Radio Physics and Radio Astronomy (Mar 2019)
PECULIARITIES IN THE IONOSPHERIC SCINTILLATION SPECTRAL INDEX BEHAVIOR BY OBSERVATIONS OF THE COSMIC RADIO SOURCES AT THE DECAMETER WAVELENGTHS
Abstract
Purpose: With relation to radio astronomy, ionospheric scintillation of discrete cosmic radio sources is an undesirable effect. At the same time, ionospheric scintillations carry information on the ionospheric turbulence and are a separate object of study. From observations at the URAN-4 radio telescope of the power cosmic radio sources (3C144, 3C274, 3C405, and 3C461) at 20 and 25 MHz, the ionospheric scintillation parameters: index, characteristic period and spectral index were estimated. Correlation between spectral index measured from scintillation time spectrum and spectral index of space spectrum of irregularities have allowed considering the first of them as an index of ionospheric irregularity structure changing. Peculiarities of the ionospheric scintillation spectral index behavior compared with ionospheric scintillation index are analyzed for several time intervals. Design/methodology/approach: For analyzing the ionospheric scintillation data, the statistical methods were used. Findings: Estimations of ionospheric scintillation parameters were obtained during 1998–2007. It has been shown that spectral index mean values for each radio source depend on height at which it is observed that was not found for scintillation index. Comparison of yearly mean trends does not show the correlation of spectral index with the solar and geomagnetic activity indices (i.e. with the F10.7–flow of solar radiation at the wave length of 10.7 cm and Ap -index). The daily-seasonal dependence is clearly seen for the monthly mean values. In general, the maximum spectral index values were revealed at night, but small increase was also observed in day-time during 9–11 hours. For different time intervals, the behavior of ionospheric scintillation parameters obtained for the radio source been observed at greater angles of elevation (3C405 and 3C461) remarkably differ from that for the radio sources observed at lower angles of elevation. Conclusions: Using the data obtained as a result of long-term monitoring of the group of discrete cosmic radio sources at the URAN-4 radio telescope made it possible to investigate the behavior of spectral indices of ionospheric scintillations over a large time interval. The peculiarities found in the ionospheric scintillation spectrum index behavior require further analysis for explaining within the limits of present conceptions of radio wave propagation in such an irregularity medium as ionosphere.
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