Influence of a solar active region on the interplanetary magnetic field

The interplanetary magnetic field has been mapped between 0.4 and 1.2 AU in the ecliptic plane, extrapolating from satellite measurements at 1 AU. The structure within sectors and the evolution of sectors are discussed. The development of a solar active region appears to produce magnetic loops in the interplanetary medium that result in the formation of a new sector.     

Fine structures of chromospheric magnetic field and material flow in a solar active region

In this paper, we analyze the relations between photospheric vector magnetic fields, chromospheric longitudinal magnetic fields and velocity fields in a solar active region. Agreements between the photospheric and chromospheric magnetograms can be found in large-scale structures or in the stronger magnetic structures, but differences also can be found in the fine structures or in other places, which reflect the variation of the magnetic force lines from the photosphere to the chromosphere. The chromospheric superpenumbral magnetic field, measured by the Hline, presents a spoke-like structure. It consists of thick magnetic fibrils which are different from photospheric penumbral magnetic fibrils. The outer superpenumbral magnetic field is almost horizontal. The direction of the chromospheric magnetic fibrils is generally parallel to the transverse components of the photospheric vector magnetic fields. The chromospheric material flow is coupled with the magnetic field structure. The structures of the H chromospheric magnetic fibrils in the network are similar to H dark fibrils, and the feet of the magnetic fibrils are located at the photospheric magnetic elements.     

Correlation between magnetic shear and magnetic tension in a solar active region

The difference between the magnetic tension and magnetic shear was calculated for four vector magnetograms of NOAA AR 4474. It was seen that this difference between the two independent angular measures of magnetic stress is less than 18° for more than 50% of the pixels. Magnetic tension is thus found to be fairly well correlated with magnetic shear for AR 4474.     

A statistical study on property of spatial magnetic field for solar active region

Magnetic fields dominate most solar activities, there exist direct relations between solar flare and the distributions of magnetic field, and also its corresponding magnetic energy. In this paper, the statistical results about the relationships between the spatial magnetic field and solar flare are given basing on vector magnetic field observed by the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS). The spatial magnetic fields are obtained by extrapolated photosphere vector magnetic field observed by SMFT. There are 23 active regions with flare eruption are chosen as data samples, which were observed from 1997 to 2007. The results are as follows: 1. Magnetic field lines become lower after flare for 16 (69 %) active regions; 2. The free energy are decreased after flare for 17 (74 %) active regions. It can conclude that for most active regions the changes of magnetic field after solar flare re coincident with the previous observations and studies.     

The basic cycle of solar activity and the global magnetic field and active phenomena distribution

We have compared the latitudinal distributions of polar faculae, green coronal emission maxima, prominences and of a new index of enhanced geomagnetic recurrence with the distribution of magnetic fields during the cycles Nos. 20 and 21.We did not find a distinct high-latitude initial stage of an extended cycle in the corona, prominences and polar faculae distribution. On the contrary, it seems that the polar faculae and their following polarity magnetic fields represent the last evolutionary phase of a magnetic activity cycle lasting 15–17 years. The enhanced recurrent geomagnetic activity seems to be related to the old cycle fields.All studied phenomena clearly display two types of latitudinal distribution: the polar belts, into which the old following polarity fields have been transported from the equatorial belt where both the polarities developin situ simultaneously, but in which the leading polarity fields only remain, crossing the equator during the minimum of activity, to play the same role on the opposite hemispheres in the new cycle.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

A magnetic bald-patch flare in solar active region 11117

With SDO observations and a data-constrained magnetohydrodynamics(MHD)model,we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch(BP)flare with strong evidence.From the photospheric magnetic field observed by SDO/HMI,we find there are indeed magnetic BPs on the polarity inversion lines(PILs)which match parts of the flare ribbons.From the 3D coronal magnetic field derived from an MHD relaxation model constrained by the vector magnetograms,we find strikingly good agreement of the BP separatrix surface(BPSS)footpoints with the flare ribbons,and the BPSS itself with the hot flaring loop system.Moreover,the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS,and the relevant change of coronal magnetic field through the flare is reproduced well by the pre-flare and post-flare MHD solutions,which match the corresponding pre-and post-flare AIA observations,respectively.Our work contributes to the study of non-typical flares that constitute the majority of solar flares but which cannot be explained by the standard flare model.     

On the magnetic field line topology in solar active regions

The field lines of closed magnetic structures above the photosphere define a mapping from the photosphere to itself. This mapping is discontinuous, and the field line connectivity to the boundary can change discontinuously in response to continuous changes of field strength and direction, if field lines either end in a singular point of the field or are tangential to the photosphere at one end. Whereas the general existence of singular points is questionable, the field has typically a cell structure due to the presence of segments of the zero line of the photospheric longitudinal field on which the transversal field is directed from negative (pointing into the Sun) to positive fields. The cell boundaries are made up of field lines which all touch the photosphere on one of these line segments. Within each of the cells the field line mapping is continuous. When during a slow evolution a substantial part of a coronal loop or of an arcade has passed from one cell into another a fast dynamic instability may set in which was previously prevented by the anchoring of field lines in the dense photosphere.     

Five-minute magnetic field fluctuations in the solar wind acceleration region

A spectral analysis of coronal Faraday rotation (FR) data obtained with the linearly polarized signals of the two Heliosspacecraft reveals that about one-third of the temporal FR spectra contain a distinct spectral line superposed onto the background power-law spectrum. The most prevalent frequency of this quasi-harmonic component (QHC) is about 4 mHz, corresponding to a 4–5 min periodic oscillation of the coronal magnetic field. Physical reasons for the existence of QHC Alfvén fluctuations in the inner solar wind are discussed. FR fluctuations (FRF) are considered to arise from both a turbulent background as well as an isolated Alfvén wave train of finite extent and duration. An estimate can be made for the conditions under which the isolated wave train is observed above the ever present background. It is shown that the wave train must have a sufficiently long duration and transverse wavelength. It is suggested that the QHC at periods near 4–5 min in the FRF spectra are most probably produced by outward-propagating Alfvén waves excited initially in the anisotropic structures of the chromospheric network.     

Numerical simulations of the magnetic field distribution in a solar complex of activity

Powerful solar complexes of activity are supposed to result from the excitation of Rossby vortices within a thin layer beneath the convection zone. Numerical simulations demonstrate that Rossby vortices generate large-scale arc-like magnetic structures. It is shown that the most powerful complex of activity observed in June-July 1982 was likely to be a result of the excitation of a Rossby anticyclone rather than a cyclone.     

Magnetic field configurations associated with polarity intrusion in a solar active region

The theoretical force-free magnetic fields in the first paper of this series, modeling magnetic configurations associated with polarity intrusion in active regions, are established to be all stable to linear ideal hydromagnetic perturbations under the boundary condition that anchors the lines of force rigidly to the photosphere. It is shown first that these force-free fields belong to an even larger class found by Chang and Carovillano (1981). A proof by the energy principle is then given to establish that all force-free magnetic fields in the larger class are absolutely stable. The physical implications of this result are discussed.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Magnetic field configurations associated with polarity intrusion in a solar active region

This paper presents a new class of exact solutions describing the non-linear force-free field above a spatially localized photospheric bipolar magnetic region. An essential feature is the variation in all three Cartesian directions and this could not be modelled adequately with previously known symmetric force-free fields. Sequences of force-free fields are constructed and analyzed to simulate the slow growth of a pair of spots on the photosphere. The axis connecting the spots executes rotational motion, distorting the photospheric neutral line separating fluxes of opposite signs. We show directly from the analytic solutions that the resulting reversal of the positions of the spots relative to the background field is associated with (i) the creation of magnetic free energy, (ii) the severe shearing of localized low-lying loops in the vicinity where the photospheric transverse field aligns with the photospheric neutral line, and (iii) the emergence and disappearance of flux from the photosphere at these highly stressed regions. The model relates theoretically for the first time these different magnetic field features that have been suggested by observation and theoretical considerations to be flare precursors. A general formula, based on the virial theorem, is also given for the free energy of a force-free field, strictly in terms of the field value at the photosphere. This formula has obvious practical application.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Skinning process stability of the magnetic field in the solar active regions

Skinning process stability of the magnetic field in homogeneous plasma is studied. A set of magnetohydrodynamic equations is used. Dependence of electrical conductivity on the plasma parameters and radiation intensity in grey-body approximation are taken into account. The investigation is carried out on the model problems in linear approximation and by means of numerical solution of MHD equations. Threshold of stability and critical gradient of magnetic field in skin-layer are obtained. The model of the phenomenon proposed in the paper indicates on overheating instability of plasma with electric current in large gradient magnetic field zones as a possible trigger mechanism of solar flare origin.     

Search for nonpotential features in the magnetic field of the solar active region SD 135 on 1984 June 4

Wir untersuchten die Struktur des Magnetfeldes in der relativ kleinen und einfachen solaren aktiven Region SD 135/1984 in der frühen, relativ ruhigen Phase am 24. Juni. Für diese Arbeit nutzten wir die Daten des Vektormagnetografen des SibIZMIR und Resultate von Modellrechnungen in der stromfreien Näherung. Wir haben das gemessene Magnetfeld mit dem Transversal-Feld der Modellrechnung verglichen. Wir konnten keinen signifikanten Nonpotential-Effekt größer als im Niveau der Sensitivität des Transversal-Magnetfeldes B_T 200 G finden. Wir schluß-folgern daher, daß die globale Magnetfeldstruktur in der untersuchten solaren aktiven Region nahezu eine Potentialstruktur besaß. Die Effekte der Entwicklung der aktiven Region auf die Magnetfeldstruktur scheinen vernachlässigbar zu sein.     

On the causes of the observed magnetic field imbalance in solar active regions

Based on a topological magnetic field model for active region (AR) 8086 observed on September 15–21, 1997, we calculate the evolution of the magnetic flux imbalance during its disk passage. We have established possible causes of the observed imbalance. Using model ARs produced by perfectly balanced magnetic field sources as examples, we show that even in this case, the observed imbalance can reach a significant value, depending on the AR size and location. The peculiar properties of the magnetic field imbalance in ARs predicted by the topological model must be taken into account when present-day magnetographic observations of the Sun are interpreted.     

Evolution of magnetic flux distribution of solar bipolar active regions

In this paper the magnetic flux distribution of bipolar active regions at the sunspot development stage is analyzed. It is shown that the ratio of the total sunspot area in an active region to the maximum one can be used as a characteristic of the development phase. Such a procedure allows combining the data attributed to different active regions for studying evolutionary changes. The expressions describing the evolution of magnetic flux distribution of bipolar active region were obtained and their interpretation with rise and descent of loop like magnetic flux tube leading to active region formation was justified.     

Structures of chromospheric magnetic fields in the solar flare producing active region 5747

In this paper, the formation and the measurement of the H line in chromospheric magnetic fields are discussed. The evolution of the chromospheric magnetic structures and the relation with the photospheric vector magnetic fields and chromospheric velocity fields in the flare producing active region AR 5747 are also demonstrated.The chromospheric magnetic gulfs and islands of opposite polarity relative to the photospheric field are found in the flare-producing region. This probably reflects the complication of the magnetic force lines above the photosphere in the active region. The evolution of the chromospheric magnetic structures in the active region is caused by the emergence of magnetic flux from the sub-atmosphere or the shear motion of photospheric magnetic fields. The filaments separate the opposite polarities of the chromospheric magnetic field, but only roughly those of the photospheric field. The filaments also mark the inversion lines of the chromospheric Doppler velocity field which are caused by the relative motion of the main magnetic poles of opposite polarities in the active region under discussion.     

Dynamics of line-of-sight velocities and magnetic field in the solar photosphere during the formation of the large active region NOAA 10488

Analysis of SOHO longitudinal magnetograms and Dopplergrams has revealed the appearance of a region of enhanced upflow of matter in the photosphere when the top of a loop-shaped magnetic flux tube forming a large active region passed through it. The maximum upflow velocity reached 2 km s^?1, the maximum size exceeded 20 000 km, and the lifetime was about 2 h.     

A new technique of observing the magnetic field of solar active regions

By fitting a new type of polarization detector after the entrance slit of a solar spectrograph, the two dimensional magnetic field of solar active regions can be obtained. Not only the field intensity, but also the longitudinal map is obtained quickly. The simultaneous observation of a few lines will also provide data on the structure of the magnetic tubes etc.     

Methods for deriving the magnetic field in solar (radio) active regions

In the present paper, in terms of the theory about the mechanisms of radio radiation, we have briefly classified, induced, summarized and reviewed the methods for deriving the magnetic field in the solar (radio) active regions. This revised version was published online in July 2006 with corrections to the Cover Date. This revised version was published online in July 2006 with corrections to the Cover Date.     

Predicting the evolution of photospheric magnetic field in solar active regions using deep learning

The continuous observation of the magnetic field by the Solar Dynamics Observatory(SDO)/Helioseismic and Magnetic Imager(HMI) produces numerous image sequences in time and space.These sequences provide data support for predicting the evolution of photospheric magnetic field. Based on the spatiotemporal long short-term memory(LSTM) network, we use the preprocessed data of photospheric magnetic field in active regions to build a prediction model for magnetic field evolution. Because of the elaborate learning and memory mechanism, the trained model can characterize the inherent relationships contained in spatiotemporal features. The testing results of the prediction model indicate that(1) the prediction pattern learned by the model can be applied to predict the evolution of new magnetic field in the next 6 hours that have not been trained, and predicted results are roughly consistent with real observed magnetic field evolution in terms of large-scale structure and movement speed;(2) the performance of the model is related to the prediction time; the shorter the prediction time, the higher the accuracy of the predicted results;(3) the performance of the model is stable not only for active regions in the north and south but also for data in positive and negative regions. Detailed experimental results and discussions on magnetic flux emergence and magnetic neutral lines finally show that the proposed model could effectively predict the large-scale and short-term evolution of the photospheric magnetic field in active regions. Moreover, our study may provide a reference for the spatiotemporal prediction of other solar activities.