Yuanyong Deng

Orientation of the magnetic fields in interplanetary flux ropes and solar filaments

Coronal mass ejections (CMEs) are often associated with erupting magnetic structures or disappearing filaments. The majority of CMEs headed directly toward the Earth are observed at 1 AU as magnetic clouds—the region in the solar wind where the magnetic field strength is higher than average and there is a smooth rotation of the magnetic field vectors. The three-dimensional structure of magnetic clouds can be represented by a force-free flux rope. When CMEs reach the Earth, they may or may not cause magnetic storms, alter Earths magnetic field, or produce the phenomena known as auroras. The geoeffectiveness of a solar CME depends on the orientation of the magnetic field in it. Two M-class solar flares erupted on 2000 February 17. The second flare occurred near a small active region, NOAA Active Region 8872. This eruption was accompanied by a halo CME. However, the February 17 CME did not trigger any magnetic activity when it arrived at the Earth. Another powerful flare, on 2000 July 14, was also associated with a halo CME, which caused the strongest geomagnetic activity of solar cycle 23. Using ACE measurements of the interplanetary magnetic fields, we study the orientation of the magnetic flux ropes in both sets of magnetic clouds and compare them with the orientation of the solar magnetic fields and disappearing filaments. We find that the direction of the axial field and helicity of the flux ropes are consistent with those of the erupted filaments. Thus, the geoeffectiveness of a CME is defined by the orientation and structure of the erupted filament and by its magnetic helicity as well. We also suggest that the geoeffectiveness of a CME can be forecasted using daily full-disk Hα and Yohkoh images and MDI magnetograms as well.

The Magnetic Rope Structure and Associated Energetic Processes in the 2000 July 14 Solar Flare

In the reconstructed nonlinear force-free magnetic field of NOAA Active Region 9077 before the X5.7/3B (10:24 UT) flare on 2000 July 14, we reveal for the first time the presence of a magnetic rope from the extrapolation of the three-dimensional magnetic field structure. This magnetic rope is located in a space above the magnetic neutral lines of the filament. The calculated field lines of the rope rotate around its axis for more than three turns. Overlying the rope are multilayer magnetic arcades with different orientations. These arcades are in agreement with the Transition Region and Coronal Explorer observations. The estimated free magnetic energy in this rope system is about 1.6 × 1032 ergs. Such magnetic field structure provides a favorable model for the interpretation of the energetic flare processes as revealed by Hα, EUV, and radio observations. In particular, the intermittent cospatial brightening of the rope in EUV 1600 A image leading to the onset of the flare suggests that the rope instability may have triggered the flare event, and the drifting pulsation structure in the decimetric frequency range is considered to manifest the initial phase of the coronal mass ejection.

Magnetic flux cancellation associated with the major solar event on 2000 July 14

The major solar event on 2000 July 14 is characterized by the simultaneous occurrence of a giant filament eruption, a great flare, and an extended Earth-directed coronal mass ejection. We examined in detail the magnetic evolution in its source active region, NOAA 9077, and found that the only obvious magnetic change in the course of the event is magnetic flux cancellation at many sites in the vicinity of the filament. Moreover, all the initial disturbance in the filament and the initial brightening around the filament took place at the cancellation sites. It is clearly indicated that the slow magnetic reconnection in the lower atmosphere, which is manifested as observed flux cancellation, is of overwhelming importance in leading to the global instability responsible for the major magnetic activity.

ON A CORONAL BLOWOUT JET: THE FIRST OBSERVATION OF A SIMULTANEOUSLY PRODUCED BUBBLE-LIKE CME AND A JET-LIKE CME IN A SOLAR EVENT

The coronal blowout jet is a peculiar category among various jet phenomena, in which the sheared base arch, often carrying a small filament, experiences a miniature version of blowout eruption that produces large-scale coronal mass ejection (CME). In this paper, we report such a coronal blowout jet with high-resolution multi-wavelength and multi-angle observations taken from Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Big Bear Solar Observatory. For the first time, we find that simultaneous bubble-like and jet-like CMEs were dynamically related to the blowout jet that showed cool and hot components next to each other. Our observational results indicate that (1) the cool component resulted from the eruption of the filament contained within the jets base arch, and it further caused the bubble-like CME; (2) the jet-like CME was associated with the hot component, which was the outward moving heated plasma generated by the reconnection of the base arch and its ambient open field lines. On the other hand, bifurcation of the jets cool component was also observed, which resulted from the uncoupling of the erupting filaments two legs that were highly twisted at the very beginning. Based on these results, we propose a model to interpret the coronal blowout jet, in which the external reconnection not only produces the jet-like CME, but also leads to the rising of the filament. Subsequently, internal reconnection starts underneath the rising filament and thereby causes the bubble-like CME.

Reevaluation of the Magnetic Structure and Evolution Associated with the Bastille Day Flare on 2000 July 14

The Bastille Day flare on 2000 July 14 was well observed by several space- and ground-based observatories and studied extensively by many researchers. Recently, we discovered that a large fraction of X-class flares are associated with a very interesting evolutionary pattern in δ sunspots: part of the outer δ spot structure decays rapidly after major flares; in the meantime, central umbral and/or penumbral structure becomes darker. These changes take place in about 1 hour and are permanent. We find that the active region NOAA AR 9077 has sunspot structure change similar to that associated with the 2000 July 14 X5.7 flare. We provide additional evidence supporting that we detected the real change in the sunspot structure after the flare. The new evidence presented in this paper include the following: (1) the Evershed velocity of decayed penumbral segments was weakened significantly following the flare, indicating actual weakening of penumbral structure; (2) based on available vector magnetograms before and after the flare, the transverse field strength decreased at the areas of penumbral decay and increased significantly near the flaring neutral line; (3) a new electric current system is found near the flare neutral line after the flare; and (4) the center-of-mass positions of opposite magnetic polarities converged toward magnetic neutral line immediately following the onset of the flare, and magnetic flux of the active region decreased steadily following the flare. There is no flare model capable of interpreting all the aspects of observations. A simple quadrupolar magnetic reconnection model may explain most of our observations: two magnetic dipoles join at the δ configuration before the flare; magnetic reconnection creates two new sets of loops: a compact flare loop and a large-scale expanding loop that might be the source of the CME. The outer penumbral fields become more vertical due to this reconnection, corresponding to the penumbral decay. Following initiation of magnetic reconnection associated with the flare, reconnected fields near the magnetic neutral line are first enhanced, then gradually weakened as it submerges. However, this model is questionable from one aspect of the observations: we failed to identify two far-end footpoints of this quadrupolar magnetic reconnection. We discuss other existing flare models in the context of our observations as well.

FORMATION OF A DOUBLE-DECKER MAGNETIC FLUX ROPE IN THE SIGMOIDAL SOLAR ACTIVE REGION 11520

In this paper, we address the formation of a magnetic flux rope (MFR) that erupted on 2012 July 12 and caused a strong geomagnetic storm event on July 15. Through analyzing the long-term evolution of the associated active region observed by the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, it is found that the twisted field of an MFR, indicated by a continuous S-shaped sigmoid, is built up from two groups of sheared arcades near the main polarity inversion line a half day before the eruption. The temperature within the twisted field and sheared arcades is higher than that of the ambient volume, suggesting that magnetic reconnection most likely works there. The driver behind the reconnection is attributed to shearing and converging motions at magnetic footpoints with velocities in the range of 0.1-0.6 km s(-1). The rotation of the preceding sunspot also contributes to the MFR buildup. Extrapolated three-dimensional non-linear force-free field structures further reveal the locations of the reconnection to be in a bald-patch region and in a hyperbolic flux tube. About 2 hr before the eruption, indications of a second MFR in the form of an S-shaped hot channel are seen. It lies above the original MFR that continuously exists and includes a filament. The whole structure thus makes up a stable double-decker MFR system for hours prior to the eruption. Eventually, after entering the domain of instability, the high-lying MFR impulsively erupts to generate a fast coronal mass ejection and X-class flare; while the low-lying MFR remains behind and continuously maintains the sigmoidicity of the active region.

Transequatorial Filament Eruption and Its Link to a Coronal Mass Ejection

We revisit the Bastille Day flare/CME Event of 2000 July 14, and demonstrate that this flare/CME event is not related to only one single active region (AR). Activation and eruption of a huge transequatorial filament are seen to precede the simultaneous filament eruption and flare in the source active region, NOAA AR 9077, and the full halo-CME in the high corona. Evidence of reconfiguration of large-scale magnetic structures related to the event is illustrated by SOHO EIT and Yohkoh SXT observations, as well as, the reconstructed 3D magnetic lines of force based on the force-free assumption. We suggest that the AR filament in AR 9077 was connected to the transequatorial filament. The large-scale magnetic composition related to the transequatorial filament and its sheared magnetic arcade appears to be an essential part of the CME parent magnetic structure. Estimations show that the filament-arcade system has enough magnetic helicity to account for the helicity carried by the related CMEs. In addition, rather global magnetic connectivity, covering almost all the visible range in longitude and a huge span in latitude on the Sun, is implied by the Nancay Radioheliograph (NRH) observations. The analysis of the Bastille Day event suggests that although the triggering of a global CME might take place in an AR, a much larger scale magnetic composition seems to be the source of the ejected magnetic flux, helicity and plasma. The Bastille Day event is the first described example in the literature, in which a transequatorial filament activity appears to play a key role in a global CME. Many tens of halo-CME are found to be associated with transequatorial filaments and their magnetic environment.

Three Super Active Regions in the Descending Phase of Solar Cycle 23

We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Tele- scope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle.

Solar Magnetism and the Activity Telescope at HSOS

A new solar telescope system is described, which has been operating at Huairou Solar Observing Station (HSOS), National Astronomical Observatories, Chinese Academy of Sciences (CAS), since the end of 2005. This instrument, the Solar Magnetism and Activity Telescope (SMAT), comprises two telescopes which respectively make measurements of full solar disk vector magnetic field and Hα observation. The core of the full solar disk video vector magnetograph is a birefringent filter with 0.1A bandpass, installed in the tele-centric optical system of the telescope. We present some preliminary observational results of the full solar disk vector magnetograms and Hα filtergrams obtained with this telescope system.

The Relationship between Magnetic Gradient and Magnetic Shear in Five Super Active Regions Producing Great Flares

We study the magnetic structure of five well-known active regions that produced great flares (X5 or larger). The six flares under investigation are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 July 14 in AR 9077, the X5.6 flare on 2001 April 6 in AR 9415, the X5.3 flare on 2001 August 25 in AR 9591, the X17 flare on 2003 October 28 and the X10 flare on 2003 October 29, both in AR 10486. The last five events had corresponding LASCO observations and were all associated with Halo CMEs. We analyzed vector magnetograms from Big Bear Solar Observatory, Huairou Solar Observing Station, Marshall Space Flight Center and Mees Solar Observatory. In particular, we studied the magnetic gradient derived from line-of-sight magnetograms and magnetic shear derived from vector magnetograms, and found an apparent correlation between these two parameters at a level of about 90%. We found that the magnetic gradient could be a better proxy than the shear for predicting where a major flare might occur: all six flares occurred in neutral lines with maximum gradient. The mean gradient of the flaring neutral lines ranges from 0.14 to 0.50 G km−1, 2.3 to 8 times the average value for all the neutral lines in the active regions. If we use magnetic shear as the proxy, the flaring neutral line in at least one, possibly two, of the six events would be mis-identified.