Paper Review Special Issue of Solar Physics (I) STEREO Science Results at Solar Minimum

1. Paper Review Special Issue of Solar Physics (I) STEREO Science Results at Solar Minimum Volume 259, Numbers 1-2 / October 2009 Yan Xu 2010 Nov. 02

3. Events Studied

4. Events Studied (CONTINUED) A comprehensive list could be found in Aschwanden et al., 2009 Solphys 256, 3 0~30 small angle stereoscopy 30~90 large angle stereoscopy 2006 Dec.  2008 Nov Other lists: RHESSI flare list, http://hesperia.gsfc.nasa.gov/hessidata/dbase/hessi_flare_list.txt LASCO CME list, http://cdaw.gsfc.nasa.gov/CME_list/ STEREO CME list, http://cor1.gsfc.nasa.gov/catalog

5. Aschwanden et al., 2009 Solphys 256, 3

6. 3D EUV Loops vs. Extrapolated Magnetic Field Lines

7. Comparison of STEREO/EUVI Loops with Potential Magnetic Field Models A.W. Sandman · M.J. Aschwanden · M.L. DeRosa · J.P. Wülser · D. Alexander

8. : vector tangent to the loop : the magnetic field vector In 3D:

10. Summary 1. The overall average misalignment angle for an Active region serves as a quantitative measure of how well the model field approximates the true field structure. 2. The potential model is not a very good approximation of solar active regions but that it is better suited to some active regions than to others. 3. We are better able to trace shorter, more central loops in 284 Å images than in 171 Å or 195 Å images, which may imply that some short loops near the neutral line are outside EUVI’s temperature range 4. We have a bias toward large-scale loops, highly sheared short or low lying loops may be underrepresented. Our results may therefore overestimate the degree of potentiality of the active regions.

11. Related Papers FIRST STEREOSCOPIC CORONAL LOOP RECONSTRUCTIONS FROM STEREO SECCHI IMAGES Feng et al., 2007 ApJ Letter 671, 205 Red  Extrapolation Yellow  Reconstruction Loops and field lines agree relatively well from this perspective because they were chosen to be close in this projection Most of the loops cannot easily be approximated by planar curve segments We find that linear force-free field models are helpful in establishing correspondences between the loops observed in the STEREO image pairs. The field lines from these linear force-free models need not be physical but only serve as a first order approximation to the final loops.

12. A CRITICAL ASSESSMENT OF NONLINEAR FORCE-FREE FIELD MODELING OF THE SOLAR CORONA FOR ACTIVE REGION 10953 DeRosa et al., 2009 ApJ 696, 1780 The current-field iteration method as run by Wheatland using the values of α in the negative (“Wh−”)

13. The field configuration of AR 10953 (30 April) departs further from potentiality with α = 25o±8o. DeRosa et al. (2009) recently studied AR 10953 using potential and nonlinear force-free fields in conjunction with stereoscopically determined 3D loop structures. They found an average misalignment angle of 24o for their computational domain, comparable to our finding of 25o. We note, however, that owing to the small field of view of the Hinode observations used to compute their field extrapolations, the area of the active region studied by DeRosa et al. is significantly smaller than the area used in this study, which encompasses the entire active region.

14. Bootstrapping the Coronal Magnetic Field with STEREO: • Unipolar Potential Field Modeling • (ApJ 2010, accepted) • Markus J. Aschwanden and Anne W. Sandman Potential Field Source Surface (PFSS) Potential Field with Unipolar Charge (PFU) Stereoscopy Error (SE) Example of parameters

15. Summary More papers coming…

16. EIT/EUV waves observed by STEREO

17. What Is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models S. Patsourakos · A. Vourlidas · Y.M. Wang · G. Stenborg · A. Thernisien EIT wave Speed: 50 – 400 km s−1 EIT wave are mostly associated with coronal mass ejections (CMEs) and not with flares. There is a tendency for the fastest EUV waves to be associated with similar phenomena in Hα, chromospheric He I, and soft X rays and to produce type II radio bursts Wave (fast-mode wave) or Non-wave (pseudo-waves, Delannée et al. (2008))? Or the hybrid model (Chen et al., 2002, 2005)?

18. Several recent studies support wave model: Long et al., 2008; Veronig, Temmer, and Vršnak, 2008; Gopalswamy et al. 2009; Patsourakos and Vourlidas 2007 This study presents observations of EUV wave from two viewpoints by STEREO Event: 2007 Dec. 07 from 4:30 to 5:15 UT in AR 10977 STEREO separation angle ~ 45O Flare: B1.4 @ 04:35 UT CME: from CACTUS, speed ~ 300km s−1

19. 1. Not pseudo-wave, which expects a quasi-circular wave shape at all times. At the early stage, the wave was not like that; 2. Not current shell, which requires a very high altitude; 3. The observed appearance is consistent with a wave driven by an impulsive loop expansion Multi-temperature….

20. Height: 90 ± 7 Mm

21. Summary (1) High-cadence (2.5-minute) 171 Å images showed a strong association between expanding loops and the wave onset and significant differences in the wave appearance between the two STEREO viewpoints during its early stages; these differences largely disappeared later; (2) The wave appears at the active region periphery when an abrupt disappearance of the expanding loops occurs within an interval of 2.5 minutes; (3) Almost simultaneous images at different temperatures showed that the wave was most visible in the 1 – 2 MK range and almost invisible in chromospheric/transition region temperatures; (4) Triangulations of the wave indicate it was rather low lying (≈90 Mm above the surface); (5) Forward-fitting of the corresponding CME as seen by the COR1 coronagraphs showed that the projection of the best-fit model on the solar surface was inconsistent with the location and size of the co-temporal EUV wave; (6) Simulations of a fast-mode wave were found in good agreement with the overall shape and location of the observed wave.

22. STEREO/SECCHI Observations on 8 December 2007: Evidence Against theWave Hypothesis of the EIT Wave Origin A.N. Zhukov · L. Rodriguez · J. de Patoul Event: 2007 Dec. 08 from 17:00 to 19:00 UT Flare: A8.3 by GOES-11 around 18:13 Post-flare arcade: 18:15 UT CME: 18:45 UT reaches the FOV of COR-1

23. Red: 195 Å Blue: 171 Å EUVI A Initial speed was around 100 km s−1; Shortly afterward (in around 3 minutes), the wave decelerated to 20 – 30 kms−1; Around 17:55 UT the wave was reaccelerated and reached around 300 km s−1; After 18:10 UT the wave speed dropped to values below 200 km s−1.

24. More accurate measurement of speed Huygens plotting (Wills-Davey and Thompson, 1999; Wills-Davey, 2006) Initial speed was around 100 km s−1; Shortly afterward (in around 3 minutes), the wave decelerated to 30 – 40 kms−1; Around 17:55 UT the wave was reaccelerated and reached around 200 km s−1; After 18:10 UT the wave speed dropped to values below 100 km s−1.

25. Discussion The propagation speed of the fast magnetosonic wave across the magnetic field is always higher than the Alfvén speed. Taking B = 1G and n = 109, then the Alfvén speed would be 70 kms−1; On the contrary, such a peculiar speed behavior can be explained if we assume that the EIT wave in our event is not a true wave but is instead linked to the CME eruption, like in Romano, Contarino, and Zuccarello (2003). The height – time curve in Figure 5 by Romano, Contarino, and Zuccarello (2003) is remarkably similar to our Figure 5. the prominence rises during the activation phase, remains at more or less the same height during the following 15 minutes, and then continues its upward motion (eruption phase).