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1.
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
2.
Ionospheric precursor of a destructive earthquake that occurred on April 6, 2009 at L’Aquila (Italy)
On the basis of the 15-min data from a series of ground-based vertical ionospheric sounding stations, a study of variations
of the foF2 critical frequency before the strong earthquake (M = 6.3) that occurred on April 6, 2009 at L’Aquila (Italy) was carried out. The earthquake epicenter was located 85 km north-eastward
from Rome. Approximately 20 h prior to the earthquake, a well-pronounced statistically significant effect of foF2 increase relative to the average background for magnetically quiet days was observed for almost 1.5 h at the Rome ionospheric
station. In this case, at control stations distanced from the earthquake epicenter, no statistically significant deviations
of foF2 from the background values were detected during the same observations period. This fact provides grounds for consideration
of the foF2 increase observed at Rome station as a possible ionospheric precursor of this earthquake. 相似文献
3.
Ionospheric disturbances at heights of the F 2 layer maximum during the strong magnetic storm (the minimum value of the Dst index was ?149 nT) and the magnetic superstorm (the minimum value of the Dst index was ?387 nT) have been compared based on the data from two pairs of magnetically conjugate midlatitude ground stations for ionospheric vertical sounding. The storms began on March 19, 2001, and March 31, 2001, respectively. It has been obtained that almost only negative ionospheric disturbances were observed in the Northern and Southern hemispheres in both cases. The maximum effect in changes in the layer critical frequency (foF2) in both hemispheres has a time delay relative to the moment of the maximum disturbance in the Dst index on the order of 3–4 h for the strong storm and about 1 h for the superstorm. The disturbed variations in the foF2 critical frequency in different hemispheres correlate well with each other in the plane of one magnetic meridian, but the correlation substantially weakens at different magnetic longitudes. An assumption is made that the revealed features of the behavior of the disturbed midlatitude ionospheric F 2 layer are caused by the complex character of the thermospheric response to the energy release in the auroral zone during the considered magnetic storms. 相似文献
4.
Changes in the critical frequencies of the F2 layer at several midlatitude stations of ionospheric vertical sounding during a sharp depletion in atmospheric pressure
under quiet solar and geomagnetic conditions are analyzed. It is shown that in such periods, the observed foF2 values differ from the mean values by approximately 10–15% and the deviations from the mean could be both negative (in the
daytime hours) and positive (at night). Such variations in foF2 could be referred to the known class of ionospheric disturbances observed under a quiet geomagnetic situation, that is,
to the so-called “Q-disturbances.” Analysis of wavelet spectra of foF2 variations shows the presence in the F region of oscillations of various periods (from 0.5 to 10 days). The decrease in the amplitude of daily variations during
pressure depletion is found. Presumably, the observed effect is caused by the dynamic impact of waves formed in the lower
atmosphere on the ionospheric F2 layer. 相似文献
5.
Normalization of the F2 layer critical frequency is put forward with a model related to the solar zenith angle at the time of observation and its local noon value. The method implies a physically based replacement of variable representing one of the key controlling parameters of the modern empirical ionospheric models. The inversion of critical frequency is analyzed with the hourly values of foF2 of seven ionospheric stations for 2000–2006 (half the solar activity cycle). The normalized critical frequency fnF2 reveals an improved correlation between the data of different stations and improved inter-seasonal correlation of the data of a particular station as compared with the initial foF2 values. A correlation radius in summer is two times greater for normalized critical frequency than for observations. The analytical model of expansion of the diurnal variation of critical frequency with four hourly values at 00, 06, 12 and 18 h of local time exhibits improved statistical features of normalized critical frequency as compared with observed critical frequency. 相似文献
6.
Ionosphere Disturbances Preceding Earthquakes according to the Data of Ground Based Station of the Vertical Ionospheric Sounding Wakkanai 总被引：1，自引：0，他引：1
S. A. Pulinets A. D. Legen’ka V. V. Hegai V. P. Kim L. P. Korsunova 《Geomagnetism and Aeronomy》2018,58(5):686-692
The paper analyzes the data of manual ionograms processing of hourly measurements of the critical frequency foF2 of the F2 ionospheric layer at the Wakkanai ionospheric vertical sounding station (Japan) in a geomagnetically quiet environment before a series of earthquakes with magnitude M > 6.0, for which the station entered the earthquake preparation zone, in order to detect possible Ionospheric Disturbances Preceding Earthquakes (IDPE), and to determine their quantitative characteristics. Detected IDPE, in the opinion of the authors, can be related to the processes of preparation of the corresponding earthquakes, i.e., to be Ionospheric Precursors of Earthquakes (IPE). 相似文献
7.
8.
V. E. Chertoprud L. N. Leshchenko G. V. Givishvili E. E. Goncharova G. S. Ivanov-Kholodny 《Geomagnetism and Aeronomy》2009,49(4):503-509
The 40-year period of observations of short-term variations (with characteristic times of up to 1–2 days) in the critical frequency of the ionospheric F2 layer (foF2) is analyzed. The continuous (with a step of 1 h) series of fluctuations (F) of the foF2 critical frequency (with eliminated daily variations) has been calculated using the hourly variations in foF2 at Moscow stations. The fractal dimension (FRH) of the fluctuations, characterizing short-term variations in foF2, has been determined and analyzed on a 30-day interval, using the Higuchi method. It has been established that FRH estimates substantially change in time. The 11-year cycle, which is in antiphase with the solar cycle, and the total annual and semiannual variations, similar to the variations observed in the normalized critical frequency of the E region and in the electron density of the D region, are clearly defined in these changes. Thus, the parameters of fast variations in the ionospheric F2 layer are affected by the phase of the 11-year solar cycle and by the position of the Earth in the orbit or seasonal variations in the atmosphere. 相似文献
9.
The consideration of the relation between the daytime and nighttime values of the critical frequency F2, foF2 of the ionospheric F2 layer, started in the previous publication of the authors, is continued. The main regularities in variations in the correlation coefficient R(foF2) characterizing this relation are confirmed using larger statistical material (more ionospheric stations and longer observational series). Long-term trends in the R(foF2) value are found: at all stations the negative value of R(foF2) increases with time after 1980. 相似文献
10.
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
11.
Variations in the critical frequency of the F2 layer at 22 ionospheric stations within the period 1990–2010 according to the SPIDR system data are considered. A confirmation of the negative trends in foF2 for seven stations considered by one of the authors earlier on the basis of median data is obtained. It is found that both negative (a decrease in foF2 with time) and positive (growth in foF2 with time) trends of the critical frequency are observed. During the later part of the considered period (after 1997), negative trends dominate. This fact manifests itself, apparently, in an increase in the role of the decrease in the thermospheric neutral temperature in the formation of foF2 trends. 相似文献
12.
The available massifs of experimental data on the critical frequency of the ionospheric F2 layer, foF2, covering the first decade of the new century, are considered. On the basis of studying these massifs, a conclusion is drawn that the scatter of foF2 values (measured by the standard deviation (SD)) relative to the dependence on solar activity has grown substantially over recent decades as compared to the period 1958–1979. The possible causes of the SD increase are considered. It is shown that the foF2 values for the period 1998–2010 decreased as compared to the period 1958–1979 by an average of 0.6 MHz which gives an estimate of the foF2 trend of ～-0.03 MHz per year. Linear trends in foF2 for some ionospheric stations are analyzed. It is obtained that, in spite of the scatter in the data, it is possible to obtain statistically significant trends for each considered situation (day and postsunset period in summer and winter). At the same time, the winter negative trends (～-0.052 MHz per year) are approximately a factor of 2 higher than the summer ones (～-0.024 MHz per year). Comparisons with the trends obtained for earlier periods show that the negative trend in foF2 increased substantially towards the first decade of our century. 相似文献
13.
Based on an analysis of data from the European ionospheric stations at subauroral latitudes, it has been found that the main ionospheric trough (MIT) is not characteristic for the monthly median of the F2-layer critical frequency (foF2), at least for low and moderate solar activity. In order to explain this effect, the properties of foF2 in the nocturnal subauroral ionosphere have been additionally studied for low geomagnetic activity, when the MIT localization is known quite reliably. It has been found that at low and moderate solar activity during night hours in winter, the foF2 data from ionospheric stations are often absent in the MIT area. For this reason, a model of the foF2 monthly median, which was constructed from the remaining data of these stations, contains no MIT or a very weakly pronounced MIT. 相似文献
14.
A. E. Stepanov V. L. Khalipov G. A. Kotova M. S. Zabolotskii I. A. Golikov 《Geomagnetism and Aeronomy》2016,56(2):181-186
The data of the ionospheric observations (the daily f plots) at the Yakutsk meridional chain of ionosondes (Yakutsk–Zhigansk–Batagai–Tixie Bay) with sharp decreases (breaks) in the critical frequency of the regular ionospheric F2 layer (foF2) are considered. The data for 1968–1983 were analyzed, and the statistics of the foF2 break observations, which indicate that these breaks are mainly registered in equinoctial months and in afternoon and evening hours under moderately disturbed geomagnetic conditions, are presented. Calculations performed using the prognostic model of the high-latitude ionosphere indicate that the critical frequency break position coincides with the equatorial boundary of large-scale plasma convection in the dusk MLT sector. 相似文献
15.
It is shown in a joint analysis of ionospheric vertical sounding data at the arctic Heiss Island and antarctic Vostok stations and the geomagnetic PC index, which characterizes the geoefficient component of the interplanetary magnetic field, that, during a disturbed geomagnetic period when PC > 2 in years of solar activity (SA) maxima in the winter season, positive phases of ionospheric disturbances are predominantly observed. In the nighttime hours, an increase in the critical foF2 frequencies by a factor of 2–3 can occur. In a disturbed geomagnetic period at the PC > 1.5 level in the summer season, negative phases of ionospheric disturbances are mainly observed. In years of maximum and moderate SA, the decrease in foF2, as compared to their median values, happens at night (∼30%). In years of low SA, the decrease value is much lower. At a substantial decrease in the PC index level, in the region of the geomagnetic pole at the Vostok station, in some cases, a substantial increase in the electron density level in the F region occurs with a delay of 0.5 h. At the same time, a significant correlation (r = −0.57) is observed between variations in the PC index and foF2. 相似文献
16.
B. V. Troitsky M. Yu. Ortikov K. A. Lobanov A. A. Vlasov A. I. Pogorel’tsev 《Geomagnetism and Aeronomy》2007,47(3):389-394
The possibility of determining the field of critical frequencies of the ionospheric F2 layer (foF2) using the maps of the total electron content, constructed based on the registration of signals from satellite radio navigation system of the GPS and GLONASS types, is considered. The calculation of foF2 is based on the SPIM (Standard Plasmasphere-Ionosphere Model) model specifying the ionospheric index of solar activity, which is determined at grid points of the map of the total electron content. The proposed method has been verified using the data of the hourly maps of the total electron content in the North American region during September 1–7, 2005. The variations in the critical frequencies for Boulder and Dyess sites, selected from the reconstructed foF2 maps, were compared with the data of the vertical sounding. The average error is ～10% during the entire period of measurements. The conclusion has been drawn that the proposed method can be used as an ionospheric support of HF radiocommunication in the cases when errors of tenths of MHz in foF2 values are permissible. 相似文献
17.
The relation between the critical frequency foF2 and F2-layer height hmF2 is considered for ten ionospheric stations in the periods before and after 1980. It is shown that in the earlier period the relation between foF2 and hmF2 is well pronounced. In the later period, a distortion of this relation is observed. The statistical characteristics of the foF2 dependence on hmF2 are spoiled. That shows that due to the cooling and contraction of the upper atmosphere the height distribution of the photochemical parameters governing the equilibrium concentration in the layer maximum changes. A larger contribution to this effect is evidently provided by changes in the atom-to-molecule concentrations ratio. 相似文献
18.
The accuracy limitations of critical frequency predictions in the ionospheric F2 layer are considered, which arise due to random variations in the Sun’s extreme UV radiation during the month. An analysis of δf (relative values of monthly rms scatters of the F2-layer critical frequencies) and the appropriate δu values (monthly rms scatters of extreme UV radiation) has shown their dependence on the solar activity level. A conclusion is drawn that when prognostic models of monthly medians are used for forecasting foF2 for a particular date, the error can hardly be less than ～7% at low solar activity and ～15% at a higher solar activity level. 相似文献
19.
Using the foF2 database obtained from satellites and ground-based ionospheric stations, we have constructed a global empirical model of the critical frequency of the ionospheric F2-layer (SDMF2—Satellite and Digisonde Data Model of the F2 layer) for quiet geomagnetic conditions (Kp < 3). The input parameters of this model are the geographical coordinates, UT, day, month, year, and the integral index F10.7 (day, τ = 0.96) of solar activity for a given day. The SDMF2 model was based on the Legendre method for the spatial expansion of foF2 monthly medians to 12 in latitude and 8 in longitude of spherical harmonics. The resulting spatial coefficients have been expanded by the Fourier method in three spherical harmonics with respect to UT. The effect of the saturation of critical frequency of the ionospheric F2-layer at high solar activity was described in the SDMF2 model by foF2 as a logarithmic function of F10.7 (day, τ = 0.96). The difference between the SDMF2 and IRI models is a maximum at low solar activity as well as in the Southern Hemisphere and in the oceans. The testing on the basis of ground-based and satellite data has indicated that the SDMF2 model is more accurate than the IRI model. 相似文献
20.
Seismoionospheric disturbances in the parameters of the ionospheric F 2 and sporadic E layers at the chain of the Japanese stations for vertical sounding of the ionosphere before strong crustal earthquakes with M>6.5 during the period from 1968 to 1992 have been considered. The dependence of the disturbance time of appearance in the ionospheric parameters on the earthquake magnitude and epicentral distance, obtained for each specific earthquake using the selected series of ionospheric stations, made it possible to consider these disturbances among medium-term precursors of earthquakes. The velocity of the disturbance front apparent motion has been determined based on the model of horizontal radially-isotropic disturbance propagation from the projection of the impending earthquake epicenter to the ionospheric altitudes. The conclusion has been made that the distinguished seismoionospheric disturbances follow the boundary of the earthquake preparation region, expanding on the Earth’s surface. 相似文献