Before solar eruptions,a short-term slow-rise phase is often observed,during which the pre-eruption structure ascends at speeds much greater than the photospheric motions but much less than those of the eruption phase...Before solar eruptions,a short-term slow-rise phase is often observed,during which the pre-eruption structure ascends at speeds much greater than the photospheric motions but much less than those of the eruption phase.Numerical magnetohydrodynamic (MHD) simulations of the coronal evolution driven by photospheric motions up to eruptions have been used to explain the slow-rise phase,but their bottom driving speeds are much larger than realistic photospheric values.Therefore,it remains an open question how the excessively fast bottom driving impacts the slow-rise phase.Here we modeled the slow-rise phase before eruption initiated from a continuously sheared magnetic arcade.In particular,we performed a series of experiments with the bottom driving speed unprecedentedly approaching the photospheric value of around 1 km s^(-1).The simulations confirmed that the slowrise phase is an ideal MHD process,i.e.,a manifestation of the growing expansion of the sheared arcade in the process of approaching a fully open field state.The overlying field line above the core flux has a slow-rise speed modulated by the driving speed’s magnitude but is always over an order of magnitude larger than the driving speed.The core field also expands with speed much higher than the driving speed but much lower than that of the overlying field.By incrementally reducing the bottom-driving speed to realistic photospheric values,we anticipate better matches between the simulated slow-rise speeds and some observed ones.展开更多
Recent observations have demonstrated the capability of mapping the solar coronal magnetic field using the technique of coronal seismology based on the ubiquitous propagating Alfvénic/kink waves through imaging s...Recent observations have demonstrated the capability of mapping the solar coronal magnetic field using the technique of coronal seismology based on the ubiquitous propagating Alfvénic/kink waves through imaging spectroscopy.We established a magnetohydrodynamic model of a gravitationally stratified open magnetic flux tube,exciting kink waves propagating upwards along the tube.Forward modeling was performed to synthesize the Fe XIII 1074.7 and 1079.8 nm spectral line profiles,which were then used to determine the wave phase speed,plasma density,and magnetic field with seismology method.A comparison between the seismologically inferred results and the corresponding input values verifies the reliability of the seismology method.In addition,we also identified some factors that could lead to errors during magnetic field measurements.Our results may serve as a valuable reference for current and future coronal magnetic field measurements based on observations of propagating kink waves.展开更多
The solar corona is the primary driver of the solar storms and space weather.In order to routinely monitor the coronal activities,a dedicated solar telescope is essential,a coronagraph.However,the site conditions suit...The solar corona is the primary driver of the solar storms and space weather.In order to routinely monitor the coronal activities,a dedicated solar telescope is essential,a coronagraph.However,the site conditions suitable for a ground-based coronagraph are rather critical and necessitate stringent site selection criteria.Among the numerous astronomical observatory site parameters,the sky background brightness of the day is recognized as a key parameter in evaluating the quality of a solar observatory for coronal observation before considering to install a coronagraph.To achieve optimal sky brightness observing condition,coronagraphs are usually installed on high mountains where the atmosphere is thin and the background scattered light effects from the sky are significantly reduced.Given the unique characteristics of the Tibetan Plateau,often referred to as the"Third Pole"of the Earth,a scientific assessment is crucial to evaluate its suitability as a potential location for the next-generation Chinese Giant Solar Telescope and large coronagraphs.Here,we report the first results of our measurements of the sky brightness at the Namco Lake location(30°45.0′N,90°40.0′E,4730 m above sea level,the highest large lake in the world),using a new Sky Brightness Monitor during the period 2013 August to December.The results show that the average value of the normalized(per airmass)sky brightness is as low as 13.84μI_(☉)for 530 nm.The excellent sky brightness conditions at the Namco Lake location demonstrate its high suitability for routine coronal observations.Therefore,the Namco site deserves attention for solar observations and we should continue to carry out in-depth monitoring and systematic study of multiple parameters in the future.展开更多
基金supported by the National Natural Science Foundation of China (NSFC,Grant No.42174200)Shenzhen Science and Technology Program (grant No.RCJC20210609104422048)+1 种基金Shenzhen Key Laboratory Launching Project (No.ZDSYS20210702140800001)Guangdong Basic and Applied Basic Research Foundation(2023B1515040021)。
文摘Before solar eruptions,a short-term slow-rise phase is often observed,during which the pre-eruption structure ascends at speeds much greater than the photospheric motions but much less than those of the eruption phase.Numerical magnetohydrodynamic (MHD) simulations of the coronal evolution driven by photospheric motions up to eruptions have been used to explain the slow-rise phase,but their bottom driving speeds are much larger than realistic photospheric values.Therefore,it remains an open question how the excessively fast bottom driving impacts the slow-rise phase.Here we modeled the slow-rise phase before eruption initiated from a continuously sheared magnetic arcade.In particular,we performed a series of experiments with the bottom driving speed unprecedentedly approaching the photospheric value of around 1 km s^(-1).The simulations confirmed that the slowrise phase is an ideal MHD process,i.e.,a manifestation of the growing expansion of the sheared arcade in the process of approaching a fully open field state.The overlying field line above the core flux has a slow-rise speed modulated by the driving speed’s magnitude but is always over an order of magnitude larger than the driving speed.The core field also expands with speed much higher than the driving speed but much lower than that of the overlying field.By incrementally reducing the bottom-driving speed to realistic photospheric values,we anticipate better matches between the simulated slow-rise speeds and some observed ones.
基金supported by the National Natural Science Foundation of China (NSFC,grant No.12425301)the Strategic Priority Research Program of the Chinese Academy of Sciences (grant No.XDB0560000)+6 种基金the National Key R&D Program of China No.2022YFF0503800support from the National Natural Science Foundation of China (NSFC,grant No.12203030)supported by the C1 grant TRACEspace of Internal Funds KU Leuven and a Senior Research Project (G088021N) of the FWO Vlaanderensupport from the Flemish Government under the long-term structural Methusalem funding program,project SOUL:Stellar evolution in full glory,grant METH/24/012 at KU Leuvensubsidized by the Belgian Federal Science Policy Office through the contract B2/223/P1/CLOSE-UPfunding under the Horizon Europe program of the European Union under grant agreement (No.101131534)support by an FWO (Fonds voor Wetenschappelijk Onderzoek-Vlaanderen)postdoctoral fellowship (1273221N)
文摘Recent observations have demonstrated the capability of mapping the solar coronal magnetic field using the technique of coronal seismology based on the ubiquitous propagating Alfvénic/kink waves through imaging spectroscopy.We established a magnetohydrodynamic model of a gravitationally stratified open magnetic flux tube,exciting kink waves propagating upwards along the tube.Forward modeling was performed to synthesize the Fe XIII 1074.7 and 1079.8 nm spectral line profiles,which were then used to determine the wave phase speed,plasma density,and magnetic field with seismology method.A comparison between the seismologically inferred results and the corresponding input values verifies the reliability of the seismology method.In addition,we also identified some factors that could lead to errors during magnetic field measurements.Our results may serve as a valuable reference for current and future coronal magnetic field measurements based on observations of propagating kink waves.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12373063 and 11533009)the Deanship of Scientific Research at King Saud University for funding this work through research group No.(RG-1440-092)。
文摘The solar corona is the primary driver of the solar storms and space weather.In order to routinely monitor the coronal activities,a dedicated solar telescope is essential,a coronagraph.However,the site conditions suitable for a ground-based coronagraph are rather critical and necessitate stringent site selection criteria.Among the numerous astronomical observatory site parameters,the sky background brightness of the day is recognized as a key parameter in evaluating the quality of a solar observatory for coronal observation before considering to install a coronagraph.To achieve optimal sky brightness observing condition,coronagraphs are usually installed on high mountains where the atmosphere is thin and the background scattered light effects from the sky are significantly reduced.Given the unique characteristics of the Tibetan Plateau,often referred to as the"Third Pole"of the Earth,a scientific assessment is crucial to evaluate its suitability as a potential location for the next-generation Chinese Giant Solar Telescope and large coronagraphs.Here,we report the first results of our measurements of the sky brightness at the Namco Lake location(30°45.0′N,90°40.0′E,4730 m above sea level,the highest large lake in the world),using a new Sky Brightness Monitor during the period 2013 August to December.The results show that the average value of the normalized(per airmass)sky brightness is as low as 13.84μI_(☉)for 530 nm.The excellent sky brightness conditions at the Namco Lake location demonstrate its high suitability for routine coronal observations.Therefore,the Namco site deserves attention for solar observations and we should continue to carry out in-depth monitoring and systematic study of multiple parameters in the future.
