In a case study (June 6-7, 2008) we report on how the internal structure of a coronal mass ejection (CME) at 1 AU can be anticipated from remote observations of white-light images of the heliosphere. Favorable circumstances are the absence of fast equatorial solar wind streams and a low CME velocity which allow us to relate the imaging and in-situ data in a straightforward way. The STEREO-B spacecraft encountered typical signatures of a magnetic flux rope inside an interplanetary CME (ICME) whose axis was inclined at 45 degree to the solar equatorial plane. Various CME direction-finding techniques yield consistent results to within 15 degree. Further, remote images from STEREO-A show that (1) the CME is unambiguously connected to the ICME and can be tracked all the way to 1 AU, (2) the particular arc-like morphology of the CME points to an inclined axis, and (3) the three-part structure of the CME may be plausibly related to the in situ data. This is a first step in predicting both the direction of travel and the internal structure of CMEs from complete remote observations between the Sun and 1 AU, which is one of the main requirements for forecasting the geo-effectiveness of CMEs.
It is assumed that HXR sources map to the primary energy release site in flares where particle acceleration occurs. Strong HXR sources are mostly observed at confined regions along the reconnecting magnetic arcade. We make a general approach on how the geometry of the reconnecting current sheet (CS) may influence the strength and localization of observed HXR sources. For this we use results from an analysis on the 3B/X3.8 flare on January 17, 2005 (Temmer et al., 2007), as well as measurements from the associated CME. Due to the close match of the CME acceleration profile and the flare HXR flux, we suppose that the CME might play a certain role in modifying the geometry of the CS ('symmetric' versus 'asymmetric' vertically stretched CS). This could be the driver for 'guiding' the accelerated particles to confined areas along the flaring arcade and might explain the spatially limited occurrence of strong HXR sources in comparison to elongated ribbons as seen in H-alpha and UV.
Acknowledgements. C. Mostl, C. Miklenic, A.V. and H.K.B. acknowledge the Austrian Science Foundation (FWF) for support under project P20145-N16. A. B. Galvin is PI, and C.J.F. is a Co-I on STEREO/PLASTIC. This work is supported by NASA grants NAS5-00132, NNG06GD41G and NNX08AD11G. M. Temmer acknowledges project APART 11262 of the Austrian Academy of Sciences. We thank the STEREO/SECCHI teams for their open data policy. CONTEXT
It is assumed that HXR sources map to the primary energy release site in flares where particle acceleration occurs. Strong HXR sources are mostly observed at confined regions along the reconnecting magnetic arcade. We make a general approach on how the geometry of the reconnecting current sheet (CS) may influence the strength and localization of observed HXR sources. For this we use results from an analysis on the 3B/X3.8 flare on January 17, 2005 (Temmer et al., 2007), as well as measurements from the associated CME. Due to the close match of the CME acceleration profile and the flare HXR flux, we suppose that the CME might play a certain role in modifying the geometry of the CS ('symmetric' versus 'asymmetric' vertically stretched CS). This could be the driver for 'guiding' the accelerated particles to confined areas along the flaring arcade and might explain the spatially limited occurrence of strong HXR sources in comparison to elongated ribbons as seen in H-alpha and UV.
We investigate an active region that produced three C-class flares and one M-class flare within 2.5 hr. The morphology and location of the C-flares indicate that these events constitute a set of homologous flares. Radio observations indicate the occurrence of a downward-moving plasmoid during the impulsive phase of the M flare. We use TRACE 1700 Å filtergrams and SOHO Michelson Doppler Imager magnetograms to examine the character of the UV brightenings; i.e., we search for re-brightenings of former flare areas both across the series of events and within one and the same event. We find that essentially the same footpoints re-brighten in each C flare. Based on the progression of both the derived magnetic flux change rate and the observed Radio Solar Telescope Network microwave emission, we speculate about a further re-brightening during the decay phase of the M flare as a further member of the series of homologous flares. We conclude that the "postflare" field is driven to repeated eruption by continuous, shear-increasing, horizontal, photospheric flows, as one end of the involved magnetic arcade is anchored in the penumbra of a large sunspot. The observed motion pattern of the UV kernels indicates that the arcade evolves during the series of events from a both highly sheared and heavily entangled state to a still sheared but more organized state.
Multipoint spacecraft observations of a magnetic cloud on 22 May 2007 have given us the opportunity to apply a multispacecraft technique to infer the structure of this large‐scale magnetic flux rope in the solar wind. Combining WIND and STEREO‐B magnetic field and plasma measurements, we construct a combined magnetic field map by integrating the Grad‐Shafranov equation, this being one of the very first applications of this technique in the interplanetary context. From this we obtain robust results on the shape of the cross section, the orientation and magnetic fluxes of the cloud. The only slightly “flattened” shape is discussed with respect to its heliospheric environment and theoretical expectations. We also relate these results to observations of the solar source region and its associated two‐ribbon flare on 19 May 2007, using H α images from the Kanzelhöhe observatory, SOHO/MDI magnetograms and SECCHI/EUVI 171 Å images. We find a close correspondence between the magnetic flux reconnected in the flare and the poloidal flux of the magnetic cloud. The axial flux of the cloud agrees with the prediction of a recent 3‐D finite sheared arcade model to within a factor of 2, which is evidence for formation of at least half of the magnetic flux of the ejected flux rope during the eruption. We outline the relevance of this result to models of coronal mass ejection initiation, and find that to explain the solar and interplanetary observations elements from sheared arcade as well as erupting‐flux‐rope models are needed.
Abstract. This paper compares properties of the source region with those inferred from satellite observations near Earth of the magnetic cloud which reached 1 AU on 20 November 2003. We use observations from space missions SOHO and TRACE together with ground-based data to study the magnetic structure of the active region NOAA 10501 containing a highly curved filament, and determine the reconnection rates and fluxes in an M4 flare on 18 November 2003 which is associated with a fast halo CME. This event has been linked before to the magnetic cloud on 20 November 2003. We model the near-Earth observations with the Grad-Shafranov reconstruction technique using a novel approach in which we optimize the results with two-spacecraft measurements of the solar wind plasma and magnetic field made by ACE and WIND. The two probes were separated by hundreds of Earth radii. They pass through the axis of the cloud which is inclined −50 degree to the ecliptic. The magnetic cloud orientation at 1 AU is consistent with an encounter with the heliospheric current sheet. We estimate that 50% of its poloidal flux has been lost through reconnection in interplanetary space. By comparing the flare ribbon flux with the original cloud fluxes we infer a flux rope formation during the eruption, though uncertainties are still significant. The multi-spacecraft Grad-Shafranov method opens new vistas in probing of the spatial structure of magnetic clouds in STEREO-WIND/ACE coordinated studies.
To test the standard flare model (CSHKP-model), we measured the magnetic-flux change rate in five flare events of different GOES classes using chromospheric/photospheric observations and compared its progression with observed nonthermal flare emission. We calculated the cumulated positive and negative magnetic flux participating in the reconnection process, as well as the total reconnection flux. Finally, we investigated the relations between the total reconnection flux, the GOES class of the events, and the linear velocity of the flare-associated CMEs. Using high-cadence H-alpha and TRACE 1600 A image time-series data and MDI/SOHO magnetograms, we measured the required observables (newly brightened flare area and magnetic-field strength inside this area). RHESSI and INTEGRAL hard X-ray time profiles in nonthermal energy bands were used as observable proxies for the flare-energy release rate. We detected strong temporal correlations between the derived magnetic-flux change rate and the observed nonthermal emission of all events. The cumulated positive and negative fluxes, with flux ratios of between 0.64 and 1.35, were almost equivalent to each other. Total reconnection fluxes ranged between 1.8 x 10^21 Mx for the weakest event (GOES class B9.5) and 15.5 x 10^21 Mx for the most energetic one (GOES class X17.2). The amount of magnetic flux participating in the reconnection process was higher in more energetic events than in weaker ones. Flares with more reconnection flux were associated with faster CMEs.
