On 2008 January 10, the twin Solar Terrestrial Relations Observatory (STEREO) A and B spacecraft conducted a high time cadence study of the solar corona with the Extreme UltraViolet Imager (EUVI) instruments with the aim of investigating coronal dynamics. Observations of the three-dimensional propagation of waves within active region coronal loops and a measurement of the true coronal slow mode...

We address the formation of 3D nullpoint topologies in the solar corona by combining Hinode/XRT observations of a small dynamic limb event, which occurred beside a non-erupting prominence cavity, with a 3D zero-β MHD simulation. To this end, we model the boundary-driven “kinematic” emergence of a compact, intense, and uniformly twisted flux tube into a potential field arcade that overlies a wea...

This paper reports the results of a survey of Doppler shift oscillations measured during solar flares in emission lines of S XV and Ca XIX with the Bragg Crystal Spectrometer (BCS) on Yohkoh. Data from 20 flares that show oscillatory behavior in the measured Doppler shifts have been fitted to determine the properties of the oscillations. Results from both BCS channels show average oscillation p...

There is not as yet full agreement on the mechanism that causes the rapid damping of the oscillations observed by TRACE in coronal loops. It has been suggested that the variation of the observed values of the damping time as function of the corresponding observed values of the period contains information on the possible damping mechanism. The aim of this Letter is to show that, for resonant abs...

A scheme is presented for mapping the connectivity of a potential magnetic field arising from an arbitrary distribution of discrete sources. The field lines interconnecting the sources are classified into Nd domains, defining the field’s connectivity. The number of domains is shown to depend on the number of sources and on the numbers of nulls and separators according to a simple relation. A cl...

We self-consistently derive the magnetic energy and relative magnetic helicity budgets of a three-dimensional linear force-free magnetic structure rooted in a lower boundary plane. For the potential magnetic energy we derive a general expression that gives results practically equivalent to those of the magnetic Virial theorem. All magnetic energy and helicity budgets are formulated in terms of ...

Multi-wavelength observations of a sigmoidal (S-shaped) solar coronal source by the EUV Imaging Spectrometer and the X-ray Telescope aboard the Hinode spacecraft and by the EUV Imager aboard STEREO are reported. The data reveal the coexistence of a pair of J-shaped hot arcs at temperatures T > 2 MK with an S-shaped structure at somewhat lower temperatures (T ≈ 1–1.3 MK). The middle section of t...

A statistical analysis of coronal loop oscillations observed by TRACE shows that 12 of 28 cases were associated with metric type II bursts. The timing is consistent with the idea that the loop oscillations in many cases result from the passage of a large-scale wave disturbance originating in a flare in the nearby active region. The GOES classifications for these flares range from C4.2 to X20. T...

The sun is often portrayed as a “laboratory for astrophysics” but it is a laboratory over which we have no control. Instead, solar physicists employ a wide range of theoretical, computational, and observational tools to study the magnetically driven activity on the sun. The challenge for these methods is that solar physics is extremely complex, making it difficult to isolate the key drivers of ...

Fine-scale structure in the corona appears not to be well resolved by current imaging instruments. Assuming this to be true offers a simple geometric explanation for several current puzzles in coronal physics, including the apparent uniform cross section of bright threadlike structures in the corona, the low EUV contrast ( long apparent scale height) between the top and bottom of active region ...