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Experimental results from two Tromso HF heating experiments in the nightside high latitudinal F region are examined. Bi-static scatter measurements of HF diagnostic signals were carried out on the London-Tromso-St. Petersburg and Pori-Tromso-St. Petersburg paths using a Doppler spectral method. The properties and behaviour of artificial field-aligned small-scale irregularities (striations) in the nightside high latitudinal F-region in course of the Tromso ionospheric modification experiments are studied. Experimental studies have been performed by the use of phased array I with a beamwidth of 6 degrees instead of 12-14 degrees in phased array 2, more often used in Tromso ionospheric modification experiments. The comparison between two experiments carried out in the same background geophysical conditions, shows the strongest striations in the field-aligned position of the heater beam. Possible explanation for this angular dependence is self-focusing of HF pump waves on striations causing the energy to be distributed asymmetrically. A principal question related to HF heating experiments is how is the disturbed auroral ionosphere modified. The results obtained on two paths simultaneously have shown that the strong heater-induced striations were observed along with natural ones. Velocities of heater-induced striations were quite different at different parts of the heated volume. It is suggested that the heater-induced striations can be grouped in two patches at different heights possibly due to the temperature-gradient-driven instability.

Представлены результаты экспериментальных исследований характеристик узкополосного искусственного радиоизлучения ионосферы (УИРИ) при воздействии на высокоширотную верхнюю ионосферу мощных КВ радиоволн необыкновенной поляризации нагревного комплекса EISCAT/Heating в г. Тромсе, Норвегия. Выполнен анализ условий возбуждения и спектральных характеристик УИРИ в зависимости от частоты нагрева и угла излучения волны накачки., We present experimental results concerning the investigations of the features of the narrowband stimulated electromagnetic emission (NSEE) in the high latitude upper ionosphere induced by the extraordinary polarized powerful HF radio waves from the EISCAT/Heating facility at Tromsø, Norway. The analysis of the generation conditions and spectral features of the NSEE depending on the heater frequency and the HF pump wave radiation angle is made.

Представлены результаты экспериментальных исследований времени развития и пороговых мощностей возбуждения ленгмюровской и ионно-акустической турбулентностей в высокоширотной верхней ионосфере при воздействии мощными КВ радиоволнами необыкновенной поляризации (комплекс EISCAT/Heating в г. Тромсе, Норвегия). Выполнено сравнение характеристик турбулентностей, вызванных воздействием волны накачки необыкновенной и обыкновенной поляризаций., Experimental results concerning the evolution in time and thresholds of excitation of the Langmuir and ion-acoustic turbulences in the high latitude upper ionosphere induced by the extraordinary polarized HF pump waves from the EISCAT/Heating facility at Tromsø, Norway, are presented. The comparison between the turbulence features under the action of HF pump waves with the extraordinary and ordinary polarization is made.