Diurnal phase variation of VLF waves at medium distances

Abstract

Methods of phase measurements at VLF are briefly described. So me r es u lts of diurnal phase m eas urements, sunrise elfects, and s olar flare effects at medium di stances and northern geographical latitud es are s ummarized. Two inhomogeneous and a nisotropic mod els are used for the interpre tation of the measurements : th e fir st correspondin g to the daytim e ionospher e and the second co rresponding to the nighttime ionospher e. Tile models are r elated to homogeneous models with s harp boundari es and effecti ve param eters of condueti vity, dielectri c con ta nt, and equivalent h eight. Th e diurnal phase lag, dependin g on distance, and the sunrise e ffects at 1000 km and 2000 km are interpreted by these models. Two critica l distanecs exist wher e the nighttim.e phase gain s a phase advantage of 360 degrees r elative to t he d ay t ime phase. An electron pro fil e of the daytime lower ionospher e is deduced from m eas ured daytime variati ons of equ ivalent height. The st ren gth of ionizin g s olar r a diation duri ng a solar flar e and th e e ffective attac hme nt coefficient of t he lower ionosphere are d eri ved fr o m mea sured vari ations of the equivalent h eight durin g a solar flare.

A study of VLF signals variations associated with the changes of ionization level in the D-region in consequence of solar conditions

“…They found the times of the amplitude minima were consistent with modal conversation taking place as the day-night boundary crossed the propagation path at specific locations. Volland (1964) presented the studies of diurnal phase and amplitude variation of VLF radio signal at medium distances where the propagation of VLF radio signal did not take place predominantly by one mode. The results were obtained on measurements of VLF data over propagation paths with distances in the range between 300 km and 3000 km at daytime medium, and at nighttime medium this range was larger.…”

A note on lower ionosphere equivalent height diurnal variation

“…The diurnal change of ionospheric heights can be studied from phase velocity measurements a t very low frequencies (VLF), assuming a sharply bounded and isotropic ionosphere, concentric with the earth's surface, constituting by this way a spherical waveguide. Assuming the first order mode of propagation asdominant in the VLF range and using a simplified form for the theory (Wait, 1959), a number of authors have studied the diurnal height changes for the upper boundary of the waveguide (Chilton et al, 1963; Volland, 1964; Bates & Albee, 1964;Kaufmann et al, 1967). It has been noticed that such height variations present a marked dependence on the considered propagation path and on the season of the year.…”

Control of WWV and WWVH standard frequency broadcasts by VLF and LF signals

“…Since some of the measurements given here were taken outside this frequency range, and within the critical second, or higher order, mode distances, and were quite sparse, direct correspondence with Blackband's results may not be expected. (See also [Volland, 1964].) An additional effect should be considered [Watt, 1964]: considerable variation may occur when diurnal shifts are measured at points which are equidistant but in different directions from the same transmitter, because of differences in day and night phase veloci· ties corresponding to each direction.…”