Radio and multiwavelength evidence of coronal loop eruption in a flare coronal mass ejection event on 15 April 1998

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1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109,, doi: /2003ja010005, 2004 Radio and multiwavelength evidence of coronal loop eruption in a flare coronal mass ejection event on 15 April 1998 Guang-Li Huang Purple Mountain Observatory, Chinese Academy of Science, Nanjing, China Received 25 April 2003; revised 18 August 2003; accepted 25 September 2003; published 6 February [1] A typical flare coronal mass ejection (CME) event is studied at the initial time and position of the flare and CME. The photospheric magnetic configuration consists of two main polarities (dipolar structure) with some emerged new polarities, similar to a quadrupolar structure, during the event. The coronal loops in soft X-ray and EUV images show the signature of the loop interaction, i.e., the storage of the magnetic energy. The radio bursts at 1 2 GHz were observed with fast frequency drifts with bidirectional drift pairs, which may provide a direct signature of upward and downward particle acceleration from the reconnection site, followed by the bulk energy release of the flare. After that, the soft X-ray and EUV loops were suddenly opened and closed again in 10 min. The open time is around the maximum phase of the flare as well as the start time of the associated CME. Meanwhile, the polarization sense of the microwave bursts suddenly reversed at GHz, which might have been caused by the fast variation of coronal loops or the magnetic field. The high-time-resolution (8 ms) data show the microwave bursts at GHz, with slow frequency drifts and zebra structures in the initial phase of the CMEs or shock formation. Hence it is suggested that flares and CMEs may be triggered simultaneously by some MHD instabilities or by reconnection in a favorable magnetic configuration to release the free magnetic energy in two different ways. INDEX TERMS: 7513 Solar Physics, Astrophysics, and Astronomy: Coronal mass ejections; 7519 Solar Physics, Astrophysics, and Astronomy: Flares; 7534 Solar Physics, Astrophysics, and Astronomy: Radio emissions; 7514 Solar Physics, Astrophysics, and Astronomy: Energetic particles (2114); 7835 Space Plasma Physics: Magnetic reconnection; KEYWORDS: radio emissions, magnetic reconnection, energetic particles, flares, coronal mass ejections Citation: Huang, G.-L. (2004), Radio and multiwavelength evidence of coronal loop eruption in a flare coronal mass ejection event on 15 April 1998, J. Geophys. Res., 109,, doi: /2003ja Introduction [2] Coronal mass ejections (CMEs) have attracted particular attention since the Large Angle and Spectrometric Coronagraph experiment (LASCO) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has been providing a large field of view from 1.1 to 30 R S, beginning in early It is suggested that CMEs may play an important role in the solar cycle evolution by ejecting a mass of g to the solar wind as well as a net magnetic flux outward through the corona to link solar activity and large transient interplanetary and geomagnetic disturbances. A key point in the study of CMEs is their relationship with solar flares. With the SOHO and Yohkoh observations, the ability to determine the start time of CMEs and flares has been improved. There are some events that may be interpreted to indicate that flare brightening may begin almost simultaneously with the associated CMEs. Copyright 2004 by the American Geophysical Union /04/2003JA CMEs may be considered as an eruption in large scale of solar upper corona at the time that the associated flares commenced in the lower corona, which may be quite independent physical processes [Low, 1996]. [3] However, it is difficult to exactly measure the start time and position of CMEs, especially when CMEs start in the solar disc rather than in the limb. The question is open for the origin of CMEs; they may result from a sudden injection of magnetic helicity by the emergence of a twisted flux tube or a global instability. A relevant question is if magnetic reconnection is important in the initiation process of CMEs or if reconnection is driven by the global instability. Multiwavelength observations combined with the magnetic configuration should be helpful in answering these questions [Neupert et al., 2001; Bastian et al., 2001]. [4] On the other hand, both flares and CMEs originate in the low and high corona, respectively, which means that radio observations may provide an important signature for the flare-cme relationship. The observations show a clear connection between radio bursts and CME development. The radio signature of flare-cme events corresponds to 1of13

2 Table 1. Event on 15 April 1998 a Band Start, UT Maximum, UT End, UT Feature Telescope X ray C8.8 GOES H a SN SVTO SXR ARC Yohkoh HXR ( kev) FS BATSE Heliograph (5.2 cm) BP SSRT GHz spectrograph III ONDREJOU GHz spectrograph IV and U CNAO GHz spectrograph III CNAO a SVTO, San Vito Solar Observatory; SXR, soft X-ray telescope; HXR, hard X-ray telescope; BATSE, Burst and Transient Source Experiment; SSRT, Siberian Solar Radio Telescope; ONDREJOU, Astronomical Institute Ondrejou; CNAO, Chinese National Astronomical Observatories. different kinds of radio bursts, such as type IV, type II, type I, and even type III bursts at metric bands [Aurass, 1996; Gopalswamy et al., 2001]. Moreover, it is widely accepted that the magnetic reconnection may start in the low corona. On the other hand, solar microwave bursts are closely associated with the impulsive phase or particle acceleration in solar flares. Does this mean that microwave bursts may possibly give a direct signature for the initial time and position of CMEs? [5] A flare-cme event on 15 April 1998 is studied in this paper. The instruments and general information on the event are introduced in section 2. The time evolution of the photospheric magnetogram based on SOHO/Michaelson Doppler Imager (MDI) data is discussed in section 3. The time evolution of the coronal loops is shown by SOHO/extreme ultraviolet imaging telescope (EIT) and Yohkoh/soft X-ray telescope (SXT) images as well as by radio observations in section 4. In section 5, evidence for magnetic reconnection or particle acceleration is given by the radio spectrograph of the Chinese National Astronomical Observatories (CNAO). Section 6 shows the microwave bursts with slow frequency drift detected by the radio spectrograph of CNAO and associated with the initial phase of CMEs. The paper is briefly summarized in section Observations 2.1. Instruments [6] A specific event on 25 August 1999 is selected to study the properties of the burst and the fine structures with full data from the radio spectrograph of CNAO at GHz and GHz, from Nobeyama Radio Polarimeters (NoRP) at 1 35 GHz, from the Nobeyama Radio Heliograph (NoRH) at 17/34 GHz, from the Yohkoh SXT and hard X-ray telescope (HXT), from the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO), and from SOHO/MDI. The references for these well-known solar instruments are given by Kosugi et al. [1991] for Yohkoh/SXT/HXT, Nakajima et al. [1994] for NoRP and NoRH, Scherrer et al. [1988] for SOHO/MDI, and Fishman et al. [1985] for BATSE. In China, the radio spectrograph with a broad bandwidth ( GHz) is composed of several bands and is located at Beijing ( GHz, GHz, GHz), Purple Mountain ( GHz), and Yunnan ( GHz) observatories. The frequency resolution is 1 10 MHz and the time resolution is 5 10 ms for all the frequency channels. The sensitivity is better than 2% of the quiet Sun level. The dynamic range is 10 db. The accuracy of the polarization measurement is better than 10% [Fu et al., 1995] General Features [7] The duration and characteristics with multiwavelength observations of the event on 15 April 1998 in AR8203 (N30W12) are listed in Table 1. Figures 1 and 2 show the time profiles of GOES and BATSE hard X ray, respectively, for the event (there are no good data of Yohkoh/HXT for the event on 15 April 1998). In Figure 3 the Stokes I and V components of NoRP at 1 GHz, 2GHz, and 3.75 GHz are given. There are strong fluctuations or Figure 1. Time profiles of the GOES 8.9 X ray for the event on 15 April of13

3 Figure 2. Time profile of the Burst and Transient Source Experiment (BATSE) hard X ray for the event on 15 April fine structures at UT in both the microwave and hard X-ray data, with a maximum phase at UT. Some enhanced fluctuations follow in the microwave burst starting at 0758 UT. [8] There are three CMEs reported in the monthly list of the C2/C3 images of SOHO/LASCO on 15 April 1998 from The first one started at 0755 UT with a central position angle of 338, a width of 56, and a primary speed of 725 km s 1. A bright patch appeared in AR8203 at 0751 UT, and then, a structured cloud with prominence pieces was ejected. 3. Photospheric Magnetogram [9] It is predicted that there are some typical photospheric magnetic configurations that are favorable for the origin of flares and CMEs, such as bipolar or quadrupolar structures. Figure 4 shows the time evolution of the SOHO/MDI magnetogram from 0136 to 1112 UT on 15 April 1998, with some evident variation during the event. For example, one upper positive pole (N2) in Figure 4 disappeared gradually. The main configuration is close to a bipolar structure. The positive pole (N1) moved away from the negative pole (S1) at a speed of 700 km h 1. Some new polarities (S2-3, N3-5) started to emerge before or after the event. Note that the configuration at the maximum phase is something like a quadrupolar structure of N1-2 and S1-2 at 0803:04 UT. The contours of the magnetic field strength overlaid on Figure 4 are 200, 400, and 800 gauss (solid lines) and 200, 400, and 800 gauss (dashed lines), respectively. 4. Coronal Loops 4.1. Loop Interaction [10] Flares and CMEs are expected to originate from the magnetic energy in the lower and higher corona, respectively. Hence these phenomena should be very sensitive to the coronal magnetic field. However, there is not a reliable method to directly measure the coronal magnetic field so far. A simple way to image the coronal magnetic configuration depends on the Yohkoh/SXT or EUV (SOHO/EIT or TRACE) loops in the corona. [11] The Yohkoh/SXT (Al12) and SOHO/EIT (195 Å) images of the event are given in Figures 5 and 6, respectively. The two top panels in Figures 5 and 6 are preflare phase, the bottom left panel is around the maximum phase, and the bottom right panel is the postflare phase. The contours overlaid on these images represent the photospheric magnetic field strength at 0803:04 UT (200, 400, and 800 gauss (solid lines), 200, 400, and 800 gauss (dashed lines)). The soft X-ray and EUV loops are complicated with some similarities. There are two recognized loops; L1 and L2 may be rooted in two bipolar structures, i.e., (N2, S2) and (N1, S1), respectively. [12] The storage of free magnetic energy is believed to start before the flare-cme events. Coronal loop interaction may trigger the energy release and provide the signature of the energy storage process. A bright spot A is located in the cross section of the two loops (L1 and L2), as marked in Figures 5 and 6. It is found that the location of the spot A is raised before the burst at a speed of about several thousand kilometers per hour in the two top panels of Figures 5 and 6. The strong fluctuations in the microwave and hard X-ray bursts in Figures 2 and 3 may be considered as the evidence of loop interaction or coalescence [Sakai and Ohsawa, 1987]. The soft X-ray and EUV loops are dramatically changed during the maximum and postflare phases in the two bottom panels of Figures 5 and 6, which are discussed in section Loop Opens and Closes Again [13] It is most interesting that the interacted coronal loops L1 and L2 were suddenly opened in both Yohkoh/ SXT and SOHO/EIT images, as in the top left of the bottom left panel of Figures 5 and 6. Unfortunately, there are no data of Yohkoh/SXT in the time interval UT. The NoRH was closed at 0645 UT, the time resolution of SOHO/EIT is limited, and the quality of the first images of TRACE was bad in these days. The EUV image with a time most close to the maximum phase is 0734 UT. Hence it is roughly estimated that the Yohkoh/ SXT loop was opened at about 0749 UT, which was about the same as the open time (0750 UT) in the SOHO/EIT images. The loop open time may correspond to the start time (0755 UT) of the first CME on 15 April The initial time or position is extrapolated from SOHO/LASCO/C1-3 images (Figure 7), in which the cycles marked the range of mass ejection. The speed of the CME is about 600 km s 1 on average. [14] The bottom left panels of Figures 5 and 6 are enlarged in Figures 8a and 8b with respect to the opened loops in soft X-ray and EUV images. The contours overlaid on the soft X-ray image are the brightness temperature of NoRH (2, 4, 6, K) at 0645 UT, and the Yohkoh/ SXT intensity (100, 150, 200) is overlaid on the EUV image. The flare center becomes too bright in Figure 8a, which may be due to the saturation of the receiver of Yohkoh/SXT. The overlaid contours may be helpful in supporting this situation of a broken loop because there is no loop configuration when the levels are small. Moreover, it is noted that the shape and direction of the open loops of Yohkoh/SXT and SOHO/EIT are quite similar. After that, 3of13

4 Figure 3. Stokes I and V components at 1 GHz, 2 GHz, and 3.75 GHz observed by the Nobeyama Radio Polarimeters for the event on 15 April of13

5 Figure 4. Time evolution of Solar and Heliospheric Observatory (SOHO)/Michaelson Doppler Imager (MDI) magnetograms in the event on 15 April The contours of the magnetic field strength overlaid on these images are 200, 400, and 800 gauss (solid lines), and 200, 400, and 800 gauss (dashed lines), respectively. 5of13

6 Figure 5. Time evolution of Yohkoh/soft X-ray telescope (SXT) images (Al12) for the event on 15 April The SOHO/MDI contours overlaid on these images are 200, 400, and 800 gauss (solid lines) and 200, 400, and 800 gauss (dashed lines), respectively. 6of13

7 Figure 6. Time evolution of SOHO/extreme ultraviolet imaging telescope (EIT) images at 195Å for the event on 15 April The SOHO/MDI contours overlaid on these images are 200, 400, and 800 gauss (solid lines) and 200, 400, and 800 gauss (dashed lines), respectively. Figure 7. The extrapolation of the initial time from the time evolution of SOHO/Large Angle and Spectrometric Coronagraph experiment (LASCO)/C1 C3 images for the event on 15 April of13

8 comparison with another band of 1 2 GHz (weakly LC in an earlier time), which is introduced in section 5. [16] Note that the reverse of the polarization sense took place only in the fast fluctuations with a short timescale and narrow bandwidth, as shown in the expanded time profile at UT in the bottom panel of Figure 3, which means that the variation of the coronal magnetic field does not change the polarization of total gyrosynchrotron radiation in full band. The fine structures at GHz may be contributed to some plasma-coherent processes in narrow band [Huang, 2003]. Figure 8. The opened coronal loop of (a) Yohkoh/SXT and (b) SOHO/EIT for the event on 15 April The overlaid contours are Nobeyama Radio Heliograph (2, 4, 6, K) at 0645 UT and Yohkoh/SXT intensity (100, 150, 200) in Figures 8a and 8b, respectively. the opened loops were closed again in 10 min, as shown in the bottom right panels of Figures 5 and Reverse of Radio Polarization Sense [15] It is well known that the polarization of microwave radiation depends on the coronal magnetic field. It is expected that some changes may take place in radio observations when the coronal loops are open and closed if these loops are associated with the coronal magnetic configuration. Figure 3 shows the polarization of NoRP in the event at 1, 2, and 3.75 GHz. The polarization sense was reversed at 3.75 GHz from the weakly left circular (LC) to strongly right circular (RC) sense at UT during the time the loops were opened and closed in the event. This reverse was also recorded by the GHz (strongly RC) radio spectrometer of the Beijing Astronomical Observatory in 5. Fast Frequency Drift in Microwave Bursts [17] The radio bursts with fast frequency drifts (type III bursts) are considered as the direct signature of particle acceleration in the reconnection site. The drift in bidirection may especially provide direct information of the upward and downward propagation of nonthermal electrons as well as of the acceleration process [Huang et al., 1998]. [18] Figure 9 shows the time profiles at multiple channels of the radio spectrograph at 1 2 GHz of CNAO for the event. There is a group of type III bursts with both positive and negative frequency drifts for the event on 15 April 1998, and bidirectional drifts started at GHz, which implied the propagation of nonthermal electrons upward and downward simultaneously from an acceleration region at the coronal range corresponding to these frequencies. The magnetic reconnection may be caused by some MHD instabilities in a very narrow current sheet, and the charged particles are accelerated quasi-periodically by the induced electric field in bidirection. The radio observation was accompanied by the HXR burst with very rich fine structures (Figures 2 and 3). The very weak LC polarization of the bursts in Figure 9 suggests that the reconnection site may be located at the top of the magnetic configuration, which is supported by the position of the loop cross section in Figures 5 and 6. [19] It is noted that the microwave type III bursts in the event were observed at the start time of both flares and CMEs. For example, the bidirectional drift pairs in Figure 9 are just before the opening of the coronal loops (Figure 8), in the time interval between 0741:10 UT (t1) and 0742:40 UT (t2) in Figure 3, which suggests that the magnetic reconnection (or MHD instabilities) may trigger both the magnetic energy release and some global instabilities in the flare-cme events. [20] The observations may support a model of magnetic breakout for CMEs [Antiochos et al., 1999]. This model is based on a quadrupolar configuration. As the central lower arcade was sheared, its expansion induced the formation of a current sheet. When the reconnection rate is small, the sheared arcade is confined by the upper one. When the reconnection rate becomes significant, the confinement by the upper arcade is removed, and the lower arcade is ejected upward. Another possibility is that the global instabilities may be driven by the photospheric motion to produce magnetic reconnection as well as flares and CMEs [Amari and Luciani, 1999a; Amari et al., 1999b]. 6. Slow Frequency Drift in Microwave Bursts [21] When the frequency drift of type III bursts gradually changes from negative to positive, it is interpreted with the 8of13

9 Figure 9. The microwave type III bursts recorded by the 1 2 GHz radio spectrograph of the Beijing Astronomical Observatory (BAO) for the event on 15 April The upward and downward drifts of nonthermal electron beams are marked by straight lines as well as the location of the reconnection or acceleration site. movement of nonthermal electrons along closed magnetic field lines. These bursts are called inverted-u bursts, or simply type U bursts [Suzuki and Dulk, 1985]. So far, type U bursts are only reported at metric bands. On the other hand, the metric continua (type IV bursts) are the most frequent radio signatures of flare-cme events [Gopalswamy and Kundu, 1993]. Type IV bursts cover a wide frequency range, from microwave to meterwave bands [Isliker and Benz, 1994]. Sometimes, type IV bursts are accompanied by their specific fine structures, such as the zebra pattern, fibre, or emission line [Chernov et al., 1998]. [22] Figures 10a 10c show different kinds of slow frequency drifts at GHz for the event on 15 April With 0.2 s resolution, there were only some type-iiilike bursts (Figure 10a). The dynamic spectra with high time resolution (8 ms) are given in respect to each type-iiilike burst; a series of type-u-like and type-iv-like bursts are displayed with some examples in Figures 10b and 10c, respectively. At first, several type-u-like bursts appeared separately at 0758: :54 UT, and one example is shown in Figure 10b. These bursts are composed of two or three parallel loop-like structures. The drift rate of the bursts is several hundred MHz per second, or the speed of the moving source is several hundred kilometers per second, which is comparable with the speed of the associated CME in Figure 7. After that, a microwave type-iv-like burst or continua appeared from 0801:27 to 0801:31 UT (Figure 10c). There are also two or three parallel loop-like structures at the high-frequency edge (something like the zebra pattern). There are a series of oscillations overlaid on the loop-like structures with a narrow band and short timescale over a broad frequency range. The similar phenomena at meter bands were recently reported and discussed by Chernov et al. [1998]. [23] It is easy to understand the relation of type U and IV bursts with CMEs. The typical speed of CMEs is 400 km s 1 [Low, 1996], which is comparable to the values calculated from the drift rates of type-u-like and type-iv-like bursts. The type U bursts may be contributed to the energetic electrons moving along the closed magnetic field lines. After the magnetic loops are opened the mass ejection as well as the type-iv-like bursts start along the open field lines. [24] The microwave type-u-like and type-iv-like bursts with a high polarization degree (80%) just correspond to the reversion of the polarization sense of NoRP time profiles at 4 GHz (Figure 3). There are also some metric type IV bursts and continua reported by the Hiraiso radio spectrograph of the Communications Research Laboratory ( MHz at UT), the radio spectrometer of the Astrophysical Institute Potsdam ( MHz at UT), and Izmiran ( MHz at UT) for this event. Note that the start time of these meter-band bursts is closer to the loop opening as well as to the start time of the associated CME. 7. Summary [25] A time series of observations in a flare-cme event started from loop interaction and the development of twisted tubes above a bipolar or quadrupolar magnetic configuration. The radio bursts with fast frequency drift were observed, followed by the bulk energy release or flares. 9of13

10 Figure 10. The dynamic spectra of (a) type-iii-like (resolution of 0.2 s), (b) type-u-like, and (c) type- IV-like (resolution of 8 ms) bursts observed by the GHz radio spectrograph of BAO for the event on 15 April The time-frequency features of some type III-like, U-like, and IV-like bursts are marked. 10 of 13

11 Figure 10. (continued) 11 of 13

12 Figure 10. After that, X-ray and EUV loops were suddenly opened and closed again in the high corona, which corresponded to the start time of the CMEs. The polarization of microwave bursts was suddenly reversed at given frequencies together with the fast variation of coronal loops. In the decay phase of the flares the microwave bursts with slow frequency drift may be associated with the initial phase of CMEs or shocks. The process is summarized in Table 2. [26] The flare-cme event in the solar disk is characterized by multiwavelength data, such as the microwave data of both fast and slow frequency drifts, X-ray and EUV data of coronal loops, and, especially, the time evolution coincident with the initial phase of flares and CMEs, which is useful for understanding the origin of the flare-cme relationship. [27] From the observations of the event, it is suggested that flares and CMEs may be triggered simultaneously by (continued) some MHD instabilities or reconnection in a favorable magnetic configuration to release the free magnetic energy in two different ways, i.e., flares and CMEs. Table 2. Summary a Observation Telescope Time Series, UT Bipolar/quadrupolar SOHO/MDI stable Loop interaction Yohkoh/SXT Twisted tubes SOHO/EIT Fast drift pairs spectrometer of CNAO Flares start BATSE, Yohkoh/HXT 0742 Loop open Yohkoh/SXT, SOHO/EIT 0749 CMEs start SOHO/LASCO 0751 Slow drifts spectrometer of CNAO Loop closed Yohkoh/SXT, SOHO/EIT 0802 a SOHO, Solar and Heliospheric Observatory; MDI, Michaelson Doppler Imager; EIT, extreme ultraviolet imaging telescope. 12 of 13

13 [28] Acknowledgments. This study is supported by NFSC projects and and by the 973 program with G The author would like to thank the Nobeyama, Yohkoh, and SOHO teams for their effort on data usage. [29] Shadia Rifai Habbal thanks both referees for their assistance in evaluating this paper. References Amari, T., and J. F. Luciani (1999a), Confined disruption of a three-dimensional twisted magnetic flux tube, Astrophys. J., 515, L81 L84. Amari, T., J. F. Luciani, Z. Mikic, and J. Linker (1999b), Confined disruption of a three-dimensional twisted magnetic flux tube, Astrophys. J., 518, L57 L60. Antiochos, S. K., C. R. De Vore, and J. A. Klimchuk (1999), A model for solar coronal mass ejections, Astrophys. J., 510, Aurass, H. (1996), Coronal mass ejections, in Coronal Physics From Radio and Space Observations: Proceedings of the CESRA Workshop, Held at Nouan le Fuzelier, France, 3 7 June 1996, vol. 3, edited by G. Trottet, pp , Springer-Verlag, New York. Bastian, T. S., M. Pick, A. Kerdraon, D. Maia, and A. Vourlidas (1998), The coronal mass ejection of 1998 April 20: Direct imaging at radio wavelengths, Astrophys. J., 558, L65 L69. Chernov, G. P., et al. (1998), New features in type IV solar radio emission: Combined effects of plasma wave resonances and MHD waves, Astron. Astrophys., 334, Fishman, G. J., et al. (1985), Burst and Transient Source Experiment (BATSE) for the Gamma Ray Observatory (GRO), Conf. Pap. Int. Cosmic Ray Conf. 19th, 3, Fu, Q. J., Z. H. Qin, H. R. Ji, and L. B. Pei (1995), A broadband spectrometer for decimeter and microwave radio bursts, Sol. Phys., 160, Gopalswamy, N., and M. R. Kundu (1993), Thermal and nonthermal emissions during a coronal mass ejection, Sol. Phys., 143, Gopalswamy, N., S. Yashiro, M. L. Kaiser, R. A. Howard, and J.-L. Bougeret (2001), Radio signatures of coronal mass ejection interaction: Coronal mass ejection cannibalism?, Astrophys. J., 548, L91 L94. Huang, G.-L. (2003), Radio signature of magnetic reconnection and bi-directional shock waves in a flare-cme event on April 15, 1998, New Astron., 8, Huang, G.-L., Z. H. Qin, G. Yang, Q. J. Fu, and Y. Y. Liu (1998), The energetic spectrum of non-thermal electrons in an acceleration region calculated from a solar microwave type III burst with both positive and negative frequency drifts, Astrophys. Space Sci., 259, Isliker, H., and A. O. Benz (1994), Catalogue of 1 3 GHz solar flare radio emission, Astron. Astrophys. Suppl. Ser., 104, Kosugi, T., et al. (1991), The hard X-ray telescope (HXT) for the Solar-A mission, Sol. Phys., 136, Low, B. C. (1996), Coronal mass ejections, Sol. Phys., 186, Nakajima, H., et al. (1994), The Nobeyama radioheliograph, Proc. IEEE, 82(5), Neupert, W. M., B. J. Thompson, J. B. Gurman, and S. P. Plunkett (2001), Eruption and acceleration of flare-associated coronal mass ejection loops in the low corona, J. Geophys. Res., 106, 25,215 25,225. Sakai, J.-I., and Y. Ohsawa (1987), Particle acceleration by magnetic reconnection and shocks during current loop coalescence in solar flares, Space Sci. Rev., 46, Scherrer, P. H., J. T. Hoeksema, R. S. Bogart, A. B. C. Walker Jr., A. M. Title, T. D. Tarbell, C. J. Wolfson, T. M. Brown Jr., J. Christensen- Dalsgaard, and D. O. Gough (1988), The SOHO mission: Scientific and technical aspects of the instruments, 25 pp., Eur. Space Agency, Noordwijk, Netherlands. Suzuki, S., and G. A. Dulk (1985), Type-III bursts, in Solar Radiophysics: Studies of Emission From the Sun at Metre Wavelengths, edited by D. J. McLean and J. N. R. Labrum, pp , chap. 12, Cambridge Univ. Press, New York. G.-L. Huang, Purple Mountain Observatory, Chinese Academy of Science, 2 West Beijing Road, Nanjing, China. (huangguangli@hotmail. com) 13 of 13