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VLF Observations of Nighttime D ‐Region Ionization Enhancement by the Scorpius XR‐1 X‐ray Source

1971; Wiley; Volume: 6; Issue: 7 Linguagem: Inglês

10.1029/rs006i007p00699

1944-799X

Charles Chilton, J. H. Crary,

Solar and Space Plasma Dynamics

In recent years, measurements by rocket, balloon, and satellite of cosmic X rays have suggested the possibility of observing ionospheric effects from celestial X‐ray sources such as Scorpius XR‐1, using low and very low frequency radio transmissions. The behavior of the nighttime D region under ionization by the X‐ray spectrum of the Scorpius source is estimated for several stellar zenith angles. Although Scorpius XR‐1 is the strongest source in the southern hemisphere, the integrated flux of all the other X‐ray sources is comparable to that of Scorpius XR‐1 and appears to modify the effect of Scorpius XR‐1 alone on VLF data recorded in the southern hemisphere. Observations of the VLF transmission NBA (18 kHz, Balboa, Panama) made at Tucuman, Argentina, during 1963–1964 show a sidereal time variation in the diurnal amplitude change that follows the variation in the per cent illumination of the propagation path by Scorpius XR‐1 during the nighttime hours. Even though the diurnal amplitude change can be shown to have a sidereal time variation, the diurnal phase change at Tucuman, Argentina, does not vary much throughout the year and yet remains consistently lower than that observed over a path of the same length from NBA to Boulder, Colorado, in the northern hemisphere. Therefore, it is suggested that the integrated effect of all the X‐ray sources illuminating the southern hemisphere is to enhance the ionization in the southern hemisphere nighttime D ‐region, thus, producing the smaller diurnal phase change observed at Tucuman compared with that observed on a Boulder recording of the NBA signal over a propagation path of the same length in the northern hemisphere.