Localized ELF nocturnal propagation anomalies

Bannister, P.

doi:10.1029/rs017i003p00627

Cited by 9 publications

(4 citation statements)

References 19 publications

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“…It is readily apparent from exceptions to this trend occurred during October [16][17][18] and day of month). It is readily apparent from Fig.…”

Section: Correlation With Geomagnetic Activitymentioning

confidence: 93%

“…One of the strongest 1978 solar-particle events occurred in February during the transition period from night conditions in December to day-night conditions in March (at local noon, the sun just barely reached the horizon at Thule). A polar cap absorption (F' CA) (6-dB riometer absorption) began at 09 50 GMT on February 13 and the time of maximum [13][14][15][16][17][18][19][20][21][22][23][24][25] million elecironvolts (MEV) proton flux was 06 00 on February 14. This event caused a 28-km drop in the VLF noontime reflection height at Thule, followed by a gradual return to normal over the next 7 days.…”

Section: Correlation With Geomagnetic Activitymentioning

confidence: 99%

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Summary of ELF propagation validation system field strength measurements, 1976 to 1978

Bannister¹

1984

IEEE J. Oceanic Eng.

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From Angust 1976 tbrongh December 1978, extremely low frequency (ELF) field strength and effective noise measurements were taken continnously in Connecticut and sporadically aboard operational submarines. This article snmmarizes the field strength measurements taken at both land (Connecticnt) and sea (North Atlantic, Western'Pacific) localions during January, March, April, and October 1977 and Jannary/ February 1978. The main conclusion is that the average field strengths measured aboard the submarines (which were located at distances of 4-12 Mm from the Wisconsin Test Facility) are in excellent agreement with previous ELF measurements taken over similar paths. Anomalous ELF field strength variations were also correlated with geomagnetic activity. Iuterfereuce between the direct and "round-the-world" paths was probably observed during the Western Pacific area daytime propagation period in early October 1977. ELF propagation effects were also observed daring the February 13,1978, significant solar particle event. ' The effective-noise spectrum level is defined as the spectrum level of ELF noise at the signal frequency minus the improvement in the level of the signalto-noise ratio (S M) using nonlinear processing [I]. The unit ofeffective-nok spectrum level is the decibel with respect to the reference quantity of one ampere per meter in a one-hertz band. The unit symbol is dB re 1 A

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“…It is readily apparent from exceptions to this trend occurred during October [16][17][18] and day of month). It is readily apparent from Fig.…”

Section: Correlation With Geomagnetic Activitymentioning

confidence: 93%

Section: Correlation With Geomagnetic Activitymentioning

confidence: 99%

Summary of ELF propagation validation system field strength measurements, 1976 to 1978

Bannister¹

1984

IEEE J. Oceanic Eng.

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“…Test Facility (WTF) for paths for which the dip angle is >•60 ø [e.g., Bannister, 1982]. For this range of dip angles it is known that azimuthal variations of modal parameters associated with nocturnal ambient profiles are very small [Pappert and Moler, 1974].…”

Section: Most Measurements Of Elf Nocturnal Fades Have Been Made Withmentioning

confidence: 99%

Broadside excitation of ELF by a horizontal dipole beneath a sporadic E environment: Theory

Pappert¹

1986

Radio Science

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A simple surface propagation model is commonly used to estimate the effects of ionospheric disturbances on extremely low frequency {ELF) propagation. Though often adequate, one shortcoming of the model is its failure to allow for excitation by the broadside component of a horizontal electric dipole. That excitation can be quite significant in a sporadic E environment because the modal polarization can then contain a substantial mixture of transverse electric component. This is demonstrated by considering a flat earth geometry with a vertical geomagnetic field superimposed on a laterally homogeneous, cylindrically symmetric disturbance centered over the transmitter. The method utilizes normal mode decomposition. Matching equations at the boundary of the disturbance are developed by evaluating height gain integrals, and it is shown that this method is tantamount to simply matching the ground vertical electric and azimuthal magnetic fields at the boundary. Results for a sporadic E type environment indicate substantial departures from other model predictions.

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“…The deepest fades occurred following magnetic storms in the postmidnight period, when the auroral oval and, presumably, precipitated energetic electrons reach their southernmost extent. Bannister [1982Bannister [ , 1984 summarizes nocturnal ELF anomalies measured simultaneously in the northeastern U.S. and the North Atlantic. The northeastern U.S. signals faded many decibels in a few hours although the propagation paths were short.…”

Section: Introductionmentioning

confidence: 99%

Focusing and shadowing of ELF signals

Field¹,

Warber²,

Joiner³

1986

Radio Science

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Phase velocity transitions in the earth-ionosphere waveguide can focus or shadow ELF signals and give rise to anomalies less than a megameter in extent. This paper develops a hybrid method to calculate those effects: it uses full-wave theory to determine local TEM mode parameters, but traces rays to describe the signal's lateral structure. The method is applied to models of the terminator and disturbed polar cap boundary, including one based on the November 22, 1982 solar proton event (SPE). During that event a receiver in the Gulf of Alaska measured a severe signal fade. That fade probably was caused by refraction of the signal away from the polar cap boundary and into the disturbed cap, where the TEM-mode phase velocity is slowest. Focusing and shadowing, lasting about an hour, are predicted for signals whose great-circle path grazes the terminator.

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Localized ELF nocturnal propagation anomalies

Cited by 9 publications

References 19 publications

Summary of ELF propagation validation system field strength measurements, 1976 to 1978

Summary of ELF propagation validation system field strength measurements, 1976 to 1978

Broadside excitation of ELF by a horizontal dipole beneath a sporadic E environment: Theory

Focusing and shadowing of ELF signals

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