Publications (5)4.04 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: The first X-class flare in four years occurred on 9 July 1996. This X2.6/1B flare reached its maximum at 09:11 UT and was located in active region 7978 (S10° W30°) which was an old-cycle sunspot polarity group. We report the SOHO LASCO/EIT/MDI and SOONSPOT observations before and after this event together with Yohkoh SXT images of the flare, radio observations of the type II shock, and GOES disk-integrated soft X-ray flux during an extended period that included energy build-up in this active region. The LASCO coronagraphs measured a significant coronal mass ejection (CME) on the solar west limb beginning on 8 July at about 09:53 UT. The GOES 8 soft X-ray flux (0.1–0.8 nm) had started to increase on the previous day from below the A-level background (10-8 W m-2). At the start time of the CME, it was at the mid-B level and continued to climb. This CME is similar to many events which have been seen by LASCO and which are being interpreted as disruption of existing streamers by emerging flux ropes. LASCO and EIT were not collecting data at the time of the X-flare due to a temporary software outage. A larger CME was in progress when the first LASCO images were taken after the flare. Since the first image of the 'big' CME was obtained after the flare's start time, we cannot clearly demonstrate the physical connection of the CME to the flare. However, the LASCO CME data are consistent with an association of the flare and the CME. No eruptive filaments were observed during this event. We used the flare evidence noted above to employ in real time a simplified Shock-Time-of-Arrival (STOA) algorithm to estimate the arrival of a weak shock at the WIND spacecraft. We compare this prediction with the plasma and IMF data from WIND and plasma data from the SOHO/CELIAS instrument and suggest that the flare - and possibly the interplanetary consequences of the 'big' CME - was the progenitor of the mild, high-latitude, geomagnetic storm (daily sum of Kp=16+, Ap=8) on 12 July 1996. We speculate that the shock was attenuated enroute to Earth as a result of interaction with the heliospheric current/plasma sheet.
- [Show abstract] [Hide abstract] ABSTRACT: The interplanetary propagation aspects of the first X-class solar flare and coronal mass ejection are discussed. The solar data relevant to this event are summarized. Data from WIND and charge element and isotope analysis system (CELIAS) show solar wind plasma and interplanetary magnetic field disturbances early on 12 July 1996. It was observed that the extrapolation of the coronal mass ejection back to the flare time suggests a close association between them. Moreover, the coronal mass ejection speed is similar to the type two shock's speed. The results suggest that the coronal mass ejection is intimately related to the shock itself.
- [Show abstract] [Hide abstract] ABSTRACT: The solar observations from GOES-8, the Solar and Heliospheric Observatory (SOHO), and the Yohkoh satellite concerning the events of the X-class flare are discussed. The Michelson Doppler imager (MDI) magnetometer shows a new region of magnetic activity in AR 7978. The rapid development and evolution of this region is shown by the MDI and the extreme-ultraviolet Doppler telescope (EDT) data. The coronal mass ejections (CMEs) observed using coronagraphs are presented. The possible association between the CME and the X-flare is considered.
- [Show abstract] [Hide abstract] ABSTRACT: Part II of a two-part paper considers the interplanetary propagation aspects of the first X-class flare (9 July 1996, 0911 UT, S10 W30) in nearly four years. The solar data relevant to this event are discussed in Part I by Andrews et al. (this proceedings). Radio observations from Tremsdorf-Potsdam show a Type II shock propagating through the corona at about 485 km/s. An operational interplanetary propagation model (STOA=Shock Time Of Arrival) was used to predict, in real-time, its arrival at Earth at 1138 UT on 12 July 1996. WIND and CELIAS data show solar wind plasma and IMF (interplanetary magnetic field) disturbances early on 12 July 1996, followed by a mild, high latitude geomagnetic storm, roughly coincident with the model prediction. We note that: (i) the "big" CME's extrapolation back to the flare time (see Part I) is strongly suggestive of a close association; and (ii) its speed is similar to the Type II shock's speed (as suggested by numerical simulations). Therefore, we suggest that the CME is intimately related to the shock which, following deceleration within the interplanetary medium, arrives at WIND and SOHO as predicted by the STOA model.