Solar Flare and CME Observations with STEREO/EUVI

STEREO/EUVI observed 185 flare events (detected above the GOES class C1 level or at >?25 keV with RHESSI) during the first two years of the mission (December 2006?–?November 2008), while coronal mass ejections (CMEs) were reported in about a third of these events. We compile a comprehensive catalog of these EUVI-observed events, containing the peak fluxes in soft X rays, hard X rays, and EUV, as well as a classification and statistics of prominent EUV features: 79% show impulsive EUV emission (coincident with hard X rays), 73% show delayed EUV emission from postflare loops and arcades, 24% represent occulted flares, 17% exhibit EUV dimming, 5% show loop oscillations or propagating waves, and at least 3% show erupting filaments. We analyze an example of each EUV feature by stereoscopic modeling of its 3D geometry. We find that EUV emission can be dominated by impulsive emission from a heated, highly sheared, noneruptive filament, in addition to the more common impulsive EUV emission from flare ribbons or the delayed postflare EUV emission that results from cooling of the soft-X-ray-emitting flare loops. Occulted flares allow us to determine CME-related coronal dimming uncontaminated from flare-related EUV emission. From modeling the time evolution of EUV dimming we can accurately quantify the initial expansion of CMEs and determine their masses. Further, we find evidence that coronal loop oscillations are excited by the rapid initial expansion of CMEs. These examples demonstrate that stereoscopic EUV data provide powerful new methods to model the 3D aspects in the hydrodynamics of flares and kinematics of CMEs.     

Cyclic Variations of CME Velocity

The semiannual mean CME velocities for the time interval of 1979–1989 have been analyzed to reveal a complex cyclic variation with a peak at the solar cycle maximum and a secondary peak at the minimum of the cycle. The growth of the mean CME width is accompanied by a growth of the mean CME velocity. It is shown that the cyclic variations of the mean CME velocity and the mean CME width are associated with the cyclic variations of the large-scale magnetic field structure and that the secondary peak of the semiannual mean CME velocity in 1985–1986 is due to a significant contribution of fast CMEs with a width of 100° at the minimum of the cycle. This peak is supposed to be due to the increasing role of the global large-scale magnetic field system with a characteristic size of cells of 70°–100° at the minimum of the cycle and the respective particularities of the large-scale magnetic field configuration in the corona.     

A Study of Solar Radio Bursts with Fine Structures during Flare/CME Events

We have selected 27 solar microwave burst events recorded by the Solar Broadband Radio Spectrometer (SBRS) of China, which were accompanied by M/X class flares and fast CMEs. A total of 70.4% of radio burst events peak at 2.84 GHz before the peaks of the related flares’ soft X-ray flux with an average time difference of about 6.7 minutes. Almost all of the CMEs start before or around the radio burst peaks. At 2.6?–?3.8 GHz bandwidth, 234 radio fine structures (FSs) were classified. More often, some FSs appear in groups, which can contain several individual bursts. It is found that many more radio FSs occur before the soft X-ray maxima and even before the peaks of radio bursts at 2.84 GHz. The events with high peak flux at 2.84 GHz have many more radio FSs and the durations of the radio bursts are independent of the number of radio FSs. Parameters are given for zebra patterns, type III bursts, and fiber structures, and the other types of FSs are described briefly. These radio FSs include some special types of FSs such as double type U bursts and W-type bursts.     

CME Classification Based on Wavelet Spectra

We study the internal structure of coronal mass ejections (CMEs) using wavelet analysis. We derive wavelet spectra, spatially integrated over regions of interest within LASCO C2 white-light coronographic images. These spectra show an inflection point, which we use to characterize each spectrum. In a diagram of flux vs. spatial scale of the inflection point, we find that the analyzed structures fall into two, distinct groups: a low-flux, small-spatial-scale group (which we call the “homogeneous” type), and a high-flux, larger-spatial-scale group (the “collimated” type). Interestingly, if we study different regions of a given image, all of the structures fall into one of the two groups described above. From a qualitative comparison with the images, it is clear that the two groups identified by the wavelet analysis correspond to two types of morphologies, which are seen as either more-homogeneous or more-collimated structures.     

Multiple CME Events Observed With LASCO

Observations are reported of two multiple CME events which were detected on 2–3 June 1997 and 9–10 June 1998, using the LASCO instrument on board SOHO. Each event consists of a group of four related CMEs which emerge from progressively higher latitudes over a time period of approximately 16 hours. In both cases there is on-disk activity visible in EIT EUV images which involves bright emission along the south polar crown filament and there is also ejection of mass from other regions of the corona during the time period of each event. We present a multi-wavelength view of these events (i.e. white-light, H, EUV and, in the case of the 2–3 June 1997 event, soft X-ray), which suggest that ejection of mass from one point in the corona can lead to a destabilization of a previously stable structure and the further ejection of mass from different regions of the corona, in a systematic way. The observations also show that the CME phenomenon is not always a localised event but can occur on a global level; and that complex CME activity can arise at relatively quiet-Sun periods as evidenced by the lack of significant X-ray flares or radio signatures.     

Cover Picture: Astron. Nachr. 2/2012

The fine structure of the proper motion in a solar active region. The contour lines represent the boundaries to the penumbra and to the umbra (see L. Beauregard et al., this issue, p. 125) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cover Picture: Astron. Nachr. 7/2012

Hα profile variations of HD 82286 in 2010. The spectral lines from the secondary star appearas increased scatter around the primary‐star lines (see K. G. Strassmeier et al., this issue, p. 663)     

Cover Picture: Astron. Nachr. 9/2012

Total view of the closed GREGOR dome on top of the tower located at the Observatorio del Teide on Tenerife (see R.H. Hammerschlag et al., this issue, p. 830) (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cover Picture: Astron. Nachr. 1/2012

Magnetic fields of T Tauri stars compared to stellar parameters (blue: fully convective stars. See G.A.J. Hussain, this issue, p. 4) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cover Picture: Astron. Nachr. 3/2012

Surface map of the radial magnetic field component for a nonaxisymmetric unstable mode excited by the MRI including Hall effect (see T. Kondic et al., this issue, p. 202) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cover Picture: Astron. Nachr. 4/2012

The detector plane of the prototype of a global soft X‐ray imaging instrument for heliophysics, planetary science, and astrophysics (see M.R. Collier et al., this issue, p. 378)     

Cover Picture: Astron. Nachr. 7/2012

A case study for the restricted 3‐body problem showing the osculating semimajor axis for the first 50 binary orbits (see B. Quarles et al., this issue, p. 551) (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)