ELF and VLF radiation from the “polar electrojet antenna”

Abstract

First, an approximate evaluation is made of the ELF/VLF dipole moment of the polar electrojet antenna established by ionospheric heating via the use of powerful HF waves amplitude modulated with frequencies in the ELF/VLF range. Then, the theory of reciprocity is used to determine the magnitude of the ELF/VLF waveguide excitation produced by such a dipole immersed in the ionosphere. Propagation under a series of ionospheres ranging from quiet auroral nightime to disturbed auroral daytime is considered. contrast between land and seawater, this method was found not to be feasible in practice [Wait, 1979; Bart, 1980]. More recently, Getmantsev et al. [1974] have shown that the D region of the ionosphere, when illuminated by a powerful source of HF radiation amplitude modulated at an extremely low frequency, can also act as a source of ELF radiation. The observed field strengths were quite small (• 10-1ttV m-•) and were explained in terms of nonlinear detection of the modulated HF signals in the ionosphere [Kotik and Trakhtengerts, 1975]. This work at midlatitudes has been continued by Ferraro et al. [1982] who, working with the powerful HF heating facility at Arecibo, have also generated ELF/VLF radiowaves in the D region of the ionosphere. Stubbe and Kopka [1977] suggested that by working at high latitudes, in the region of the polar electrojet, a much more effective VLF/ELF transmitting source could be produced in the ionosphere. Such a system has been in operation near Tromso in Norway for 3 years, and typical field strengths • 100 ttV m-x have been recorded 20 km south of the heating site when operating with an HF effective radiated power of 100 MW modulated at a few kilohertz [Stubbe et al., 1981[Stubbe et al., , 1982. ELF radiation from the electrojet, when heated byRussian low-frequency transmitters, has also been invoked as a mechanism to explain the reception of 1-kHz "pips" on ELF receivers in Northern Europe [Cannon, 1982]. Initial estimates of the radiation efficiency of the polar electrojet antenna (PEJ) have assumed the antenna to be in free space [Stubbe and Kopka, 1977; Cannon et al., 1982], but more recent calculations at ELF by Bart and Stubbe [1983] have shown that these simplistie analyses tend to overestimate the effective radiated power. This current work extends the ELF calculations of Barr and Stubbe into the VLF range and calculates the excitation of the five least 1111 FROM POLAR ELECTROJET 1113 BARR AND STUBBE: RADIATION FROM POLAR ELECTROJET Wait, J. R., On natural slot antennas, Radio Sci., 14(5), 765-766, ß 1979. R. Barr,

Numerical Simulations of Elf/VLF Wave Generated by Modulated Beat-Wave Ionospheric Heating in High Latitude Regions

“…The first one, which is in the altitude range 60 km-85 km, is caused by the increasing of electron temperature, and the other, which is in the altitude range 90 km-95 km, is aroused by the increase of electron density. In Figure 5(a), the jumping phase near 77 km cancels out part of Pedersen currents; therefore, the Pedersen currents decrease, and this result is similar to the conclusion in reference [20].…”

ELF wave generation in the ionosphere using pulse modulated HF heating: initial tests of a technique for increasing ELF wave generation efficiency

“…The six curves in each panel indicate how the normalized ELF response varies with the duty cycle of the pulse waveform for ionospheric cooling time constants varying from 0.1s h to 30s h . This range of time constants is similar to that calculated for the Hall current in the Dregion of the ionosphere (Rietveld et al, 1986) and the Hall current is normally regarded as the dominant current producing the ELF/VLF magnetic ®eld signatures at the Earth's surface (Barr and Stubbe, 1984b). The response axes in Fig.…”

“…14 together with below by powerful HF waves modulated at ELF (3 kHz). They computed the time constants for the Hall current in preference to the Pedersen current as the Hall current had been shown to produce the dominant integrated dipole moment in studies used to determine the eective excitation of the Earth-ionosphere-waveguide by ELF current sources in the ionosphere produced by amplitude modulated HF heating (Barr and Stubbe, 1984b). In Fig.…”

Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

“…All the trajectories were in the south-to-north direction. Barr et al, 1985Barr et al, , 1986Rietveld et al, 1989). Also, Getmantsev et al (1974) performed the first ground-based observation of radiation at combination frequencies under HF heating, while Kotik and Trakhtengerts (1975) provided a theoretical treatment of this effect.…”