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  • 1
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    High resolution topside in situ data of electron densities and VHF/GHz scintillations in the equatorial region (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: GEOPHYSICS
    Type: AD-A125353 , AFGL-TR-83-0032 , Journal of Geophysical Research; 88; Jan. 1
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  • 2
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    Equatorial scintillations - A review (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Scintillation observations of equatorial irregularities by techniques such as in situ, radar backscatter, airglow, and total electron content are reviewed, with an emphasis on GHz measurements. New aspects of the spread-F analysis from ionograms are mentioned, followed by a discussion of scintillation morphology, and the longitudinal control of the equatorial scintillations is emphasized. A coordinated multitechnique observation of the equatorial irregularities is described in detail, the study being divided into two parts: (1) an examination of the large field-aligned irregularity structures and their association with discrete patches of scintillation activity, and (2) an investigation of the coexistence of km-scale-irregularities with meter scales and a description of the evolution of the irregularity and scintillation spectra during the various phases of irregularity generation and decay. Unsolved problems are also reviewed, e.g., it is stated that the effects of steep spatial gradients in the electron density structures and their subsequent erosion on both CW and pulse propagation need to be evaluated both from the point of view of theory and experiments.
    Keywords: GEOPHYSICS
    Type: AD-A108218 , AFGL-TR-81-0332
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  • 3
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    Coordinated study of equatorial scintillation and in situ and radar observations of nighttime F region irregularities (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A coordinated set of Atmospheric Explorer E (AE-E) satellite in situ, VHF radar backscatter, and scintillation measurements performed during 1977 over a common ionospheric volume is used to study the relationship between the plasma depletions or bubbles, the extended 3-m irregularity structures known as plumes, and bursts of scintillation activity or patches in the nighttime equatorial F region. The implications of the observed spatial structures and the level of ambient concentration on the generation of 3-m irregularities and scintillation modeling are discussed.
    Keywords: GEOPHYSICS
    Type: AD-A093714 , AFGL-TR-80-0376 , Journal of Geophysical Research; 85; Oct. 1
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  • 4
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    F region electron density irregularity spectra near auroral acceleration and shear regions (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Two orbits of the Atmosphere Explorer D yielded data on F region electron irregularities in the high latitude ionosphere. Data were taken with a retarding potential analyzer, an ion drift meter, a low energy electron experiment and a photoelectron spectrometer. Auroral forms were simultaneously visually sighted by DMSP spacecraft. The irregularities were associated with auroral excitation and large structured flow regions. Steep spectra with one-dimensional spectral index values for wavelengths over 1 km were observed in the acceleration region. Large amplitude irregularities appeared in large structured flow regions and displayed shallow spectra, indicating the presence of large power spectral densities at scale lengths of about 100 m. It is suspected that large velocities or shears in the velocities in adjacent precipitation regions cause the F region density perturbations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5554-556
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  • 5
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    The role of in-situ measurements in scintillation modelling (1981)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: It is shown that the conflicting equatorial scintillation observations obtained from greatly separated ground stations can be organized in the framework of a longitudinal variation of irregularity occurrence, given satellite-borne, in situ measurements of irregularity amplitude of the global F-region irregularity morphology's general features. High-inclination satellite data are used to delineate the morphological features of the polar cap by means of such a method. The lack of diurnal and magnetic control of the irregularity morphology within the low solar flux, northern winter polar cap distinguishes this region from the auroral oval regime. A polar-orbiting communication system sensitive to phase perturbations may observe large differences in the phase-to-amplitude scintillation ratio, as it traverses the auroral oval and proceeds into the polar cap, with its sun-aligned arc system.
    Keywords: GEOPHYSICS
    Type: Symposium on the Effect of the Ionosphere on Radiowave Systems; Apr 14, 1981 - Apr 16, 1981; Washington, DC
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  • 6
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    Modelling of equatorial phase and amplitude scintillations from OGO-6 and AE irregularity data (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The technique of modelling equatorial phase and amplitude scintillations from in-situ measurements of irregularity amplitude, ambient ionization density and irregularity power spectrum is outlined. The in-situ measurements do not directly provide information on irregularity layer thickness for which radar backscatter observations are utilized. The equatorial scintillation models developed from OGO-6 and AE-C in-situ measurements during the two solstices are presented. Considerable differences in the longitude variation of scintillations are predicted during the two solstices. The model estimates are in good agreement with the available ground based phase and amplitude measurements. Problems associated with the use of bottomside spread-F data for transionospheric propagation modelling at VHF/UHF are also discussed.
    Keywords: GEOPHYSICS
    Type: Low latitude aeronomical processes; May 29, 1979 - Jun 09, 1979; Bangalore; India
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  • 7
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    Scintillations associated with bottomside sinusoidal irregularities in the equatorial F region (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Multisatellite scintillation observations and spaced receiver drift measurements are presented for a category of equatorial F region plasma irregularities characterized by nearly sinusoidal waveforms in the ion number density. The observations were made at Huancayo, Peru, and the measurements at Ancon, Peru, associated with irregularities observed by the Atmospheric-Explorer-E satellite on a few nights in December 1979. Utilizing ray paths to various geostationary satellites, it was found that the irregularities grow and decay almost simultaneously in long-lived patches extending at least 1000 km in the east-west direction.
    Keywords: GEOPHYSICS
    Type: AD-A164917 , AFGL-TR-86-0039 , Journal of Geophysical Research (ISSN 0148-0227); 91; 270-276
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  • 8
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    The localized origin of equatorial F region irregularity patches (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: An intensive study of nighttime irregularities of electron density in the equatorial ionosphere was performed in October 1976 by making 50-MHz radar backscatter measurements at Jicamarca, Peru, and scintillation measurements of 249-MHz transmissions from Les 9 at two ground stations (Ancon and Huancayo, both in Peru) as well as by aircraft flying in the vicinity of the stations. The 137-MHz scintillations from the orbiting Wideband satellite were also recorded at Huancayo. The results of such measurements made on October 16-17, 1976, are discussed in this report. We find that on this particular night a large-scale irregularity patch evolved first in the west, as was detected by the radar at Jicamarca, and drifted eastward to cause successive onsets of scintillation activity on propagation paths from Ancon and Huancayo. The observations indicate the east-west dimension of the large-scale structure to be 400 km drifting eastward at a speed of approximately 100 m/s, having a lifetime of several hours, and containing a hierarchy of irregularity scale sizes in the range of kilometers to meters causing both scintillations at 249 MHz and radar backscatter at 50 MHz.
    Keywords: GEOPHYSICS
    Type: AD-A055329 , AFGL-TR-78-0135 , Journal of Geophysical Research; 83; Apr. 1
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  • 9
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    Preliminary comparisons of VHF radar maps of F-region irregularities with scintillations in the equatorial region (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Multiantenna 50 MHz radar backscatter maps of echo power from night-time F-region equatiorial irregularities obtained at Jicamarca, Peru were compared with simultaneous VHF scintillation observations from Huancayo at 137 and 254 MHz during the period 20 November to 12 December 1975. Saturation of VHF scintillations in excess of 20 dB was observed at both these frequencies during times when radar maps showed large intense plume structures rising into the topside ionosphere. On nights when only thin layers of bottomside irregularities were observed, moderate to weak scintillations were recorded at VHF. Preliminary values of east-west horizontal irregularity drift velocities were obtained and compared with scintillation rate observations. Using the 1.5-deg and 4.5-deg longitudinal separation between the Jicamarca radar and ionospheric observation points of the two satellites from Huancayo, information was derived regarding large-scale east-west structure during the development phase of the irregularities.
    Keywords: GEOPHYSICS
    Type: AD-A053278 , AFGL-TR-78-0084
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  • 10
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    Rocket measurements within a polar cap arc - Plasma, particle, and electric circuit parameters (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Results are presented from the Polar Ionospheric Irregularities Experiment (PIIE), conducted from Sondrestrom, Greenland, on March 15, 1985, designed for an investigation of processes which lead to the generation of small-scale (less than 1 km) ionospheric irregularities within polar-cap F-layer auroras. An instrumented rocket was launched into a polar cap F layer aurora to measure energetic electron flux, plasma, and electric circuit parameters of a sun-aligned arc, coordinated with simultaneous measurements from the Sondrestrom incoherent scatter radar and the AFGL Airborne Ionospheric Observatory. Results indicated the existence of two different generation mechanisms on the dawnside and duskside of the arc. On the duskside, parameters are suggestive of an interchange process, while on the dawnside, fluctuation parameters are consistent with a velocity shear instability.
    Keywords: GEOPHYSICS
    Type: AD-A214008 , Journal of Geophysical Research (ISSN 0148-0227); 94; 6692-671
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