Solar-terrestrial disturbances of June-September 1982, 4

Sudden increases in total electron content (SITECs) in the ionosphere produced by extreme ultra-violet (EUV) and soft X-ray bursts emitted from solar flares during the period June-August 1982 are studied by means of Faraday rotation measurement of the 136 MHz signal from the geostationary satellite ETS-II. During this period, fifty-nine SITECs were observed at Hiraiso. After a mini review of the ionospheric effects of enhanced solar EUV and soft X-ray emissions, two typical examples of SITECs are compared with the hard and soft X-ray data from the solar flare observation satellite HINOTORI to find that there are two types of SITECs, called here impulsive-type and slow-type depending on its appearance. Then, other examples obtained during relatively large flares are presented to clarify the difference between two types of SITECs. Finally, the relationship between the maximum increment of TEC and the soft X-ray (1-8 A) intensity for impulsive-type SITEC is investigated to find a relatively good correlation between them which indicates that EUV emission is closely related to soft X-ray emission. (author)