Signature of high-order azimuthal MHD body modes in sunspot's low atmosphere

The five-minute oscillations inside sunspots appear to be the absorption of the solar p-mode. It is a potential tool to probe a sunspot＇s sub-structure. We studied the collective properties of five-minute oscillations in the power and phase distribution at the sunspot＇s umbra-penumbra boundary. The azimuthal distributions of the power and phase of five-minute oscillations enclosing a sunspot＇s umbra were obtained with images taken with the Solar Dynamics Observatory/Atmospheric Imaging Assembly （SDO/AIA）. The azimuthal modes were quantified with periodogram analysis and justified with significance tests. The azimuthal nodal structures in an approximately ax- ially symmetric sunspot AR 11131 （2010 Dec 08） were investigated. Mode numbers ra = 2, 3, 4, 7, 10 were obtained in both 1700 A and 1600A bandpasses. The 1600A channel also revealed an extra mode at m = 9. In the upper atmosphere （304 A）, fewer modes were detected at m = 3, 4, 7. The azimuthal modes in the sunspot＇s low atmo- sphere could be interpreted as high-order azimuthal MHD body modes. They were detected in the power and phase of the five-minute oscillations in sunspot AR 11131 with SDO/AIA data. Fewer modes were detected in the sunspot＇s upper atmosphere.

Simulating the Escaping Atmosphere of GJ 436 b with Two-fluid Magnetohydrodynamic Models

Observations of transmission spectra reveal that hot Jupiters and Neptunes are likely to possess escaping atmospheres driven by stellar radiation.Numerous models predict that magnetic fields may exert significant influences on the atmospheres of hot planets.Generally,the escaping atmospheres are not entirely ionized,and magnetic fields only directly affect the escape of ionized components within them.Considering the chemical reactions between ionized components and neutral atoms,as well as collision processes,magnetic fields indirectly impact the escape of neutral atoms,thereby influencing the detection signals of planetary atmospheres in transmission spectra.In order to simulate this process,we developed a magnetohydrodynamic multi-fluid model based on MHD code PLUTO.As an initial exploration,we investigated the impact of magnetic fields on the decoupling of H^(+)and H in the escaping atmosphere of the hot Neptune GJ436b.Due to the strong resonant interactions between H and H^(+),the coupling between them is tight even if the magnetic field is strong.Of course,alternatively,our work also suggests that merging H and H^(+)into a single flow can be a reasonable assumption in MHD simulations of escaping atmospheres.However,our simulation results indicate that under the influence of magnetic fields,there are noticeable regional differences in the decoupling of H^(+)and H.With the increase of magnetic field strength,the degree of decoupling also increases.For heavier particles such as O,the decoupling between O and H^(+)is more pronounced.Our findings provide important insights for future studies on the decoupling processes of heavy atoms in the escaping atmospheres of hot Jupiters and hot Neptunes under the influence of magnetic fields.

日冕物质抛射的理想MHD模型研究

概括了日冕物质抛射的一些观测结果和它们与其它太阳活动现象的相关性。简要回顾了较早期日冕物质抛射的理论研究，着重介绍了最近研究得较多的理论机制，即能量储存机制，以及其中的磁通量绳突变模型与其它理论模型的MHD数值和解析研究以及相应的重要应用．

耀斑瞬交流的MHD特性

本文统计研究了第20太阳周内持续时间≥1.5小时的主要耀斑所引起的1天文单位处瞬交流的MHD特性。着重比较亮耀斑与非亮耀斑产生的瞬交流及其与共转流特性上的差别。亮耀斑与非亮耀斑瞬交流的主要差别是前者的磁压力相对于热压力和动能密度的比值均明显地增高,而后者则反比背景值有所降低。亮耀斑瞬交流与共转流的主要差别是前者的前部磁马赫数较低,而后部则声马赫数较高,而共转流则始终具有低声马赫数和磁马赫数的特点。

色球和日冕的MHD加热机制

扼要地介绍了色球和日冕加热问题的研究历史。随着空间太阳观测技术的进步，人们认识到色球和日冕加热机制主要与MHD过程有关。因此，在本文中着重介绍四种MHD色球和日冕加热机制：（1）阿尔芬波；（2）MHD湍动；（3）场向电流；（4）磁重联。由于这四种加热机制的有效性都需要通过高分辨率观测来判定，所以空间太阳观测对于研究色球和日冕加热问题具有重大意义。

Studies of grand minima in sunspot cycles by using a flux transport solar dynamo model

We propose that grand minima in solar activity are caused by simultane- ous fluctuations in the meridional circulation and the Babcock-Leighton mechanism for the poloidal field generation in the flux transport dynamo model. We present the following results： （a） fluctuations in the meridional circulation are more effective in producing grand minima; （b） both sudden and gradual initiations of grand minima are possible; （c） distributions of durations and waiting times between grand minima seem to be exponential; （d） the coherence time of the meridional circulation has an effect on the number and the average duration of grand minima, with a coherence time of about 30 yr being consistent with observational data. We also study the occurrence of grand maxima and find that the distributions of durations and waiting times between grand maxima are also exponential, like the grand minima. Finally we address the question of whether the Babcock-Leighton mechanism can be operative during grand minima when there are no sunspots. We show that an a-effect restricted to the upper portions of the convection zone can pull the dynamo out of the grand minima and can match various observational requirements if the amplitude of this a-effect is suitably fine-tuned.

On the Line Formation in Stellar Magnetized Atmospheres

The line formation process in stellar magnetized atmospheres is studied by observing the wavelength- dependence of Stokes contribution functions. The influence of magnetic field on the escape line photon distribution and line absorption is obtained by comparing with the null magnetic field case. Two models airs adopted. One assumes limited distributions of both the line absorption and magnetic field where a hypothetical magneto-sensitive line is formed. The other is a model atmosphere of sunspot umbra in which MgI 5172.7 forms. It is found that the magnetic field influences the formation region of Stokes I at wavelengths sufficient close to the Zeeman splitting points ±△ H. The formation regions at wavelengths far away from the Zeeman splitting points generally show a non-magnetic behaviour. Further, if the line core is split by the Zeeman effect, the line formation core introduced in the previous paper disappears. On the other hand, Stokes Q, U, V at each wavelength within the line form in the same layers where both the line absorption and magnetic field are present in the models accepted for the lines used. When the line absorption and magnetic field ubiquitously exist, the formation regions of the T peaks or valleys of Stokes Q, U and those of σ of Stokes V generally cover the widest depth range. It is pointed out that such a study is instructive in the explanation of solar polarized filtergrams. It can tell us at each observation point where the received line photons of wavelengths within the bandpass come from and where their polarization states are formed or give us the distributions of these photons as well as their polarization intensities. Thus a three-dimensional image can be constructed for a morphologic study of the observed area from serial filtergrams.

Propagating slow sausage waves in a sunspot observed by the New Vacuum Solar Telescope

A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves,which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe the magnetic and thermal structure of a sunspot.In this study,we used the New Vacuum Solar Telescope and took highresolution image sequences simultaneously in both Ti O(7058±10?A)and Hα(6562±2.5?A)bandpasses.We extracted the area and total emission intensity variations of sunspot umbra and analyzed the signals with synchrosqueezing transform.We found that the area and emission intensity varied with both three and five minute periodicity.Moreover,the area and intensity oscillated in phase with each other,this fact hold in both Ti O and Hαdata.We interpret this oscillatory signal as a propagating slow sausage wave.The propagation speed is estimated at about 8 km s^-1.We infer that this sunspot's umbra could have temperature as low as 2800–3500 K.

Ellerman Bombs, Type Ⅱ White-light Flares and Magnetic Reconnection in the Solar Lower Atmosphere

Ellerman bombs and Type Ⅱ white-light flares share many common features despite the large energy gap between them. Both are considered to result from local heating in the solar lower atmosphere. This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere, with the aim to account for the common features of the two phenomena. Our numerical results manifest the following two typical characteristics of the assumed reconnection process: (1) magnetic reconnection saturates in -600-900 s, which is just the lifetime of the two phenomena; (2) ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection, making the heating effect most significant in the lower chromosphere. The application of the reconnection model to the two phenomena is discussed in detail.

Electric resistivity of partially ionized plasma in the lower solar atmosphere

The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma.We calculate the electric resistivity in the solar photosphere and chromosphere,which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current sheet.The calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom collisions.We find that under the typical conditions of the quiet Sun,electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere,and mostly by the ion-hydrogen collisions,i.e.ambipolar diffusion,in the chromosphere.In magnetic reconnection events with strong magnetic fields,the ambipolar diffusion,however,may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen atoms.We conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.

Spatial distributions of sunspot oscillation modes at different temperatures

Three-and five-minute sunspot oscillations have different spatial distributions in the solar atmospheric layers.The spatial distributions are crucial for revealing the physical origin of sunspot oscillations and to investigate their propagation.In this study,six sunspots observed by Solar Dynamics Observatory/Atmospheric Imaging Assembly were used to obtain the spatial distributions of three-and five-minute oscillations.The fast Fourier transform method is applied to represent the power spectra of oscillation modes.We find that,from the temperature minimum to the lower corona,the powers of the fiveminute oscillation exhibit a circle-shape distribution around its umbra,and the shapes gradually expand with temperature increase.However,the circle-shape disappears and the powers of the oscillations appear to be very disordered in the higher corona.This indicates that the five-minute oscillation can be suppressed in the high-temperature region.For the three-minute oscillations,from the temperature minimum to the high corona,their powers mostly distribute within an umbra,and part of them are located at the coronal fan loop structures.Moreover,those relative higher powers are mostly concentrated in the position of coronal loop footpoints.

The induced electric field distribution in the solar atmosphere

A method of calculating the induced electric field is presented. The induced electric field in the solar atmosphere is derived by the time variation of the magnetic field when the accumulation of charged particles is neglected. In order to derive the spatial distribution of the magnetic field, several extrapolation methods are introduced. With observational data from the Helioseismic and Magnetic Imager aboard NASA＇s Solar Dynamics Observatory taken on 2010 May 20, we extrapolate the magnetic field from the photosphere to the upper atmosphere. By calculating the time variation of the magnetic field, we can get the induced electric field. The derived induced electric field can reach a value of 102 V cm-1 and the average electric field has a maximum point at the layer 360 km above the photosphere. The Monte Carlo method is used to compute the triple integration of the induced electric field.

Modelling of the Phenomenon Known as “the Miracle of the Sun” as the Reflection of Light from Ice Crystals Oscillating Synchronously

The work includes a mathematical model of the phenomenon seen by the witnesses on 13th October, 1917 in the Cova da Iria near Fatima, and similar phenomena recorded in recent years throughout the world, known as the “miracle of the Sun”, allowing for qualitative and quantitative analysis of the phenomenon. The work includes a mathematical model of a cloud of the vibrating charged ice crystals. The paper shows the dynamic optical effects associated with the passage of light through such a vibrating medium. It also presents the simplest solution to the model in the form of graphs, which have been compared with the graphs obtained from the analysis of the amateur observations of the phenomenon in question.

Period ratios for standing kink and sausage modes in magnetized structures with siphon flow on the Sun

Standing oscillations with multiple periods have been found in a number of atmospheric struc- tures on the Sun. The ratio of the period of the fundamental to twice the one of its first overtone, P1/2192, is important in applications of solar magneto-seismology. We examine how field-aligned flows impact P1/2P2 of standing modes in solar magnetic cylinders. For coronal loops, the flow effects are significant for both fast kink and sausage modes. For kink modes, they reduce P1/2P2 by up to 17% relative to the static case even when the density contrast between the loop and its surroundings approaches infinity. For sausage modes, the reduction in P1/2P2 due to flow is typically ≤ 5.5% compared with the static case. However, the threshold aspect ratio, only above which can trapped sausage modes be supported, may increase dramatically with the flow magnitude. For photospheric tubes, the flow effect on P1/2P2 is not as strong. However, when applied to sausage modes, introducing field-aligned flows offers more possibilities in interpreting the multiple peri- ods that have recently been measured. We conclude that field-aligned flows should be taken into account to help better understand what causes the departure of P1/2P2 from unity.

Numerical simulations for MHD coronal seismology

Magnetohydrodynamic（MHD） processes are important for the transfer of energy over large scales in plasmas and so are essential to understanding most forms of dynamical activity in the solar atmosphere. The introduction of transverse structuring into models for the corona modifies the behavior of MHD waves through processes such as dispersion and mode coupling. Exploiting our understanding of MHD waves with the diagnostic tool of coronal seismology relies upon the development of sufficiently detailed models to account for all the features in observations. The development of realistic models appropriate for highly structured and dynamical plasmas is often beyond the domain of simple mathematical analysis and so numerical methods are employed. This paper reviews recent numerical results for seismology of the solar corona using MHD.

Observation of Standing Slow Magneto-acoustic Waves in a Flaring Active Region Corona Loop

Intensity fluctuations are frequently observed in different regions and structures of the solar corona.These fluctuations may be caused by magneto-hydrodynamic(MHD)waves in coronal plasma.MHD waves are prime candidates for the dynamics,energy transfer,and anomalous temperature of the solar corona.In this paper,analysis is conducted on intensity and temperature fluctuations along the active region coronal loop(NOAA AR 13599)near solar flares.The intensity and temperature as functions of time and distance along the loop are extracted using images captured by the Atmospheric Imaging Assembly(AIA)instrument onboard the Solar Dynamics Observatory(SDO)space telescope.To observe and comprehend the causes of intensity and temperature fluctuations,after conducting initial processing,and applying spatial and temporal frequency filters to data,enhanced distance-time maps of these variables are drawn.The space-time maps of intensities show standing oscillations at wavelengths of 171,193,and 211A with greater precision and clarity than earlier findings.The amplitude of these standing oscillations(waves)decreases and increases over time.The average values of the oscillation period,damping time,damping quality,projected wavelength,and projected phase speed of standing intensity oscillations are in the range of 15-18 minutes,24-31 minutes,1.46″-2″,132″-134″,and 81-100 km s^(-1),respectively.Also,the differential emission measure peak temperature values along the loop are found in the range of 0.51-3.98 MK,using six AIA passbands,including 94,131,171,193,211,and 335?.Based on the values of oscillation periods,phase speeds,damping time,and damping quality,it is inferred that the fluctuations in intensity are related to standing slow magneto-acoustic waves with weak damping.

Physics-informed Neural Network for Force-free Magnetic Field Extrapolation

In this paper,we propose a physics-informed neural network extrapolation method that leverages machine learning techniques to reconstruct coronal magnetic fields.We enhance the classical neural network structure by introducing the concept of a quasi-output layer to address the challenge of preserving physical constraints during the neural network extrapolation process.Furthermore,we employ second-order optimization methods for training the neural network,which are more efficient compared to the first-order optimization methods commonly used in classical machine learning.Our approach is evaluated on the widely recognized semi-analytical model proposed by Low and Lou.The results demonstrate that the deep learning method achieves high accuracy in reconstructing the semianalytical model across multiple evaluation metrics.In addition,we validate the effectiveness of our method on the observed magnetogram of active region.

可见到近红外波段整层大气光谱透过率的测量研究

利用太阳光谱辐射计进行了可见到近红外波段整层大气连续光谱透过率的测量研究·在对太阳辐射计可靠定标的条件下,通过测量太阳直射光谱,运用Langley方法推算到达大气层顶的太阳辐射,最终获得了该波段范围内的连续大气光谱透过率及特殊波长上的透过率的实际变化情况·通过分析晴天无云大气条件下不同时间、不同气溶胶含量、不同季节、不同气溶胶模式下的大气透过率特征,初步获得了其变化规律,为大气层外目标探测提供了一些基础·

气调贮藏对金太阳杏贮藏品质的影响

为提高金太阳杏的贮藏品质和延长其货架期,探讨不同气体组分对金太阳杏的贮藏效果,以期得出较为理想的金太阳杏气调技术参数。试验在温度为0~1℃、相对湿度为95%的条件下,设5个气调处理：2%O2、2%O2＋3%CO2、5%O2、5%O2＋3%CO2和空气（CK）。结果显示：在50 d的贮藏期内,5%O2＋3%CO2的气体组合可有效降低杏果实的腐烂率、腐烂指数和褐变度,减少杏果肉中可滴定酸度、可溶性固形物、可溶性总糖、抗坏血酸的损失,保持含水量和硬度,延缓可溶性果胶的增加,提高金太阳杏的贮藏品质。

地基消光测量确定大气气溶胶模型

分别取大陆型、海洋型、城市型和Junge谱分布气溶胶模型,用6S辐射传输算法计算出对应于太阳光度计测量时的各波段大气气溶胶光学厚度。将模式计算值与测量值进行比较,确定测量地区的大气气溶胶模型。将该方法用于2004年在北京地区测量的太阳光度计数据,结果显示该地区当日实际大气在几种气溶胶模型中较为符合城市型气溶胶模型。