Model of Equatorial Scintillations from in Situ Measurements
Model of Equatorial Scintillations from in Situ Measurements

Author: Sunanda Basu

Publisher:

Published: 1976

Total Pages: 32

ISBN-13:

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In situ measurements of F-region irregularity amplitude and ambient electron density made by the retarding potential analyzer (RPA) on OGO-6 near perigee altitude of 400 km have been utilized to derive the variation of electron density deviation over the equatorial region. Based on these measured electron density deviations and other assumed model parameters, including a three-dimensional power-law form of irregularity spectrum of index 4, a model of equatorial scintillations is developed in the framework of diffraction theory. The percentage occurrence contours of estimated equatorial scintillations greater than or equal to 4.5 dB at 140 MHz during 1900 to 2300 LMT for the period November to December 1969 and 1970 have been derived. The model is found to depict a pronounced longitude variation with the scintillation belt width and percentage occurrence being maximum over the African sector. The latitude extent of the spatial scintillation belt narrows over the American sector without much decrease in the scintillation occurrence whereas over the Indian and Far Eastern sectors both the extent and the occurrence are found to decrease. The percentage occurrence of scintillations estimated from this model is found to be consistent with VHF scintillation measurements at Ghana, Huancayo, and Calcutta. In addition, the model was found to be in qualitative agreement with GHz observations at various longitudes made by the COMSAT group. The effect of varying model parameters on scintillation estimates at VHF, UHF and GHz are discussed. Implications of the observed longitudinal variation of scintillations on current theories of equatorial irregularity formation are indicated. (Author).

Global Morphology of Ionospheric Scintillations
Global Morphology of Ionospheric Scintillations

Author: Jules Aarons

Publisher:

Published: 1970

Total Pages: 48

ISBN-13:

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Amplitude fluctuations produced by small irregularities in electron density in the F-layer of the ionosphere (at 300 to 400 km height) can be a problem to communication and navigation systems in the VHF-UHF range. Recent measurements, primarily by AFCRL, are shown with emphasis on results at high and equatorial latitudes. At high latitudes an irregularity region exists whose lower boundary reaches 57 degrees invariant latitude near midnight. During magnetic storms the boundary descends to lower latitudes and the fading becomes deeper. Over the polar cap scintillations are somewhat diminished. When observing synchronous satellites through the irregularity region, deep and fast fading is frequently seen, with fade rates to one per second. Irregularities produce deep scintillations in the VHF range plus or minus 15 degrees from the geomagnetic equator. In equatorial regions maximum occurrence of high level scintillations takes place between 2100 and 2400 local time during the equinoxes; a minimum occurrence is observed during the solstices. When the sunspot number decreases, the equatorial irregularity region spreads and becomes larger. The data for various latitudes has been placed in statistical form, that is, distribution of amplitudes for 15-min samples as well as for periods of 1 yr and longer. (Author).

Space Physics and Aeronomy, Ionosphere Dynamics and Applications
Space Physics and Aeronomy, Ionosphere Dynamics and Applications

Author: Chao Huang

Publisher: John Wiley & Sons

Published: 2021-05-11

Total Pages: 47

ISBN-13: 1119507553

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A comprehensive review of global ionospheric research from the polar caps to equatorial regions It's more than a century since scientists first identified the ionosphere, the layer of the Earth’s upper atmosphere that is ionized by solar and cosmic radiation. Our understanding of this dynamic part of the near-Earth space environment has greatly advanced in recent years thanks to new observational technologies, improved numerical models, and powerful computing capabilities. Ionosphere Dynamics and Applications provides a comprehensive overview of historic developments, recent advances, and future directions in ionospheric research. Volume highlights include: Behavior of the ionosphere in different regions from the poles to the equator Distinct characteristics of the high-, mid-, and low-latitude ionosphere Observational results from ground- and space-based instruments Ionospheric impacts on radio signals and satellite operations How earthquakes and tsunamis on Earth cause disturbances in the ionosphere The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals. Find out more about the Space Physics and Aeronomy collection in this Q&A with the Editors in Chief

A Survey of Scintillation Data and Its Relationship to Satellite Communications
A Survey of Scintillation Data and Its Relationship to Satellite Communications

Author: Jules Aarons

Publisher:

Published: 1970

Total Pages: 130

ISBN-13:

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Contents: VHF atmospheric studies and communications and navigation systems; The definition of scintillation index and its use for characterizing ionospheric effects; Summary of properties of F-region irregularities; Application of the statistics of ionospheric scintillation to VHF and UHF systems; Special problems in scintillations; and Propagation delays of VHF waves.

Report on Peru Scintillation Tests
Report on Peru Scintillation Tests

Author: H. E. Whitney

Publisher:

Published: 1977

Total Pages: 146

ISBN-13:

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A large scale test program was developed jointly by AFGL and AFAL to evaluate the effects of equatorial ionospheric irregularities on UHF (250 MHz) satellite communications to map the temporal and spatial extent of the equatorial scintillation region, and to determine the geophysical mechanisms leading to the formation of irregularities in the equatorial ionosphere and thus to scintillations. Of specific interest were scintillation characteristics and effects observed by airborne terminals and their relation to simultaneously obtained results from ground based terminals. The test results are based on radio propagation and geophysical measurements conducted from ground and airborne stations and show the general scintillation patterns, latitudinal dependence, heading dependence and signal statistics. Backscatter measurements from the Jicamarca radar and optical observations from the all sky imaging photometer show the development and motion of the irregularity structure. Scintillation plots for several satellites received at the ground stations and on the aircraft are included. (Author).