- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Structural properties of the solar flare-producing coronal current system developed in an emerging magnetic flux tube
摘要： The activity of a magnetic structure formed in the solar corona depends on a coronal current system developed in the structure, which determines how an electric current flows in the corona. To investigate structural properties of the coronal current system responsible for producing a solar flare, we perform magnetohydrodynamic simulation of an emerging magnetic flux tube which forms a coronal magnetic structure. Investigation using fractal dimensional analysis and electric current streamlines reveals that the flare-producing coronal current system relies on a specific coronal current structure of two-dimensional spatiality, which has a sub-region where a nearly anti-parallel magnetic field configuration is spontaneously generated. We discuss the role of this locally generated anti-parallel magnetic field configuration in causing the reconnection of a three-dimensional magnetic field, which is a possible mechanism for producing a flare. We also discuss how the twist of a magnetic flux tube affects structural properties of a coronal current system, showing how much volume current flux is carried into the corona by an emerging flux tube. This gives a way to evaluate the activity of a coronal magnetic structure.
关键词： magnetohydrodynamics (MHD),Sun: magnetic fields,Sun: corona,methods: numerical,Sun: flares
更新于2025-09-23 15:21:01
-
A new approach to the maser emission in the solar corona
摘要： Aims. The electron plasma frequency ωpe and electron gyrofrequency Ωe are two parameters that allow us to describe the properties of a plasma and to constrain the physical phenomena at play, for instance, whether a maser instability develops. In this paper, we aim to show that the maser instability can exist in the solar corona. Methods. We perform an in-depth analysis of the ωpe/Ωe ratio for simple theoretical and complex solar magnetic ?eld con?gurations. Using the combination of force-free models for the magnetic ?eld and hydrostatic models for the plasma properties, we determine the ratio of the plasma frequency to the gyrofrequency for electrons. For the sake of comparison, we compute the ratio for bipolar magnetic ?elds containing a twisted ?ux bundle, and for four di?erent observed active regions. We also study how ωpe/Ωe is a?ected by the potential and non-linear force-free ?eld models. Results. We demonstrate that the ratio of the plasma frequency to the gyrofrequency for electrons can be estimated by this novel method combining magnetic ?eld extrapolation techniques and hydrodynamic models. Even if statistically not signi?cant, values of ωpe/Ωe ≤ 1 are present in all examples, and are located in the low corona near to photosphere below one pressure scale-height and/or in the vicinity of twisted ?ux bundles. The values of ωpe/Ωe are lower for non-linear force-free ?elds than potential ?elds, thus increasing the possibility of maser instability in the corona. Conclusions. From this new approach for estimating ωpe/Ωe, we conclude that the electron maser instability can exist in the solar corona above active regions. The importance of the maser instability in coronal active regions depends on the complexity and topology of the magnetic ?eld con?gurations.
关键词： magnetohydrodynamics (MHD),masers,Sun: radio radiation,Sun: magnetic ?elds
更新于2025-09-19 17:15:36
-
Preprocessing photospheric vector magnetograms for nonlinear force-free field extrapolation of the global corona
摘要： Nonlinear force-free magnetic field (NLFFF) extrapolation based on the observed photospheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric magnetograms contain magnetic forces and small-scale noises, and fail to be consistent with the force-free assumption of NLFFF models. The procedure for removing the forces and noises in observed data is called preprocessing. In this paper, we extend the preprocessing code of Jiang & Feng to spherical coordinates for a full sphere. We first smooth the observed data with Gaussian smoothing, and then split the smoothed magnetic field into a potential field and a non-potential field. The potential part is computed by a numerical potential field model, and the non-potential part is preprocessed using an optimization method to minimize the magnetic forces and magnetic torques. Applying the code to synoptic charts of the vector magnetic field from SDO/HMI, we find it can effectively reduce the noises and forces, and improve the quality of data for a better input which will be used for NLFFF extrapolations applied to the global corona.
关键词： magnetohydrodynamics (MHD),magnetic fields,methods: numerical,Sun: corona
更新于2025-09-10 09:29:36
-
Prospective White-light Imaging and In Situ Measurements of Quiescent Large-scale Solar-wind Streams from the <i>Parker Solar Probe</i> and <i>Solar Orbiter</i>
摘要： Deep-space exploration of the inner heliosphere is in an unprecedented golden age, with the recent and forthcoming launches of the Parker Solar Probe (PSP) and Solar Orbiter (SolO) missions, respectively. In order to both predict and understand the prospective observations by PSP and SolO, we perform forward MHD modeling of the 3D inner heliosphere at solar minimum, and synthesize the white-light (WL) emission that would result from Thomson scattering of sunlight from the coronal and heliospheric plasmas. Both solar rotation and spacecraft trajectory should be considered when reconstructing quiescent large-scale solar-wind streams from PSP and SolO WL observations. When transformed from a static coordinate system into a corotating one, the elliptical orbit of PSP becomes a multiwinding spiral. The innermost spiral winding of this corotating PSP orbit takes the form of a closed “heart shape” within around 80 Re of the Sun. PSP, when traveling along this “heart-shaped” trajectory, can cross a single corotating interaction region (CIR) twice. This enables in situ measurements of the same CIR to be made in both the corona and heliosphere. As PSP approaches perihelion, the WL radiance from the corona increases. Polarization can be used to localize the main WL scattering region in the corona. Large-scale structures around PSP can be further resolved in the longitudinal dimension, using additional WL imagery from the out-of-ecliptic perspective of SolO. Coordinated observations between PSP and SolO are very promising in the quest to differentiate background CIRs from transient ejecta.
关键词： Sun: heliosphere,methods: numerical,solar wind,Sun: corona,magnetohydrodynamics (MHD)
更新于2025-09-09 09:28:46
-
Radiative transfer with POLARIS
摘要： Aims. We present POLARIS (POLArized RadIation Simulator), a newly developed three-dimensional Monte-Carlo radiative transfer code. POLARIS was designed to calculate dust temperature, polarization maps, and spectral energy distributions. It is optimized to handle data that results from sophisticated magneto-hydrodynamic simulations. The main purpose of the code is to prepare and analyze multi-wavelength continuum polarization measurements in the context of magnetic ?eld studies in the interstellar medium. An exemplary application is the investigation of the role of magnetic ?elds in star formation processes. Methods. We combine currently discussed state-of-the-art grain alignment theories with existing dust heating and polarization algorithms. We test the POLARIS code on multiple scales in complex astrophysical systems that are associated with di?erent stages of star formation. POLARIS uses the full spectrum of dust polarization mechanisms to trace the underlying magnetic ?eld morphology. Results. Resulting temperature distributions are consistent with the density and position of radiation sources resulting from magneto-hydrodynamic (MHD) – collapse simulations. The calculated layers of aligned dust grains in the considered cirumstellar disk models are in excellent agreement with theoretical predictions. Finally, we compute unique patterns in synthetic multi-wavelength polarization maps that are dependent on applied dust-model and grain-alignment theory in analytical cloud models.
关键词： magnetic ?elds,polarization,dust, extinction,radiative transfer,magnetohydrodynamics (MHD),methods: numerical
更新于2025-09-09 09:28:46