Sudden phase anomalies produced by solar flares have been observed simultaneously on several long VLF propagation paths. The paths providing useful data are NBA (18 kc/s) Panama to Boulder, Colorado; to Maui, Hawaii; to Frankfort, Germany; and to College, Alaska; and GBR (16 kc/s) Rugby, England, to Boulder; and NPG (18.6 kc/s) Seattle to College, Alaska. The observations show that during a solar flare the magnitude of the mean change of reflection height Δh on each sunlit path can apparently be related to the mean of log sec χ along the path, where χ is the solar zenith angle. Different flares, however, produce different curves of Δh versus the mean of log sec χ. These results are discussed in terms of a layer produced below the normal height of reflection, and the energy (wavelength) and intensity (flux density) of the X rays that produced the new layer are estimated.
For short periods of time during June and July of 1963 t he U.S. Navy t rans mitters located at Jim Creek, Wash. (NPG), and Balboa, Panama (NBA), simulta neo usly t ransmitted a frequency stabilized signal of 18 kc/s . The phase and relative amplit ud c of these s ignals were monitored at Boulder, Colo.; College, Alaska; lVlau i, H awaii ; and Tu cum{m, Argentin a. A sc mi e mpirical method by which the mean r elative phase velocity can be calculated from t he measurements of ph ase made at t hese four l"rcording s ites is demonstrated. The va lues of t he mean r elative phase velocity a t 18 kc/s w hi ch are obtain ed for daytime and nighttime propagation cond itions are resp ectively, (Vp / c)
The sunrise variations of phase and amplitude of VLF signals received over a single long path, at frequencies between 9.2 and 26.1 kHz are interpreted as interference between waveguide modes. The deduced differences in phase velocity and attenuation rates of the first two modes are in accordance with theoretical calculations and with earlier observations in a more restricted frequency range.
Papers have recently been published describing the behavior of the phase of VLF signals propagating over long VLF paths after the high‐altitude nuclear explosion of July 9, 1962 [Burtt, 1962; Zmuda et al., 1963]. These papers have been concerned with the effects within a few minutes of the explosion. In this note we intend to show that effects were also produced which lasted for at least one week.
On July 9, 1962, at around 0900 UT, the event known as Starfish took place. This was the detonation of a 1.4‐MT nuclear weapon at a height of 400 km [Zmuda et al., 1963] over Johnson Island in the Pacific. Figure 1 shows the diurnal phase variation [Chilton et al., 1963] of the signals at 19.8 kc/s from NPM in the Hawaiian Islands received at Boulder during the month of July 1962. The initial effect of the explosion on this path, near 0900 UT on July 9, resulted in the phase of the signal approaching or possibly passing its daytime value, although the path was in complete darkness at this time. Almost immediately afterward the phase began to return to normal and was still recovering when the eastern end of the path became sunlit. During the days following, the figure shows that the diurnal variation was much reduced, and it was not until July 17 that the diurnal phase change returned to the value it had before the event.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.