Ionospheric effects of solar flares. I. The statistical relationship between X-ray flares and SID's

Deshpande, S. D. ; Subrahmanyam, C. V. ; Mitra, A. P. (1972) Ionospheric effects of solar flares. I. The statistical relationship between X-ray flares and SID's Journal of Atmospheric and Terrestrial Physics, 34 (2). pp. 211-227. ISSN 0021-9169

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/002191...

Related URL: http://dx.doi.org/10.1016/0021-9169(72)90165-1

Abstract

The Sudden Ionospheric Disturbances (SID's) produced in the Earth's ionosphere by enhanced solar radiation during solar flares are examined in the light of recent information on flare X-ray emission. The SID's cover the VLF-LF as well as HF effects. It is found that the occurrence probability of SID's with X-ray flares increases as the emission extends towards the shorter end of X-ray spectrum. An X-ray enhancement concurrent with both Ha and radio events is generally large and is capable of producing all SID effects including the sudden frequency deviation (SFD) and a crochet in 80 per cent of the cases. A threshold flux of 1×10-3 erg cm-2sec-1 (T = 2×106 °K) in the 0-8 Å band and a threshold ratio of 0–3 Å to 0–8 Å flux level of 1.5×10-2 is sufficient to produce a detectable SID effect. The size of an SID effect increases with X-ray enhancements in 0–3 Å, 0–8 Å, 2–12 Å bands, but the relationship is not linear. The relaxation time of most SID effects (excluding SFD) with reference to X-ray flares in 0–8 Å, 2–12 Å and 8–12 Å band is 2–3 min. The time curves of SID's are similar to those of X-rays in 0–3 Å, 0–8 Å and 2–12 Å bands but there are differences in details.

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