurora,at a scale of~30 kilometers,was reported recently using ground camera.The small-scale dune aurora occurs on the duskside and exhibits a monochromatic oscillation in the auroral emission,implying fundam...The dune aurora,at a scale of~30 kilometers,was reported recently using ground camera.The small-scale dune aurora occurs on the duskside and exhibits a monochromatic oscillation in the auroral emission,implying fundamental energy conversions.However,whether the dune auroras correspond to atmospheric waves or are associated with magnetospheric dynamics should be determined.This paper reports a dune aurora that occurred during a storm;further,we demonstrate that it was the substructure of the sawtooth aurora that was generated by plasmapause surface waves.Conjugate observations in the magnetospheric source region suggest that the exohiss waves,which are periodically modulated by the plasmapause surface wave-excited ultralow frequency wave,might be responsible for the generation of the dune aurora.Most reported dune aurora events have occurred simultaneously with sawtooth auroras,suggesting that both are plasmapause-driven cross-scale auroral structures.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
What mechanism causes the symmetrical distribution of two oval-ring auroras approximately around the geomagnetic poles but uneven brightness distribution of them? To answer this question, we firstly describe the charg...What mechanism causes the symmetrical distribution of two oval-ring auroras approximately around the geomagnetic poles but uneven brightness distribution of them? To answer this question, we firstly describe the charged particles like electrons or protons emitted from the Sun and the magnetic ions formed in the Earth’s atmosphere. Then, the interaction dynamics of two-type particles between electron and ion is given under the non-relativistic limit. Finally, under the relativistic frame, auroras deduced are higher energy density formed by the orthogonal interaction of solar charged particles and geomagnetic ions in the narrow regions centered on the upper geomagnetic poles. The physical nature of ideal oval-ring auroras with uneven brightness distribution is an optical phenomenon that occurs when solar charged particles collide orthogonally with ions and the magnetic axis inclines to the solar radiation. For actual aurora distribution, the impact of multiple factors is discussed. Therefore, the aurora is a natural illustration of an orthogonal collider in the Earth’s upper atmosphere.展开更多
基金jointly funded by the Canada Foundation for Innovationthe Alberta Economic Development and Trade organization+1 种基金the University of Calgarysupported by the Canadian Space Agency。
文摘The recently deployed Transition Region Explorer(TREx)-RGB(red-green-blue)all-sky imager(ASI)is designed to capture“true color”images of the aurora and airglow.Because the 557.7 nm green line is usually the brightest emission line in visible auroras,the green channel of a TREx-RGB camera is usually dominated by the 557.7 nm emission.Under this rationale,the TREx mission does not include a specific 557.7 nm imager and is designed to use the RGB green-channel data as a proxy for the 557.7 nm aurora.In this study,we present an initial effort to establish the conversion ratio or formula linking the RGB green-channel data to the absolute intensity of 557.7 nm auroras,which is crucial for quantitative uses of the RGB data.We illustrate two approaches:(1)through a comparison with the collocated measurement of green-line auroras from the TREx spectrograph,and(2)through a comparison with the modeled green-line intensity according to realistic electron precipitation flux measurements from low-Earth-orbit satellites,with the aid of an auroral transport model.We demonstrate the procedures and provide initial results for the TREx-RGB ASIs at the Rabbit Lake and Lucky Lake stations.The RGB response is found to be nonlinear.Empirical conversion ratios or formulas between RGB green-channel data and the green-line auroral intensity are given and can be applied immediately by TREx-RGB data users.The methodology established in this study will also be applicable to the upcoming SMILE ASI mission,which will adopt a similar RGB camera system in its deployment.
基金supported by the Research Council of Norway under contracts 223252/F50 and 300844/F50the Trond Mohn Foundation。
文摘Global images of auroras obtained by cameras on spacecraft are a key tool for studying the near-Earth environment.However,the cameras are sensitive not only to auroral emissions produced by precipitating particles,but also to dayglow emissions produced by photoelectrons induced by sunlight.Nightglow emissions and scattered sunlight can contribute to the background signal.To fully utilize such images in space science,background contamination must be removed to isolate the auroral signal.Here we outline a data-driven approach to modeling the background intensity in multiple images by formulating linear inverse problems based on B-splines and spherical harmonics.The approach is robust,flexible,and iteratively deselects outliers,such as auroral emissions.The final model is smooth across the terminator and accounts for slow temporal variations and large-scale asymmetries in the dayglow.We demonstrate the model by using the three far ultraviolet cameras on the Imager for Magnetopause-to-Aurora Global Exploration(IMAGE)mission.The method can be applied to historical missions and is relevant for upcoming missions,such as the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission.
基金supported by the National Natural Science Foundation of China(42222408,41931073)supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Y2021027)supported by the Key Research Program of the Institute of Geology&Geophysics,Chinese Academy of Sciences(grant IGGCAS-201904).
文摘The dune aurora,at a scale of~30 kilometers,was reported recently using ground camera.The small-scale dune aurora occurs on the duskside and exhibits a monochromatic oscillation in the auroral emission,implying fundamental energy conversions.However,whether the dune auroras correspond to atmospheric waves or are associated with magnetospheric dynamics should be determined.This paper reports a dune aurora that occurred during a storm;further,we demonstrate that it was the substructure of the sawtooth aurora that was generated by plasmapause surface waves.Conjugate observations in the magnetospheric source region suggest that the exohiss waves,which are periodically modulated by the plasmapause surface wave-excited ultralow frequency wave,might be responsible for the generation of the dune aurora.Most reported dune aurora events have occurred simultaneously with sawtooth auroras,suggesting that both are plasmapause-driven cross-scale auroral structures.
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.
文摘What mechanism causes the symmetrical distribution of two oval-ring auroras approximately around the geomagnetic poles but uneven brightness distribution of them? To answer this question, we firstly describe the charged particles like electrons or protons emitted from the Sun and the magnetic ions formed in the Earth’s atmosphere. Then, the interaction dynamics of two-type particles between electron and ion is given under the non-relativistic limit. Finally, under the relativistic frame, auroras deduced are higher energy density formed by the orthogonal interaction of solar charged particles and geomagnetic ions in the narrow regions centered on the upper geomagnetic poles. The physical nature of ideal oval-ring auroras with uneven brightness distribution is an optical phenomenon that occurs when solar charged particles collide orthogonally with ions and the magnetic axis inclines to the solar radiation. For actual aurora distribution, the impact of multiple factors is discussed. Therefore, the aurora is a natural illustration of an orthogonal collider in the Earth’s upper atmosphere.
