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The current spectral density I(щ) dependence on the width of the frequency band and sweep period is studied. The relation between the required accuracy of measurement an the optional parameters of the sweeping process is formulated. [ABSTRACT FROM AUTHOR]

A series of absorption measurements covering more than two years, carried out by the A3 method (oblique incidence) on 1538 kHz at the Panská Ves Observatory, is studied. The measuring equipment is shortly described, as well as calibration and the measuring path. Both the diurnal variation of absorption, including its asymmetry, and the seasonal variation of absorption, including the winter anomaly, are observed in a predicted form. The computed height profile of absorption shows that nearly all the absorption is formed in the middle and upper D-region. The 1538 kHz absorption measurements could serve as a very good tool for studying the D-region, but there are still some difficulties attributed to the determination of the zero level of absorption. Suggestions are given how to remove this difficulty. [ABSTRACT FROM AUTHOR]

On the basis of long period measurements of ionospheric absorption in five A3 circuits in Central Europe, it is shown that the considerable seasonal variation of the diurnal asymmetry of absorption, found in [1], exhibits practically no year-to-year variability and is well-developed at equivalent frequencies f≲ 1 MHz, while it vanishes at F ≲ 2 MHz. The limited data on the diurnal asymmetry of the D-region electron concentration are consistent with the seasonal pattern of the diurnal asymmetry in absorption. A tentative hypothesis of nitric oxide variability as the cause of the seasonal variation of the asymmetry is proposed. [ABSTRACT FROM AUTHOR]

The 272 kHz ionospheric absorption has been measured at the Průhonice Observatory by the A3 method (oblique incidence) for a long period. The results of the comparison of these absorption data with indices of solar, geomagnetic and cosmic ray activity are presented for large solar zenith angles. The day-time absorption (x ≈ 75° - 85°) is described well by these indices and appears to be affected particularly by direct solar Lyman-α radiation. The night-time absorption (x>100°), however, is not described sufficiently by the indices used. [ABSTRACT FROM AUTHOR]

The results of the winter anomaly observations at the Panská Ves Observatory on 2775 kHz and 2614 kHz (A3 method, f≈1 and 0.8 MHz) are studied for the winters of 1971/72 and 1972/73. Ionospheric responses to minor (1972) and major stratospheric warmings are found to be different and relatively small. A regular winter-anomaly background absorption increase with a maximum in January was observed during both winters studied. Magnetic storms are found to play an insignificant, if any, role in the winter-anomaly phenomenon. The relation between magnetic activity and ionospheric absorption seems to be better in non-anomalous periods. [ABSTRACT FROM AUTHOR]

The assymetry of the diurnal variation of radio-wave ionospheric absorption, measured by the A3 method on the 2775 kHz Kiel - Panská Ves circuit, is studied. Almost full symmetry of absorption is observed in winter and autumn. It is explained by electron concentration variations. A remarkable diurnal asymmetry of absorption is observed in spring and particularly in summer. The observed diurnal asymmetry of the electron concentration seems to be insufficient to account completely for the great absorption asymmetry observed. [ABSTRACT FROM AUTHOR]

The difference observed between the electron temperature, T, and the neutral atmosphere temperature, T, is shown to be able to contribute significantly to the observed variability of ionospheric radio-wave absorption ( A1 and HF-A3 measurements). [ABSTRACT FROM AUTHOR]