Rapid Rotation of an Erupting Prominence and the Associated Coronal Mass Ejection on 13 May 2013

In this paper, we report the multiwavelength observations of an erupting prominence and the associated CME on 13 May 2013. The event occurs behind the western limb in the field of view of SDO/AIA. The prominence is supported by a highly twisted magnetic flux rope and shows rapid rotation in the counterclockwise direction during the rising motion. The rotation of the prominence lasts for $\sim$47 minutes. The average period, angular speed, and linear speed are $\sim$806 s, $\sim$0.46 rad min$^{-1}$, and $\sim$355 km s$^{-1}$, respectively. The total twist angle reaches $\sim$7$\pi$, which is considerably larger than the threshold for kink instability. Writhing motion during 17:42$-$17:46 UT is clearly observed by SWAP in 174 {\AA} and EUVI on board the behind STEREO spacecraft in 304 {\AA} after reaching an apparent height of $\sim$405\,Mm. Therefore, the prominence eruption is most probably triggered by kink instability. A pair of conjugate flare ribbons and post-flare loops are created and observed by STA/EUVI. The onset time of writhing motion is consistent with the commencement of the impulsive phase of the related flare. The 3D morphology and positions of the associated CME are derived using the graduated cylindrical shell (GCS) modeling. The kinetic evolution of the reconstructed CME is divided into a slow-rise phase ($\sim$330 km s$^{-1}$) and a fast-rise phase ($\sim$1005 km s$^{-1}$) by the writhing motion. The edge-on angular width of the CME is a constant (60$^{\circ}$), while the face-on angular width increases from 96$^{\circ}$ to 114$^{\circ}$, indicating a lateral expansion. The latitude of the CME source region decreases slightly from $\sim$18$^{\circ}$ to $\sim$13$^{\circ}$, implying an equatorward deflection during propagation.Comment: 28 pages, 20 figures, accepted for publication in Solar Physics, comments are welcom

Enhanced three-minute oscillation above a sunspot during a solar flare

Three-minute oscillations are a common phenomenon in the solar chromosphere above a sunspot. Oscillations can be affected by the energy release process related to solar flares. In this paper, we report on an enhanced oscillation in flare event SOL2012-07-05T21:42 with a period of around three minutes, that occurred at the location of a flare ribbon at a sunspot umbra-penumbra boundary, and was observed both in chromo-spheric and coronal passbands. An analysis of this oscillation was carried out using simultaneous ground-based observations from the Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO) and space-based observations from the Solar Dynamics Observatory (SDO). A frequency shift was observed before and after the flare, with the running penumbral wave that was present with a period of about 200 s before the flare co-existing with a strengthened oscillation with a period of 180 s at the same locations after the flare. We also found a phase difference between different passbands, with the oscillation occurring from high-temperature to low-temperature passbands. Theoretically, the change in frequency is strongly dependent on the variation of the inclination of the magnetic field and the chromospheric temperature. Following an analysis of the properties of the region, we find the frequency change is caused by the slight decrease of the magnetic inclination angle to the local vertical. In addition, we suggest that the enhanced three-minute oscillation is related to the additional heating, maybe due to the downflow, during the EUV late phase of the flare

Early Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares

This Letter is to investigate the physics of a newly discovered phenomenon -- contracting flare loops in the early phase of solar flares. In classical flare models, which were constructed based on the phenomenon of expansion of flare loops, an energy releasing site is put above flare loops. These models can predict that there is a vertical temperature gradient in the top of flare loops due to heat conduction and cooling effects. Therefore, the centroid of an X-ray looptop source at higher energy bands will be higher in altitude, for which we can define as normal temperature distribution. With observations made by {\it RHESSI}, we analyzed 10 M- or X-class flares (9 limb flares). For all these flares, the movement of looptop sources shows an obvious U-shaped trajectory, which we take as the signature of contraction-to-expansion of flare loops. We find that, for all these flares, normal temperature distribution does exist, but only along the path of expansion. The temperature distribution along the path of contraction is abnormal, showing no spatial order at all. The result suggests that magnetic reconnection processes in the contraction and expansion phases of these solar flares are different.Comment: 11 pages, 4 figure