mi010.manoharan01 Posted: 16-Sep-95 Updated: 07-Jul-96 Events specified: solar particle event of 25-Oct-94
P.K. Manoharan, M. Pick, L. Van Driel-Gesztelyi. Observatoire de Paris, DASOP.
On 25 October 1994, the Ulysses spacecraft observed particles of solar origin at a heliographic latitude of 74 degree (Pick et al. GRL submitted). The Nancay Radio heliograph operating at multi-frequency mode has shown several periods of activity during this day, in particular, an out burst starting at about 10:00 UT. We propose to make analysis of this event using both the X-ray and radio data in order to understand the solar origin of accelerated particles and their injection towards the interplanetary medium.
Update 07-Jul-96
Abstarct of contribution presented at the Yohkoh Conference, Bath.
Flare associated large-scale magnetic reconnection
P.K. Manoharan, L. van Driel-Gesztelyi, M. Pick, and P. Demoulin
Although the soft X-ray and radio emissions caused by solar flares are produced by different physical mechanisms of the corona, they are intimately related to the magnetic field configuration of the sun. The combined study of X-ray and radio measurements is important in the understanding of the large-scale MHD disturbances and related phenomena produced by a flare. Here, we report a unique set of observations, for a low heliolatitude flare, obtained with the Yohkoh/SXT and Nancay Radioheliograph, together with supporting magnetic field data from Kitt Peak observatory. This flare starts with the expansion of spectacularly twisted loops, followed by sporadic radio bursts (some of them are detected at high heliolatitude, 65 degree South) and formation of two coronal holes on opposite hemisphere of the sun. The timing and location of these events provide evidence for a large-scale magnetic reconnection between the expanding twisted flare loops and overlying huge loops inter-connecting quiet regions on the sun. The proposed scenario can also explain the source of energetic electrons measured by Ulysses at high heliolatitude (74 degree South).
Evidence for large-scale solar magnetic reconnection from radio and X-ray measurements
P.K. Manoharan, L. van Driel-Gesztelyi, M. Pick, and P. Demoulin
Utilizing Yohkoh/SXT and Nancay radioheliograph data we present, for the first time, observations of expanding twisted X-ray loops and a series of non-thermal radio bursts which follow the loop expansion in time and space up to about 12 arcmin distance. The loops were produced during a long-duration C4.7 flare close to the disc center on 25 October 1994 at 10:49 UT. The series of radio bursts were observed on the Southern hemisphere above a weak positive polarity region. Kitt Peak magnetogram shows the existence of a weak negative polarity region on the Northern hemisphere at the same helio-longitude. Simultaneously with the non-thermal radio bursts we observed the appearance of two remote X-ray brightenings and subsequent formation of two coronal holes above these weak (quiet) magnetic regions of opposite polarity which strongly suggest the involvement of these remote regions in the event. During the 6-hour long gradual phase of the flare new X-ray loop connections developed among the active region (AR) and the remote quiet regions. A non-thermal radio continuum emission originating from the AR was also observed.
We propose that the series of radio bursts, two remote X-ray brightenings and new coronal loop connections were all signatures of a large-scale reconnection process between the expanding twisted flare loops and overlying trans-equatorial loops connecting quiet-Sun regions. The reconnection was only partial, the external part of the overlying large-scale fields were pushed out in the solar wind by the expanding twisted loops, leading to the formation of the coronal holes. The interaction between the AR and the large-scale fields seemed to be active during the entire gradual phase of the flare. This scenario may also explain the measurement of high energy electrons in the interplanetary medium from 74 degree south helio-latitude as observed by Ulysses (Pick et al. 1995).