Comparison of features of phenomena in the high latitude ionospheric F-region induced by powerful HF radio waves radiated by antennas with narrow and wide beam patterns

Abstract

Physical experiments in natural free plasma (ionosphere) using controlled injection of powerful HF radio waves (HF pump waves) into the high latitude upper (F-region) ionosphere allow the investigation of various nonlinear phenomena. HF pump waves with ordinary (O-mode) polarization are commonly used for the modification of the upper ionosphere (F-region). This is due to the fact that extraordinary (X-mode) polarized HF pump waves are reflected from altitudes significantly below the reflection altitude of the O-polarized HF pump wave and the altitude of electrostatic plasma waves. Because of that they are not able to generate such waves or, as a consequence, cause artificial plasma turbulence and accompanying phenomena. However, the results of experiments carried out by AARI researchers at the EISCAT/Heating facility (Tromsø, Norway) have clearly demonstrated for the first time that X-polarized HF pump waves are able to produce artificial ionosphere disturbances which may be much stronger compared with O-mode disturbances. This opens up new possibilities for the investigation of nonlinear phenomena and ionospheric disturbances in the upper ionosphere, leading to the development of technologies allowing one to observe the processes in the Arctic zone ionosphere. In contrast to the traditional investigations of artificial ionospheric disturbances induced by O-mode HF pump waves, X-mode disturbances in the upper ionosphere are poorly investigated, the mechanisms of their generation are not understood. Therefore, such investigations require serious experimental and theoretical development. We present investigation results of the influence of the HF Phased Array beam width at the EISCAT/Heating facility (Tromsø, Norway) on the features of artificial disturbances in the high latitude upper (F-region) ionosphere induced by powerful HF radio waves. The paper analyzes the features, behavior, and spatial structure of electron density and temperature (Ne and Te), Langmuir and ion-acoustic plasma waves, artificial field-aligned irregularities (AFAIs), and narrowband (±1кHz relative to heating frequency) stimulated electromagnetic emission (NSEE) induced by X-mode HF pumping by phased Arrays with a narrow beam width of 5–6° (A1) and a wide beam width of 10–12° (at — 3 dB level) (A3). It is shown that the spatial size in the north-south direction of the Neducts and HF-enhanced plasma and ion lines (HFPL and HFIL) depends on the width of the HF Heating facility antenna beam. It corresponds to the angle width of 7° for the A3 antenna and 4° for A1, which is approximately two times less than the width of th pattern of A3 and A1. The relationship between the Ne duct transverse size and the size of the region occupied by the X-mode artificial irregularities is found. It has been established that the intensities of all the discrete components in the NSEE spectra are 10–20 dB higher when a powerful X-wave is emitted to the antenna A1, providing ERP = 820 MW, compared to radiation to the antenna A3, providing ERP = 230 MW. A comparison is made of the influence of the radiation pattern width of the antennas A1 and A3 on the characteristics of disturbances during O- and X-mode HF pumping. It is shown that Ne ducts and narrow band stimulated electromagnetic emission during O-mode heating, at frequencies below the critical frequency of the F2 layer, are not excited at all when the pump wave is emitted by both antennas A1 and A3. However, perturbations in the electron temperature, AFAI intensity, and the size of the region occupied by AFAIs are greater during O-mode heating than during X-mode heating.