1 / 9

EUV vs. B-field Comparisons

EUV vs. B-field Comparisons. Yingna Su Smithsonian Astrophysical Observatory Coauthours: Leon Golub, Aad Van Ballegooijen, Maurice Gros. HMI/AIA Science meeting 2006/02/13. Introduction.

gent
Download Presentation

EUV vs. B-field Comparisons

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EUV vs. B-field Comparisons Yingna Su Smithsonian Astrophysical Observatory Coauthours: Leon Golub, Aad Van Ballegooijen, Maurice Gros. HMI/AIA Science meeting 2006/02/13

  2. Introduction • A two-ribbon structure in the chromosphere and transition region (e.g., in Hα, UV, and EUV) is often seen during a solar flare, especially for those long-duration events associated with coronal mass ejections (CMEs).For two-ribbon eruptive flares, the generally accepted picture is: the flare energy release is driven by the eruption of a magnetic flux rope from the sheared core of a closed bipolar magnetic field(Moore 1988; Forbes 1992). • Masuda, Kosugi, and Hudson (2001) reported observations of the evolution of the HXR (Yohkoh/HXT) footpoints from a strong to weak sheared structure, which was also found in Hα(Sartorius Refractor at Kwasan Observatory, Asai et al., 2003), HXR (RHESSI) and microwave (Nobeyama Radioheliograph, Kundu, Schmahl, and Garaimov, 2004) observations. • In this work, we focus on the question: could the change from the impulsive to gradual phase be related to the magnetic shear change?To answer this question, we have selected a particularly well-observed X17 solar flare on 2003 October 28 which shows obvious shear change via the evolution of the EUV footpoints observed by TRACE, and examined the temporal evolution of the shear and the rate of change of the shear.

  3. Observation (I) The most prominent conjugate footpoints have been identifiedmanually by studying the evolution of the EUV bright kernels.There are three factors that we considered in identifyingbrightenings as conjugate footpoints: (1) the two brighteningsappear simultaneously, (2) the light curves of the twobrightenings are very similar, (3) the two brightenings areconnected by post-flare loops. Figure 1 shows an example of how weidentify the conjugate footpoints in this flare. Figure 1 (a) Gray boxes representingEUV brightenings are overlaid on the EUV image closest in time to HXR Peak 9 which is marked as a vertical solid line. (b)Gray boxes representing EUV brightenings areoverlaid on a later EUV image of the post-flare loops. (c)SOHO/MDI photospheric magnetogram overlaid with MDI contourswhere white and black contours refer to negative and positivemagnetic filed, respectively. The black dotted line represents thelocus of the filament. The field of view is240’’x160’’. (d), (e) EUV light curves of the two brightening pairs “P”/”P1” and “Q”/”Q1”. ACS/HXR light curve is represented by the thick solid line.

  4. Observation (II) Figure 2 TRACE/EUV contours at differenttimes are overlaid on an earlier Hα image from BBSO. Thetimes of the EUV contours are marked on each image, and the blacklines connecting to the EUV bright kernels represent the possibleconjugate EUV footpoints (Fig. 1 shows an example about how to identify these conjugate footpints). Different kind of line refer todifferent group of brightening pairs. The field of view is240’’x160’’ for each image. • The EUV brighteningpairs start at a position close to the magnetic inversion line but widely separated along the inversion line (Fig. 1a), and change to straight across and far from the inversion line (Fig. 1d) gradually during the impulsive phase.

  5. Observation (III) • The shear change is very fast during the early impulsive phase, but stops in the middle of the impulsive phase (Fig. 2b). • The change from impulsive to gradual phase does not correspond to the cessation of magnetic shear change in this event. Figure 3 HXR light curve and the temporal evolution of the shearangle and the change rate of this angle. (a) TheACS/HXR lightcurve of the solar flare on 2003 October 28. (b) The evolution ofthe shear angle (solid line with asterisk sign), and theevolution of the change rate of this angle (dashed line with plussign).

  6. Interpretation Figure 4 Cartoon of the evolution of the magnetic field in the standard model of solar flares. This observed shear change can be understood in terms of the standard model for solar flares (e.g., Moore et al. 1995, 2001). According to this model the pre-flare magnetic field contains a highly sheared core field overlying the magnetic inversion line (MIL) with a relatively less sheared envelope, which is underlying the unsheared magnetic field (Fig. 4a). As soon as the pre-flare configuration becomes unstable to eruption, the core sheared field begins to erupt, and this allows the legs of the sheared immediate envelope to impact together and begin reconnecting just below the rising core field (Fig. 4b), which can explain the conjugate footpoints start as highly sheared. In this model the cessation of shear change of the footpoints during the early impulsive phase corresponds to the splitting of the sheared envelope of the highly sheared core field (Fig. 4c)

  7. Conclusions • A strong-to weak shear change of EUV footpoints is observed in 2003 October 28 flare. • The shear change is very fast during the early impulsive phase, but stops in the middle of the impulsive phase. The change from impulsive to gradual phase does not correspond to the cessation of magnetic shear change in this event. • This observed shear change can be understood in terms of the standard model for solar flares (e.g., Moore et al. 1995, 2001).The cessation of shear change of the footpoints during the early impulsive phase corresponds to the splitting of the sheared envelope of the highly sheared core field. • Our preliminary result of a survey shows that 82% (37 out of 45) two-ribbon flares (M and X class) observed by TRACE show this shear change of footpoints. Detailed information about this statistical work can be found in our poster (#42).

  8. Advantages of AIA and HMI on this topic • Larger field of view (AIA) We will see the whole two ribbons in all the two-ribbon flares, which is helpful for us to get a better statistical result. • AIAwill obtain images in multiple EUV and UV pass bands We may see the loop cooling process more completely, which will help us to identify the conjugate footpoints. • Higher Cadence(AIA) If AIA can obtain some images with 1 s time resolution during the flare, we will get better correlation between the EUV and HXR peaks, which will be helpful for us to identify the generation mechanism of the EUV brightenings. • Higher spatial resolution (HMI) The alignment between the EUV image and magnetogram will be more accurate, because HMI and AIA are onboard the same satellite.

  9. Thank You !

More Related