We study the properties of the He I 10830 Å line under the bombardment of nonthermal electron beam. Using radiative hydrodynamics method, we obtain the line profiles from different model atmospheres by varying the electron beam fluxes. Below a certain electron flux, the spectra become much more absorptions as nonthemal flux increases. Above the threshold, the spectral intensities increase as the flux goes up. We also investigate the temporal evolution of the spectra under the nonthermal heating. For weak electron flux, the profiles evolve from weak absorptions to strong absorptions. For strong nonthermal heating, the profiles can be significantly changed from absorptions to emissions. The spectra also show red or blue asymmetries.

Two flares occurred simultaneously in active region NOAA 9433 on 2001 April 25. The GOES X-ray fluxes show only one peak during the two flares. The negative magnetic polarities in the two flaring regions exhibited a clockwise rotation motion around the positive polarities, which can be seen from the evolution of the SOHO/MDI magnetograms. Through analyzing the potential fields extrapolated from the MDI magnetogram, we find that there is a channel strode by a group of magnetic field lines connecting the two flaring regions.

We analyze coronagraph observations of a polar jet eruption observed by SECCHI/STEREO. The brightness distribution of the jet in white-light coronagraph images is compared with a kinetic particle model. In this first application, we consider only gravity as the dominant force on the jet particles along the magnetic field. The kinetic model explains well the observed brightness evolution. The initial particle velocity distribution is fitted by Maxwellian distributions and we find deviations of the high energy tail from the Maxwellian distributions. The jets total mass is between 3.2×1014 and 1.8×1015 g. The total kinetic energy of all the particles in the jet source region amounts from 2.1×1028 to 2.4×1029 ergs.

We surveyed 28 year of Solar X-ray flares and sunspot group records supplied by the National Geophysical Data Center (NGDC) to study the dependence of different class Xray flares on the magnetic structure of sunspot groups statistically. It is found that 82.5% X-class flare, 51.4% M-class flare, 26.3% C-class flare, and 10.1% B-class flare occurred in the sunspot group with βγδ structure. There are 6.6% X-class flares, 17.5% M-class flare, 39.1% C-class flare, and 60.4% B-class flare occurred out of sunspot group.

We test a nonlinear force-free field (NLFFF) optimization code in spherical geometry with an analytical solution from Low and Lou. The potential field source surface (PFSS) model is served as the initial and boundary conditions where observed data are not available. The analytical solution can be well recovered if the boundary and initial conditions are properly handled. Next, we discuss the preprocessing procedure for the noisy bottom boundary data, and find that preprocessing is necessary for NLFFF extrapolations when we use the observed photospheric magnetic field as bottom boundaries. Finally, we apply the NLFFF model to a solar area where four active regions interacting with each other. An M8.7 flare occurred in one active region. NLFFF modeling in spherical geometry simultaneously constructs the small and large scale magnetic field configurations better than the PFSS model does.

Solar jets are typical proxies of small-scale magnetic reconnection events in the solar atmosphere. In this paper, we observe a small-scale jet in a solar quiet region, using data from SDO/Atmospheric Imaging Assembly (AIA), Helioseismic and Magnetic Imager (HMI), with supplemental data from STEREO/EUVI. From HMI magnetograms and calculated photospheric flows, we find that the jet is related to the interaction between unipolar network fields and emerging internetwork bipoles at the boundary of a supergranular cell. In AIA extreme-ultraviolet images, the jet actually includes two successive plasma ejections along different directions. The first ejection follows a distorted path which guides plasma into a small filament channel nearby. However, the second one shot straight along another direction that is parallel with extrapolated potential magnetic field lines on the local. According to these observations, we advocate that during the jet eruption new emerging magnetic fields are reconnecting at the edge of the supergranular cell with different kinds of ambient fields from low (magnetic canopy) to high (high-reaching loops) to allow the occurrence of successive ejections along different directions.

Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with large (X- or M-class) solar flares. However, few observations have been reported about small flares. In this paper we find the observational evidence of changing photospheric vector magnetic fields associated with a B4.2-class flare obtained with the Solar Magnetic Field Telescope (SMFT) installed at Huairou Solar Observing Station (HSOS) of Nation Astronomical Observatories of Chinese Academy of Sciences.

In this paper, we study twisting motions of the penumbral filaments of active region NOAA 10930. At first, they made unwinding motions. After unwinding, the filaments are found to twist again and developed the opposite chirality in them. These observational results indicate that penumbral filaments are more inclined to be the twisted magnetic flux tubes in nature.

We study an EUV wave initiated in active region (AR) 11261 on 2011 August 4 by using the SDO/AIA and the Hinode/EIS. We found that: (1) the EUV wave interacted with AR loops between AR 11261 and AR 11263, and exited mass flows in these loops. (2) EIS observations of AR loops in AR 11263 revealed that at the time of the wave transit, the original red-shifted feature had an increase of about 3 km s−1, and the original blue-shifted feature slightly weakened. These findings could be explained in the framework of a fast-mode magnetosonic wave interpretation for EUV waves.

In this paper, the availability, applicability and deviation of nonlinear force-free (NLFF) fields extrapolated by Approximate Vertical Integration (AVI), Boundary Integral Equation (BIE) and Optimization (Opt.) methods are studied based on the comparison with two semi-analytical fields (Low & Lou 1990). These NLFF extrapolations based on the observational vector magnetograms are used to study the spatial magnetic field in the quiet Sun.

In February 2009, during recent deepest solar minimum, Polish Solar Photometer in X-rays (SphinX) begun observations of the Sun in the energy range of 1.2–15 keV. SphinX was almost 100 times more sensitive than GOES X-ray Sensors. The silicon PIN diode detectors used in the experiment were carefully calibrated on the ground using Synchrotron Radiation Source BESSY II. The SphinX energy range overlaps with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) energy range. The instrument provided us with observations of hundreds of very small flares and X-ray brightenings. We have chosen a group of solar flares observed simultaneously with GOES, SphinX and RHESSI and performed spectroscopic analysis of observations wherever possible. The analysis of thermal part of the spectra showed that SphinX is a very sensitive complementary observatory for RHESSI and GOES.

Five non-potential parameters are calculated to investigate the temporal and spatial variations of vector magnetic field in active region 11158. An area that had evident changes of the azimuth of the vector magnetic field was found. The sunspot rotation may lead to an increase of the non-potentiality. Rapid and prominent increases are found in the variations of unsigned helicity.

We present 3D zero-beta ideal MHD simulations of the solar flare/CME event that occurred in Active Region 11060 on 2010 April 8. The initial magnetic configurations of the two simulations are stable nonlinear force-free field and unstable magnetic field models constructed by Su et al. (2011) using the flux rope insertion method. The MHD simulations confirm that the stable model relaxes to a stable equilibrium, while the unstable model erupts as a CME. Comparisons between observations and MHD simulations of the CME are also presented.

A microwave quasi-periodic pulsation with zigzag pattern (Z-QPP) in a solar flare on 2005-01-15 is observed by the Chinese Solar Broadband Spectrometer in Huairou (SBRS/Huairou) at 1.10-1.34 GHz. The zigzag pulsation occurred just in the early rising phase of the flare with weakly right-handed circular polarization. Its period is only several decades millisecond. Particularly, before and after the pulsation, there are many spectral fine structures, such as zebra patterns, fibers, and millisecond spikes. The microwave Z-QPP can provide some kinematic information of the source region in the early rising phase of the flare, and the source width changes from ~1000 km to 3300 km, even if we have no imaging observations. The abundant spectral fine structures possibly reflect the dynamic features of non-thermal particles.

A GPU-based acceleration for the direct boundary integral equation method (GPU-DBIE) to extrapolate solar coronal magnetic fields is developed, which is about 1000 times faster than the original DBIE. The 3-d coronal magnetic field is reconstructed for NOAA 11158 on 14-Feb-2011 with the SDO/HMI vector magnetogram as bottom boundary condition. The extrapolated results agree well with the projected SDO/AIA, EUV loops and the STEREO EUV sideviews, which verifies the correctness of our GPU-DBIE method. It is also found that the group of bright EUV loops along magnetic neutral lines agree well with current lines, which may have played an important role in the flare process of the active region.

In this paper, we focus to study the frequency and time properties of a group of spikes recorded by the 1.08-2.04 GHz spectrometer of NAOC on 27 October 2003. At the first we calculate the mean and minimum bandwidth of the spikes. We apply two different methods based on the wavelet analysis according to Messmer & Benz (2000). The first method determines the dominant spike bandwidth scale based on their scalegram, and the second method is a feature detection algorithm in the time-frequency plane. Secondly the time profile of each single spike was fitted and analyzed. In particular, we determined the e-folding rise and decay times corresponding to the ascending and decaying parts of the time profile, respectively. Several important correlations were studied and compared with the results in earlier literature, i.e. those between duration and frequency, e-folding rise time and decay time, e-folding decay time and duration, and e-folding decay time and peak flux. Finally some parameters of source region were estimated and the possible decaying mechanism was discussed.

Observations of the interplanetary shock provide us with strong evidences of particle acceleration to multi-MeV protons in a coronal mass ejection (CME). Diffusive shock acceleration (DSA) is an efficient mechanism for cosmic ray (CR). This work presents a dynamical Monte Carlo simulation of a CME-driven shock on 14-Dec-2006 by using a series of Gaussian scattering angular distributions. With the simulated results, we find that particle energy spectrum is affected by energy injection processes under the anisotropic scattering law.

We study the correlation between the speed of two-ribbon separation and the magnetic flux density during the 2001 April 10 solar flare. A weak negative correlation is found between the ribbon separation speed (Vr) and the longitudinal magnetic flux density (Bz). In addition, we estimate the magnetic reconnection rate (Erec). Along the flare ribbons, Erec fluctuates in the small range except near the HXR source. The localized enhancement of the reconnection rate corresponds to the position of the HXR source.

Using photospheric data obtained by vector magnetograph in Huairou Solar Observing Station of China, we have statistically studied the strength evolution of several magnetic nonpotentiality measures, along with a quantified parameter characterizing the active-region magnetic complexity – effective distance, and their relationship with associated flares during the latest 22nd and 23rd solar cycles. And the flare-prediction performance of these magnetic nonpotentiality and complexity parameters is verified by a machine learning technique.

We investigated the variations of 74 microwave ZP structures observed by Chinese Solar Broadband Radio Spectrometer at 2.6–3.8 GHz in 9 solar flares, found that the ratio between the plasma density scale height LN and the magnetic field scale height LB in emission source displays a tendency of decrease during the flaring process, indicates that LB increases faster than the LN during solar flares. The detailed analysis of the step-wise decrease of LN/LB in three typical X-class flares reveals the magnetic field relaxation relative to the plasma density.