Pergamon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Adv. Space Res. Vol. 25, No. 9, pp. 1879-1882,200O Q 2000 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain www.elsevier.ni/locate/asr PII: SO273-1177(99)00600-6 0273-1177/00 $20.00 + 0.00 zyxwvutsr DYNAMICS IN RESTRUCTURING ACTIVE REGIONS OBSERVED DURING SOHO/YOHKOH/GBO CAMPAIGNS B. Schmieder’t*, Y. Deng3, C. H. Mandrini 4, P. Rudawy5, N. NittaG, H. Mason7, L. Fletcher6, P. Martensg, N. Brynildsen* ’ Observatoire de Paris, 92195, Meudon Cedex Principal * Institute of Oslo, N-0315 Blindern, Oslo 3, Norway 3 Beijing Astronomical Observatory, Beijing, 100080,China 4 Instituto de Astronomia y Fisica de1 Espacio, IAFE, CC 67, Sue 28, 1428 Buenos Aires, Argentina 5 Astronomical Institute of the Wroclaw University, 51-622 Wroclaw Poland 6 Lockheed, 3251 Hanover street, Palo Alto, CA 94304, USA 7 Department of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge CB3 9EW, UK * NASA/GSFC, Greenbelt, MD 20771, USA ABSTRACT JOP17 and JOP 33 are SOHO Joint Observing Programs in collaboration with Yohkoh/SXT and ground based observatories (GBO’s), dedicated to observe dynamical events through the atmosphere. During runs of these programs we observed in restructuring active regions (ARs), surges, subflares, bright knots, but not large flares and jets. From these observations we have been able to derive some of the responses of the coronal and chromospheric plasma to the evolution of the photospheric magnetic field. Emerging flux in an AR led to the formation of Arch Filament Systems in the chromosphere, hot loops and knots in the transition region, and X-ray loops. Frequent surges have been observed in relation to parasitic or mixed polarities, but coronal jets have not yet been found. We discuss the possible mechanisms acting during the restructuring of the active regions (reconnection or “sea-serpent” geometries). 0 2000 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION The evolution of active regions is mainly due to emerging flux, while in For the decaying phase nothing is really clear in this “boiling” magnetic field (review of van Driel-Gesztelyi, 1998). The concept of emergence due to an Q - loop is relatively classical. Another interesting effect that should be considered in this great activity is the emergence of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA a U-loop (Parker 1984, Spruit et al. 1987). U-loops are horizontal subsurface flux tubes which have two ends in the photosphere. Small sections of the horizontal loop can be brought up by turbulence and create mixed polarity fields through a “sea serpent” process. In moat regions around sunspots this phenomena is well observed. It could be responsible for filament formation (Low 1996). We present two active regions which were the seat of constant emerging flux. OBSERVATIONS Two solar active regions were mainly observed by SOHO/MDI (full disk magnetograms with a time step of 96 minutes), by Yohkoh/SXT (full disk soft X-ray images), by SOHO/EIT (full disk images in He11 304 A, FeIX-X 171 A, FeXV 284 A and FeXII 195 A) and by the large telescope at Bialkow (Poland). Magne- tograms and white light images were obtained in Huairou and Debrecen, respectively (Schmieder et al. 1998). AR 8048 was mainly stable in the sense that the flux stayed constant but its area was increasing, which is a sign that the AR is in its decaying phase (van Driel-Gesztelyi, 1998). Following the evolution of the magnetic field, we find three interesting zones which could be places suitable for ejections. Around the leading spot a moat region is evolving. Such a region is generally related to surge and X-ray jet activity (Canfield et al., 1996). The moat region consists of bipolar elements moving radially away from the spot. The outer edge of the moat cell has the same negative polarity as the sunspot. When the leading cells of positive polarity reach the boundary they merge and disappear (Fig. 1). In the middle of the AR we observe some dark fibrils in the Ha line and bright X-ray loops (EIT, CDS and Yohkoh images in Schmieder et al., 1998). This is the signature of emerging flux at the centre of the AR. 1879