The global character of the Earth-directed coronal mass ejection and its trigger Xuepu Zhao and J. Todd Hoeksema Stanford University The Firs SDO Workshop,

Abstract Schrijver and Title (2011) discovered a great solar storm on Aug. 1, It is found that all events of substantial coronal activity are connected by a wide-ranging system of magnetic fault, such as separatrices, separators, and quasi-separatrix layers. Based on observations of SOHO/LASCO, STEREO/COR1 and COR2 we determine the angular width of the associated Earth-directed CME to be more than 140 degrees which is greater than the upper width limit of limb CMEs [Burkepile et al., 2004]. It is found that all substantial coronal activity and the associated magnetic fault zone are located within a great coronal closed field region sandwiched between opposite polarity coronal holes [Zhao and Webb, 2003]. Based on this finding and the observation of SDO/HMI, the underlying trigger of the great sympathetic solar storm are discussed.

1. Purpose Schrijver and Title (2011) discovered a "global solar storm“ based on SDO/AIA and STEREO/A COR1 data observed on The global storm consists of various coronal activities, such as flares, filament eruption, CMEs, occurred nearly simultaneously at source regions separated by more than 180 degrees. To determine its morphology, we measure the central axis, the angular width of the Earth directed CME on the basis of COR2 images of STEREO A and B, and discuss the trigger on the basis of the result and the HMI magnetograms.

2. The global character of the Earth-directed CME According to the _22:00 USAF/NOAA Report of Solar and Geophysical Activity, there were two halo CMEs on Aug. 1, One is a partial-halo CME associated with the 07:50 UT disappearing filament centered near N37W32 and the other is a full-halo CME associated with the 08:26 UT long-duration flare at N13E21 in AR

Fig 1. Six white-light difference images observed by SOHO/LASCO C3 between 14:18 UT and16:48 Aug. 1, 2010 (There were data gap before 14:18 UT). All images show full-halo with complicated structure, suggesting that it probably consists of one partial- and one full-halo CMEs, as mentioned above. 2.1 The central axis direction of the full-halo CME

To find the elliptic outline of the full- and partial-halo CMEs, we tried to select five points located on the well-recognized half of outer edge of halos (see the five green dots in the middle and right panels of Figure 2). Fig 2 The three elliptic outlines obtained based on the five green dots in the two panels. The elliptic outlines in the left and right panels are for the case of Full-halo and Partial-halo CMEs.

By using the elliptic cone ( ZEC ) model and the halo parameters we can find the direction of the central axis of halo CME to be N25E09. From STEREO A and B (with the longitude of W78.4 & E71.2 from the Earth) the direction becomes N25E87 & N25W62. Thus The earth directed CME observed by STEREO A must be a east limb CME, and may be a partial halo observed by STEREO B. Table 1 Five Halo parameters SAx Say Dse ψ α Full-halo 10.4 Rs 13.7 Rs 1.35 Rs -12° -108° Partial-halo 6.8 Rs 10.0 Rs 4.15 Rs -22° -13° Based on the outlines in Figure 2 we obtained the five halo parameters as shown in Table 1

2.2 The angular width of the Earth-directed limb CMEs Fig. 3 The COR2 images observed by STEREO Ahead (right column) and Behind (left column) between 08:24:00 and 10:24:00. The CME on east limb is a limb CME with angular width greater than 110°, which is the upper angular- width limit of limb CMEs (Burkepile et al., 2004).

Figure 4. The difference images of COR2 (from CACTUS web page) show more clearly the character of the wide limb CMEs. The COR2 movie (sun.stanford.edu/~xuepu/DATA/ SDOW1/moviec2_color.mpg, sun.stanford.edu/~xuepu/DATA/ SDOW1/movieCACT.mpg) clearly shows that the west and east wide CMEs follow a west and east narrow (50°) limb CME.

3. The trigger of the global solar storm Two possible causes have been suggested in literature for the sympathetic flares: (1) propagation of impulse signal excited by one coronal activity along magnetic field lines joining related regions to other(s), (2) simultaneously changes of magnetic field in related wide-separated source regions. The fact that the wide separation of source regions and small difference of onset times rejects the first cause because it is impossible for signal carrier like waves and corpuscular flow to propagate so fast!

3.1 The global changes of the photospheric magnetic field The arc-second resolution and 45-second candence HMI magnetograms make it possible to examine the global change of the photospheric magnetic field between 05:00:00 and 07:30:00. The change must be rapid to generate coronal activity, and may be manifested in feature’s location, size and field strength. It depends on the time interval between adjacent frames.

HMI _05:00: _05:30: _06:00: _06:30: _07:00: _07:30:00 Figure 5. The HMI magnetograms between 05:00 and 07:30. In the two and half hours, no significant and rapid change can be identified (sun.stanford.edu/~xuepu/DATA/SDOW1/movie_45s2_45s.150.mpg).

_05:00: :00: _07:30: :30:00 Figure second difference images, showing no significant rapid change of field strength in the time interval of 45 second (see sun.stanford.edu/~xuepu/DATA/SDOW1/movie_45s2.m45s.250.mpg).

HMI _05:00: _06:30: _07:30:00 HMI _06:00: _05:30: _07:00:00 Figure 7. Difference images between the 6 images in Figure 5 and the first image. The very similar shape & size between adjacent bright and white features in each panel suggest that no significant change of their shape (sun.stanford.edu/~xuepu/DATA/SDOW1/movie_45s2.m mpg).

_05:00: _05:30: _06:00: _06:30: _07:00: _07:30:00. Figure 8. Difference images in time interval of 12 minutes. It shows that no significant change of field strength occurs in the time interval of 12 minutes (sun.stanford.edu/~xuepu/DATA/SDOW1/movie_45s2.m12m.250.mpg).

3.2 Large closed region and Global CME trigger CMEs must originate in coronal closed field regions if they are generated by free magnetic energies. All coronal closed regions are sandwiched by coronal open field regions, i.e, coronal holes. The angular width of CMEs are often associated with the angular width of the source closed region.

Fig. 9 The open and closed regions shown in AIA 193 and EIT 195 images. The HMI & WSO magnetograms show the dark thick polarity-inversion lines(PIL). The dark regions along the PILs are not coronal holes. The symbol H in AIA image denotes coronal holes. N37W32 N20E35 AIA _23HMI 08.01_23 WSO 08.01_18 EIT _00 H H H H H H

: : : :00 Figure 10 The whole-surface distribution of observed coronal holes. The middle Panels are the earth- and far-side view of solar hemisphere. The left (right) panels are east- (west-) side view of solar hemisphere. H H

The closed field region sandwiched between the two coronal holes, H, contains a few bright regions, extend more than 140°. The outside closed field lines of the closed region confine all active regions or bipoles inside. On the basis of PFSS modeling, Schrijver and Title (2011) have showed that the source of various coronal activities are physically related through magnetic linkage, and all coronal activities are connected by "magnetic faults", i.e., separatrices, separators, and quasi-separatrix layers. The magnetic faults before onset of acticities are in metastable configuration where small changes in surrounding plasma currents can set off big electromagnetic storms.

As shown in the AIA movie (sun.stanford.edu/~xuepu/ DATA/SDOW1/globaldisruption.mov), firstly a filament centered at N37W32 near the north polar hole expand upward, then erupt, and finally all magnetic arcades at different active regions expand and erupt simultaneously. It appears that this filament eruption opened up the outer closed magnetic field lines of the wide closed field region that originally confine all metastable structures through magnetic stress, and this disappearence of the stress make those metastable configuration becoming unstable or loss of equilibrium all at once, i.e., triggers the global Earth-directed CME or the great solar storm.

4. Summary 4.1 We find that the global character of CME is Its wide angular width. For the event studied here, the width is ~140°, significantly greater than the upper angular-width limit of limb CME. 4.2 Before the global coronal mass ejection, the high-cadence HMI images do not show any rapid change of the photospheric magnetic fields over the hemisphere.

4.3 We find that the extreamly wide CME occurs in very wide coronal closed field region. Before the onset of the wide CME, there was a filament eruption within the wide closed field region. Based on these finding, we suggest a new mechanism to trigger the global solar storm.