Paul Kossey

Subionospheric VLF observations of transmitter‐induced precipitation of inner radiation belt electrons

[1] Ionospheric effects of energetic electron precipitation induced by controlled injection of VLF signals from a ground based transmitter are observed via subionospheric VLF remote sensing. The 21.4 kHz NPM transmitter in Lualualei, Hawaii is keyed ON-OFF in 30 minute periodic sequences. The same periodicity is observed in the amplitude and phase of the sub ionospherically propagating signals of the 24.8 kHz NLK (Jim Creek, Washington) and 25.2 kHz NLM (LaMoure, North Dakota) transmitters measured at Midway Island. Periodic perturbations of the NLK signal observed at Palmer, Antarctica suggest that energetic electrons scattered at longitudes of NPM continue to be precipitated into the atmosphere as they drift toward the South Atlantic Anomaly. Utilizing a model of the magnetospheric waveparticle interaction, ionospheric energy deposition, and subionospheric VLF propagation, the precipitated energy flux induced by the NPM transmitter is estimated to peak at

Propagation of high‐power microwave pulses in air breakdown environment

A chamber experiment is conducted to study the propagation of high‐power microwave pulses through the air. Two mechanisms responsible for two different degrees of tail erosion have been identified experimentally. The optimum pulse amplitude for maximum energy transfer through the air has also been determined.

Stimulated thermal instability for ELF and VLF wave generation in the polar electrojet

Generation of ELF and VLF waves in the HF heating wave modulated polar electrojet is studied. Through the Ohmic heating by the amplitude-modulated HF heating wave, the conductivity and thus the current of the electrojet is modulated to set up the ionospheric antenna current. However, it is shown that a stimulated thermal instability is also excited by the amplitude-modulated HF heating wave. This instability introduces an electron temperature modulation more effectively than that by the passive Ohmic heating process and is expected to improve considerably the intrinsic efficiency of ELF and VLF wave generation by the amplitude-modulated HF heating wave. Moreover, the generation efficiency and signal quality also depend on the HF wave modulation scheme. Thus, four amplitude-modulation schemes are examined and compared.

Numerical comparison of two schemes for the generation of ELF and VLF waves in the HF heater‐modulated polar electrojet

Generation of ELF and VLF waves in the HF heater modulated polar electrojet is numerically studied. Illuminated by an amplitude modulated HF heater, the electron temperature of the electrojet is modulated accordingly. This, in turn, causes the modulation of the conductivity and thus the current of the electrojet. Emissions are then produced at the modulation frequency and its harmonics. The present work extends the previous one on a thermal instability to its nonlinear saturation regime. Two heater modulation schemes are considered. One modulates the heater by a rectangular periodic pulse. The other one uses two overlapping heater waves (beat wave scheme) having a frequency difference equal to the desired modulation frequency. It is essentially equivalent to a sinusoidal amplitude modulation. The nonlinear evolutions of the generated ELF and VLF waves are determined numerically. Their spectra are also evaluated. The results show that the signal quality of the second (beat wave) scheme is better. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency, consistent with the Tromso observations.

Major enhancement of extra-low-frequency radiation by increasing the high-frequency heating wave power in electrojet modulation

Extra-low-frequency (ELF) wave generation by modulated polar electrojet currents is studied. The amplitude-modulated high-frequency (HF) heating wave excites a stimulated thermal instability to enhance the electrojet current modulation by the passive Ohmic heating process. Inelastic collisions of electrons with neutral particles (mainly due to vibrational excitation of N2) damp nonlinearly this instability, which is normally saturated at low levels. However, the electron’s inelastic collision loss rate drops rapidly to a low value in the energy regime from 3.5 to 6 eV. As the power of the modulated HF heating wave exceeds a threshold level, it is shown that significant electron heating enhanced by the stimulated thermal instability can indeed cause a steep drop in the electron inelastic collision loss rate. Consequently, this instability saturates at a much higher level, resulting to a near step increase (of about 10–13 dB, depending on the modulation wave form) in the spectral intensity of ELF radiation....

Contrasting O/X-mode Heater Effects on O-Mode Sounding echo and the Generation of Magnetic Pulsations

Abstract : The effects on the ionosphere of powerful O-mode and X-mode pump waves, modulated 3 minutes on and 1 minute off, were explored. The experiments were monitored using the digisonde and magnetometer located at the HAARP facility. The results show that the virtual heights of the O-mode sounding echoes shifted down/up as the O/X mode heater was turned on; the ionosphere also moved downward/upward accordingly. Enhanced spread-f was also observed in O-mode heater-on periods. Heater-induced magnetic pulsation was observed. Its intensity increased progressively in the heater on/off sequence and X-mode heater was more effective than O-mode heater in the generation of magnetic pulsation. In the last X-mode heater-on period, when the magnetic pulsation reached the highest level, pc 3 pulsations, with increasing intensity, were also observed.

Amplification of whistler waves for the precipitation of trapped relativistic electrons in the magnetosphere

Energetic electrons trapped in the radiation belts undergo bounce motion about the geomagnetic equator. The behaviors of the trajectories of these electrons interacting with a large amplitude whistler wave are explored, with the electron energy and wave amplitude as variable parameters. A surface of section technique is used to examine the chaoticity of the system graphically. The wave amplitude required causing an electron trajectory to become chaotic decreases with increasing electron energy. Once the trajectory of an electron becomes chaotic, it can wander into the loss cone and subsequently precipitates into the ionosphere and/or the upper atmosphere. This chaotic scattering process requires a threshold field for the commencement of chaotic behavior in the electron trajectories. Therefore, a loss-cone negative mass instability process to amplify whistler waves by electrons in the bulk of the energy distribution is also studied. The numerical results show that the injected whistler waves can be amplified by more than 20 dB, agreeing with the experimental results. This amplification process reduces considerably the required field intensity of injected whistler wave for the purpose of precipitating those tail electrons in the megaelectronvolt range.

Modelling and numerical simulation of microwave pulse propagation in an air-breakdown environment

The dependences of the propagation characteristics of an intense microwave pulse on the intensity, frequency, width and shape of the pulse in an air-breakdown environment are examined. Numerical simulations lead to a useful empirical relation P 3 W = α = const, where P and W are the incident power and width of the pulse and α depends on the percentage of the pulse energy transferred from the source point to a given position. The results also show that, using a single unfocused microwave pulse transmitted upwards from the ground, the maximum electron density produced at, for example, 50 km altitude is limited by the tail erosion effect to below 10 6 cm -3 . Repetitive-pulse and focused-beam approaches are then examined. Both approaches can increase the maximum electron density by no more than an order of magnitude. Hence a scheme using two obliquely propagating pulses intersecting at the desired height (e.g. 50 km) is considered. It is shown that the generated electron density at the lowest intersecting position can be enhanced by more than two orders of magnitude.

Laboratory chamber experiments exploring the potential use of artificially ionized layers of gas as a Bragg reflector for over‐the‐horizon signals

A set of parallel plasma layers is generated by two intersecting microwave pulses in a chamber containing dry air at a pressure comparable to the upper atmosphere. The dependence of breakdown conditions on the pressure and pulse length is examined. The results are shown to be consistent with the appearance of tail erosion of microwave pulse caused by air breakdown. Bragg scattering experiments, using the plasma layers as a Bragg reflector, are then performed. Both time domain and frequency domain measurements of wave scattering are conducted. The experimental results are found to agree very well with the theory. Moreover, the time domain measurement of wave scattering provides an unambiguous way for determining the temporal evolution of electron density during the first 100 μs period. A Langmuir double probe is then used to determine the decay rate of electron density during a later time interval (1 to 1.1 ms). The propagation of high-power microwave pulses through the air is also studied experimentally. The mechanisms responsible for two different degrees of tail erosion have been identified. The optimum amplitude of a 1.1 μs pulse for maximum energy transfer through the air has been determined.

Precipitation of Trapped Relativistic Electrons by Amplified Whistler Waves in the Magnetosphere

Numerical study of a loss-cone negative mass instability to amplify whistler waves by energetic electrons in the radiation belts is presented. The results show that a very low intensity whistler wave can be amplified by 50keV electrons more than 25dB, consistent with the Siple experimental result [Helliwell et al., J. Geophys. Res. 85, 3360 (1980)]. The dependencies of the amplification factor on the energetic electron density and on the initial wave intensity are evaluated. It is shown that the amplification factor decreases as the initial wave intensity increases. However, this gain can still exceed 15dB for a 30dB increase of the initial wave intensity, which is needed for the purpose of precipitating MeV electrons in the radiation belts. We then show that there exists a double resonance situation, by which, as an example, a wave is simultaneously in cyclotron resonance with 50keV electrons as well as with 1.5MeV electrons; the wave is first amplified by 50keV electrons and then precipitates 1.5MeV ele...