Prediction of Central Axis Direction of Magnetic Clouds Xuepu Zhao and Yang Liu Stanford University The West Pacific Geophysics Meeting, Beijing, China July 25, 2006

1. Introduction 1.1 The central axis direction (CAD) of magnetic clouds (MCs) determines the strength and duration of the - Bz component in MCs (Zhao & Hoeksema, 1998), and thus determines the geoeffectiveness of the MCs & their solar counterpart. Prediction of the CAD of MCs is one of key issues in the space weather.

1.2 Many MCs are associated with CMEs that occur in closed field regions underlying the HCS, and the CAD of these MCs may be predicted using the CAD of the associated disappearing solar filaments (DSFs) (Zhao & Hoeksema,1997) or the inclination of the HCS overlying the associated CMEs (Zhao & Webb, 2003).

S1 & ICME1  28 Oct halo CME N  S, left-handed MC (Hu et al, 2005) with low proton density & not-low temperature. S2 & ICME2  29 Oct halo CME There is no southward HMF component (??) (Farrugia et al., 2005, Hu et al., 2005) Fig. 1 Adopted from Farrugia et al., 2005

1.3 The 29 & 31 Oct MCs are originated in NOAA AR486 and there is no DSF or HCS associated with these events. Yurchyshyn et al (2005) studied these events recently. This work is trying to find a unified way to predict the CAD of MCs that are originated in any closed field regions, both underlying or not underlying the HCS.

2. Coronal flux ropes in two kinds of closed field regions 2.1 Magnetic clouds are a segment of coronal flux ropes expanding into the heliosphere as a loop of nested coils connected to the Sun at both ends. The coronal flux ropes are believed to be formed above the polarity inverse line in 3D arcades due to flux cancellation, emergency, or shearing and converging photospheric motions.

2.2 The existence of the correlation between the CAD of MCs and the CAD of SDFs (Marubashi, 1986; Bothmer & Schwenn, 1994) suggests that the CAD of coronal flux ropes remains basically constant while expanding into the heliosphere. 2.3 The CAD of coronal flux ropes is expected to be aligned with the locus of the outmost arcade tops

Fig. 2 Sketched two kinds of closed regions. Adopted from Hundhausen, 1972 Fig. 3 Calculated two kinds of closed regions between holes 2.4 The locus of the arcade tops in “Bipolar” & “Unipolar” closed field regions (Zhao & Webb, 2003) BCR: the base of the HCS UCR: ?

Fig. 4 All magnetic arcades anchored at |Bl| > 50 G and calculated using the MDI _09.35 synoptic frame and the PFSS model with N=200. Blue-red lines denote closed field lines with blue segment upward. The joint between blue and red segments is arch top. 3. Magnetic arcade system calculated above AR486 AR0486

Fig.5 Calculated magnetic arcades anchored all pixes with different top ranges. AR0486 is located in a UCR; The highest arcade top is 1.10 Rs AR0486

Fig. 6 The locus of arcade tops above the X17 flare is parallel to the left-handed EIT bright structure, predicting a MC with a leading northward HMF component, consistent with ACE obs. EIT _13.13 (11.00) 4. Prediction of the CAD of MCs associated with UCR- CMEs

EIT _10.36 (10.18) Fig 7 The locus of arcade top above the M8 flare is parallel to the EIT left-handed bright structure

Movie 1

EIT _22.00 (20.37) Fig. 8 The locus of arcade tops above the X10 flare is parallel to the EIT left-handed arcade, predicting a MC with a northward HMF component, consistent with ACE observation.

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5. Summary 5.1 We have shown that AR486 occurred in an unipolar closed field region. The top of calculated magnetic arcades in UCR is significantly lower than in BCR. 5.2 Combining with the observed handedness of the EIT post-flare bright arcade, the magnetic arcade calculated using the PFSS model and the MDI synoptic frame can be used to predict the central axis direction of the 29 and 31 Oct 2003 MCs. This method may be used for BCR- as well as UCR-CME associated MCs. 5.3 High quality arcade images from AIA/SDO & KuaFu are expected to be able to more accurately determine the handedness of magnetic arcades.

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Fig. 1 Dependence of D & S of Bs on the orientation of MC