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Studies of solar flares using optical, X-ray and radio data

Zirin, H. (1978) Studies of solar flares using optical, X-ray and radio data. Solar Physics, 58 (1). pp. 95-120. ISSN 0038-0938. doi:10.1007/bf00152557.

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I have studied a number of flares for which good X-ray and optical data were available. An average lag of 5.5 s between hard X-ray (HXR) start and Hα start, and HXR peak and Ha peak was found for 41 flares for which determination was possible. Allowing for time constants the time lag is zero. The peak Hα lasts until 5–6 keV soft X-ray (SXR) peak. The level of Hα intensity is determined by the SXR flux. Multiple spikes in HXR appear to correspond to different occurrences in the flare development. Flares with HXR always have a fast Hα rise. Several flares were observed in the λ 3835 band; such emission appears when the 5.1–6.6 keV flux exceeds 5 × 10⁴ ph cm⁻² s⁻¹ at the Earth. Smaller flares produce no λ3835 emission; we conclude that coronal back conduction cannot produce the bright chromospheric network of that wavelength. The nearly simultaneous growth of Hα emission at distant points means an agent travelling faster than 5 × 10³ km s⁻¹ is responsible, presumably electrons. In all cases near the limb an elevated Ha source is seen with the same time duration as HXR flux; it is concluded that this Hα source is almost always an elevated cloud which is excited by the fast electrons. A rough calculation is given. Another calculation of Hα emission from compressed coronal material shows it to be inadequate. In several cases homologous flares occur within hours with the same X-ray properties. Radio models fit, more or less, with field strengths on the order of 100G. A number of flares are discussed in detail.

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Additional Information:© 1978 Kluwer Academic Publishers. Provided by the NASA Astrophysics Data System. Received 9 May, 1977; in final form 20 March, 1978. I wish to thank Ron Moore for many discussions; John Barnard and David Kodama for collecting the data on OGO-5 events; and particularly the X-ray experimenters: K. Frost, P. Hoyng, D. Datlowe, M. Elcan, and S. Kane for making available their data. This work was supported by NASA under Grant NGR 05-002-034, NSF under Grant ATM76-21132 and AFGL under Contract F19628-77-C-0106.
Funding AgencyGrant Number
NASANGR 05-002-034
Air Force Office of Scientific Research (AFOSR)F19628-77-C-0106
Subject Keywords:Flare; Solar Flare; Chromospheric Network; Multiple Spike; Small Flare
Issue or Number:1
Record Number:CaltechAUTHORS:20200616-073210741
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Official Citation:Zirin, H. Studies of solar flares using optical, X-ray and radio data. Sol Phys 58, 95–120 (1978).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103938
Deposited By: Tony Diaz
Deposited On:22 Jun 2020 17:32
Last Modified:16 Nov 2021 18:26

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