We present the first quantitative comparison between the total magnetic reconnection flux in the low corona in the wake of coronal mass ejections (CMEs) and the magnetic flux in magnetic clouds (MCs) that reach 1 AU 2Y3 days after CME onset. The total reconnection flux is measured from flare ribbons, and the MC flux is computed using in situ observations at 1 AU, all ranging from 10 20 to 10 22 Mx. It is found that for the nine studied events in which the association between flares, CMEs, and MCs is identified, the MC flux is correlated with the total reconnection flux È r . Further, the poloidal (azimuthal) MC flux È p is comparable with the reconnection flux È r , and the toroidal (axial) MC flux È t is a fraction of È r . Events associated with filament eruption do not exhibit a different È t, p -È r relation from events not accompanied by erupting filaments. The relations revealed between these independently measured physical quantities suggest that for the studied samples, the magnetic flux and twist of interplanetary magnetic flux ropes, reflected by MCs, are highly relevant to low-corona magnetic reconnection during the eruption. We discuss the implications of this result for the formation mechanism of twisted magnetic flux ropes, namely, whether the helical structure of the magnetic flux rope is largely pre-existing or formed in situ by low-corona magnetic reconnection. We also measure magnetic flux encompassed in coronal dimming regions (È d ) and discuss its relation to the reconnection flux inferred from flare ribbons and MC flux.
An observational relationship has been well established among magnetic reconnection, high-energy flare emissions and the rising motion of erupting flux ropes. In this paper, we verify that the rate of magnetic reconnection in the low corona is temporally correlated with the evolution of flare nonthermal emissions in hard X-rays and microwaves, all reaching their peak values during the rising phase of the soft X-ray emission. In addition, however, our new observations reveal a temporal correlation between the magnetic reconnection rate and the directly observed acceleration of the accompanying coronal mass ejection (CME) and filament in the low corona, thus establishing a correlation with the rising flux rope. These results are obtained by examining two well-observed two-ribbon flare events, for which we have good measurements of the rise motion of filament eruption and CMEs associated with the flares. By measuring the magnetic flux swept through by flare ribbons as they separate in the lower atmosphere, we infer the magnetic reconnection rate in terms of the reconnection electric field E rec inside the reconnecting current sheet (RCS) and the rate of magnetic flux convected into the diffusion region. For the X1.6 flare event, the inferred E rec is~5.8 V cm À1 and the peak mass acceleration is 3 km s À2 , while for the M1.0 flare event E rec is~0.5 V cm À1 and the peak mass acceleration is 0.2-0.4 km s À2 .
A systematic motion of Ha kernels during solar Ñares can be regarded as the chromospheric signature of progressive magnetic reconnection in the corona, in that the magnetic Ðeld lines swept through by the kernel motion are those connected to the di †usion region at the reconnection point. In this paper, we present high-cadence and high-resolution Ha[1.3 observations of an impulsive Ñare that exhibits a A systematic kernel motion and relate them to the reconnecting current sheet (RCS) in the corona. Through analyses of X-ray and microwave observations, we further examine the role of the macroscopic electric Ðeld inside the RCS in accelerating electrons. We measure the velocity of the kernel motion to be 20[100 km s~1. This is used together with the longitudinal magnetic Ðeld to infer an electric Ðeld as high as 90 V cm~1 at the Ñare maximum. This event shows a special magnetic Ðeld conÐguration and motion pattern of Ha kernels, in that a light bridge divides a Ñare kernel into two parts that move in di †erent manners : one moving into the stronger magnetic Ðeld and the other moving along the isogauss contour of the longitudinal magnetic Ðeld. The temporal variation of the electric Ðeld inferred from the former type of kernel motion is found to be correlated with 20È85 keV hard X-ray light curves during the rise of the major impulsive phase. This would support the scenario of magnetic energy release via current dissipation inside the RCS, along with the hypothesis of the DC electric Ðeld acceleration of X-rayÈemitting electrons below 100 keV. However, there is no good temporal correlation between the hard X-ray emission and the inferred electric Ðeld from the other motion pattern. Furthermore, the microwave emission, which supposedly comes from higher energy electrons, shows a time proÐle and electron spectrum that di †ers from those of the X-ray bursts. We conclude that either the twodimensional magnetic reconnection theory related to the Ha kernel motion is applicable to only some part of the Ñare region due to its special magnetic geometry, or the electron acceleration is dominated by other mechanisms depending on the electron energy.
Magnetic reconnection is essential to release the flux rope during its ejection. The question remains: how does the magnetic reconnection change the flux rope structure? Following the original study of Qiu et al. (2007), we compare properties of ICME/MC flux ropes measured at 1 AU and properties of associated solar progenitors including flares, filaments, and CMEs. In particular, the magnetic field-line twist distribution within interplanetary magnetic flux ropes is systematically derived and examined. Our analysis shows that for most of these events, the amount of twisted flux per AU in MCs is comparable with the total reconnection flux on the Sun, and the sign of the MC helicity is consistent with the sign of helicity of the solar source region judged from the geometry of post-flare loops. Remarkably, we find that about one half of the 18 magnetic flux ropes, most of them being associated with erupting filaments, have a nearly uniform and relatively low twist distribution from the axis to the edge, and the majority of the other flux ropes exhibit very high twist near the axis, of up to 5 turns per AU, which decreases toward the edge. The flux ropes are therefore not linear force free. We also conduct detailed case studies showing the contrast of two events with distinct twist distribution in MCs as well as different flare and dimming characteristics in solar source regions, and discuss how reconnection geometry reflected in flare morphology may be related to the structure of the flux rope formed on the Sun.
We have studied the evolution of the photospheric magnetic Ðeld in active region NOAA 8668 for 3 days while the formation of a reverse S-shaped Ðlament proceeded. From a set of full-disk line-of-sight magnetograms taken by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO), we have found a large canceling magnetic feature that was closely associated with the formation of the Ðlament. The positive Ñux of the magnetic feature was initially 1.5 ] 1021 Mx and exponentially decreased with an e-folding time of 28 hr throughout the period of observations. We also have determined the transverse velocities of the magnetic Ñux concentrations in the active region by applying local correlation tracking. As a result, a persistent pattern of shear motion was identiÐed in the neighborhood of the Ðlament. The shear motion had a speed of 0.2È0.5 km s~1 and fed negative magnetic helicity of [3 ] 1042 Mx2 into the coronal volume during an observing run of 50 hr at an average rate of [6 ] 1040 Mx2 hr~1. This rate is an order of magnitude higher than the rate of helicity change due to the solar di †erential rotation. The magnetic Ñux of the Ðeld lines created by magnetic reconnection and the magnetic helicity generated by the photospheric shear motion are much more than enough for the formation of the Ðlament. Based on this result, we conjecture that the Ðlament formation may be the visible manifestation of the creation of a much bigger magnetic structure that may consist of a Ñux rope and an overlying sheared arcade.
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