Search

Представлены результаты экспериментальных исследований возбуждения продольных плазменных волн (ленгмюровских и ионно-акустических) в высокоширотной F области ионосферы, вызванных воздействием мощных КВ радиоволн обыкновенной (О-мода) или необыкновенной (Х-мода) поляризации. Частота излучения комплекса fH EISCAT/Heating (г. Тромсе, Норвегия) была близка критической частоте слоя F2 fH ~ foF2 и частоте гирорезонанса электронов fH ~ nfce. Определены пороговые (минимальные) значения электрического поля волны накачки, необходимые для возбуждения плазменных (ленгмюровских) ЕionPL и ионно-акустических ЕionIL волн., We present experimental results related to the studies of the excitation of elongated plasma waves (Langmuir and ion-acoustic) in the high latitude ionosphere F-region induced by the ordinary (Omode) and extraordinary (X-mode) HF heating near the critical frequency of the F2 layer and electron gyroresonance frequency. Experiments have been carried out at the EISCAT/Heating facility located near Tromsø by using the power stepping of effective radiated power. The threshold values of the electric field required for the excitation of Langmuir and ion-acoustic plasma waves, were determined.

Представлены результаты исследований влияния ширины диаграммы направленности антенны КВ нагревного стенда EISCAT/Heating на характеристики явлений в высокоширотной верхней (F-область) ионосфере, вызванных воздействием мощных КВ радиоволн необыкновенной (Х-мода) поляризации. Выполнено сравнение характеристик мелкомасштабных искусственных ионосферных неоднородностей, электронной концентрации и температуры, ленгмюровских и ионно-акустических плазменных волн, а также узкополосного (в полосе ± 1кГц относительно частоты нагрева) искусственного радиоизлучения ионосферы при излучении мощной КВ радиоволны на фазированные антенные решетки с шириной 5 6° и 10 12° (на уровне – 3 дБ)., The results of investigations of the influence of the HF antenna beam width of EISCAT/Heating facility on characteristics of artificial disturbances in the high latitude upper (F-region) ionosphere induced by the powerful extraordinary (X-mode) polarized HF radio waves are presented. The comparison between features of artificial field-aligned irregularities, electron density and temperatures, Langmuir and ion-acoustic plasma waves, and narrowband (± 1кHz from the heater frequency) stimulated electromagnetic emission induced by HF pumping on the phased Arrays with the beam width of 5 6° и 10 12° (at – 3 dB level is performed.

We report experimental results from multi-instrument diagnostic tools related to phenomena in the high latitude ionosphere F-region, induced by the simultaneous action of powerful extraordinary (X-mode) and ordinary (O-mode) polarized HF radio waves at EISCAT (European Incoherent SCATter) during magnetically quiet background geophysical conditions. HF pump waves were injected towards the magnetic zenith at a frequency of 5.423 MHz, which was just below the critical frequency of the F2 layer when the excitation of X- and O-mode phenomena was possible. In the course of the experiment, the effective radiated power (ERP) of the X-mode wave was 130.5 MW, while the portion of the O-mode ERP was 29.9 MW (about 20% of the full ERP). It was found that simultaneous action of the X- and O-mode pump waves lead to the excitation of effects typical for both X- and O-mode HF pump waves. Namely, the excitation of small-scale field-aligned irregularities due to the thermal parametric (resonance) instability and a downshifted maximum (DM) component in the wideband stimulated electromagnetic emission (WSEE) spectra, typical for the O-mode HF pumping, was observed, together with multiple ion gyro-harmonic structures in the narrowband stimulated electromagnetic emission (NSEE) spectra. These latter results were recorded at a large (more than 1000 km) distance from the EISCAT/heating facility, typical only for an X-mode HF pumping. The results obtained are compared with “pure” O-mode heating and discussed in detail.

По результатам анализа радиозатменных измерений FORMOSAT-3/COSMIC обнаружено поглощение ДМ-радиоволн (длина волны ~19 см) в нижней высокоширотной ионосфере Земли. Величина максимального поглощения составляет ~3 dB в интервале ~60 – ~100 км и в отдельных случаях достигает ~10 dB на высотах от 90 до 95 км. Предложена методика определения вертикальных профилей коэффициента поглощения путём решения обратной задачи радиозондирования в нижней ионосфере Земли. Надёжно идентифицированы слои поглощения в отдельных сеансах, обусловленные мощными всплесками рентгеновского излучения и сильными изменениями геомагнитных условий во время бури. Найдено, что на высотах от 90 до100 км величина коэффициента поглощения ДМ-радиоволн достигала значений (5.69 ± 1.35)∙10-3dB/km., Based on the results of the analysis of FORMOSAT-3/COSMIC radio occultation measurements, the absorption of DMradio waves (wavelength ~19 cm) in the lower high-latitude ionosphere of the Earth was detected. The maximum absorption value is ~3 dB in the range of ~60 ~90 km and in some cases reaches ~10 dB at altitudes from 90 to 95 km.A method for determining the vertical profiles of the absorption coefficient by solving the inverse problem of radiosonding in the lower ionosphere of the Earth is proposed.The absorption layers in individual sessions caused by powerful bursts of X-ray radiation and strong changes in geomagnetic conditions during the storm were reliably identified.It was found that at altitudes from 90 to 100 km, the value of the absorption coefficient of DM radio waves reached values (5.69 ± 1.35)∙10-3 dB/km.

Bu çalışmada, Aralık 1971-Eylül 1972 tarihleri arasında yüksek enlem bölgesi olarak tanımlanan 60o-90odeğişmeyen manyetik enlem arasındaki 7 iyonsonda istasyonundan alınan saatlikfoF2 verilerinin değişmeyen manyetik enleme göredeğişimleri, farklı jeomanyetik aktivite durumları için incelenmiştir.Analizlerden elde edilen sonuçlara göre, gündüz saatlerindeki foF2değerlerinin, gece saatlerindeki değerlerden büyük olduğu, ayrıca bu saatlerdefoF2 değerlerinin değişmeyen manyetik enlem artışı ile68o-72o değişmeyen manyetik enlemleri arasındaki artışdışında azaldığı tespit edilmiştir. Gece saatlerinde ise foF2değerlerinin yaklaşık 66o-72o değişmeyen manyetik enlemleri arasında arttığı, bu enlemlerden dahabüyük ve daha küçük enlemlerde ise foF2 değerlerinin azalarak çukura benzer bir yapı oluşturduğu gözlemlenmiştir. Ayrıcamevsimsel ve jeomanyetik aktivite değişimlerinin, foF2 değerlerininenlemsel değişimleri üzerinde önemli bir etkiye sahip olduğu tespit edilmiştir.Jeomanyetik pasif durumdaki foF2 değerleri, jeomanyetik aktif durumdaki foF2değerlerinden büyüktür. Özellikle jeomanyetik aktif durumdaki Aralık döneminde,polar cap ve polar oval bölgeleri daha belirgin ve bu bölgeler enlemsel olarakdaha geniş bir yapıya sahiptir., In this study, changes according to invariant magnetic latitude of thehourly foF2 data that are taken from seven ionosondes stations are situated atbetween 60o-90o invariant magnetic latitude as known highlatitude region are investigated for different geomagnetic activity conditionsduring December 1971-September 1972. According to the results obtained from theanalyzes, it was found that the foF2 values in the daytime are larger thanthose in the nighttime, and the foF2 values in these hours decreases with theincreasing of the invariant magnetic latitude the except for between about 68oand 72o invariant magnetic latitude. At night time, it was observedthat the foF2 values increases between about 66o and 72o invariantmagnetic latitude, while the foF2 values exhibit a trough structure at largerand smaller latitudes than these latitudes. It is also observed that seasonaland geomagnetic activity changes have a significant influence on thelatitudinal changes of the foF2 values. The foF2 values in the geomagneticquiet condition are larger than the foF2 values in the geomagnetic activeconduction. Especially in the geomagnetic active conduction of the December,the polar cap and polar oval zones are more prominent and have a largerlatitudinal structure.

Electron density irregularities influence Global Navigation Satellite System (GNSS) signals, manifesting as ionospheric scintillation. Scintillation poses a service risk to safety-critical GNSS applications at high latitudes. It is difficult to predict, as ionospheric instability processes are not yet fully characterised. This research combines the fields of ionospheric imaging and scintillation monitoring, to investigate the causes of scintillation in the Antarctic and Arctic.Results revealed a plasma patch structure above Antarctica, in response to the impact of a solar wind shock front. Measurements from a network of Global Positioning System scintillation receivers across the continent revealed moderate levels of phase scintillation associated with Total Electron Content (TEC) gradients at the patch break-off point. Scintillation was also driven by solar particle precipitation at E and F region altitudes, verified with in situ spectrometers on polar-orbiting satellites. The current receiver coverage in the region provided the Multi-Instrument Data Analysis Software (MIDAS) tomography tool with sufficient data to track the lifetime of the plasma patch without a convection model.A second experiment was performed at the South Pole, using a collocated GPS scintillation receiver and auroral imager. This allowed simultaneous line-of-sight tracking of GPS signals through the optical auroral emissions. Results showed the first statistical evidence that auroral emissions can be used a proxy for ionospheric irregularities causing GPS scintillation. The relationship was strongest during the presence of discrete auroral arcs. Correlation levels of up to 74% were found over periods of 2-3 hours. The use of multiple emission wavelengths provided basic altitude discrimination.Current capability of ionospheric TEC mapping in the Arctic was tested, where GPS receiver distribution is extensive compared to present Antarctic coverage. Analysis of the ionosphere’s response to a storm event revealed a sequential picture of polar cap patch activity, without the aid of plasma convection modelling. The electron density enhancements of the auroral oval were imaged in completeness for the first time using GPS tomography. Reconstructions were verified using ultraviolet auroral imagery from polar-orbit satellites, and vertical profiles from an incoherent scatter radar.

We present a multi-instrumented approach for the analysis of the Arctic ionosphere during the 19 February 2014 highly complex, multiphase geomagnetic storm. The geomagnetic storm was the result of two powerful and subsequent Earth-directed coronal mass ejections (CMEs). The first one was launched from the solar corona on 16 February and the second one on 18 February. We focus on effects of such solar-originated geomagnetic disturbances on the high latitude ionosphere because our present understanding of the fundamental ionospheric processes – particularly during perturbed times – in this region is still incomplete.