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1.
The relation of the long-period variations in the midnight and noon values of the critical frequency of the ionospheric F 2 layer at three midlatitude stations (Irkutsk, Moscow, and Boulder) to the daily mean index of geomagnetic activity in years of different solar activity has been studied. It has been found that the correlation coefficients between the above parameters depend on time of day, season, and solar activity level. The correlation coefficients are higher at night than in the daytime, especially at low solar activity. The highest absolute values of the correlation coefficient most often appear during equinoxes: April–May and September–October. It has been shown that the variability of the critical frequencies of the midlatitude ionospheric F 2 layer depends not only on geomagnetic activity but also (to a considerable degree) on the effect of the lower atmosphere. 相似文献
2.
V. A. Ivanova N. M. Polekh K. G. Ratovskii D. V. Ivanov 《Geomagnetism and Aeronomy》2011,51(8):1105-1108
A morphological analysis of vertical sounding data obtained in Irkutsk from 2003 to 2008 has been performed. The AE index was used to determine the geomagnetic activity level, and the storm main phase onset was registered based on the D
st index. The ionospheric response to a magnetic storm was estimated based on the relative deviation of the critical frequency
and altitude of the ionospheric F2 region from the median values. Superstrong magnetic storms and storms without positive initial phases were not considered
when the data were selected. We found that positive ionospheric disturbances, which were accompanied by an increase in the
F2 region maximum altitude, predominated between the storm initial phase and main phases during all considered magnetic storms.
Between these storm phases, negative disturbances were only registered at night. Predominance of positive ionospheric disturbances
over negative ones can be related to the selection of storms for studies. 相似文献
3.
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
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.
The dependence of the origination of G conditions in the ionospheric F region on solar and geomagnetic activity has been determined based on numerical simulation of the ionosphere over points
50° N, 105° E and 70° N, 105° E for summer conditions at noon. It has been found that the threshold value of the Kp geomagnetic activity index (Kp
S
), beginning from which a G condition can originate, is minimal for a low solar activity level at relatively high latitudes during the recovery phase
of a geomagnetic storm. On average, Kp
S
increases with increasing solar activity, but G conditions can originate at high solar activity levels and be absent at moderate ones for certain Kp values, which was apparently predicted for the first time. These properties of the origination of G conditions do not contradict the known results of a G-condition statistical analysis performed based on the data from the global network of ionospheric stations. 相似文献
6.
The ratio of the values of the F
2, layer critical frequencies 2 h after the sunset and at 1400 LT has been considered. It is assumed that this ratio is a good
indicator of the intensity of wind processes in the thermosphere. For 18 ionospheric stations, the dependences of this ratio
on the F
wl, solar activity index have been constructed for the period before 1980. It has been found that the standard deviation (S), from this dependence has been increased after 1980 at all stations. An increase in S, is interpreted as an indication of the existence of long-term trends in th e wind regime after approximately 1980. 相似文献
7.
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
8.
G. V. Vergasova E. S. Kazimirovskii N. M. Polekh J. Xiong L. Liu 《Geomagnetism and Aeronomy》2011,51(6):762-773
Results of studies of the wave structure of the critical frequencies of the ionospheric F2 layer with periods of planetary waves for two Asian stations—Irkutsk and Wuhan (China)—are presented. Estimates of the appearance
frequency, amplitudes, and the lifetime of oscillations with periods typical of planetary waves (2–25 days) are obtained.
It is shown that these characteristics depend on the season and place of observation. The appearance of joint periodicities
in the critical frequencies at both stations, as well as in the planetary index of geomagnetic activity Ap, is noted. 相似文献
9.
G. P. Kushnarenko G. M. Kuznetsova K. G. Ratovskii O. E. Kolpakova 《Geomagnetism and Aeronomy》2012,52(3):356-363
An analysis of ionospheric data obtained during geomagnetic disturbances in April and September 2005 is performed in order to obtain information on the behavior of some ionospheric parameters at heights of the F1 layer. The results of measurements by an Irkutsk digisonde at hourly and 5- and 15-min time intervals were used. It is shown that in September all parameters very actively responded to geomagnetic disturbances in short measurement time intervals. It is also shown that the electron concentration behaves more stable at lower heights of the F1 layer both during strong and moderate disturbances. 相似文献
10.
A. Rimóczi-Paál 《Pure and Applied Geophysics》1980,119(4):703-710
The variations of the upper atmosphere air density during geomagnetic disturbances have been investigated by many authors. According to the analysis of satellite orbits, in most cases an increase in the air density may be observed when the indexA
phas a maximum. Having ionospheric data from stations in Europe, Asia and Australia we might be able to study the global behaviour of the electron density in theF
2 region during such geomagnetic disturbances when an increase of the air density had been observed. In these cases we found, that at the peak of the ionospheric layer, the electron density decreased 0–3 days later than theA
pmaximum. 相似文献
11.
Morphological analysis of variations of the critical frequency foF2 in the midlatitude ionosphere at various sectors of local time is carried out on the basis of data from ground-based stations
of vertical sounding of the ionosphere in the period when during use of the incoherent scatter radar at Saint-Santin an anomalously
strong increase in the electric field was observed at heights of the ionospheric F region in the period of enhanced geomagnetic activity (4+ < Kp < 6−). The obtained picture of the space-time distribution of disturbances in foF2 makes it possible to assume that they could be caused by penetration to middle latitudes of the large-scale electric field
of the magnetospheric convection directed westward in the nighttime and morning hours and eastward in the noon and evening
sectors. 相似文献
12.
The influence of geomagnetic disturbances on electron density Ne at F1 layer altitudes in different conditions of solar activity during the autumnal and vernal seasons of 2003–2015, according to the data from the Irkutsk digital ionospheric station (52° N, 104° Е) is examined. Variations of Ne at heights of 150–190 km during the periods of twenty medium-scale and strong geomagnetic storms have been analyzed. At these specified heights, a vernal–autumn asymmetry of geomagnetic storm effects is discovered in all periods of solar activity of 2003–2015: a considerable Ne decrease at a height of 190 km and a weaker effect at lower levels during the autumnal storms. During vernal storms, no significant Ne decrease as compared with quiet conditions was registered over the entire analyzed interval of 150?190 km. 相似文献
13.
D. Altadill 《Annales Geophysicae》1996,14(7):716-724
The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f0E and f0F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and aN index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere. 相似文献
14.
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
15.
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
16.
Disturbances in the magnetic field and magnetospheric and ionospheric plasma registered on December 14–16, 2006, during a
strong magnetic storm caused by a solar flare of 4B/X3.4 class are studied. It is shown that in the north of Yakutia, interactions between the Earth’s magnetosphere and the region
of high dynamic pressure of the solar wind led to the formation of sporadic layers in the ionospheric E and F regions, depletion of the critical frequency of the F2 layer, and total absorption. At the end of the magnetic storm’s main phase, anomalously high values of foF2 exceeding the quiet level by a factor of 1.5–1.7 were detected. It was found that the disturbances detected by ground-based
observatories had developed on the background of changes in the temperature, density, and the pitch-angle distribution of
particles at the geostationary orbit manifesting radial shifts of magnetospheric structures (magnetopause, cusp/cleft, and
plasma sheet) relative to the observation points. A conclusion is drawn that in this case, changes in the near-Earth plasma
and magnetic field manifest the dynamics of the physical conditions at the magnetospheric boundary and diurnal rotation of
the Earth. 相似文献
17.
M. V. Klimenko V. V. Klimenko K. G. Ratovsky L. P. Goncharenko 《Geomagnetism and Aeronomy》2011,51(3):364-376
This study presents the ionospheric effects caused by the series of geomagnetic storms of September 9–14, 2005. The behavior
of different ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill and Arecibo stations during the considered period
have been numerically calculated, using a global self-consistent model of the thermosphere, ionosphere, and protonosphere
(GSM TIP) developed at WD IZMI-RAN. The model calculations of disturbances of the ionospheric parameters during storms qualitatively
agree with the experimental data at these midlatitude stations. We suggest that the causes of the quantitative differences
between the model calculations and the observational data were the use of the 3-hour Kp index of geomagnetic activity and the dipole approximation of geomagnetic field in GSM TIP, with additional contributions
from the effects of solar flares which are not considered in GSM TIP. 相似文献
18.
E. V. Liperovskaya 《Geomagnetism and Aeronomy》2008,48(6):807-811
The observations of spread F during the nighttime hours (0000–0500 LT) have been statistically analyzed based on data of Tokyo, Akita, Wakkanai, and Yamagawa Japan vertical ionospheric sounding stations for the time intervals a month before and a month after an earthquake. The disturbances in the probability of spread F appearance before an earthquake are revealed against a background of the variations depending on season, solar activity cycle, geomagnetic and solar disturbances. The days with increased solar (Wolf number W > 100) and geomagnetic (ΣK > 30) activity are excluded from the analysis. The spread F effects are considered for more than a hundred earthquakes with magnitude M > 5 and epicenter depth h < 80 km at distances of R < 1000 km from epicenters to the vertical sounding station. An average decrease in the spread F occurrence probability one-two weeks before an earthquake has been revealed using the superposed epoch method (the probability was minimal approximately ten days before the event and then increased until the earthquake onset). Similar results are obtained for all four stations. The reliability of the effect has been estimated. The dependence of the detected effect on the magnitude and distance has been studied. 相似文献
19.
The relation between the daytime in the nighttime values of the critical frequencies (foF2) of the ionospheric F 2 layer is considered. The correlation coefficient of foF2 measured at 1400 and 0200 LT of the same day is considered in various seasons of years with different solar activity (during the complete cycle of solar activity in 1979–1989). Special accent is made on the dependencies of the above mentioned correlation on a choice of magnetically quiet days with various limitations on maximal values of geomagnetic index Ap. It has been obtained that a statistically significant negative correlation between the foF2(1400) and foF2(0200) is more pronounced in the periods of high solar activity. The effect increases with increasing limitation of the considered days on value of Ap: the largest values of the correlation coefficient are observed if only very quiet days are considered (Ap < 6). There are preliminary indications that the considered relation between daytime and nighttime foF2 values depends on latitude. 相似文献
20.
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