Quick changes of photospheric magnetic field during flare-associated surges Leping Li, Huadong Chen, Suli Ma, Yunchun Jiang National Astronomical Observatory/Yunnan Astronomical Observatory, Chinese Academy of Sciences

We report the impulsive loss of magnetic flux and corresponding changes of sunspots in the course of three surges associated with X- ray M class flares.

Event 1: 2001 March 27 Location: N21E33 AR9401 Flare: M2.2, 16:25--16:30--16:32 UT (duration: 7 minutes) Data: BBSO full-disk Ha images MDI magnetograms, Dopplergrams and continuum intensity images Event 2: 2002 July 26 Location: S22E18 AR10044 Flare: M1.0, 18:57--19:03--19:06 UT (duration: 9 minutes) Data: BBSO High-Resolution Ha images. MDI magnetograms, Dopplergrams and continuum intensity images TRACE WL and 1600 Å images EIT EUV images RHESSI hard X-ray (HXR) images Event 3: 2002 July 29 Location: S20W14 AR10044 Flare: M4.8, 02:29--02:38--02:46 UT (duration: 17 minutes) Data: YNAO full-disk Ha images MDI magnetograms and continuum intensity images TRACE WL and 171 Å images RHESSI HXR images

Event 1: Surge & Flare Fig. 1: BBSO Ha images show the evolution of the event 1. Flare: a bright patch in Ha. a compact flare with duration of only 7 minutes. Surge: (1) first ejected from the flaring patch as a bright feature as the flare started (see the arrow in 16:28 UT image). (2) then a dark component developed along the same path after the flare end (see the arrow in 16:39 UT image) and another smaller dark surge appeared to its west (see the arrow in 16:43 UT image).

Event 1: BBSO Ha Fig.1. BBSO Ha center-line images showing the evolution of the 2001 March 27 event. The field of view (FOV) is 220 ''×260''. The white box indicates the FOV of Fig. 2.

Event 1: Magnetic field, Sunspots and Velocity Fig. 2: MDI magnetograms, intensity images and Dopplergrams on the surge foot region. (1) A patch of negative flux began to emerge 40 hours before the surge, and then slowly canceled with the nearby positive flux (see Liu and Kurokawa, 2004). (2) Within the flare duration, the cancellation quickly increased so the negative flux quickly dropped about 20% (see Fig. 3). This gives an average flux loss rate of about 1.2×10 17 Mxs -1. The impulsive loss of magnetic flux was involved in the sudden disappearance of a small sunspot (indicated by the white arrow 1 in Fig.2b). Two blueshift patches appeared in the MDI Dopplergrams around the canceling site during the flare (indicated by the white arrows 1 and 2 in Fig.2b).

Event 1:MDI Observations Fig.2. MDI magnetograms (a), intensity images (b) and Dopplergrams (c). In Dopplergrams, the black (white) patches represent blueshifts (redshifts). The white contours indicate the area, in which the changes of the negative magnetic flux are measured and plotted in Fig. 3. The black arrows indicate the emergence and cancellation of the negative flux, and the white arrows, `1' and `2', the locations of the appearances of upflows during the impulsive loss of magnetic flux. To aid matching, an Ha image at the flare peak time is given in (b). Noted the sudden disappearance of a small sunspot indicated by the white arrow 1 in (b). The FOV, indicated by the white box in Fig. 1, is 90''×90''.

Event 1:Changes of magnetic flux Fig. 3. Time profiles of the GOES-8 soft X-ray in the energy channel of 1-8 Å and the changes of negative magnetic flux in the white contour area in Fig. 2. To improve clarity, the absolute values for the negative flux are plotted.

Event 2: Surge & Flare Fig. 4: BBSO Ha and EIT EUV images show the evolution of the event 2. Flare: a compact flare with duration of only 9 minutes (see the black arrow in Fig. 4a). Ha dark surge: first ejected from the flare site after the flare end (see the white arrow in Fig. 4a). EUV jet was clearly seen in EIT observations (see Fig. 4b).

Event 2: BBSO Ha & EIT EUV Fig. 4. Temporal evolution of the 2002 July 26 event: (a) BBSO high-resolution Ha center-line and (b) EIT EUV images. The black arrow indicates the flare at its peak time, and the white arrow, the surge foot. The FOV is 180'' × 195''. The white box indicates the FOV in Fig. 5.

Event 2: RHESSI HXR Source Fig. 5: RHESSI HXR contours superposed on Ha, TRACE WL and 1600 Å images, as well as MDI magnetogram and Dopplergram. The HXR source was located near the Ha surge foot and over the neutral line of photospheric magnetic field.

Event 2: RHESSI HXR Source Fig. 5. Ha (a),TRACE WL (c) and 1600 Å (d) images, MDI magnetogram (e) and Dopplergram (f) near flare maximum, as well as Ha image near maximum phase of surge (b) with superposed RHESSI kev HXR black contours (levels are 75%, 85% and 95% of the maximum counts) accumulated from 19:02:08 to 19:03:08 UT. The white contour indicates the area, in which the changes of the positive flux are measured and plotted in Fig. 7. The FOV, indicated by the white box in Fig. 4, is 80'' × 80''. The white box indicate the FOV of Fig.6.

Event 2: Magnetic field, Sunspots and Velocity Fig. 6: MDI magnetograms, TRACE WL images and MDI Dopplergrams on the surge foot region. (1)An impulsive loss of magnetic flux was also observed on the surge foot region within the flare duration. (2)The positive magnetic flux quickly dropped about 10% and the average flux loss rate is about 8.3 ×10 16 Mxs -1 (see Fig. 7). This magnetic flux loss was relevant to the motion of a small positive sunspot,`p2', toward and then collision and cancellation with a negative sunspot,`n' (see Fig. 6b). A blueshift patch also appeared in the MDI Dopplergrams around the canceling site during the flare (indicated by the white arrow in Fig. 6c).

Event 2:MDI & TRACE Observations Fig. 6. MDI magnetograms (a), TRACE WL images (b) and MDI Dopplergrams (c) with superposed RHESSI kev HXR black contours (also see Fig. 5). Three small sunspots are denoted as `n', `p1' and `p2'. Noted that the p2 of positive polarity moved toward and then collided with the n and p1. The white arrow in (c) indicates the appearances of upflows during the impulsive loss of magnetic flux. The FOV, indicated by the white box in Fig. 5, is 25'' × 25''.

Event 2:Changes of magnetic flux Fig. 7. Time profiles of the GOES-10 soft X-ray in the energy channel of 1-8 Å (dashed line) and the changes of positive magnetic flux in the white contour area in Fig. 5.

Event 3: Jet, Surge & Flare Fig. 8: TRACE 171 Å and YNAO Ha images show the evolution of the event 3. Flare: a compact flare with duration of 17 minutes. Jet and Surge: (1) Just after the flare start, an initial EUV jet appeared like two loops (marked as L1 and L2 in Fig. 8) ejecting from the flare site. (2) then the jet divided into two components: one was bright and the other, dark. (3) An Ha surge appeared to be cospatial with the dark component of the EUV jet (see Asai, Ishii and Kurokawa 2001; Chae et al. 1999). An interesting fact is the motion of the RHESSI HXR source from east to west in the 171 Å flaring ribbon during the flare.

Event 3: TRACE 171 & YNAO Ha Fig. 8. TRACE 171 Å (a--d) and YNAO Ha (e--f) images showing the evolution of the 2002 July 29 event. In 171 Å images, the black contours are from 1 minute RHESSI maps in the energy range of kev with levels of 30%, 50%, and 70% of each maximum value, and the outlines of the Ha surge are superposed as white contours. In Ha images, the MDI longitudinal fields are shown by dashed (solid) contours for positive (negative) polarity. For convenience of showing the HXR source motion, two black vertical lines are overplotted. The FOV is 180'' × 130''.

Event 3: Magnetic field and Sunspots Fig. 9: two pre- and post-flare MDI intensity images, their difference image and MDI magnetogram on the flare region. (1) An impulsive loss of magnetic flux was again observed on the surge foot region within the flare duration. (2) The positive magnetic flux quickly dropped about 13% and the average flux loss rate is about 1.1 × Mxs -1 (Fig.10a). This magnetic flux loss was due to the rapid and permanent decay of a penumbral segment below the flare site (see Fig. 9c and Fig. 10b).

Fig.9. Pre- (a) and post- (b) flare MDI intensity images, their difference image (c) and MDI magnetogram (d). D marks the decaying penumbra with area outlined by the solid curves. The triangle symbols represent the maximum values of RHESSI HXR source in the energy range of kev with 1 minute integration time, and their increasing size represents the increasing times from 02:31 to 02:51 UT. The thick arrows indicate the motion direction of the HXR source, and the boxes mark the area, in which the changes of the positive magnetic flux are measured and plotted in Fig. 10. The FOV is the same as in Fig. 8.

Event 3:Changes of magnetic flux Fig. 10. (a) Time profiles of the GOES-10 soft X- ray in the energy channel of 1-8 Å (dashed line) and the changes of positive magnetic flux in the white box area in Fig. 9. (b) Mean intensity around the decayed penumbra as a function of time. Intensity data are from TRACE (diamonds) and MDI (pluses).

Summary 1) All of the three surges were associated with compact flares of X-ray M class. 2) During these flares, the magnetic flux around the flare sites quickly fell down. 3) The impulsive loss of magnetic flux was associated with different changes in sunspots: * For the event 1: sudden disappearance of a small sunspot (also see Wang et al. 2002; Liu et al. 2003). * For the event 2: motion, collision and cancellation of sunspots. * For the event 3: rapid decay of a penumbral segment (also see Wang et al. 2004; Deng et al. 2005; Liu et al. 2005) 4) For two events for which MDI Dopplergrams were available, upflows were found on the surge foot regions in the course of the sudden loss of magnetic flux (see Yurchyshyn and Wang, 2001; Chae et al. 2004). 5) The RHESSI HXR flare kernel was just located on the surge foot for the event 2, while moved across the decayed penumbra for the event 3.

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Thank you!