During the total solar eclipse of July 22, 2009, we carried out a white-light observation in Anji, Zhejiang, China. The aim wasto observe the polar plumes (PPs) with high spatial and temporal resolutions in white-light. With the observational data, weinvestigate the properties and evolution of the PPs and compare them with those of the low-latitude plumes (LPs). We find thatboth the PPs and the LPs have comparable lengths and widths, and the mean length and width are 300 Mm and 16 Mm, re-spectively. The average inclination angle (13 degree) of the PPs is smaller than that (32 degree) of the LPs. Generally, theplumes which are closer to the coronal hole center are more vertical. We trace the PPs and the LPs in the sequence of imagesand find that none of them disappears and no new one is created. Additionally, neither plasma outflow nor transverse oscilla-tion is observed. These imply that the evolution process of plumes is much longer than the timescale of eclipse.
Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for 1055 active regions. We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples. Using the long-term accumulated MDI data, we build the solar flare prediction model by using a data mining method. Furthermore, the decision boundary, which is used to divide flaring from non-flaring samples, is determined by the decision tree algorithm. Finally, the performance of the prediction model is evaluated by 10-fold cross validation technology. We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method.
We analyzed the correlation of the solar magnetograms and Dopplergrams from SOHO/MDI and SDO/HMI respectively. It is found that the full disk correlation coefficient of Dopplergrams is more than 0.80 between SOHO/MDI and SDO/HMI. The full disk correlation coefficient of magnetograms is about 0.73 and is more than 0.95 for active regions only. We also analyzed the distribution of the cross helicity （velocity-magnetic-field correlation） on the solar surface. It is found that the latitude distributions of the cross helicity based on SOHO/MDI data and SDO/HMI data have similar tendencies, and in the analysis of solar active regions the amplitude of the horizontal component of the mean cross helicity is about two times the line-of-sight one.
With the aim of studying the relationship between the relative motions of the loop-top （LT） source and footpoints （FPs） during the rising phase of solar flares, we give a detailed analysis of the X7.1 class flare that occurred on 2005 January 20. The flare was clearly observed by RHESSI, showing a distinct X-ray flaring loop with a bright LT source and two well-defined hard X-ray （HXR） FPs. In particular, we correct the projection effect for the positions of the FPs and magnetic polarity inversion line. We find that： （1） The LT source showed an obvious U-shaped trajectory. The source of the higher energy LT shows a faster downward/upward speed. （2） The evolution of FPs was temporally correlated with that of the LT source. The converging/separating motion of FPs corresponds to the downward/upward motion of the LT source. （3） The initial flare shear of this event is found to be nearly 50 degrees, and it has a fluctuating decrease throughout the contraction phase as well as the expansion phase. （4） Four peaks of the time profile of the unshearing rate are found to be temporally correlated with peaks in the HXR emission flux. This flare supports the overall contraction pic- ture of flares： a descending motion of the LT source, in addition to converging and unshearing motion of FPs. All results indicate that the magnetic field was very highly sheared before the onset of the flare.
Tuan-Hui ZhouJun-Feng WangDong LiQi-Wu SongVictor MelnikovHai-Sheng Ji
Ever since the magnetohydrodynamic （MHD） method for extrapolation of the solar coronal magnetic field was first developed to study the dynamic evolution of twisted magnetic flux tubes, it has proven to be efficient in the reconstruction of the solar coronal magnetic field. A recent example is the so-called data-driven simu- lation method （DDSM）, which has been demonstrated to be valid by an application to model analytic solutions such as a force-free equilibrium given by Low and Lou. We use DDSM for the observed magnetograms to reconstruct the magnetic field above an active region. To avoid an unnecessary sensitivity to boundary conditions, we use a classical total variation diminishing Lax-Friedrichs formulation to iteratively compute the full MHD equations. In order to incorporate a magnetogram consistently and sta- bly, the bottom boundary conditions are derived from the characteristic method. In our simulation, we change the tangential fields continually from an initial potential field to the vector magnetogram. In the relaxation, the initial potential field is changed to a nonlinear magnetic field until the MHD equilibrium state is reached. Such a stable equilibrium is expected to be able to represent the solar atmosphere at a specified time. By inputting the magnetograms before and after the X3.4 flare that occurred on 2006 December 13, we find a topological change after comparing the magnetic field before and after the flare. Some discussions are given regarding the change of magnetic con- figuration and current distribution. Furthermore, we compare the reconstructed field line configuration with the coronal loop observations by XRT onboard Hinode. The comparison shows a relatively good correlation.
Using the multi-wavelength data from the Atmospheric Imaging Assembly （AIA） onboard the Solar Dynamics Observatory （SDO） spacecraft, we study a jet occurring in a coronal hole near the northern pole of the Sun. The jet presented distinct upward helical motion during ejection. By tracking six identified moving features （MFs） in the jet, we found that the plasma moved at an approximately constant speed along the jet＇s axis. Meanwhile, the MFs made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of the axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radii of the jet are 114 km s-1, 136 km s-1, 0.81° s-1, 452 s and 9.8 × 10^3 km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that at heights of 1 × 10^4 -7 × 10^4 km from the base of the jet, the flux density in the jet decreases from about 15 to 3 G as a function of B = 0.5（R/R） - 1）-0.84 （G）. A comparison was made with other results in previous studies.
In a solar flare or coronal mass ejection （CME）, observations of the subse- quent interplanetary shock provide us with strong evidence of particle acceleration to energies of multiple MeV, even up to GeV. Diffusive shock acceleration is an efficient mechanism for particle acceleration. For investigating the shock structure, the energy injection and energy spectrum ofa CME-driven shock, we perform a dynamical Monte Carlo simulation of the CME-driven shock that occurred on 2006 December 14 using an anisotropic scattering law. The simulated results of the shock＇s fine structure, par- ticle injection, and energy spectrum are presented. We find that our simulation results give a good fit to the observations from multiple spacecraft.
The growth rate of solar activity in the early phase of a solar cycle has been known to be well correlated with the subsequent amplitude （solar maximum）. It provides very useful information for a new solar cycle as its variation reflects the temporal evolution of the dynamic process of solar magnetic activities from the initial phase to the peak phase of the cycle. The correlation coefficient between the solar maximum （Rmax） and the rising rate （βa） at Am months after the solar minimum （Rmin） is studied and shown to increase as the cycle progresses with an inflection point （r = 0.83） at about Am = 20 months. The prediction error of Rmax based on βa is found within estimation at the 90% level of confidence and the relative prediction error will be less than 20% when Am ≥ 20. From the above relationship, the current cycle （24） is preliminarily predicted to peak around October, 2013 with a size of Rmax = 84 ＋ 33 at the 90% level of confidence.
