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1.
M. Yu. Andreev D. V. Blagoveshchensky V. M. Vystavnoi V. S. Mingalev G. I. Mingaleva 《Geomagnetism and Aeronomy》2007,47(4):502-509
The experimental ionograms of the oblique-incidence sounding of the ionosphere, obtained on the St. Petersburg-Spitsbergen high-latitude HF radio path during the magnetically quiet period December 14–15, 2001, are compared with the model calculations of radiowave trajectories. For this purpose, the corresponding oblique-incidence ionograms are numerically synthesized using the technique based on the shooting method and the computer program for constructing HF radiowave trajectories. The three-dimensional electron density distribution, calculated using the mathematical model of the high-latitude ionosphere previously developed at the Polar Geophysical Institute (PGI), is used to model radio propagation. The numerical calculations make it possible mainly to explain the specific features of the experimental data on the oblique-incidence sounding of the ionosphere. 相似文献
2.
Geomagnetism and Aeronomy - A model of the medium of the ionosphere and magnetosphere, including the distributions of the concentrations and temperatures, collision frequencies, and magnetic field... 相似文献
3.
The insufficiently known phenomenon of MF-wave propagation from the Earths surface through the magnetosphere (guiding) to the conjugate hemisphere and back to the transmitter has been experimentally studied. Computer modelling fulfilled on the basis of ray tracing showed that guiding was possible only from area of the main ionospheric trough. The effect of MF guiding is most useful for the diagnostics of the plasmapause, poleward edge of the trough, the diffuse precipitation boundary and so on. 相似文献
4.
The X17 solar flare occurred on October 28, 2003, and was followed by the X10 flare on October 29. These flares caused very strong geomagnetic storms (Halloween storms). The aim of the present study is to compare the variations in two main ionospheric parameters (foF2 and hmF2) at two chains of ionosondes located in Europe and North America for the period October 23–28, 2003. This interval began immediately before the storm of October 28 and includes its commencement. Another task of the work is to detect ionospheric precursors of the storm or substorm expansion phase. An analysis is based on SPIDR data. The main results are as follows. The positive peak of δfoF2 (where δ is the difference between disturbed and quiet values) is observed several hours before the magnetic storm or substorm commencement. This peak can serve as a disturbance precursor. The amplitude of δfoF2 values varies from 20 to 100% of the foF2 values. The elements of similarity in the variations in the δfoF2 values at two chains are as follows: (a) the above δfoF2 peak is as a rule observed simultaneously at two chains before the disturbance; (b) the δfoF2 variations are similar at all midlatitude (or, correspondingly, high-latitude) ionosondes of the chain. The differences in the δfoF2 values are as follows: (a) the effect of the main phase and the phase of strong storm recovery at one chain differs from such an effect at another chain; (b) the manifestation of disturbances at high-latitude stations of the chain differ from the manifestations at midlatitude stations. The δhmF2 variations are approximately opposite to the δfoF2 variations, and the δhmF2 values lie in the interval 15–25% of the hmF2 values. The performed study is useful and significant in studying the problems of the space weather, especially in a short-term prediction of ionospheric disturbances caused by magnetospheric storms or substorms. 相似文献
5.
Specific features of the variations and structure of the ionosphere above northern Europe during the known magnetospheric storm of January 10, 1997, have been analyzed using the oblique-incidence backscatter (OIB) methods. The OIB equipment installed near St. Petersburg, Gor’kovskaya (AANII), represent a BIZON small radar, the data of which were compared with the CUTLASS radar data, GPS observations of TEC, and geophysical data of the Sweden, Finnish, and Russian high-latitude observatories. A local substorm that occurred from 1451 to 1655 UT has been studied in detail, and 52 OIB ionograms have been obtained. The types of reflections from the MIT polar wall and the narrow ionization trough have been identified. 相似文献
6.
Geomagnetism and Aeronomy - Synchronous studies have been conducted on the high-latitude ionosonde at Sodankyulä station and the low-latitude ionosonde in Cyprus Island, as well as on two... 相似文献
7.
Specific variations in the critical frequency of the ionospheric F 2 layer during magnetospheric substorms have been found based on the data of vertical sounding stations in Europe and North America. Maximal attention has been paid to the positive peaks of ΔfoF2 with a duration of 6–8 h before the beginning of the substorm expansion phase (T 0). The possible physical mechanisms by which these peaks are formed (related to the impact of fast particles in the foreshock region of the solar wind on the Earth’s magnetosphere and different for middle and high latitudes) have been considered. The positive peaks of ΔfoF2 can be used in a short-term prediction of the ionospheric disturbance onset and space weather on the whole. 相似文献
8.
D. V. Blagoveshchensky 《Geomagnetism and Aeronomy》2014,54(5):568-574
Fifty-one magnetic storms occurred during the last solar half-cycle of transition from the epoch minimum to the epoch maximum are considered. Ionospheric (foF2) and magnetic (X component) data from Sodankyla observatory, Finland, were used for the analysis, as well as values of the ΣKp indices of magnetic activity. The dependence of variations in the critical frequency foF2 was studied before, during, and after each storm. It has been revealed that a major effect (ME) takes place for all of the storms analyzed. It consists in the following: the first maximum in foF2 values occurs several days before the onset of the active phase of a storm, then foF2 attains its minimum during the active phase, and the second maximum occurred after the active phase. Five principals, the most frequent types of variation in foF2 during a storm, have been revealed. However, special cases (30%) in which an ME exists but shifts rightward several days along the time axis are observable. Ionospheric “memory” (inertia) from 8–9 h to 2 days has been revealed. It has been ascertained that the occurrence of the first ME maximum can be considered a magnetic storm precursor. Such a precursor potentially can be used for forecasting the beginning of magnetic storm development, which is important for space weather problems. 相似文献
9.
The specific features of radio propagation from the viewpoint of physics of processes in the polar ionosphere have been studied in the present work based on the oblique-incidence sounding of the ionosphere (OISI) on the St. Petersburg-Belyi Nos (Amderma) polar radio path during substorm activity in the summer months of 1997. The OISI data were used to find the following parameters: maximum observable frequency during signal reflection from the E s layer (EsMOF), maximum observable frequency during signal reflection from the F 2 layer (F2MOF), and lowest observable frequencies for the E s and F 2 layers (EsLOF and F2LOF, respectively). Absolute MOF and LOF values were also found out. The total number of received rays was determined in addition to the above parameters. Isolated substorms against a quiet background were selected for the studies. These substorms resulted in substantial changes in the ionospheric radio channel and propagation conditions along the path. The results of the studies are as follows. (1) The following distinct regularities in the HF propagation along the path have been determined: (i) the range of operational frequencies Δ = MOF-LOF becomes substantially narrower during substorms; (ii) the radio propagation mechanism changes during a substorm; (iii) during substorms, the auroral absorption substantially and partially increases in the course of the expansion and recovery phases, respectively; (iv) multiray effect sharply increases at the beginning of the substorm active phase (T 0). (2) The indications of changes in the radio propagation parameters, which can possibly be used to predict the beginning of substorm development, have been formulated. (3) All revealed regularities in the HF propagation in the auroral zone have been explained from the geophysical viewpoint. It is important to use these regularities to organize radio communication and to solve the problems within the scope of the Space Weather Program. 相似文献
10.
D. V. Blagoveshchensky 《Geomagnetism and Aeronomy》2016,56(1):19-29
Two high-latitude high-frequency (HF) paths of oblique-incidence ionospheric sounding were selected: Gor’kovskaya (GRK)–Dixon Island (DIK) and GRK–Lovozero (LOZ).The following propagation parameters were studied: F2MOF and F2MUF for the main signal, F2MOFl for lateral signals, EsMOF for a signal reflected from the sporadic ionospheric layer, and MOFm for the propagation modes of the M (or N) type. Here MOF and MUF are the maximum observed and usable frequencies, respectively. It was found that the reciprocal theorem is satisfied on two radio paths depending on the studied propagation parameter: the path length and location, time of day, and degree of magnetospheric disturbance. It was found that the reciprocal theorem is satisfied in 78, 50, and 30% of cases on the first path for the F2MUF values in the daytime under moderately disturbed conditions, in the morning, and at night, respectively. For the MOFm and moderately disturbed conditions on this path, the reciprocal theorem is satisfied in 40, 35, and 20% of cases in the daytime, morning, and at night, respectively. For the F2MUF values on the second path, reciprocity is satisfied in 73% of cases in the daytime and under moderately disturbed conditions and in 30% of cases at night during a quiet period. On this path, reciprocity is satisfied in 33% of all cases at night under strongly disturbed conditions. An unusual fact was also detected when ionograms of oblique-incidence ionospheric sounding were analyzed: the F2MUF values in the LOZ–GRK direction are almost always slightly (by 1–4%) larger than in the GRK–LOZ direction. A similar difference in the F2MUF values in the forward and backward directions can apparently be explained by the steep horizontal gradient in the electron density distribution from north to south in the reflection region of this path. Such a situation is not observed on the DIK–GRK line. 相似文献