My 20 Years of Research at Stanford Solar Physics Group

I. Improvement of inner boundary condition for data-based coronal models (WSO, MDI, HMI).

II. Development of two magneto-hydrostatic coronal models for modeling large-scale outer coronal magnetic fields (WSO, MDI, HMI).

III. Prediction of disturbances in the corona and heliosphere (CISM, WSO, MDI, HMI).

(See sun.stanford.edu/~xuepu/PUBLICATION/ for details of 110 papers)

I. Improvement of inner boundary condition of C. models

I.1 The uniqueness of the PFSS model solution (Zhao & Hoeksema, 1993).

I.2 The “Synoptic frame” (Zhao et al., 1996; ...).

I.3 The “Synchronic frame" (Zhao et al., 2010; …).

II. Development of two magneto-hydrostatic coronal models

II.1 The HCCSSS model (Zhao & Hoeksema, 1994; …): The latitude-independence of Br, The radial variation of HCS, The north-south displacement of HCS, Define and identify the base of the heliosphere.II.2 The non-force-free helical coronal magnetic field

model (Zhao and Hoeksema, 2000; …).

III. Prediction of the disturbances in corona and heliosphere

III.1 Relationship among IMF Bs events, the orientation of magnetic clouds, the orientation of post-eruption X-ray arcades, and the local inclination of the HCS

(Zhao & Hoeksema, 1998, ...).III.2 The circular (Zhao et al., 2002; …) & elliptic cone

models (Zhao, 2005; 2008, …).III.3 Predict ICME arrival time at Earth using cone

model parameters (Odstrcil, Riley & Zhao, 2004; ...). NOAA/SWPC

III.4 New algorithm for inverting 3-D direction (Zhao, 2011).

III.5 Modeling two kinds of coronal closed regions and two kinds of boundary layers between coronal holes (Zhao & Webb, 2003).

III.6 Predict the existence of the interaction between fast stream and slow CME based on observation of shock pairs ( Zhao, 1992).

(See sun.stanford.edu/~xuepu/PUBLICATIONFor details)

The 2010.08.01 Wide CME and its Trigger: A New Cause of

Sympathetic Coronal Activities

The solar group meeting, 2011.05.20

1. The 20100801 ``global solar storm’’

Schrijver and Title (2010) find a "global solar storm“ on 2010.08.01.

Partial-haloN37W32 07:50UT

Full-haloN13E2108:26UT

Figure 1. The sources of partial- and full-halo CMEs from the 20100801 USAF/NOAA Report .

Great CMEs must originate in coronal closed field regions since the CMEs are generated by free magnetic energies.

The angular width of CMEs are often associated with the angular width of their source closed region.

To understand the cause of formation, we need to first quantitatively estimate the spatial size of the full halo CME or the global solar storm, then find out the CME source region, and finally figure out the possible trigger.

2. The wide angular width of the 2010.08.01 full-halo CME

• The apparent angular width of limb CMEs approximately represents the true angular width of CMEs. The upper limit of the limb CME width is ~110° (Burkepile et al., 2004).

• To estimate the spatial size of the event, we need to find out the limb CME that corresponds to the 20100801 SOHO full-halo CME.

Fig 2 The full (left) and partial (right) halo CMEs and their elliptic outlines identified using 5-point method (the five green dots in the two panels).

SOHO C3

Combining the elliptic outline and our ZEC model we can find out thepropagation direction of the full halo CMEs to be N25E09.

STEREO A (B) was located at the longitude of W78.4 (E71.2 ) from the Earth. Thus STEREO A (B) would observe an east limb CME (a west partial halo CME). That is why CACTUS code did not work for the west CME.

Figure 3. The difference images of STEREO COR2 (from CACTUS web page) show that the angular width of the east limb CME is 144°, as shown by the two dashed white lines.

The CACTUS code is good for Identifying limb CME. The code fails in the west CME suggests that it is a partial halo CME, instead of a limb CME.

Behind Ahead

3. A narrow east limb CME preceding the wide east limb COM

Fig. 4 The COR2 images observed by STEREO Ahead and Behind between 08:24:00 and 10:24:00. It shows a narrow east limb CMEpreceding the east wide limb CME

Behind Ahead

The COR2 movie shows that the wide CMEs follow a narrow (50°) limb CME.

4. The trigger of the 2010.08.01 wide CME & 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!

4.1 Is the global changes of the photospheric field the cause?

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. If the global change is the cause, the change must be rapid to generate coronal activities, and may be manifested in feature’s location, size and

field strength.

The movie of 45s HMI ls images between 05:00:00 and 07:30:00. No significant global time variation in shape & size!

The movie of difference images between images and the first 0500 image between 0500 & 0730. No siginificant emerging in 2.5 hours.

The movie of fifference images in time interval of 12 min.No significant global change in field strength. The global change of field should also not be the cause!!!

4.2 Large closed region and Global CME trigger

• CMEs must originate in coronal closed field regions, and all coronal closed regions are sandwiched by coronal holes (Zhao & Webb, 2003).

• Based on observed coronal holes and the location of the partial- and full-halo CMEs,

we can determine the coronal closed region that contains all associated coronal activities.

Fig. 5 The HMI & WSO magnetograms show the thick polarity-inversion lines(PIL). The open (coronal hole, H) and closed (bright) regions shown in AIA 193 and EIT 195 images. The AIA dark regions along PILs are not coronal holes.

N37W32

N20E35

AIA 193 08.01_23

HMI 08.01_23

WSO 08.01_18EIT 195 08.01_00

H

H

H HH

H

2010-08-01 23:00

2010-08-05 23:00 2010-07-19 23:00 2010-0725 23:00

Figure 6 The whole-surface distribution of observed coronal holes. The wide closed region between two identified holes is the source region of the global storm. Its angular width is similar to the wide CME.

H

H

H

The wide closed field region contains a few BMRs. The outmost closed field lines of the wide closed region confine all underlying BMRs.

Schrijver and Title (2010) have shown 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 the acticities are in metastable configuration where small changes in surrounding plasma currents can set off big electromagnetic storms.

As shown in the AIA movie and EUVI movie, firstly a filament near the north polar hole expand upward, then erupt, and finally all magnetic arcades at different BMRs expand and erupt nearly simultaneously. It appears that this filament eruption opened up the outermost closed field lines of the wide closed field region that originally confine all metastable structures through magnetic stress, and the loss of the stress makes those metastable structures becoming unstable (or loss of equilibrium) all at once, i.e., triggers the wide Earth-directed CME or the global solar storm.

5. Summary and Discussion

5.1 We show that the angular width of the full halo CME or the global solar storm on 2010.08.01 is ~140°, significantly wider than the upper angular-width limit of CMEs. This wide angular width can be estimated from corresponding limb CMEs, and

provides a way to define the global solar storm. 5.2 The two causes of formation suggested for

sympathetic flares do not work for the 2010.08.01 wide CME or global solar storm.

5.3 We show that the 2010.08.01 wide CME occurs in a very wide coronal closed region and that the closed region contains a few metastable BMRs confined by its outmost magnetic field lines. The open-up of the outmost magnetic field lines by the filament eruption within the closed region makes all underlying metastable structures to be unstable.This is the trigger of the 2010.08.01 wide CMEand global solar storm. It may also be the cause of other sympathetic coronal activities.