Ionospheric response on natural and man-made impacts

Pokhotelov, O.A.

Автор: Pokhotelov O.A.
Сборник: Февральские чтения, Программа III Международной Научно-Практической Молодежной Конференции "Творческий потенциал молодежи в решении авиакосмических проблем"
Тезисы
Год издания: 2018
Место издания: Февральские чтения, Программа III Международной Научно-Практической Молодежной Конференции "Творческий потенциал молодежи в решении авиакосмических проблем", Национальная академия авиации г. Баку, Азербайджан, 12-14 февраля, 2018 г
Первая страница: 26
Последняя страница: 26
Аннотация: There was a great deal of research in recent years related to the generation in the ionosphere of electromagnetic waves in the VLF/ULF frequency range generated by the natural and man-made sources in the topside ionosphere. These oscillations are commonly observed at all local times by both ground and satellite observations of electric and magnetic fields. A special attention is paid to the generation of such waves in the so-called ionospheric Alfven resonator (IAR). Using the realistic model of the topside ionosphere, we have reanalyzed the physical properties of the IAR interaction with the magnetospheric convective flow. It is found that in the absence of the convective flow the IAR eigenmodes exhibit a strong damping due to the leakage of the wave energy through the resonator upper wall and Joule dissipation in the conductive ionosphere. The maximum of the dissipation rate appears when the ionospheric conductivity approaches the IAR wave conductivity and becomes infinite. However, the presence of Hall dispersion, associated with the coupling of Alfven wave mode with compressional (magnetosonic) perturbations, reduces the infinite damping. The increase in the convection electric field leads to a substantial modification of the IAR eigenmode frequencies and to reduction of the eigenmode damping rates. For the given perpendicular wavelength the position of the maximum damping rate shifts to the region with lower ionospheric conductivity. When the convection electric field approaches a certain critical value, the resonator becomes unstable. This results in the IAR feedback instability. The physical mechanism of this instability is similar to the Cherenkov radiation in the collisionless plasmas. The favourable conditions for the instability onset are realized when the ionospheric conductivity is low, i.e., for the nighttime conditions. This effect may result in the decrease of the critical value of the electric field of the magnetospheric convection that is necessary for the formation of the turbulent Alfven boundary layer and appearance of the anomalous conductivity in the IAR region. The artificial generation of these waves using ionospheric heaters such as EISCAT, HIPAS and HAARP is also reviewed. Modelling the ground signatures of such waves is complicated by the fact that at these frequencies, the collisionless skin depth is comparable to the ionospheric thickness and thus the vertical structure of the ionosphere must be resolved. Furthermore, the Hall conductivity in the ionosphere couples compressional (magnetosonic) waves to shear Alfven mode providing a complex scenario for the wave dynamics. The present report describes a novel model for generating magnetosonic waves by F-region modulated HF heating that does not depend on the presence of electrojet currents and can thus be generated even by facilities located away from electrojet regions as well as in the absence of electrojets. The report presents the theoretical foundations of the model and concludes with a discussion of future experiments and an outline of the relevance of the model to space science.
Добавил в систему: Похотелов Олег Александрович

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