Solar ultraviolet（UV） bursts are small-scale compact brightenings in transition region images. The spectral profiles of transition region lines in these bursts are significantly enhanced and broadened, often with ch...Solar ultraviolet（UV） bursts are small-scale compact brightenings in transition region images. The spectral profiles of transition region lines in these bursts are significantly enhanced and broadened, often with chromospheric absorption lines such as Ni ii 1335.203 and 1393.330 ? superimposed. We investigate the properties of several UV bursts using a coordinated observation of the Interface Region Imaging Spectrograph（IRIS）, Solar Dynamics Observatory（SDO）, and Hinode on February 7, 2015. We have identified 12 UV bursts, and 11 of them reveal small blueshifts of the Ni ii absorption lines. However, the Ni ii lines in one UV burst exhibit obvious redshifts of ～20 km s-1, which appear to be related to the cold plasma downflows observed in the IRIS slit-jaw images. We also examine the three-dimensional magnetic field topology using a magnetohydrostatic model, and find that some UV bursts are associated with magnetic null points or bald patches. In addition, we find that these UV bursts reveal no obvious coronal signatures from the observations of the Atmospheric Imaging Assembly（AIA） on board SDO and the EUV Imaging Spectrometer（EIS） on board Hinode.展开更多
Understanding structures and evolutions of the magnetic fields and plasma in multiple layers on the Sun is very important. A force-free magnetic field which is an accurate approximation of the solar corona due to the ...Understanding structures and evolutions of the magnetic fields and plasma in multiple layers on the Sun is very important. A force-free magnetic field which is an accurate approximation of the solar corona due to the low plasma β has been widely studied and used to model the coronal magnetic structure. While the force-freeness assumption is well satisfied in the solar corona, the lower atmosphere is not force-free given the high plasma β. Therefore, a magnetohydrostatic(MHS) equilibrium which takes into account plasma forces, such as pressure gradient and gravitational force, is considered to be more appropriate to describe the lower atmosphere. This paper reviews both analytical and numerical extrapolation methods based on the MHS assumption for calculating the magnetic fields and plasma in the solar atmosphere from measured magnetograms.展开更多
ZEUS is a magnetohydrodynamics simulation code widely used in astrophysical research.However,it was recently found that the code may produce artificial shocks in the rarefaction region in some numerical tests since it...ZEUS is a magnetohydrodynamics simulation code widely used in astrophysical research.However,it was recently found that the code may produce artificial shocks in the rarefaction region in some numerical tests since it is not upwinded in fast and slow waves.We propose a method of magnetosonic characteristics to evolve compressional waves.The tests indicate that this method cures the "rarefaction shocks" problem to a large extent and it also greatly reduces some post shock oscillations.展开更多
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA17040507)the National Natural Science Foundation of China(Grant Nos.11825301,11790304(11790300),41774183&41861134033)the Strategic Pioneer Program on Space Science of Chinese Academy of Sciences(Grant Nos.XDA15011000&XDA15010900)
文摘Solar ultraviolet（UV） bursts are small-scale compact brightenings in transition region images. The spectral profiles of transition region lines in these bursts are significantly enhanced and broadened, often with chromospheric absorption lines such as Ni ii 1335.203 and 1393.330 ? superimposed. We investigate the properties of several UV bursts using a coordinated observation of the Interface Region Imaging Spectrograph（IRIS）, Solar Dynamics Observatory（SDO）, and Hinode on February 7, 2015. We have identified 12 UV bursts, and 11 of them reveal small blueshifts of the Ni ii absorption lines. However, the Ni ii lines in one UV burst exhibit obvious redshifts of ～20 km s-1, which appear to be related to the cold plasma downflows observed in the IRIS slit-jaw images. We also examine the three-dimensional magnetic field topology using a magnetohydrostatic model, and find that some UV bursts are associated with magnetic null points or bald patches. In addition, we find that these UV bursts reveal no obvious coronal signatures from the observations of the Atmospheric Imaging Assembly（AIA） on board SDO and the EUV Imaging Spectrometer（EIS） on board Hinode.
基金the National Key R&D Program of China (Grant No. 2021YFA1600500) and mobility program (Grant No. M-0068) of the Sino-German Science Centerfinancial support by the UKs Science and Technology Facilities Council (STFC) (Grant Nos. ST/S000402/1 and ST/W001195/1) financial support by DLR-grant 50 OC 2101。
文摘Understanding structures and evolutions of the magnetic fields and plasma in multiple layers on the Sun is very important. A force-free magnetic field which is an accurate approximation of the solar corona due to the low plasma β has been widely studied and used to model the coronal magnetic structure. While the force-freeness assumption is well satisfied in the solar corona, the lower atmosphere is not force-free given the high plasma β. Therefore, a magnetohydrostatic(MHS) equilibrium which takes into account plasma forces, such as pressure gradient and gravitational force, is considered to be more appropriate to describe the lower atmosphere. This paper reviews both analytical and numerical extrapolation methods based on the MHS assumption for calculating the magnetic fields and plasma in the solar atmosphere from measured magnetograms.
基金supported by the National Basic Research Program of China(Grant No. 2011CB811406)the National Natural Science Foundation of China (Grant Nos. 10921303,10733020,10803011,40890161 and10973020)
文摘ZEUS is a magnetohydrodynamics simulation code widely used in astrophysical research.However,it was recently found that the code may produce artificial shocks in the rarefaction region in some numerical tests since it is not upwinded in fast and slow waves.We propose a method of magnetosonic characteristics to evolve compressional waves.The tests indicate that this method cures the "rarefaction shocks" problem to a large extent and it also greatly reduces some post shock oscillations.
