Efimov A. I., Lukanina L. A., Rogashkova A. I., Samoznaev L. N., Chashei I. V., Bird M. K., Pätzold M. Coronal Radio Occultation Experiments with the Helios Solar Probes: Correlation/Spectral Analysis of Faraday Rotation Fluctuations. Solar Physics , 2015 , 290 (9). С. 2397-2408. ISSN 0038-0938
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The coronal Faraday rotation (FR) experiments using the linearly polarized signals of the Helios-1 and Helios-2 interplanetary probes remain a unique investigation of the magnetic field of the solar corona and its aperiodic and quasi-periodic variations. The unexpectedly long lifetime of these spacecraft (1974 – 1986) enabled studies from very deep solar-activity minimum (1975 – 1976) into the strong activity maximum (1979). Important experimental data were also obtained for the rising (1977 – 1978) and declining (1980 – 1984) branches of the solar-activity cycle. Previous publications have presented results of the initial experimental data only for coronal-sounding experiments performed during individual solar-conjunction opportunities. This report is a more detailed analysis of the Helios FR measurements for the entire period 1975 – 1984. Radial profiles of the FR fluctuation (FRF) intensity recorded during the deepest solar-activity minimum in 1975 – 1976 are shown to differ distinctly from those during the strong solar-activity maximum in 1979. In particular, the decrease of the FRF intensity with solar-offset distance is substantially steeper in 1979 than in 1975/1976. In all cases, however, the FR data reveal quasi-periodic wave-like fluctuations in addition to the random background with a power-law spectrum. The dominant period of these fluctuations, recorded during 35 % of the total measurement time, is found to be close to five minutes. Large-scale FR variations at considerably longer periods (1.1 – 2.7 hours) were observed during 20 % of the measurement time. Knowing the intrinsic motion of the radio ray path from spacecraft to Earth and making a reasonable assumption about the solar-wind velocity, FRF observations at widely spaced ground stations have been used to estimate the velocity of coronal Alfvén waves. The velocity values range between 290 and 550 km s−1 at heliocentric distances between 3.5 and 4.5 R⊙ and are marginally lower (150 – 450 km s−1) at distances between 5.5 and 6.5 R⊙. Occasional FR variations with a period near 160 minutes and harmonics with periods 60, 30, and 20 minutes were also observed.
| Тип объекта: | Статья |
|---|---|
| Авторы на русском. ОБЯЗАТЕЛЬНО ДЛЯ АНГЛОЯЗЫЧНЫХ ПУБЛИКАЦИЙ!: | Ефимов А.И., Луканина Л.А., Рогашкова А.И., Самознаев Л.Н., Чашей И.В., Бёрд М.К., Петцольд М. |
| Подразделения (можно выбрать несколько, удерживая Ctrl): | 114 лаб. исследований космической плазмы радиофизическими методами |
| URI: | http://cplire.ru:8080/id/eprint/937 |
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