Introduction to ionospheric heating at Tromsø—I. Experimental overview

The review is based in a report presented by the author at the RAS Physical Sciences Division's session in honor of Vitaly L Ginzburg's 90th birthday. It examines the current status of theoretical and experimental research on nonlinear phenomena arising when a powerful radio wave propagates in the ionosphere. The focus is on the modification of the ionosphere under the resonance excitation of natural plasma oscillations by radio waves. The upper-hybrid resonance gives rise to strong upper- and lower-hybrid plasma waves; excites strongly elongated ionospheric irregularities, and induces artificial ionospheric radio emission. Nonlinear processes are found to undergo complete transformation near double resonances, when the upper-hybrid frequency is close to a multiple of the electron gyromagnetic frequency. In the neighborhood of the Langmuir resonance, intense plasma waves and ion-sound waves are excited, electrons are effectively accelerated, and an artificial glow of the ionosphere appears.

https://iopscience.iop.org/article/10.1070/PU2007v050n11ABEH006212/pdf

Nonlinear effects in the ionosphere

A high frequency electromagnetic pump wave transmitted into the ionospheric plasma from the ground can stimulate electromagnetic radiation with frequencies around that of the ionospherically reflected pump wave. The numerous spectral features of these stimulated electromagnetic emissions (SEE) and their temporal evolution on a wide range of time scales are reviewed and related theoretical, numerical, and simulation results are discussed. On long (thermal) time scales the SEE constitutes a self-organization of the ionospheric plasma which depends on the interaction of nonlinear processes in a hierarchy of time scales in response to the electromagnetic pumping. Particularly, the appearance of the rich SEE spectrum is associated with the slow self-structuring of the plasma density into a spectrum of magnetic field-aligned density striations. The dependence of the SEE on electron gyroharmonic effects and the presence of density striations suggests that the existence of a magnetic field in the plasma is important for plasma turbulence to dissipate into non-thermal electromagnetic radiation during the long time quasi-stationary state of the turbulence evolution.

Stimulated electromagnetic emissions by high-frequency electromagnetic pumping of the ionospheric plasma

Review of ionospheric modification experiments at Tromsø

EISCAT: early history and the first ten years of operation

The ionosphere was modified with powerful, high-frequency radio waves transmitted by the Heating facility near Tromso, Norway. The modified ionosphere was observed using the Tromso and Kiruna European Incoherent Scatter (EISCAT) UHF system together with a 145-MHz portable CW radar and equipment for reception of stimulated electromagnetic emissions (SEE). Enhanced ion and plasma lines were observed. They persisted throughout heater periods of more than a minute, contrary to earlier observations at Tromso. Spectral features in the plasma lines were repeatedly observed at frequency shifts which are not explained by current theories. The SEE amplitude variation on long time scale (seconds to tens of seconds) shows similarity with the long–time scale behavior of the amplitude of the plasma lines observed by EISCAT. No obvious correlation seems to exist between the SEE and discovered radar spectral features.

Simultaneous bistatic European Incoherent Scatter UHF, 145‐MHz radar and stimulated electromagnetic emission observations during HF ionospheric modification

G. Wannberg

Papers

Simultaneous bistatic European Incoherent Scatter UHF, 145‐MHz radar and stimulated electromagnetic emission observations during HF ionospheric modification