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The fine structure of the E-region Belrose, John Skelton

Abstract

Introduction Very little is known about the fine structure of the E-region of the ionosphere. The pulse method devised by Breit and Tuve is used to study the E-region in detail. Observations were made at Vancouver for the months of July and August 1951. The frequency 1.5 to 5 mc/s. (down to .5 mc/s. after midnight) was swept manually recording in 100 kc/s. intervals the virtual height, h’, to the nearest kilometer. Experimental (h’,t) records were also taken at 15 minute intervals throughout the day on 2 mc/s. The (h’,f) curves were analysed for fine structure details of the region which are not recorded by ionospheric equipment used for routine observations of the entire ionosphere. The following investigations were attempted: 1. Fine Structure of Night-Time E-Region. 2. Diurnal Variation of Fine Structure of E-Region. 3. Sunrise Effects of E-Region. 4. Occurrence of Echoes from Levels Below the E-Region. 5. Diurnal Variation of Critical Penetration Frequency of E-Region. 6. Determination of Scale Height of the E-Region. Results 1. Fine Structure of Night-Time E-Region Throughout the night ionization generally appears as patches from random clouds. Near sunrise short-lived echoes are found between 80 and 200 kms. Few usable results showing fine structure details are found. 2. Diurnal Variation of Fine Structure of E-Region Experimental (h',f) curves are compared to derived curves for a simple parabolic region with an E8 layer appearing as a sharp boundary embedded in the simple region. Good fits to the theoretical curves are normally found below the cusp frequency. The Hail' appearing after the cusp frequency generally has a slope greater then that predicted. Various types of ledges found in the --region are discussed. Moving ledges are often found with an approximate quasi-period (i.e. time to pass through the region) of half an hour. The variation of the penetration frequency of high smooth Es regions also appears to have a similar period. Once during the period of observation both these phenomena occurred together. Very pronounced ledges are sometimes found above the normal maximum. 3. Sunrise Effects of E-Region Day-time ionization of the E-region commences before ground sunrise. Commencement time is found to be approximately that time at which the sun*8 rays strike the E-region after grazing a spherical surface 39 kms. above the earth. 4. Occurrence of Echoes from Levels Below the E-Region Strong indications of region D are found. Often patches of ionization, as though from small ionic clouds, appear at various heights from 80 to 200 kms. No retardation effects are observed for any of these records. 5. Diurnal Variation of Critical Penetration Frequency of E-Region The critical frequency of the E-region is found to obey approximately a law fc = k oosⁿ X where X is the sun's zenith angle. The average morning value for the index, n, is .301 and the average afternoon value is .35. The average morning and afternoon value is .325. Examination of the (log fc , log cos X ) curves show that the afternoon values usually fall more nearly in a straight line. 5. Determination of Scale Height of the E-Region a. Analysis of (h',t) records From plots of the function Ln f(x) = constant + h/H H is found to be 11.3 kms. b. Analysis of (h',f) records From plots of the function h' = hN + φ(f/fc) H is found to be 9.4 kms. When this is corrected for a parabolic assumption giving the best fit to a Chapman distribution, H = 11.28 kms.

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