SH41B-01 INVITED
Early Results From the SECCHI Extreme Ultraviolet Imager on STEREO
The two STEREO-SECCHI Extreme Ultraviolet Imagers (EUVI) have been observing the solar corona since December 2006, and from two significantly different vantage points since about March 2007. The continuous simultaneous observations from both telescopes, combined with multi-wavelength, full sun coverage open up a new way to study the 3-dimensional structure and dynamics of the corona, including coronal mass ejections. Members of the SECCHI team are working on 3-D reconstructions of coronal phenomena, and on other techniques that take advantage of the multi-point aspect of the observations. This talk will showcase movies of selected phenomena, and present some of the work in progress. Access to the observations, and the data analysis tools are reaching a level of maturity that allows the general solar physics community to participate in this exciting investigation.
SH41B-02
Stereoscopic Analysis of CME-related Coronal Activity using STEREO/SECCHI Observations
In May 2007, STEREO/SECCHI observed a series of coronal mass ejections (CMEs). Here we present results from an analysis SECCHI and other observations to study the relationship between the low-corona flaring activity, as viewed stereoscopically by SECCHI's ultraviolet imager EUVI, and the CMEs observed by the SECCHI coronagraphs. Activity observed includes prominence activation, eruption and ejection and post-flare loop arcade formation. For several May CME events, we will show the EUVI flaring activity and the corresponding GOES X-ray flare event that is most closely associated with the CME initiation. In some cases, the ejecta can be seen stereoscopically (in 3D) as it crosses the solar disk, allowing a clear identification with the CME material observed off the disk by the SECCHI/COR1 coronagraphs. During this period, the STEREO A and B spacecraft had reached sufficient separation (>6 degrees) to apply stereoscopic analysis to simultaneous EUVI images from the two spacecraft. We will report results of 3D reconstruction of flaring coronal loops and prominences using "tiepointing" and stereoscopy (aka triangulation). This work addresses STEREO's science objective: to understand the causes and evolution of coronal mass ejections.
SH41B-03
Comparison of 3D Numerical Simulations with STEREO Observations of Coronal Jets
Recent solar observations have revealed that coronal jets are a more frequent phenomenon than previously believed. It is widely accepted that magnetic reconnection is the fundamental mechanism that gives rise to the jets. The improved spatial and temporal resolution of the STEREO observations in combination with stereoscopy yields new insights into the origins of coronal jets, and provides detailed data that can be used to test and refine models. We present the results of a 3D numerical simulation of our model for coronal jets. The simulations were performed with our state-of-art adaptive mesh MHD solver ARMS. The basic idea of the model is that a jet is due to the release of twist as a closed field region undergoes interchange reconnection with surrounding open field. We compare the structure and dynamics of the simulated jet with actual EUVI observations, focusing on how the reconfiguration of the 3D magnetic field explains observed properties of the jet. We also discuss possible signatures for STEREO of twisted structures within jets. Finally, we discuss the implications of our simulations for future stereoscopic observations with STEREO. This work was supported, in part, by NASA and ONR.
SH41B-04
3D Geometry of Coronal Loops Measured with STEREO / EUVI
Using images from the STEREO/EUVI A and B spacecraft we developed an accurate method that performs stereoscopic triangulation and reconstruction of the 3D geometry of curvi-linear structures in the solar corona, such as loops, filaments, prominence threads, or wave features. We test the coalignment of stereoscopic images and establish an accuracy of better than <0.1 pixels in east-west direction, <0.3 pixels in north-south direction, and <0.05 degrees in roll angle. We reconstruct the 3D geometry of some 100 coronal loops loops in active regions in May 2007, when the spacecraft had a separation angle of ~10 degrees. We find that complete loops or incomplete segments of loops can only be reconstructed up to altitudes of about one hydrostatic scale height, which is h<50 Mm at a coronal temperature of T=1 MK. The determination of the 3D geometry of coronal loops is an important and necessary step to model their hydrodynamic structure. We show also that this method can be used to determine quantitatively the eigen-motion, oscillation, twisting, expansion, acceleration, or other dynamics of coronal loops, erupting filaments, and MHD wave fronts, in particular in association with flares and CMEs. http://www.lmsal.com/~aschwand/
SH41B-05
Two contrasting events from multiple viewpoints
Two contrasting events are described by studying data from both STEREO and earth-Sun line of sight instruments. In each case the image registration and alignment issues are addressed and the specific science benefits of the separation angles of the three viewpoints are highlighted. In the first event (25-Jan-2007), a small flare in a slowly evolving active region ejecting a fast moving CME is studied using EUVI/COR1/COR2 from both STEREO spacecraft, with additional information from EIT/LASCO and RHESSI.The benefits of small spacecraft separation are exploited as pre-CME EUVI (behind) images show significant loop 'opening', with a RHESSI thermal energy source detected prior to the post-flare loops cooling thru the EUVI passbands. The CME passes is studied as it passes thru COR1/COR2 and LASCO, and is followed by a slow moving thermal energy source in its wake. In the second event (1-May-2007), a rapidly rotating (but non-erupting) filament as the source of a slowly rising, non radial, feature is studied using both STEREO spacecraft, SOHO and the Mk-IV coronagraph. The benefits of larger spacecraft separation are exploited to give three plane of sky height time plots to determine the 'actual' velocity profile of the slow moving feature. The differences in EIT and EUVI are used to study the filament rotational motion in detail
SH41B-06
First Stereoscopic Coronal Loop Reconstructions From STEREO/SECCHI Images
We for the first time use simultaneously observed EUV images to reconstruct the 3D shape of magnetic loops which emerge from an active region. The images were taken by the two EUVI cameras of the SECCHI telescopes onboard the STEREO spacecraft. At the time the data was taken, the heliocentric separation of the two STEREO probes was 12 degrees. We show that under these conditions it is possible to obtain a reliable three- dimensional reconstruction of suciently bright loops as they usually emerge from an active region. The result is compared with field lines derived from a coronal magnetic field model extrapolated from a surface magnetogram. The magnetogram was abserved by SOHO/MDI only 9 seconds before the the EUV images were taken.
SH41B-07
STEREO 3D Data of the Fast Formation of the Ribbon-Like Prominences and Their Dynamics During Eruption
We have analyzed STEREO/SECCHI/EUVI Helium 304Å data and created 3-dimensional geometrical models for the two erupting prominences observed by STEREO. 3D STEREO movies, made by combining views from the two spacecraft, allow us to understand the true 3D structure of the prominences before and during eruption. In a movie from 12 May 2007 we can see the fast filling of the existing filament channel by plasma. This fast formation of the prominence allows us to trace in time and space the appearance of the main structural parts of the prominence: the barbs and the flat ribbon shape of the whole body of the prominence. We have analyzed the formation and development these structures before eruption and the motion of the erupting part of the prominence during eruption. We found that the motion of the erupting prominence shows the roll effect of the top of prominence. The STEREO movie from 16 May 2007 shows us another clear example of the roll effect during prominence eruption. The observed fast filling of the existing filament channel by plasma and the quick formation of the prominence with the ribbon-like geometrical structure, followed by the partial eruption with the obvious roll effect are the clear evidence of non flux rope magnetic nature of prominences. Our qualitative model of prominence formation by cancelling of magnetic flux at the photosphere and magnetic reconnection in the chromosphere and corona is in agreement with the STEREO observational facts of formation and eruption of prominences.