We present a new method to measure the rotational height gradient in the solar photosphere. The method is inspired from differential interferometric techniques, we applied it to spectroscopic observations in the FeI 630.15 nm obtained at the solar telescope THEMIS which is equipped with an efficient adaptive optics system. The spectroscopic data was used to obtain images of the granulation at different line cords formed at different heights in the photosphere. Cross-correlation allows us to measure small systematic shifts between similar images. When observations are performed out of the center of the solar disk, the perspective effect gives rise to a radial shift between images formed at different heights. The measurement of this shift provides us with their formation-height difference. At the center of the disk the perspective effect vanishes but we measured a systematic retrograde shift along the east/west direction of the images formed at higher heights. The measured shifts are proportional to the formation height of the images. We interpret these findings as the evidence of a decrease of the rotational velocity with height in the low photosphere of the Sun and we give an estimate of this gradient.

This short reviewing article is intended to introduce a possibly existing relevance for three important macroscopic behaviors of solar flares. The behaviors include the contraction of flare loops (implosion), the rapid change of magnetic fields and seismic waves during flares. We show that the phenomena basically reflects a process of rapid restructuring of sheared magnetic field by a release of free magnetic energy. The contraction and rapid magnetic changes might be the direct consequences of the restructuring. Also the flattening of magnetic loops caused by the contraction in the corona will impart momentum down to the photosphere even to the solar interior. Part of the energy transported by the downward momentum can account for seismic waves. All phenomena, putting together, show that the magnetic reconnection process during the early impulsive phase is quite different from during the gradual phase and plays a dominant role in powering solar flares.

In this presentation, we will summarize the progress in the observation and instrumentation for the measurement of solar magnetic field. And furthermore, some new Chinese projects in this aspect, such as the Space Solar Telescope, Chinese Giant Solar Telescope, etc., will be introduced too.

Recent Solar Dynamic Observatory observations reveal that some coronal mass ejections (CMEs) consist of multi-temperature structures: a hot channel and a cool leading edge (LE). The channel first appears as a twisted loop and lies along the polarity inversion line; it then gradually develops into the less twisted semicircular structure during the impulsive phase of CME acceleration. In the meantime, the hot channel compresses the surrounding magnetic field and plasma, which successively stack into the CME leading front. Here, we study two well observed CMEs, which occurred on 2010 November 3 and 2011 March 8, respectively. We find that, the hot channel rises earlier than the first appearance of the CME leading front and the onset of the associated flare, and that the speed of the hot channel is always larger than that of the leading front. Further differential emission measure analysis shows that the channel often has significant emission at high temperatures. We thus conclude that the observed hot channel is likely to be magnetic flux rope that acts as a driver of the CME acceleration in the early phase.

We develop mathematical models describing plasma heating in the corona by heat fluxes from a super-hot (T \hbox{$ \stackrel{>}{_\sim}}$\mathit{T}\stackrel{\mathit{>}}{{}_{\mathrm{~}}}{\mathrm{10}}^{\mathrm{8}}$ 108 K) reconnecting current layer in solar flares. The effect of collisional relaxation is shown to be important in these conditions. Taking this effect into account, we have computed the electron-temperature distributions in the vicinity of the current layer, differential and integral emission measures of the heated plasma, the intensities of spectral lines Fe XXVI (1.78 and 1.51 Å) and Ni XXVII (1.59 Å). The theoretical results are compared with observations.

We performed 2.5D compressible resistive MHD simulations of magnetic reconnection with gravity considered. The background magnetic field is a canopy-type configuration which is rooted at the boundary of the solar supergranule. By changing the bottom boundary conditions in the simulations, an emerging flux rises up at the center of the supergranule and reconnects with the canopy magnetic field. We successfully simulate the coronal and chromospheric microflares, whose current sheets locate at the corona and chromosphere respectively. The coronal microflare is triggered by the reconnection at the corona, whose size and temperature enhancement is bigger and higher than the chromospheric one. We also found a hot jet (~1.8 × 106 K) relating to the observational EUV/SXR jet and a cold jet (~104 K) corresponding to the observational Hα/Ca surge or brightening in the coronal case. Whereas there is only Hα/Ca bright point in the chromospheric one.

We present a tomographic reconstruction of polar plumes as observed in the Extreme Ultraviolet in January 2010. Plumes are elusive structures visible in polar coronal holes that may play an important role in the acceleration of the solar wind. However, despite numerous observations, little is irrefutably known about them. Because of line of sight effects, even their geometry is subject to debate. Are they genuine cylindrical features of the corona or are they only chance alignments along the line of sight? Tomography provides a means to reconstruct the volume of an optically thin object from a set of observations taken from different vantage points. In the case of the Sun, these are typically obtained by using a solar rotation worth of images, which limits the ability to reconstruct short lived structures. We present here a tomographic inversion of the solar corona obtained using only 6 days of data. This is achieved by using simultaneously three space telescopes (EUVI/STEREO and SWAP/PROBA2) in a very specific orbital configuration. The result is the shortest possible tomographic snapshot of polar plumes. The 3D reconstruction shows both quasi-cylindrical plumes and a network pattern that can mimic them by line of sight superimpositions. This suggests that the controversy on plume geometry is due to the coexistence of both types of structures.

The Franco-Algerian Monitor of Solar Images (MISOLFA) was developped in order to study the effect of optical turbulence on diameter measurements from ground-based solar observations. Some first results obtained with MISOLFA are presented.

We introduce a new method to perform high resolution astrometry of the solar diameter from the ground, through the observations of eclipses. A discussion of the solar diameter and its variations is linked to the Limb Darkening Function (LDF) using the luminosity evolution of a Baily’s Bead and the profile of the lunar limb available from satellite data. The inflexion point of the LDF is defined as the solar limb. The method proposed is applied for the videos of the eclipse in January, 15, 2010 recorded by Richard Nugent in Uganda and Andreas Tegtmeier in India. An upper limit for the inflexion point position has been set for that eclipse.

In order to clear up the origin and possibly explain some solar limb and disc spicule quasi-periodic recurrences produced by overlapping effects, we present a simulation model assuming quasi- random positions of spicules. We also allow a set number of spicules with different physical properties (such as: height, lifetime and tilt angle as shown by an individual spicule) occurring randomly. Results of simulations made with three different spatial resolutions of the corresponding frames and also for different number density of spicules, are analyzed. The wavelet time/frequency method is used to obtain the exact period of spicule visibility. Results are compared with observations of the chromosphere from i/ the Transition Region and Coronal Explorer (TRACE) filtergrams taken at 1600 angstrom, ii/ the Solar Optical Telescope (SOT) of Hinode taken in the Ca II H-line and iii/ the Sac-Peak Dunn’s VTT taken in H? line. Our results suggest the need to be cautious when interpreting apparent oscillations seen in spicule image sequences when overlapping is present, i.e.; when the spatial resolution is not enough to resolve individual components of spicules.

Magnetic Cloud Boundary Layer (MCBL) is formed by the interaction between a magnetic cloud ejected by the Sun and the ambient solar wind, which may be linked to the outer loops of an Interplanetary Coronal Mass Ejection (ICME) and often display the properties of magnetic reconnection. We study the relation between current sheets, turbulence, and magnetic reconnection at the leading edge of an ICME intercepted by the four Cluster spacecraft in the solar wind, upstream of the Earth’s bow shock, on 2005 January 21. We obtain the observational evidence of a fully-developed magnetic turbulence in the vicinity of two current sheets at the leading edge of ICME. Each current sheet shows the signatures of magnetic reconnections with oppositely propagating Alfven waves and jets. The current density of bifurcated current sheets is computed by the curlometer technique using multi-spacecraft data.

Observations of jet- like phenomena near the solar limb are reported for a long time, first in Hα (Secchi observations of spicules in the 1870 ies), and after, from eclipse high resolution coronal images taken in white-light (1920–1973) as spiky structures. EUV jets were reported in the 70 ies from rocket and space-borne CIV filtergrams and finally X-EUV jets were reported from SXT observations of Yohkoh and from EIT and CDS SoHO observations. There is now little doubt that they are of magnetic origin although no magnetic field measurements exist for these regions and thermo-dynamical models are still work out. New observations of both spicules and jets with the SOT/SXT of Hinode were subjected to an analysis showing the influence of the null point(s) of the magnetic field. The collective behavior of the H CaII SOT(Hinode) time sequences of processed with the Madmax operator images of limb spicules show the torsional effects which were partly suggested before from the interpretation of high resolution limb spectra taken on Russian coronagraphs and the VTT at SacPeak. 100 s and shorter period waves are recorded. We propose a reconnection process occurring at the top of an emerging twisted flux tube for explaining some peculiarities of the spicular eruptions and possibly, as a viable mechanism for explaining the SXR jet eruptions. The result of a numerical 3D modeling illustrates this erupting mechanism although the behavior of the magneto-plasma structure near a null point, as shown by coronal filtergrams, does not necessary imply reconnections, especially the case of jets making a long coronal ray we observed in white-light with Lasco C2.

Magnetic flux emergence as the mechanism leading to the formation of magnetized structures in the solar atmosphere plays a key role in the dynamic of the Sun. Observed as a whole, emerging flux regions show clear signs of twisted structure, bearing the magnetic free energy necessary to power active events. The high resolution observations of the recent solar observatories (e.g. Hinode, SDO) have revealed how intermittent the magnetic field appears and how various active events induced by flux emergence are. Magnetic field reconstructions methods show that the topology of the field in interspot regions presents a serpentine structure, i.e. field lines having successive U and Ω parts. Associated with the appearance of magnetic polarities, a tremendous number of brief small scale brightening are observed in different photospheric and chromospheric lines, e.g. Ellerman Bombs, along with small scale jet-like structures. These events are believed to be the observational signatures of the multiple magnetic reconnections which enable the magnetic field to emerge further up and magnetically structure the corona above active region. Meanwhile a world-wide effort to numerically model the emergence of magnetic field forming solar active region is been carried on. Using different types of physical paradigm – e.g. idealized magnetohydrodynamic model, advanced treatment of the physical equations, data-driven simulations – these numerical experiments highlight how electric currents can build-up during flux emergence, lead to reconnection and thus explain the formation of the different observed transients.

The heating of the solar corona and the origin and acceleration of the solar wind are among the important unsolved problems of space plasma and solar physics. During the SOHO era, coronal holes as source regions of the fast solar wind have been investigated by using UV/EUV spectroscopic data observed with high-resolution spectrometers. At the base of the coronal hole, a detailed picture concerning the origin of the fast solar wind was first obtained by SUMER observations. For example, the Dopplergram deduced from the line profile of Ne VIII and other transition-region lines showed strong evidence that the wind originates in the chromospheric network and starts flowing out of the corona in magnetic funnels. Solar wind mass is suggested to be supplied through supergranule-scale magnetoconvection in the chromosphere and transition region. However, the spectral lines used in these studies are mainly obtained in the transition region and the behaviours of the nascent solar wind at higher temperatures have not yet been understood. Recent spectroscopic and imaging observations with instruments on Hinode and SDO provide further information about the coronal holes seen in EUV lines formed in the solar corona. Some interesting results, e.g., ubiquitous episodic outflow (jets) and enhanced emission in the blue wing of coronal line profiles, are found from the new observations. The purpose of this presentation is to review recent research progress on solar-wind source regions revealed by UV/EUV spectroscopic and imaging observations. Such observational studies and further interpretations of the data may provide crucial constraints and implications for future studies on both observations and theoretical models concerning coronal heating and acceleration of the nascent solar wind.

We study the evolution of the emerging and eruptive Active Region (AR) 10930 for which the coronal magnetic field is reconstructed as a nonlinear force-free field along with vector magnetograms obtained from Hinode/SOT/SP data. We show that the AR evolves quasi-statically during several days through a sequence of equilibria until the time of the eruption. In addition this sequence emphasizes the formation and expansion of a coronal Twisted Flux Rope (TFR) which is related to other observed coronal structures. On the other hand, the pre-eruptive and post-eruptive magnetic configurations show that the pre-eruptive TFR plays a crucial role during the eruption.

In this contribution, we present our recent effort in understanding the solar small-scale magnetic field. Firstly, with the unique data from MDI/SOHO in an interval embodying solar cycle 23, we find three categories of small-scale magnetic elements, and their number variations shows no correlation, anti-correlation and correlation with sunspots, respectively. The possible sources for the three categories of small-scale magnetic elements are discussed. Secondly, by the observations from SOT on board Hinode, we study the properties of vector magnetic field in quiet Sun. The following results are summarized. (1) Two categories of horizontal magnetic elements are disclosed, and most of horizontal elements are associate with the emergence of U-loop. (2) The magnetic field of quiet region is obviously non-potential. The filigrees and network bright points are characterized by strong longitudinal field, large electric helicity and free energy density. (3) For quiet region, the intra-network region displays a predominance of weak field concentration, but network region shows the coexisting of weak field with strong field; For polar region, the strong field occupies 6.7% of the region. (4) On quiet region, the magnetic field mainly resides in the inter-granular lanes. By the observation, we reconstruct an average granular model, for which the detailed distributions of vector fields, Doppler velocity and intensity are obtained.

We present the Mirror Advanced technology Coronagraph (MAC) as a new generation solar telescope to be put at suitable high altitude coronal sites in order to resolve modern problems of solar physics, like the origin of the heating of the chromosphere and of the corona, the analysis of the mesospheric layers of the solar atmosphere and the effects of shearing the photospheric magnetic fields on the dynamics of the upper coronal layers.

Coronal “EIT wave” is a large-scale wavelike phenomenon propagating across the major part of the Sun. Debates are being continued regarding a more suitable name for it, its source driver, and its nature. “EIT waves” have been widely explained in terms of fast-mode waves, despite that the model contradicts with many observational features. Two-types of EUV waves were predicted 10 years ago. With the recent high-cadence observations, mainly from SDO/AIA telescope, more and more evidence has been revealed in favor of the two-wave model. In this paper, after summarizing different names used for EIT waves in the literature, we show how the community are getting close to reaching a consensus on the nature of EIT waves.

We present results from quiet sun observations in the metric range. Solar images where obtained through rotational aperture synthesis at a number of frequencies, using the Nançay radioheliograph in its latest version, from 2004 to 2011. The main morphology is described, and compared to the magnetic field topology. We also measured on-disk spectra, of the average sun and of coronal holes, and equatorial and polar limb profiles. From these measurements, simple temperature/density atmospheric models are derived and briefly discussed.