Theory of spread<i>F</i>based on aspect-sensitive backscattered echoes

Renau, Jacques

doi:10.1029/jz065i008p02269

Cited by 11 publications

(5 citation statements)

References 4 publications

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“…geometries proposed by Eckersley [1937Eckersley [ , 1940 and Dieminger [1951]. Similar models have also been used by Peterson [1951], Gassmann [1957], Bates [1960], Renau [1960], and Booker [1961]. The present model considers the relatively simple geometry operating in the equatorial case, as revealed by previous experimentation concerning the nature of the scattering irregularities.…”

Section: Characteristics Of the Scattering Irregularitiesmentioning

confidence: 95%

The interpretation and synthesis of certain spread-Fconfigurations appearing on equatorial ionograms

Calvert¹,

Cohen²

1961

J. Geophys. Res.

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On ionograms obtained near the magnetic equator the rectangular configuration called ‘equatorial spread F’ arises from scattering in the vertical plane (passing through the ionosonde) normal to thin, magnetic field‐aligned irregularities located at or beneath the base of the F layer [Cohen and Bowles, 1961]. It is shown in the present paper that some strikingly different spread‐F configurations on equatorial ionograms are due to irregularities of the same kind, but embedded in the F layer. Since these other configurations result from similar irregularities, the category of ‘equatorial spread F’ is generalized to include them. An ‘ionogram’ corresponding to scattering from an individual ‘equatorial spread F’ irregularity can be calculated. A composite ionogram resulting from a number of such scatterers can then be synthesized by superposition. By appropriate distributions of scattering centers in the east‐west plane, many features of the ‘equatorial spread‐F’ configurations observed on Huancayo ionograms can be simulated. This process of ionogram synthesis constitutes a new technique for the determination of (1) the height of patches of small‐scale irregularities in the F region; (2) the horizontal distance of the patches from the ionosonde in the vertical east‐west plane; (3) the thickness of the patches; (4) their‐east‐west extent; and (5) the east‐west component of their drift velocity. The patches are measured to have an east‐west extent of up to 300 km and a thickness between 10 and 50 km. Their drift velocity is eastward, gradually decreasing from 200 to 100 meters/sec after 2100 hours local time.

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Section: Characteristics Of the Scattering Irregularitiesmentioning

confidence: 95%

The interpretation and synthesis of certain spread-Fconfigurations appearing on equatorial ionograms

Calvert¹,

Cohen²

1961

J. Geophys. Res.

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“…This condition is in direct contrast to the north-south scattering postulated by Pitteway and Cohen, but the pr, esumpfion has been verified by direction-finding measuremen+,s at times, when equatorial spread F was being observed on the ionosonde. The term scattering, as used by Calvert and Cohen, appears to mean aspect sensitive backscatter similar to the type discussed by Renau [1960], which is really partial reflection.…”

Section: Ox • Q-o? -1-4•r"(1 --X)e -0mentioning

confidence: 99%

Spread F and ionospheric F‐region irregularities

Herman¹

1966

Reviews of Geophysics

116

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The results of ionospheric observations by means of a variety of techniques are summarized to show that magnetic field-aligned irregularities exist in the ionosphere. The irregularities appear in patches having horizontal dimensions up to 1000 km in the east-west direction and several hundred kilometers in the north-south direction. Size of the irregularities is typically about I km transverse to the magnetic field and elongated along the field line. Irregularities associated with spread F occur in the altitude range from 250 km up to the height of F .... Correlations between ionogram spread F and other ionospheric observations indicate that spread echoes are closely related to the field-aligned irregularities. A critique of theories explaining why the irregularities cause spread echoes is given. Statistical studies of the geographic and temporal variations in spread-F occurrence are summarized. The fundamental question of how irregularities causing spread F are produced in the ionosphere is discussed. Now at Lowell Technological Institute Research Foundation, Lowell, Massachusetts. 255 256 JOHN R. HERMAN rather well known. These variations and their correlations are summarized in section 4.Two types of irregularities are differentiated in the literature: large patches (hereaoe•er re•erred to as large-scale irregularities), which may have a horizontal exten• up to several hundred kilometers, and individual field-aligned irregularities (small scale), whose sizes transverse •o the magnetic field line are on the order ooe I km. It appears that the large patches are in actuality a collection of small-scale irregularities, and spread F will be seen as long as the patch is over an observing station. Observational evidence connecting the two types of irregularities is discussed in section 5.One ooe the important problems in a complete theory ooe spread F is the explanation of how the field-aligned irregularities are produc,ed. The explanation could, ooe course, be applicable to the phenomena ooe radio star and satellite scintillations as well. An acceptable irregularity production mechanism must be compatible with the observed •emporal and geographical variations in spread-F occurrence frequency and known correlations with o•her geophysical phenomena, and it must permit irregularity sizes that allow spreading in range, fr, equency of the ionosonde echo, or both. The observational evidence suggests that the mechanisms for irregularity production may be different in equatorial regions than in polar regions, so that a single model would not necessarily have. to explain spread F in both regions. In section 6 prevalent theories of irregularity formation are discussed.After a fairly short section of summary and conclusions (section 7), a rather complete bibliography is given. Some pertinent papers which might have been missed in this paper may be found in the references for previous reviews, including those by Little et al. [1956], Dagg [1957a], Glover [1960], Calvert [1962], Singleton [1962/], and Clemesha and Wright [1964]....

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“…At present the diffuse echoes have been ascribed to backscatter echoes arriving at oblique incidence. However, if one maintains that the concept of aspect applies [Weaver, 1958;Renau, 1960] Figure 10). According to these recommendations, the penetration frequency of loft.…”

Section: The B Type Spread As Illustrated By Figure Lamentioning

confidence: 99%

“…of a spread F type B ionogram is to be identified with the well-defined inside edge of the spread (low-frequency side); the first multiple trace, when present, will also usually exhibit a sharp inner edge at the same frequency as the sharp inner edge of the normal trace, thus confirming the choice of the inside edge as being indicative of loft.. However, when the penetration frequency is determined as recommended, the theoretical studies of spread F [Renau, 1959[Renau, , 1960 leave unexplained a large class of frequently observed type B spread F. Yet if we were to consider the outer shape edge as the penetration frequency, the theoretical results would then predict the virtual heights associated with echoes relative to the outer sharp edge frequency of the ob-served spread without explaining the nature of the inner sharp edge.…”

Section: The B Type Spread As Illustrated By Figure Lamentioning

confidence: 99%

A study of observed spreadF

Renau¹

1960

J. Geophys. Res.

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The main types of spread F have been illustrated, and in order to facilitate their study they have been categorized. Thereafter, our effort is concentrated in studying the morphology of a particular type of spread F observed at various magnetic and geographic latitudes (northern hemisphere). The total number of ionograms scanned during these studies amounts to about a hundred thousand. The first of these studies shows that the spread F type B (sharp inner and outer frequency edge) may be due either to the bifurcation of the layers or to large horizontal patches of ionization with varying degrees of electron density and tilted in a manner to reflect specularly, with scattered echoes superimposed on the structures thus obtained. As for the amount of frequency spreading fs = fmax ‐ fmin, the spread seems to be magnetically controlled, having its maximum at the magnetic north, decreasing with decreasing magnetic latitude down to 40°N, and increasing again at the magnetic equator.

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Theory of spreadFbased on aspect-sensitive backscattered echoes

Cited by 11 publications

References 4 publications

The interpretation and synthesis of certain spread-Fconfigurations appearing on equatorial ionograms

The interpretation and synthesis of certain spread-Fconfigurations appearing on equatorial ionograms

Spread F and ionospheric F‐region irregularities

A study of observed spreadF

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