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The Trend of Ionospheric Absorption During Shortwave Fade‐Outs Related to the Trend of Enhancement of Solar X‐ray Flux
Author(s) -
Schwentek H.,
Hartmann G.,
Kreplin R. W.
Publication year - 1971
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs006i001p00035
Subject(s) - shortwave , riometer , ionosphere , ionospheric absorption , fade , shortwave radiation , absorption (acoustics) , environmental science , flux (metallurgy) , wavelength , physics , atmospheric sciences , radiative transfer , optics , astronomy , materials science , radiation , acoustics , metallurgy
During the period July 1967 to July 1968 about 60 shortwave fade‐outs, both weak and strong, were observed at Lindau through simultaneous use of several shortwave paths particularly established for absorption measurements. The frequencies used were 2.50, 2.614, 2.775, and 6.09 MHz; the distance between transmitter and receiver was about 300 km. Moreover, a riometer was used with a corner reflector antenna directed at the polestar (27.6 MHz). For the quoted shortwave fade‐outs the Naval Research Laboratory made available stored data of solar X‐ray flux in minute intervals; the data were obtained from satellites OGO 4 and Solrad 9 in the wavelength ranges 0.5–3, 1–8, 8–20, and 44–60 Å. The analysis of the various effects shows that there is a very good correlation between the enhancements of solar X‐ray flux and the enhancements of ionospheric absorption. The beginning and maximum of the shortwave fade‐outs are delayed by 0.5 to 4 minutes in relation to the beginning and maximum of the bursts, with the longer delay corresponding to the shorter wavelength. The end of the effects cannot be determined so definitely; the time differences between bursts and shortwave fade‐outs vary between ±7 minutes. Usually, the trend and detail of the shortwave fade‐outs very nearly follow the trend of the burst; thus, bursts may be considered equivalent to shortwave fade‐outs. For a number of very clear weaker effects the additional absorption Δ L has been found to be proportional to the additional flux Δ X E . For a very strong effect after a saturation Δ L increases again. The relative maximums of absorption Δ L / L during shortwave fade‐outs are proportional to the relative enhancement of flux Δ X E / X E .