The global character of the 2010.08.01 Earth-directed coronal mass ejection and its trigger Xuepu Zhao and J. Todd Hoeksema Stanford University The Firs.

The global character of the 2010.08.01 Earth-directed coronal

mass ejection and its trigger

Xuepu Zhao and J. Todd HoeksemaStanford University

The Firs SDO Workshop, 2011.05.01-05

AbstractSchrijver and Title (2011) discovered a great solar storm on Aug. 1,2010. It is found that all events of substantial coronal activity areconnected by a wide-ranging system of magnetic fault, such asseparatrices, separators, and quasi-separatrix layers. Based onobservations of SOHO/LASCO, STEREO/COR1 and COR2 we determinethe angular width of the associated Earth-directed CME to be morethan 140 degrees which is greater than the upper width limit of limbCMEs [Burkepile et al., 2004]. It is found that all substantial coronalactivity and the associated magnetic fault zone are located within agreat coronal closed field region sandwiched between oppositepolarity coronal holes [Zhao and Webb, 2003]. Based on this findingand the observation of SDO/HMI, the underlying trigger of the2010.08.01 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 on2010.08.01. The global storm consists of various coronalactivities, such as flares, filament eruption, CMEs, occurrednearly simultaneously at source regions separated by morethan 180 degrees. To determine its morphology, we measurethe central axis, the angular width of the 2010.08.01 Earthdirected CME on the basis of COR2 images of STEREO A and B,and discuss the trigger on the basis of the result and the HMImagnetograms.

2. The global character of the 2010.08.01 Earth-directed CME

According to the 20100801_22:00 USAF/NOAAReport of Solar and Geophysical Activity, therewere two halo CMEs on Aug. 1, 2010. One is apartial-halo CME associated with the 07:50 UTdisappearing filament centered near N37W32and the other is a full-halo CME associated withthe 08:26 UT long-duration flare at N13E21 in AR11092.

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 2010.08.01 global solar storm

Two possible causes have been suggested in literature forthe sympathetic flares: (1) propagation of impulse signal excited by one coronal activity along magnetic field linesjoining related regions to other(s), (2) simultaneouslychanges of magnetic field in related wide-separated sourceregions. The fact that the wide separation of source regionsand small difference of onset times rejects the first cause

because it is impossible for signal carrier like waves andcorpuscular 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 2010.08.01_05:00:00 2010.08.01_05:30:00 2010.08.01_06:00:00

2010.08.01_06:30:00 2010.08.01_07:00:00 2010.08.01_07:30:00

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

2010.08.01_05:00:45 -- 05:00:00 2010.08.01_07:30:45 -- 07:30:00

Figure 6. 45-second difference images, showing no significantrapid change of field strength in the time interval of 45 second(see sun.stanford.edu/~xuepu/DATA/SDOW1/movie_45s2.m45s.250.mpg).

HMI 2010.08.01_05:00:00

2010.08.01_06:30:00 2010.08.01_07:30:00

HMI 2010.08.01_06:00:002010.08.01_05:30:00

2010.08.01_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.m00.150.mpg).

2010.08.01_05:00:00 2010.08.01_05:30:00 2010.08.01_06:00:00

2010.08.01_06:30:00 2010.08.01_07:00:00 2010.08.01_07:30:00

. Figure 8. Difference images in time interval of 12 minutes. It shows thatno 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 193 08.01_23 HMI 08.01_23 WSO 08.01_18

EIT 195 08.01_00

H

H

H HH

H

2010-08-01 23:002010-08-05 23:00

2010-07-19 23:00

2010-0725 23:00

Figure 10 The whole-surface distribution of observed coronal holes. The middlePanels 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 acticitiesare 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 wideclosed 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. Summary4.1 We find that the global character of CME isIts wide angular width. For the event studiedhere, the width is ~140°, significantly greaterthan the upper angular-width limit of limb CME. 4.2 Before the global coronal mass ejection, thehigh-cadence HMI images do not show any rapidchange of the photospheric magnetic fields overthe hemisphere.

4.3 We find that the extreamly 2010.08.01 wideCME 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.