Search

The 6 June 2007 16:55 UT flare was well observed with high time-cadence sparse raster scans by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. The observation covers an active region area of 240 arcsec × 240 arcsec with the 1 arcsec slit in about 160 seconds. We describe here spectral properties of a 'pre-flare brightening' to this flare, which started about nine minutes prior to flare-ribbon onset. This flare brightening looks like two small loops apparently having a cusp-shape structure about 40 - 50 arcsec west of the main flaring loops, which show dynamic behavior in velocity during the early phases of the flare: The He ii line at 256.32 Å shows the existence of a bi-directional flow along the Sun-Earth line of sight of about −70 and +100 km s. On the other hand, the Fe xvi line at 262.98 Å formed at higher coronal temperatures shows only a slight increase in intensity at the location of these loops, and the Fe xxiii line at 263.76 Å barely appears. Electron density at the site derived from the intensity ratios of the Fe xiv line pair at 264.78 Å and 274.20 Å is lower than the average of 10 cm in other parts of the active-region outskirts. Combining a time series of STEREO-A/B SECCHI-EUVI 171 Å images, we conclude that the pre-flare-brightening region may be heated via magnetic reconnection taking place as a result of loop-loop interaction. [ABSTRACT FROM AUTHOR]

We previously found a temperature-dependent upflow in the dimming region following a coronal mass ejection observed by the Hinode EUV Imaging Spectrometer (EIS). In this paper, we reanalyzed the observations along with previous work on this event and provided boundary conditions for modeling. We found that the intensity in the dimming region dramatically drops within 30 minutes from the flare onset, and the dimming region reaches the equilibrium stage after ~1 hr. The temperature-dependent upflows were observed during the equilibrium stage by EIS. The cross-sectional area of the flux tube in the dimming region does not appear to expand significantly. From the observational constraints, we reconstructed the temperature-dependent upflow by using a new method that considers the mass and momentum conservation law and demonstrated the height variation of plasma conditions in the dimming region. We found that a super-radial expansion of the cross-sectional area is required to satisfy the mass conservation and momentum equations. There is a steep temperature and velocity gradient of around 7 Mm from the solar surface. This result may suggest that the strong heating occurred above 7 Mm from the solar surface in the dimming region. We also showed that the ionization equilibrium assumption in the dimming region is violated, especially in the higher temperature range. [ABSTRACT FROM AUTHOR]

We report a spectroscopic analysis of an EUV Imaging Telescope (EIT) wave event that occurred in active region 11081 on 2010 June 12 and was associated with an M2.0 class flare. The wave propagated nearly circularly. The southeastern part of the wave front passed over an upflow region near a magnetic bipole. Using EUV Imaging Spectrometer raster observations for this region, we studied the properties of plasma dynamics in the wave front, as well as the interaction between the wave and the upflow region. We found a weak blueshift for the Fe XII λ195.12 and Fe XIII λ202.04 lines in the wave front. The local velocity along the solar surface, which is deduced from the line-of-sight velocity in the wave front and the projection effect, is much lower than the typical propagation speed of the wave. A more interesting finding is that the upflow and non-thermal velocities in the upflow region are suddenly diminished after the transit of the wave front. This implies a significant change of magnetic field orientation when the wave passed. As the lines in the upflow region are redirected, the velocity along the line of sight is diminished as a result. We suggest that this scenario is more in accordance with what was proposed in the field-line stretching model of EIT waves [ABSTRACT FROM AUTHOR]

For large eruptions on the Sun, it is often a problem that the core dimming region cannot be observed due to the bright emission from the flare itself. However, spectroscopic data can provide the missing information through the measurement of Doppler velocities. In this paper we analyse the well-studied flare and coronal mass ejection that erupted on the Sun on 13 December 2006 and reached the Earth on 14 December 2006. In this example, although the imaging data were saturated at the flare site itself, by using velocity measurements we could extract information on the core dimming region, as well as on remote dimmings. The purpose of this paper is to determine more accurately the magnetic flux of the solar source region, potentially involved in the ejection, through a new technique. The results of its application are compared to the flux in the magnetic cloud observed at 1 AU, as a way to check the reliability of this technique. We analysed data from the Hinode EUV Imaging Spectrometer to estimate the Doppler velocity in the active region and its surroundings before and after the event. This allowed us to determine a Doppler velocity 'difference' image. We used the velocity difference image overlayed on a Michelson Doppler Imager magnetogram to identify the regions in which the blue shifts were more prominent after the event; the magnetic flux in these regions was used as a proxy for the ejected flux and compared to the magnetic cloud flux. This new method provides a more accurate flux determination in the solar source region. [ABSTRACT FROM AUTHOR]

Solar flares take place in regions of strong magnetic fields and are generally accepted to be the result of a resistive instability leading to magnetic reconnection. When new flux emerges into a pre-existing active region it can act as a flare and coronal mass ejection trigger. In this study we observed active region 10955 after the emergence of small-scale additional flux at the magnetic inversion line. We found that flaring began when additional positive flux levels exceeded 1.38×10 Mx (maxwell), approximately 7 h after the initial flux emergence. We focussed on the pre-flare activity of one B-class flare that occurred on the following day. The earliest indication of activity was a rise in the non-thermal velocity one hour before the flare. 40 min before flaring began, brightenings and pre-flare flows were observed along two loop systems in the corona, involving the new flux and the pre-existing active region loops. We discuss the possibility that reconnection between the new flux and pre-existing loops before the flare drives the flows by either generating slow mode magnetoacoustic waves or a pressure gradient between the newly reconnected loops. The subsequent B-class flare originated from fast reconnection of the same loop systems as the pre-flare flows. [ABSTRACT FROM AUTHOR]

A series of flares (GOES class M, M and C) and a CME were observed in close succession on 20 January 2004 in NOAA 10540. Radio observations, which took the form of types II, III and N bursts, were associated with these events. We use the combined observations from TRACE, EIT, Hα images from Kwasan, MDI magnetograms and GOES to understand the complex development of this event. Contrary to a standard interpretation, we conclude that the first two impulsive flares are part of the CME launch process while the following long-duration event flare represents simply the recovery phase. Observations show that the flare ribbons not only separate but also shift along the magnetic inversion line so that magnetic reconnection progresses stepwise to neighboring flux tubes. We conclude that “tether cutting” reconnection in the sheared arcade progressively transforms it to a twisted flux tube, which becomes unstable, leading to a CME. We interpret the third flare, a long-duration event, as a combination of the classical two-ribbon flare with the relaxation process following forced reconnection between the expanding CME structure and neighboring magnetic fields. [ABSTRACT FROM AUTHOR]

The energy released in solar flares derives from a reconfiguration of magnetic fields to a lower energy state, and is manifested in several forms, including bulk kinetic energy of the coronal mass ejection, acceleration of electrons and ions, and enhanced thermal energy that is ultimately radiated away across the electromagnetic spectrum from optical to x rays. Using an unprecedented set of coordinated observations, from a suite of instruments, we here report on a hitherto largely overlooked energy component--the kinetic energy associated with small-scale turbulent mass motions. We show that the spatial location of, and timing of the peak in, turbulent kinetic energy together provide persuasive evidence that turbulent energy may play a key role in the transfer of energy in solar flares. Although the kinetic energy of turbulent motions accounts, at any given time, for only ∼(0.5-1)% of the energy released, its relatively rapid (∼1-10 s) energization and dissipation causes the associated throughput of energy (i.e., power) to rival that of major components of the released energy in solar flares, and thus presumably in other astrophysical acceleration sites. [ABSTRACT FROM AUTHOR]