首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The data, obtained using the methods of partial reflections and ionosphere vertical sounding on the Kola Peninsula and in Scandinavia, at Tumannyi (69.0° N, 35.7° E) and Sodankyla (67.37°N, 26.63°E) observatories, have been analyzed in order to detect earthquake responses. The strong earthquakes have been considered: one earthquake with a magnitude of 7.7 occurred at 0819:25 UT on July 17, 2006, on the western coast of Indonesia (9.33° S, 107.26° E), and another earthquake with a magnitude of 6.2 occurred 2253:59 UT on May 26, 2006, on Yava (7.94° S, 110.32° E). These earthquakes, the epicenters of which were located in the same region and at identical depths (10 km), were observed under quiet conditions in the geomagnetic field (ΣK p = 5.7 and 6.3) and during small solar flares. The response of the ionosphere to these flares was mainly observed in the parameters of the lower ionosphere in the D and E regions. It has been found out that the period of variations in the ordinary component of the partially reflected signal at altitudes of the E region increased before the earthquake that occurred on July 17, 2006. The f min variations at Sodankyla observatory started 20 h before the earthquake. The periods of these variations were 3–6 h. The same periods were found in the variations in other ionospheric parameters (foEs and h’Es). The variations in the ordinary component of partially reflected signals with periods of 2–5 hours were observed on the day of another earthquake (May 26, 2006). Internal gravity waves with periods of several hours, which can be related to the earthquakes, were detected in the amplitude spectra of the ordinary component of partially reflected signals and in other parameters in the lower ionosphere.  相似文献   

2.
The results of observations in the Vasil’sursk Laboratory (56.1° N, 46.1° E) of partial solar eclipses of August 11, 1999, August 1, 2008, and March 20, 2015 are discussed. Ionospheric observations in the eclipse periods and on control days were conducted by the method of resonant scatter of radio waves at artificial periodic irregularities of the ionospheric plasma and the partial reflection method based on radio wave scatter by natural irregularities in the D region. The lower ionosphere reaction to solar eclipses, including variations in the electron concentration and characteristics of the signals scattered by APIs, was studied. An intensification of the lower ionosphere turbulization, an increase in the signal amplitudes backscattered by APIs in the E region, stratification of the D region, and the arrival of scattered signals from mesopause heights were observed during the eclipses. A decrease in the electron concentration of the D region up to a factor of 3–5 was found by the partial reflection method. Above 88 km, the ionospheric response was delayed by 20–25 min relative to the moment of the eclipse maximum phase, whereas this delay in the lower part of the D region was 2–4 min.  相似文献   

3.
Results of the observations of the ionospheric effects of two solar flares in April 2004 performed using partial reflections are presented. The studies were carried out at the measuring facilities located in different latitudinal regions: at Vasil’sursk station in the Nizhni Novgorod region and at Tumannyi station in the Murmansk region. The quantitative estimates of the electron density in the polar and midlatitude D region under quiet conditions and during solar flares were obtained. The correlation between rapid variations in electron concentration at heights of about 80 km at these stations was found and it was shown that during solar flares the electron density at heights of 60–70 km corresponds to the intensity of the X-ray flux in the range of 0.5–3 Å, which points to the action of the linear law of recombination in the ionospheric D region.  相似文献   

4.
A morphological analysis of the results of sounding the lower equatorial ionosphere (the D region) in the region of action of strong tropospheric vortex disturbances (tropical cyclones, TC) is presented in this work. Based on the rocket sounding of the lower ionosphere at Thumba rocket site (8° N, 77° E) in May–June 1985 and on the satellite monitoring of TC in the northern Indian Ocean, it is demonstrated that a sharp depletion (by a factor of 2–4) of the electron concentration at altitudes of 60–80 km could be a response of the ionosphere during the TC active phase. In this case the lower boundary of the D region rose by several kilometers (not more than 5 km), and the temperature in the region of the stratopause slightly (by 2°–3°) increases. It is assumed that internal gravity waves (IGWs) generated by TC cause the effect on the lower ion-osphere.  相似文献   

5.
The results of studying the ionospheric response to solar flares, obtained from the data of the GPS signal observations and incoherent scatter radars and as a result of the model calculations, are presented. It is shown that, according to the GPS data, a flare can cause a decrease in the electron content at altitudes of the topside ionosphere (h > 300 km). Similar effects of formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, with the Arecibo incoherent scatter radar. The mechanism by which negative disturbances appear in the topside ionosphere during solar flares has been studied in this work based on the theoretical model of the ionosphere-plasmasphere coupling. It has been indicated that the formation of the electron density negative disturbance in the topside ionosphere is caused by an intense removal of O+ ions into the overlying plasmasphere under the action of an abrupt increase in the ion production rate and thermal expansion of the ionospheric plasma.  相似文献   

6.
Results of studying the ionospheric response to solar flares, obtained based on the incoherent scatter radar observations of the GPS signals and as a result of the model simulations, are presented. The method, based on the effect of partial “shadowing” of the atmosphere by the globe, has been used to analyze the GPS data. This method made it possible to estimate the value of a change in the electron content in the upper ionosphere during the solar flare of July 14, 2000. It has been shown that a flare can cause a decrease in the electron content at heights of the upper ionosphere (h > 300 km) according to the GPS data. Similar effects in the formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, at the Arecibo incoherent scatter radar. The mechanism by which negative disturbances are formed in the upper ionosphere during solar flares has been studied based on the theoretical model of the ionosphere-plasmasphere coupling. It has been shown that an intense ejection of O+ ions into the above located plasmasphere under the action of a sharp increase in the ion production rate and the thermal expansion of the ionospheric plasma cause the formation of a negative disturbance in the electron concentration in the upper ionosphere.  相似文献   

7.
S. K. Sarkar  B. K. De 《Annales Geophysicae》1994,12(10-11):1119-1126
The statistical behaviour of the sudden enhancement in signal strength (SES) in relation to solar X-ray flares has been studied for the near east-west propagation of 40 kHz radio waves from Sanwa (36°11’N; 139°51’E) in Japan to Calcutta (22°34’N; 88°24’E) over a long distance path of 5100 km for a period of two years. The period has been divided into four phases - P1, P2, P3 and P4, according to the position of the overhead sun. The change in signal strength during X-ray flares is dependent on the solar zenith angle and climatic conditions. The statistical modal values of the time lag of the SES peak with respect to that solar X-ray flare is found to increase as solar zenith angle increases. The relative rates of increase and decrease of the signal strength (RRISS and RRDSS respectively) have been evaluated for a number of SES which are related to large X-ray flares. Their characteristics have also been investigated. The modal values of the relaxation time have been found to be highly correlated with climatic conditions like temperature and humidity of the propagation path.  相似文献   

8.
The GPS-derived total electron content (TEC) and NmF2 are measured at the Chung-Li ionosonde station (24.9°N, 121°E) in order to study the variations in slab thickness (τ) of the ionosphere at low-latitudes ionosphere during 1996–1999, corresponding to half of the 23rd solar cycle. This study presents the diurnal, seasonal, and solar flux variations in τ for different solar phases. The seasonal variations show that the average daily value is greater during summer and the reverse is true during equinox in the equatorial ionization anomaly (EIA) region. Moreover, the τ values are greater during the daytime (0800–1600 LT) and nighttime (2000–0400 LT) for summer and winter, respectively. The diurnal variation shows two abnormal peaks that appear during the pre-sunrise and post-sunset hours. The peak values decrease as the sunspot number increases particularly for the pre-sunrise peak. Furthermore, the variation in the F-peak height (hpF2) indicates that a thermospheric wind toward the equator leads to an increase in hpF2 and an enhancement in τ during the pre-sunrise period. Furthermore, the study shows the variations of τ values for different geophysical conditions such as the geomagnetic storm and earthquake. A comprehensive discussion about the relation between τ and the geophysical events is provided in the paper.  相似文献   

9.
Taking the sampled every minute values of the horizontal, declination and vertical componentsH, D, Z and the intensity of total field F calculated fromH andZ on the magnetograms at ten geomagnetic observatories in China in the same periods, and at the China Antarctic Great Wall Station (CAGWS), the authors conducted the maximum entropy analysis and band-pass filtration of these data and obtained the following results: (1) At the periodT=10 ? 90 min geomagnetic solar flare effect (sfe) is evident on the sunlit hemisphere. It is more pronounced at periods 15, 20, 25 and 30 min, and most prominent at 30 – 35 min. The solar X-ray spectra at the same time showed their peaks at 10 and 15 min; (2) The periodT=10 ? 70 min of sfe at the CAGWS in the western Hemisphere was also recognizable after spectral analysis and filtration, but the corresponding period of the maximum amplitude was different from that in the sunlit hemisphere. The results further proved that the geomagnetic effect of solar flares could also be observed in the dark hemisphere; (3) The subsolar points of two solar flares were found around Lanzhou, and the associated current density in the ionosphere was about 24 A/km. The transitional zone from positive to negative sfe was found around the geographic latitude?=22° ? 24°N, where the sfe inH-crochet was almost illegible.  相似文献   

10.
Variations in the electron density in the midlatitude ionospheric D region during launches and flights of different-type rockets at various distances from the launching site have been experimentally studied using partial reflections. It has been established that medium and heavy launch vehicles can generate short-term pulsating disturbances of electron density in the lower ionosphere at distances up to several thousand kilometers. These effects are apparently caused by stimulated pulsating electron fluxes from the Earth’s magnetosphere into the lower ionosphere with an energy of ～102–10 keV and fluxes of p ～ 108–109m?2 s?1.  相似文献   

11.
On the basis of the ion chemistry theoretical model, the impact of a powerful solar flare on variations in the ion composition and electron density in the D region of the polar ionosphere is considered. Good agreemnt between the model profiles of the electron density N e (h) and the experimental data obtained during the flare by the partial reflection method is found. It is shown that the decrease in the effective recombination coefficient observed during disturbances is explained by the depletion of the relative content of the rapidly recombining complex ion clusters.  相似文献   

12.
Global Positioning System (GPS) derived total electron content (TEC) measurements were analyzed to investigate the ionospheric response during the X-class solar flare event that occurred on 5-6 December 2006 at geomagnetic conjugate stations: Syowa, Antarctica (SYOG) (GC: 69.00°S, 39.58°E; CGM: 66.08°S, 71.65°E) and árholt, Iceland (ARHO) (GC: 66.19°N, 342.89°E; CGM: 66.37°N, 71.48°E). Bernese GPS software was used to derive the TEC maps for both stations. The focus of this study is to determine the symmetry or asymmetry of TEC values which is an important parameter in the ionosphere at conjugate stations during these solar flare events. The results showed that during the first flares on 5 December, effects were more pronounced at SYOG than at ARHO. However, on 6 December, the TEC at ARHO showed a sudden spike during the flare with a different TEC variation at SYOG.  相似文献   

13.
With the use of data from topside sounding on board the Interkosmos-19 (IK-19) satellite, the region of permanent generation of large-scale irregularities in the daytime winter ionosphere of the Southern Hemisphere is differentiated. This region is characterized by low values of foF2 and hmF2 and occupies a rather large latitudinal band, from the equatorial anomaly ridge to ~70° S within the longitudinal range from 180° to 360°. Irregularities with a dimension of hundreds kilometers are regularly observed in the period from 0700–0800 to 1800–1900 LT, i.e., mainly in the daytime. In the IK-19 ionograms, they normally appear in the form of an extra trace with a critical frequency higher than that of the main trace reflected from the ionosphere with lower density. The electron density in the irregularity maximum sometimes exceeds the density of the background ionosphere by nearly a factor of 3. A model of the ionosphere with allowance for its irregular structure was created, and it was shown on the basis of trajectory calculations how the IK-19 ionograms related to these irregularities are formed. A possible mechanism of the generation of large-scale irregularities of the ionospheric plasma is discussed.  相似文献   

14.
Between 100 and 120 km height at the Earth's magnetic equator, the equatorial electrojet (EEJ) flows as an enhanced eastward current in the daytime E region ionosphere, which can induce a magnetic perturbation on the ground. Calculating the difference between the horizontal components of magnetic perturbation (H) at magnetometers near the equator and about 6–9° away from the equator, ΔH, provides us with information about the strength of the EEJ. The NCAR Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIE-GCM) is capable of simulating the EEJ current and its magnetic perturbation on the ground. The simulated diurnal, seasonal (March equinox, June solstice, December solstice), and solar activity (F10.7=80, 140 and 200 units) variations of ΔH in the Peruvian (76°W) and Philippine (121°E) sectors, and the relation of ΔH to the ionospheric vertical drift velocity, are presented in this paper. Results show the diurnal, seasonal and solar activity variations are captured well by the model. Agreements between simulated and observed magnitudes of ΔH and its linear relationship to vertical drift are improved by modifying the standard daytime E region photoionization in the TIE-GCM in order to better simulate observed E region electron densities.  相似文献   

15.
A possible mechanism of earthquake triggering by ionizing radiation of solar flares is considered. A theoretical model and results of numerical calculations of disturbance of electric field, electric current, and heat release in lithosphere associated with variation of ionosphere conductivity caused by absorption of ionizing radiation of solar flares are presented. A generation of geomagnetic field disturbances in a range of seconds/tens of seconds is possible as a result of large-scale perturbation of a conductivity of the bottom part of ionosphere in horizontal direction in the presence of external electric field. Amplitude-time characteristics of the geomagnetic disturbance depend upon a perturbation of integral conductivity of ionosphere. Depending on relation between integral Hall and Pedersen conductivities of disturbed ionosphere the oscillating and aperiodic modes of magnetic disturbances may be observed. For strong perturbations of the ionosphere conductivities amplitude of pulsations may obtain ~102 nT. In this case the amplitude of horizontal component of electric field on the Earth surface obtains 0.01 mV/m, electric current density in lithosphere –10–6 A/m2, and the power density of heat release produced by the generated current is 10–7 W/m3. It is shown that the absorption of ionizing radiation of solar flares can result in variations of a density of telluric currents in seismogenic faults comparable with a current density generated in the Earth crust by artificial pulsed power systems (geophysical MHD generator " Pamir-2” and electric pulsed facility " ERGU-600”), which provide regional earthquake triggering and spatiotemporal variation of seismic activity. Therefore, triggering of seismic events is possible not only by man-made pulsed power sources but also by the solar flares. The obtained results may be a physical basis for a novel approach to solve the problem of short-term earthquake prediction based on electromagnetic triggering phenomena.  相似文献   

16.
In this paper, we investigate the solar flare effects of the ionosphere at middle latitude with a one-dimensional ionosphere theoretical model. The measurements of solar irradiance from the SOHO/Solar EUV Monitor (SEM) and GOES satellites have been used to construct a simple time-dependent solar flare spectrum model, which serves as the irradiance spectrum during solar flares. The model calculations show that the ionospheric responses to solar flares are largely related to the solar zenith angle. During the daytime most of the relative increases in electron density occur at an altitude lower than 300 km, with a peak at about 115 km, whereas around sunrise and sunset the strongest ionospheric responses occur at much higher altitudes (e.g. 210 km for a summer flare). The ionospheric responses to flares in equinox and winter show an obvious asymmetry to local midday with a relative increase in total electron content (TEC) in the morning larger than that in the afternoon. The flare-induced TEC enhancement increases slowly around sunrise and reaches a peak at about 60 min after the flare onset.  相似文献   

17.
The present paper focuses on planetary wave type responses of the thermosphere/ionosphere system to forcing from above and below during the Arctic winter of 2005/2006. The forcing from above is described by the sunspot numbers, the solar wind speed, the Bz-component of the IMF and the geomagnetic Kp-index, while the forcing from below, i.e. by upward propagating atmospheric waves, is represented by the SABER/TIMED temperatures. The observed global ionospheric zonally symmetric oscillations with periods of ～9, ～14 and ～24–27 days were approved to be of solar origin. The most persistent ～9-day oscillation is linked to a triad of solar coronal holes distributed roughly 120° apart in solar longitude. The ～18-day westward propagating wave with zonal wavenumber 1, observed in the ionospheric currents (detected by magnetometer data), and in the F-region plasma (foF2 and TEC) could be allocated to a simultaneous 18-day westward propagating planetary wave observed in the stratosphere/mesosphere/lower thermosphere region with large (～70 km) vertical wavelength.  相似文献   

18.
Variations in the photospheric magnetic field in the region of solar flares, related to halo coronal mass ejections (HCMEs) with velocities V > 1500, 1000 < V < 1500, and V < 650 km/s, have been studied based on SOHO/MDI data. Using data with a time resolution of 96 min, it has been indicated that on average the ??B L?? and ??|B L|?? field characteristics increase nonmonotonically during 1?C1.5 days before a flare and decrease during 0.5?C1 days after a flare for groups of ejections with V > 1000 km/s for all considered HCME groups. Angle brackets designate averaging of the measured B L magnetic field component and its magnitude |B L| within an area with specified dimensions and the center coincident with the projection onto the region where the flare center field is measured. It has been established that a solar flare related to an HCME originates when the ??B L?? and ??|B L|?? values are larger than the boundary values in the flare region. Based on 1-min data, it has been found for several HCMEs with V > 1500 km/s that the beginning of powerful flares related to ejections is accompanied by rapid impulsive or stepped variations in ??B L?? and ??|B L|?? near the center of a flare with a size of approximately 4.5°. It has been established that the HCME velocity positively correlates with the |??B L??| value at the flare onset.  相似文献   

19.
The measurements of an increase in the total electron content (TEC) of the ionosphere during solar flares, obtained based on the GPS data, indicated that up to 30% of TEC increments corresponded to the ionospheric regions above 300 km altitude in some cases, and TEC increased mainly below altitudes of 300 km in other cases. The theoretical model of the ionosphere and plasmasphere was used to study the obtained effects. The altitude-time variations in the charged particle density in the ionospheric region from 100 to 1000 km were used depending on the solar flare spectrum. An analysis of the modeling results indicated that an intensification of the flare UV emission in the 55–65 and 85–95 nm spectral ranges results in a pronounced increase in the electron density in the topside ionosphere (above 300 km). The experimental dependences of the ionospheric TEC response amplitude on the localization and peak power of flares on the Sun in the X-ray range, obtained based on the GPS data, are also presented in the work.  相似文献   

20.
The altitude profiles of particulate extinction in the upper troposphere and lower stratosphere (UTLS) obtained from SAGE-II in the latitude region 0–30°N over the Indian longitude sector (70–90°E) are used to study the latitudinal variation of its annual pattern in this region during the volcanically quiescent period of 1998–2003. The SAGE-II data is compared with the lidar measurements from Gadanki (13.5°N, 79.2°E) when the satellite had an overhead occultation pass over a small geographical grid centered at this location. The particulate optical depth (τp) in the UT region shows a general decrease with increase in latitude and a pronounced summer–winter contrast with relatively low values during winter and high values during summer. In general, these variations are in accordance with the latitudinal variation of convective available potential energy (CAPE) and thunderstorm activity, which are good representative indices of tropospheric convection. While the particulate extinction (and τp) in the 18–21 km (LS1) region is relatively low in the equatorial region up to 15°N, it shows an increase in the off-equatorial region, beyond 15°N. While the annual variation of τp in the LS1 region is almost insignificant near the equator, it is rather well pronounced in latitude region between 10 and 15°N with relatively high values during winter and low values during summer. Beyond 20°N, this shows a prominent peak during summer. At a higher altitude, the 21–30 km (LS2) region, the latitude variation of τp shows a different pattern with high values near the equator and low values in the off-equatorial region confirming the existence of a stratospheric aerosol reservoir. Low values of τp at lower regime (LS1) near the equator could be due to rapid transport of particulates from the near equatorial region to higher latitudes, while the equatorial high at upper regime (LS2) could be due to lofting and subsequent accumulation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号