Oblique Incidence Ionospheric Absorption Near the Magnetic Equator
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Date
1984-07
Authors
Shamsi, S.
Journal Title
Journal ISSN
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Publisher
University of Lagos
Abstract
Measurement of equatorial ionospheric absorption made by the A3 Method for quiet
conditions near a period of maximum solar activity (1979 to 1981) are used for a detailed
examination of Absorption of Radio Waves in equatorial ionosphere. Assuming an index law
of the form L = L0COSmX for the absorption (X being zenith angle of the sun), the diurnal
and seasonal characteristics of the variation are obtained for two frequencies (4.9 MHz and
7.1 MHz) and compared with existing theories. Problems posed for an index law for seasonal
variation of absorption by the experimental evidence as indicated. Effect of solar activity on
absorption of radio Waves is studied and an improved form of the variation of absorption
with solar activity is presented. The new form of variation of absorption with solar activity
also explains the seasonal variation of absorption.
Examples of solar flare effects on the ionospheric absorption are presented for the two
frequencies. A study has been made for the correlation between the occurrence of solar
flares as reported in Solar Geophysical Data (Noaa Boulder Colorado) and the observed
ionospheric effect. Special features observed include a pronounced absorption near layer sunrise, and an
apparent enhancement of signal strength around sunset. Arguments are advanced for
possible physical mechanism governing these phenomena.
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Keywords
Ionosphere , Wave Absorption , Equatorial Ionosphere , Radio Waves
Citation
Shamsi, S (1984), Oblique Incidence Ionospheric Absorption near the Magnetic Equator. University of Lagos School of Postgraduate Studies PhD Thesis and Dissertation Abstracts, 259p.