No abstract

We report on observations of an extreme-ultraviolet (EUV) wave event in the Sun on 2011 January 13 by Solar Terrestrial Relations Observatory (STEREO ) and Solar Dynamics Observatory (SDO ) in quadrature. Both the trailing edge and the leading edge of the EUV wave front in the north direction are reliably traced, revealing generally compatible propagation velocities in both perspectives and a velocity ratio of about 1/3. When the wave front encounters a coronal cavity near the northern polar coronal hole, the trailing edge of the front stops while its leading edge just shows a small gap and extends over the cavity, meanwhile getting significantly decelerated but intensified. We propose that the trailing edge and the leading edge of the northward propagating wave front correspond to a non-wave coronal mass ejection (CME) component and a fastmode magnetohydrodynamic (MHD) wave component, respectively. The interaction of the fast-mode wave and the coronal cavity may involve a mode conversion process, through which part of the fast-mode wave is converted to a slow-mode wave that is trapped along the magnetic field lines. This scenario can reasonably account for the unusual behavior of the wave front over the coronal cavity.

We present a case study for the global extreme-ultraviolet (EUV) wave and its chromospheric counterpart the Moreton-Ramsey Wave associated with the second X-class flare in Solar Cycle 25 and a halo coronal mass ejection (CME). The EUV wave was observed in the Hα and EUV passbands with different characteristic temperatures. In the 171 Å and 193/195 Å images, the wave propagates circularly with an initial velocity of 600–720 km s−1 and a deceleration of 110–320 m s−2. The local coronal plasma is heated from log(T/K) ≈ 5.9 to log(T/K) ≈ 6.2 during the passage of the wave front. The Hα and 304 Å images also reveal signatures of wave propagation with a velocity of 310–540 km s−1. With multiwavelength and dual-perspective observations, we found that the wave front likely propagates forwardly inclined to the solar surface with a tilt angle of ∼53°.2. Our results suggest that this EUV wave is a fast-mode magnetohydrodynamic wave or shock driven by the expansion of the associated CME, whose wave front is likely a dome-shaped structure that could impact the upper chromosphere, transition region, and corona.

Coronal mass ejection (CME) velocities have been studied over recent decades. We present a statistical analysis of the relationship between CME velocities and X-ray fluxes of the associated flares. We study two types of CMEs. One is the FL type associated only with flares, while the other is the intermediate type associated with both filament eruptions and flares. It is found that the velocities of the FL type CMEs are strongly correlated with both the peak and the time-integrated X-ray fluxes of the associated flares. However, the correlations between the intermediate type CME velocities and the corresponding two parameters are poor. It is also found that the correlation between the CME velocities and the peak X-ray fluxes is stronger than that between the CME velocities and the time-integrated X-ray fluxes of the associated flares.

We analyzed and modeled an M1.2 non-eruptive solar flare on 2011 September 9. The flare exhibits a strong late-phase peak of the warm coronal emissions (∼3 MK) of extreme-ultraviolet (EUV), with peak emission over 1.3 times that of the main flare peak. Multiple flare ribbons are observed, whose evolution indicates a two-stage energy release process. A non-linear force-free field (NLFFF) extrapolation reveals the existence of a magnetic null point, a fan-spine structure, and two flux ropes embedded in the fan dome. Magnetic reconnections involved in the flare are driven by the destabilization and rise of one of the flux ropes. In the first stage, the fast ascending flux rope drives reconnections at the null point and the surrounding quasi-separatrix layer (QSL), while in the second stage, reconnection mainly occurs between the two legs of the field lines stretched by the eventually stopped flux rope. The late-phase loops are mainly produced by the first-stage QSL reconnection, while the second-stage reconnection is responsible for the heating of main flaring loops. The first-stage reconnection is believed to be more powerful, leading to an extremely strong EUV late phase. We find that the delayed occurrence of the late-phase peak is mainly due to the long cooling process of the long late-phase loops. Using the model enthalpy-based thermal evolution of loops (EBTEL), we model the EUV emissions from a late-phase loop. The modeling reveals a peak heating rate of 1.1 erg cm −3 s −1 for the late-phase loop, which is obviously higher than previous values.

We find that the solar cycles 9, 11, and 20 are similar to cycle 23 in their respective descending phases. Using this similarity and the observed data of smoothed monthly mean sunspot numbers (SMSNs) available for the descending phase of cycle 23, we make a date calibration for the average time sequence made of the three descending phases of the three cycles, and predict the start of March or April 2008 for cycle 24. For the three cycles, we also find a linear correlation of the length of the descending phase of a cycle with the difference between the maximum epoch of this cycle and that of its next cycle. Using this relationship along with the known relationship between the rise-time and the maximum amplitude of a slowly rising solar cycle, we predict the maximum SMSN of cycle 24 of 100.2±7.5 to appear during the period from May to October 2012.

Aims. In large gradual solar energetic particle (SEP) events, especially the ground-level enhancement (GLE) events, where and how energetic particles are accelerated is still a problem. Methods. By using imaging data from TRACE, Yohkoh/HXT, SOHO/MDI and SOHO/EIT, along with the data from the GOES, Apatity NM, and SOHO/LASCO CME catalog, the evolution of the X5.7 two-ribbon flare and the associated SEP event on 14 July 2000 are studied.Results. It is found that the magnetic reconnection in this event consists of two parts, and the induced electric field Erec is temporally correlated with the evolution of hard X-ray and γ-ray emission. In particular, the first hard X-ray and γ-ray emission peak occurred at 10:22 UT, corresponding to the magnetic reconnection in the western part of the flare ribbons and the maximum Erec of ∼ 9.5 V/cm; the second emission peak at 10:27 UT, corresponding to the eastern part and the maximum Erec of ∼ 13.0 V/cm. We also analyze the SEP injection profiles as functions of time and CME-height, and find two-component injection which may result from different acceleration mechanisms. Conclusions. A reasonable conclusion is that reconnection electric field makes a crucial contribution to the acceleration of relativistic particles and the impulsive component of the large gradual SEP event, while CME-driven shocks play a dominant role in the gradual component.

Abstract. This paper presents the spectro-polarimetric measurements of a big quiescent filament observed by the MSDP mode of the THEMIS on August 24, 2000. The Hα, CaII 8542 and NaI D2 line profiles of a segment of the filament were obtained. By use of the Hα images with high spatial resolution, the two barb endpoints were identified. The parameters at the barbs' endpoints, including intensity, velocity and longitudinal magnetic field were measured. Using the data with high spatial resolution (0.16 per pixel), we have found the following results. 1) There was mass motion at the barb endpoints in the chromosphere, the values and the directions of the mass motion at the barb endpoints change in several minutes. 2) The two barb endpoints are located between the majority polarities and the minority polarities.