1. Flare Ribbon Expansion and Energy Release Ayumi ASAI Kwasan and Hida Observatories, Kyoto University Explosive Phenomena in Magnetized Plasma – New Development of Reconnection Research – March 17 – 19, 2004 @Kyoto 1. INTRODUCTION Magnetic reconnection mechanism is a key process for the energy release and the particle acceleration during solar flares. We estimated the amount of the released energy quantitatively, based on the magnetic reconnection model and by using observable values. We estimate the energy release rate, by using the separation speeds of two ribbons and the photospheric magnetic field strengths. The estimated reconnection rate and the Poynting flux along each slit show good correlation with the nonthermal bursts (Fig. 5). They are also locally large enough at the HXR sources, and can explain the difference of spatial distributions between HXR and H  images. For more accurate estimation, we have to take into account the relation between B c and B p Fig.2 H  image overlaid with HXR contour image HXR sources strong energy release 2. ENERGY RELEASE RATE Fig1. H  full disk image obtained with Flare Monitoring Telescope at Hida Obs. NOAA 9415 Energy release rate ( dE/dt ) is written as: B c : coronal magnetic field strength v i : in flow velocity A : area of reconnection region 3. RESULTS The dynamic range of HXT is about10. Therefore, if the released energy at the HXR sources are (at least) 10 times larger than those at the other H  kernels, the difference of appearance can be explained. Fig.3 Cartoon of magnetic reconnection Slits were put in the direction of the flare ribbon separation, and calculated B p v f and B p 2 v f at the outer edges of flare ribbons. We followed the temporal evolutions of these values. Fig.5 Time profiles of microwave (NoRH 17GHz), HXR (Yohkoh/HXT), reconnection rate ( B p v f ), and Poynting flux (B p 2 v f ) for slit I (05:19 UT burst) and slit II (05:26 UT burst). Qualitatively, both of the estimated reconnection rates ( B p v f ) and Poynting fluxes ( B p 2 v f ) reconstruct peaks of the light curves of the nonthermal emissions. We made extensive use of Yohkoh Data Center, and SOHO MDI Data Service. B c v i = B p v f B c 2 v i ∝ B p 2 v f Reconnection rate Poynting Flux (conservation of magnetic flux) ( B c ∝ B p is assumed) The difference of the spatial distributions are caused by the difference of released energy!? Comparing the H  images with the HXR images (Fig 2.), we found the difference between the spatial distribution of the H  kernels and that of the HXR sources: only two sources, which are accompanied by the H  kernels, are seen in the HXR image. Sartorius telescope @Kwasan Obs. Flare (Fig 1.) April 10, 2001 05:00UT NOAA 9415 GOES X2.3 Data H  …Kwasan Obs., Sartorius Tele. Magnetogram…SOHO / MDI hard-X ray (HXR)…Yohkoh / HXT Microwave…NoRH Here, we estimate the reconnection rate B p v f, and the Poynting flux B p 2 v f along the slits which pass the HXR sources, as the parameters of the energy release rates. BpBp vfvf neutral line other Ha kernels weak energy release Although it is very difficult to estimate corona physical values ( B c, v i ), assuming the conservation law of magnetic flux, and using observable values ( B p, v f ), we estimate the energy release rate. conservation of magnetic flux flare ribbon B c : coronal magnetic field strength v f : speed of ribbon separation Fig.4 Method of the analyses reconnected loop microwave HXR reconnection rate Poynting flux HXR burst at 05:19 UT microwave HXR reconnection rate Poynting flux 4. SUMMARY slit I slit II HXR burst at 05:26 UT slit I slit II slit Quantitatively, both of the reconnection rates and Poynting fluxes are enhanced enough (more than 10 times larger) at the HXR sources, compared with those at the other H  kernels. Table 1 Comparison of the reconnection rates and the Poynting fluxes between the H  kernels with HXR sources and those without ones reconnection rate (ratio) B p v f [V m -1 ] Poynting flux (ratio) v f B p ２ [erg cm -2 s -1 ] K1 2.6×10 2 (0.52) 1.3×10 9 (0.27) K2 7.7×10 3 (16) 7.6×10 11 (150) K3 4.9×10 2 (1.0) 5.0×10 9 (1.0) K3 K1 K2 K2 : HXR sources P1