3-D Pre-Eruption Magnetic Field Configuration Involved in 28 Oct 2003 Fast Halo CMEs Xuepu Zhao Stanford University 36 Th COSPAR Assembly Beijing, China, July 19, 2006

1. Purpose of the work This work tries to study the cause of extreme solar eruptions occurred in AR486 The time variation of AR486 ~ rope Conditions for an emerging flux rope to generate an extreme solar eruption The 3-D field configuration above AR486 Summary & discussion

2. Time variation of AR486 Movie Within AR486, reverse “S” structures have been Identified in pre-X17-flare Hαfilament & post-X17-flare EIT arcade (Yurchyshyn et al., 2005)  left-handed flux rope (Fan & Gibson, 2004)

Fig. 1 shows the time variation of the AR area (top panel), total line-of-sight field strength (middle panel), & the mean line-of-sight field (bottom panel) of AR0486 from Oct 22 to Nov The symbols + and – lines denote the parameters for outward and inward polarities. The green & red lines denote the total of unsigned and signed parameters, respectively. Positive area decreases, & Negative area increases; Bl+ ~ Bl- => Emerging flux rope!

3. Conditions for emerging rope to generate extreme solar eruption 3.1 Fan & Gibson (2004) Before kink instability, Quasi-equilibrium: expand, displace arcade potential => non-potential 3.2 Upward buoyancy is balanced by downward plasma weight & magnetic force in the arcade. It is the plasma weight …. Fig. 2 Adopted from Fan & Gibson

3.3 The buoyancy depends on density in ropes N decreases, buoyancy increases 3.4 The plasma weight depends on the volume of the arcade overlying the rope. The volume depends on what kind of closed field region the AR486 is located

The top of the outmost arcade in UCR is lower than in BCR. Plasma weight in UCR is in general less than in BCR Fig. 3 Bipolar (underlying HCS) and Uni-polar (underlying plasma sheet with like polarity) Closed Region (BCR & UCR) (Hundhausen, 1972; Zhao & Webb, 2003) Fig. 4 A sketch of the 12 November 1966 eclipse adopted from Saito & Tandberg-Hanssen [ 1973] The condition for EFRs to generate extreme solar eruptions is Low- density twisted ropes emerging within UCRs

Fig 5 Magnetic arcades anchored at |Bl| > 50 G calculated using _09.35 synoptic frame & the PFSS model with Nmax=200. The top of outmost arcade above AR486 looks lower than others 4. The 3-D field configuration above AR486 before newly emergence of flux rope

Fig. 6 Left panel shows the calculated magnetic arcades with top less than 1.10 Rs. The calculated arcade above the red dot is similar to the observed bright arcade. EIT _13.13

Fig. 7 Magnetic arcade calculated starting from all pixels with the arcade top (l-t) (r-t) (l-b) (r-b) AR486 was located in UCR with outmost arcade top less than 1.1 Rs

5. Summary and Discussion 5.1 We have shown The evidence that suggests that AR486 may be an emerging left-handed twisted flux rope Low-density twisted ropes emerging within UCRs are the condition for emerging flux ropes to generate extreme solar eruptions The AR0486 is located in an UCR and the top of outmost arcade anchored within AR486 before the emergency of the flux rope is mostly, if not all, less than 1.10 Rs, implying that the plasma weight that confines the emerging flux rope is small.

5.2 If the evolution of emerging flux ropes discussed above is valid, the plasma density in the emerging flux rope must be low to satisfy the condition for AR486 to generate extreme solar eruptions. 5.3 On Oct. 29, 2003 a left-handed magnetic cloud with low density was observed by ACE, and the cloud has been shown to be the interplanetary counterpart of the 28 Oct 2003 X17-flare-associated halo CME (Hu et al., 2005, also see Fig. 8), consistent with the inference of It has been shown that most of halo CMEs occur within BCRs (Zhao & webb, 2003) and most of magnetic clouds contain low plasma temperature, implying that the BIG plasma weight of the overlying arcade and the SMALL buoyancy of ropes, thus the emergence of flux ropes may be ceased before the kink instability takes place. Shearing and converging flows may be necessary to drive break-out CMEs.

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