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Early observations by the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory indicated that propagating diffuse wave fronts, now conventionally referred to as ''EIT waves,'' can often be seen on the solar disk with a propagation velocity several times smaller than that of H Moreton waves. They are almost always associated with coronal mass ejections. We have previously confirmed the existence of such a wave phenomenon with numerical simulations, which indicate that there does exist a slower moving ''wave'' much behind the coronal counterpart of the H Moreton wave. Further observations have disclosed many new features of the EIT waves: the waves stop near the separatrix between active regions, sometimes they experience acceleration from the active region to the quiet region, and so on. Here we report on MHD simulations performed to demonstrate how the typical features of EIT waves can all be accounted for within our theoretical model, in which the EIT waves are thought to be formed by successive stretching or opening of closed field lines driven by an erupting flux rope. The relationship between EIT waves, H Moreton waves, and type II radio bursts is discussed, with an emphasis on reconciling the discrepancies among different views of the ''EIT wave'' phenomenon.

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By use of the high-resolution spectral data obtained with THEMIS on 2002 September 5, the characteristics of 14 well-observed Ellerman bombs ( EBs) have been analyzed. Our results indicate that 9 of the 14 EBs are located near the longitudinal magnetic polarity inversion lines. Most of the EBs are accompanied by mass motions. The most obvious characteristic of the EB spectra is the two emission bumps at the two wings of both H and Ca ii k8542. For the first time both thermal and nonthermal semiempirical atmospheric models for the conspicuous and faint EBs are computed. In computing the nonthermal models, we assume that the electron beam resulting from magnetic reconnection is produced in the lower chromosphere. The reasons are that it requires much lower energies for the injected particles and that it gives rise to a more profound absorption at the H line center, in agreement with our observations. The common characteristic is the heating in the lower chromosphere and the upper photosphere. The temperature enhancement is about 600-1300 K in the thermal models. If the nonthermal effects are included, then the required temperature increase can be reduced by 100-300 K. These imply that the EBs could probably be produced by the magnetic reconnection in the solar lower atmosphere. The radiative and kinetic energies of the EBs are estimated, and the total energy is found to be 10 26 to 5 ; 10 27 ergs. According to the characteristics of EBs, we tentatively suggest that EBs could be called ''submicroflares.''

The dynamics of a filament channel are observed with imaging and spectroscopic telescopes before and during the filament eruption on 2011 January 29. The extreme ultraviolet (EUV) spectral observations reveal that there is no EUV counterparts of the Hα counter-streamings in the filament channel, implying that the ubiquitous Hα counter-streamings found by previous research are mainly due to longitudinal oscillations of filament threads, which are not in phase between each other. However, there exist larger-scale patchy counter-streamings in EUV along the filament channel from one polarity to the other, implying that there is another component of uni-directional flow (in the range of ±10 km s −1 ) inside each filament thread in addition to the implied longitudinal oscillation. Our results suggest that the flow direction of the larger-scale patchy counter-streaming plasma in the EUV is related to the intensity of the plage or active network, with the upflows being located at brighter areas of the plage and downflows at the weaker areas. Besides, we propose a new method to determine the chirality of an erupting filament based on the skewness of the conjugate filament drainage sites. It suggests that the right-skewed drainage corresponds to sinistral chirality, whereas the left-skewed drainage corresponds to dextral chirality.

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Helical magnetic flux rope (MFR) is a fundamental structure of coronal mass ejections (CMEs) and has been discovered recently to exist as a sigmoidal channel structure prior to its eruption in the EUV high-temperature passbands of the Atmospheric Imaging Assembly (AIA). However, when and where the MFR is built up are still elusive. In this paper, we investigate two MFRs (MFR1 and MFR2) in detail, whose eruptions produced two energetic solar flares and CMEs on 2014 April 18 and 2014 September 10, respectively. The AIA EUV images reveal that for a long time prior to their eruption, both MFR1 and MFR2 are under formation, which is probably through magnetic reconnection between two groups of sheared arcades driven by the shearing and converging flows in the photosphere near the polarity inversion line. At the footpoints of the MFR1, the Interface Region Imaging Spectrograph Si IV, C II, and Mg II lines exhibit weak to moderate redshifts and a non-thermal broadening in the pre-flare phase. However, a relatively large blueshift and an extremely strong non-thermal broadening are found at the formation site of the MFR2. These spectral features consolidate the proposition that the reconnection plays an important role in the formation of MFRs. For the MFR1, the reconnection outflow may propagate along its legs, penetrating into the transition region and the chromosphere at the footpoints. For the MFR2, the reconnection probably takes place in the lower atmosphere and results in the strong blueshift and non-thermal broadening for the Mg II, C II, and Si IV lines.

A novel selective fluorescent chemosensor based on an 8-hydroxyquinoline-appended fluorescein derivative (L1) was synthesized and characterized. Once combined with Cu(2+), it displayed high specificity for sulfide anion. Among the various anions, only sulfide anion induced the revival of fluoresecence of L1, which was quenched by Cu(2+), resulting in "off-on"-type sensing of sulfide anion. What's more, the sensor was retrievable to indicate sulfide anions with Cu(2+), and S(2-), in turn, increased. With the addition of Cu(2+), compound L1 could give rise to a visible pink-to-yellow color change and green fluorescence quenching. The resulting yellow solution could change to pink and regenerate to green fluorescence immediately upon the addition of sulfide anion; however, no changes were observed in the presence of other anions, including CN(-), P(2)O(7)(4-), and other forms of sulfate, making compound L1 an extremely selective and efficient sulfide chemosensor. The signal transduction occurs via reversible formation-separation of complex L1Cu and CuS. What's more, the biological imaging study has demonstrated that the chemosensor can detect sulfur anions in biological systems at a relatively low concentration.