Soft X-ray observation of a large-scale coronal wave and its exciter
- 71 Downloads
Recent extreme ultraviolet (EUV) observations from SOHO have shown the common occurrence of flare-associated global coronal waves strongly correlated with metric type II bursts, and in some cases with chromospheric Moreton waves. Until now, however, few direct soft X-ray detections of related global coronal waves have been reported. We have studied Yohkoh Soft X-ray Telescope (SXT) imaging observations to understand this apparent discrepancy, and describe the problems in this paper. We have found good X-ray evidence for a large-scale coronal wave associated with a major flare on 6 May 1998. The earliest direct trace of the wave motion on 6 May consisted of an expanding volume within 20 Mm (projected) of the flare-core loops, as established by loop motions and a dimming signature. Wavefront analyses of the soft X-ray observations point to this region as the source of the wave, which began at the time of an early hard X-ray spike in the impulsive phase of the flare. The emission can be seen out to a large radial distance (some 220 Mm from the flare core) by SXT, and a similar structure at a still greater distance by EIT (the Extreme Ultraviolet Imaging Telescope) on SOHO. The radio dynamic spectra confirm that an associated disturbance started at a relatively high density, consistent with the X-ray observations, prior to the metric type II burst emission onset. The wavefront tilted away from the vertical as expected from refraction if the Alfvén speed increases with height in the corona. From the X-ray observations we estimate that the electron temperature in the wave, at a distance of 120 Mm from the flare core, was on the order of 2–4 MK, consistent with a Mach number in the range 1.1–1.3.
KeywordsFlare Extreme Ultraviolet Extreme Ultraviolet Image Telescope Moreton Wave Coronal Wave
Unable to display preview. Download preview PDF.
- Hudson, H. S. and Karlický, M.: 2000, in R. Ramaty and N.Mandzhavidze (eds.), High Energy Solar Physics-Anticipating HESSI, ASP Conf. Ser. 206, 268.Google Scholar
- Hudson, H. S. and Webb, D. A.: 1997, in N. Crooker, J. Joselyn, and J. Feynman (eds.), Coronal Mass Ejections: Causes and Consequences, Geophysical Monographs 99, 27.Google Scholar
- Kerdraon, A. and Delouis, J.-M.: 1997, in G. Trottet (ed.), Coronal Physics from Radio and Space Observations, Lecture Notes in Physics 483, 192.Google Scholar
- Klimchuk, J. A., Acton, L. W., Harvey, K. L., Hudson, H. S., Kluge, K. L., Sime, D. G., Strong, K. T., and Watanabe, Ta.: 1994, in Y. Uchida, T. Watanabe, K. Shibata, and H. S. Hudson (eds.), X-ray Solar Physics from Yohkoh, Universal Academy Press, Tokyo, p. 181.Google Scholar
- Kondo, T., Isobe, T., Igi, S., Watari, S., and Tokumaru, M.: 1995, J. Commun. Res. Lab. 42, 111.Google Scholar
- Moore, R. L. and LaBonte, B. J.: 1985, Proc. Symposium on Solar and Interplanetary Dynamics, D. Reidel Publ. Co., Dordrecht, Holland, pp. 207-210.Google Scholar
- Nelson, G. J. and Melrose, D. B.: 1985, in D. J. McLean and N. R. Labrum (eds.), Solar Radiophysics, Cambridge University Press, Cambridge, p. 333.Google Scholar
- Priest, E.: 1982, Solar Magnetohydrodynamics, Cambridge University Press, Cambridge.Google Scholar