Studying the effects of solar flares by slant probing of the ionosphere

Abstract

satisfactory coincidence between the theoretical and experimental relationships between changes in field strength and range. The authors would like to thank V. B. Belyanskii for his useful discussions of the ques- tion pertaining to antenna directivity patterns in the experiment [2]; furthermore, we express our gratitude to M. Ichinose, the author of [i], for providing us with much additional ma- terial relating to [i], and also to T. A. Ivanov, V. V. Radul, and G. M. Smirnov, for their assistance in preparing this paper. i. 2. 3. 4. 5. 6. 7. LITERATURE CITED M. Ichinose, Y. Kuratani, and I. Y. Yamazaki, J. Radio Res. Lab., 32, No. 136, 61 (1985). I. A. Tushentsova, D. I. Fishchuk, and E. E. Tsedilina, Preprint IZMIRAN, No. 12(701), Moscow (1987). M. No Fatkullin et al., Empirical Models of the Middle-Latitude Ionosphere [in Russian], Nauka, Moscow (1981). N. I. Manaenkova and E. E. Tsedilina, Izv. Vyssh. Uchebn. Zaved., Radiofiz., 25, No. 5, 508 (1982). Monthly Forecast of Maximum Utilized Frequencies (MUF); November 1981, December 1981 [in Russian], Gidrometeoizdat, Moscow (1981). V. Ya. Vovk, Author's Abstract of Candidate's Dissertation, IZMIRAN, Moscow (1985). I. Kuriki, I. Kasuya, H. Hojo, and K. Tanohata, J. Radio Res. Lab., 21, No. 105, 161 (1974). STUDYING THE EFFECTS OF SOLAR FLARES BY SLANT PROBING OF THE IONOSPHERE N. F. Blagoveshchenskaya, V. A. Bubnov, and V. T. Ustinovich UDC 550.388.2 We examine the results obtained in a study of the effects of solar flares by means of a method of slant probing of the ionosphere (SPI) along a subauroral path some 9.0 thousand km long throughout 1981-1982. The SPI data are com- pared against results obtained in recording sudden ionospheric disturbances of the SWF, SPA, SEA, and SFD types, as well as against the parameters of the solar radio emissions in the 650-15,000 MHz waveband. The increase in the intensity of x-ray and ultraviolet emissions during solar flares leads to an elevated concentration of electrons in the ionosphere. The immediate effects of solar flares on the ionosphere (sudden ionospheric disturbances) are recorded in a variety of ways that yield information as to changes in the state of the ionosphere at various alti- tude levels. We know [i] that solar flares produce minimal increases in the pulse reflection frequen- cy fmin, as well as a change in the critical frequencies of the E and F2 layers when the ionosphere is probed vertically. Measurements of fmin over more frequent probing periods can be used both to monitor absorption as well as for quantitative estimates. Nevertheless, because of the smallness of Afmin, the use of fmin as an absorption indicator is limited. From this point of view, of considerably greater potential is the method of slant probing of the ionosphere (SPI). When radio waves are emitted obliquely, the trajectories in the ionosphere are considerably longer than in the case of vertical emissions. Consequently, the direct effects of solar flares in the case of slant probing must become more clearly defined. In this case, the amplitudes of the disturbances, estimated in terms of the maxi- mum deviation of the lowest observed frequencies (LOF) from the undisturbed level along the radio-wave transmission path covered by a slant probing system, will be significantly greater than in the case of vertical probing emissions. Moreover, observations along the radio trans- Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. i, pp. 17-21, January, 1989. Original article submitted April 14, 1987; revision submitted September 8, 1987. 0033-8443/89/3201-0013512.50 9 1989 Plenum Publishing Corporation 13