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1.
Large-scale disturbances in the ionospheric plasma, caused by the spacecraft launches from the Baikonur site, have been analyzed based on the incoherent scatter radar measurements. The altitude-time dependences of the main plasma parameters (electron density and electron and ion temperatures at altitudes of ～100–600 km) have been analyzed. It has been indicated that spacecraft launches and flights are accompanied by the generation of wave-like disturbances in all considered parameters. It has been obtained that the relative amplitudes of these wave-like disturbances were usually 0.03–0.10, and the variation period was 20–60 min. The variations were shifted in phase relative to each other. The propagation velocities of wave-like disturbances were ～0.5–0.6 and 1.5–2 km/s. The up-to-date methods of spectral analysis, including the wavelet analysis, were used to estimate the parameters of the wave-like disturbances.  相似文献   

2.
An analysis was conducted of time variations in geomagnetic field components on the day of the Chelyabinsk meteorite event (February 15, 2013) and on control days (February 12 and 16, 2013). The analysis uses the data collected by magnetic observatories in Novosibirsk, Almaty, Kyiv, and Lviv. The distance R from the explosion site to the observatories varies in the range 1200–2700 km. The flyby and explosion of the Chelyabinsk cosmic body is found to have been accompanied by variations mainly in the horizontal component of the geomagnetic field. The variations are quasi-periodic with a period of 30–40 min, an amplitude of 0.5–2 nT for R ≈ 2700?1200 km, respectively, and a duration of 2–3 h. The horizontal velocity of the geomagnetic field disturbances is close to 260–370 m/s. A theoretical model of wave disturbances is proposed. According to the model, wave disturbances in the geomagnetic field are caused (a) by the motion of the gravity wave generated in the atmosphere by the falling space body and (b) by traveling ionospheric disturbances, which modulate the ionospheric current at dynamo altitudes. The calculated amplitudes of the wave disturbances are 0.6–1.8 nT for R ≈ 2700?1200 km, respectively. The estimates are in good agreement with the observational data. Disturbances in the geomagnetic field level (geomagnetic pulsations) in the period range 1–1000 s are negligible (less than 1 nT).  相似文献   

3.
The observations of the geomagnetic field variations in the range of periods 1–1000 s, which accompanied the launches of 65 Soyuz and Proton rockets from the Baikonur site in 2002–2006, have been analyzed. The measurements were performed near Kharkov (the distance from the launching site is R ≈ 2100 km). Three groups of disturbances, with delays of 6–7, 30–70, and 70–130 min dependent on the time of day, have been revealed. The disturbance duration was 10–30, 50–70, and 45–70 min, respectively. Periods of 3–6, 6–12, and 6–12 min, respectively, predominated in the geomagnetic pulsations. The amplitudes of these pulsations reached 3–6 nT. The physical model of the observed geomagnetic disturbances, which generally agrees with the measurements, has been proposed.  相似文献   

4.
The observation results of the effects in the geospace plasma during a partially (magnitude ～0.42) solar eclipse are presented. The experimental data were obtained with an incoherent scatter radar of the Institute of the Ionosphere (near Kharkov). During the eclipse, the density at the F2 layer maximum decreased by 32%, the foF2 critical frequency decreased by 17.5%, and the altitude of the F2 layer maximum increased insignificantly. At altitudes of 290–680 km, the electron density decreased by ～25%. During the eclipse, the electron and ion temperature decreased by 70–180 and 0–140 K, respectively, at altitudes of 190–490 km. Near the eclipse main phase, the plasma velocity vertical component decreased by 10–45 m/s at altitudes of 200–470 km, respectively. At the time of the eclipse main phase, the hydrogen ion fractional density increased by 50% as compared to the reference day at altitudes of 450–650 km.  相似文献   

5.
The polar wind is an ambipolar outflow of thermal plasma from the high-latitude ionosphere to the magnetosphere, and it primarily consists of H+, He+ and O+ ions and electrons. Statistical and episodic studies based primarily on ion composition observations on the ISIS-2, DE-1, Akebono and Polar satellites over the past four decades have confirmed the existence of the polar wind. These observations spanned the altitude range from 1000 to ∼50,500 km, and revealed several important features in the polar wind that are unexpected from “classical” polar wind theories. These include the day–night asymmetry in polar wind velocity, which is 1.5–2.0 times larger on the dayside; appreciable O+ flow at high altitudes, where the velocity at 5000–10,000 km is of 1–4 km/s; and significant electron temperature anisotropy in the sunlit polar wind, in which the upward-to-downward electron temperature ratio is 1.5–2. These features are attributable to a number of “non-classical” polar wind ion acceleration mechanisms resulting from strong ionospheric convection, enhanced electron and ion temperatures, and escaping atmospheric photoelectrons. The observed polar wind has an averaged ion temperature of ∼0.2–0.3 eV, and a rate of ion velocity increase with altitude that correlates strongly with electron temperature and is greatest at low altitudes (<4000 km for H+). The rate of velocity increase below 4000 km is larger at solar minimum than at solar maximum. Above 4000 km, the reverse is the case. This suggests that the dominant polar wind ion acceleration process may be different at low and high altitudes, respectively. At a given altitude, the polar wind velocity is highly variable, and is on average largest for H+ and smallest for O+. Near solar maximum, H+, He+, and O+ ions typically reach a velocity of 1 km/s near 2000, 3000, and 6000 km, respectively, and velocities of 12, 7, and 4 km/s, respectively, at 10,000 km altitude. Near solar minimum, the velocity of all three species is smaller at high altitudes. Observationally it is not always possible to unambiguously separate an energized “non-polar-wind” ion such as a low-energy “cleft ion fountain” ion that has convected into a polar wind flux tube from an energized “polar-wind” ion that is accelerated locally by “non-classical” polar-wind ion acceleration mechanisms. Significant questions remain on the relative contribution between the cleft ion fountain, auroral bulk upflow, and the topside polar-cap ionosphere to the O+ polar wind population at high altitudes, the effect of positive spacecraft charging on the lowest-energy component of the H+ polar wind population, and the relative importance of the various classical and non-classical ion acceleration mechanisms. These questions pose several challenges in future polar wind observations: These include measurement of the lowest-energy component in the presence of positive spacecraft potential, definitive determination and if possible active control of the spacecraft potential, definitive discrimination between polar wind and other inter-mixed thermal ion populations, measurement of the three-dimensional ion drift velocity vector and the parallel and perpendicular ion temperatures or the detailed three-dimensional velocity distribution function, and resolution of He+ and other minor ion species in the polar wind population.  相似文献   

6.
The results of observations of the solar eclipse ionospheric effects on March 29, 2006, are presented. The observations were conducted using the partial reflection method near Nizhni Novgorod and the vertical sounding method at the automatic ionospheric station near Murmansk. It has been obtained that the electron density at altitudes of 77 and 91 km decreases by a factor of more than 4; in this case the response of the ionosphere at an altitude of 91 km lags behind the eclipse maximum phase on the Earth by approximately 20 min. It has been established that the eclipse in the E and F1 regions of the polar ionosphere causes a change in the electron density by 15–20%. The delay time of this effect varies from 12 to 24 min depending on the altitude. It has been registered that the reflection virtual altitude at altitudes of the ionospheric F region increases in Murmansk and Nizhni Novgorod.  相似文献   

7.
Rayleigh lidar observations at Gadanki (13.5°N, 79.2°E) show an enhancement of the nightly mean temperature by 10–15 K at altitudes 70–80 km and of gravity wave potential energy at 60–70 km during the 2009 major stratospheric warming event. An enhanced quasi-16-day wave activity is observed at 50–70 km in the wavelet spectrum of TIMED–SABER temperatures, possibly due to the absence of a critical level in the low-latitude stratosphere because of less westward winds caused by this warming event. The observed low-latitude mesospheric warming could be due to wave breaking, as waves are damped at 80 km.  相似文献   

8.
The amplitudes and relative amplitudes of electron density wave-like disturbances (WDs) with periods of 30–120 min at altitudes of 125–500 km (100–1000 km in individual experiments) under the conditions of a quiet ionosphere during magnetic and ionospheric storms and two solar eclipses are analyzed. The observations of the WD amplitudes and their altitude variations corresponded to the data of theoretical simulation in a number of cases. On the whole, the altitude variations in the WD amplitudes are more complicated than such variations derived from a simple theoretical model presented here.  相似文献   

9.
Wave-like disturbances (WDs) with periods of 30–120 min at altitudes of 125–500 km (100–1000 km in individual experiments) have been studied. The measurements of total duration more than 400 h have been performed under the conditions of a quiet ionosphere as well as during magnetic and ionospheric storms and two solar eclipses. It has been indicated that WDs exist almost permanently in the ionosphere. The effect of powerful energy sources leads to a change in the WD character and to variations in the WD spectral composition and amplitudes. The latter substantially vary during a day and depending on the disturbance of the ionosphere. The WD relative amplitudes vary from several percent to several tens of percent.  相似文献   

10.
《Journal of Geodynamics》1999,27(4-5):567-583
Upper mantle P and S wave velocities in the western South America region are obtained at depths of foci from an analysis of travel time data of deep earthquakes. The inferred velocity models for the Chile–Peru–Ecuador region reveal an increase of P velocity from 8.04 km/s at 40 km to 8.28 km/s at 250 km depth, while the S velocity remains almost constant at 4.62 km/s from 40 to 210 km depth. A velocity discontinuity (probably corresponding to the L discontinuity in the continental upper mantle) at 220–250 km depth for P and 200–220 km depth for S waves, with a 3–4% velocity increase, is inferred from the velocity–depth data. Below this discontinuity, P velocity increases from 8.54 km/s at 250 km to 8.62 km/s at 320 km depth and S velocity increases from 4.81 km/s at 210 km to 4.99 km/s at 290 km depth. Travel time data from deep earthquakes at depths greater than 500 km in the Bolivia–Peru region, reveal P velocities of about 9.65 km/s from 500 to 570 km depth. P velocity–depth data further reveal a velocity discontinuity, either as a sharp boundary at 570 km depth with 8–10% velocity increase or as a broad transition zone with velocity rapidly increasing from 560 to 610 km depth. P velocity increases to 10.75 km/s at 650 km depth. A comparison with the latest global average depth estimates of the 660 km discontinuity reveals that this discontinuity is at a relatively shallow depth in the study region. Further, a velocity discontinuity at about 400 km depth with a 10% velocity increase seems to be consistent with travel time observations from deep earthquakes in this region.  相似文献   

11.
The relationship between the directions of polar acoustic gravity waves and a wind at 250–350 km altitudes has been studied based on an analysis of the Dynamics Explorer 2 satellite measurements. A method, which makes it possible to determine the direction of these waves relative to the satellite velocity vector based on one-point measurements of different neutral atmosphere parameters, is presented. It has been established that acoustic gravity waves observed over the polar caps systematically propagate upwind, which argues for their spatial wind filtering. In the polar regions, waves mainly propagate in two directions: toward magnetic noon and 15–16 MLT. Waves tend to move counterclockwise and clockwise over the northern and southern polar caps, respectively.  相似文献   

12.
Results of the spectral measurements of ionospheric noise in the meter band are presented. The events lasting several milliseconds (the emission maximum of which drifts upward (in frequency), is reflected (stops), and drifts downward) have been distinguished. Moreover, multiple harmonics are observed. The frequency-time structure of such events have been considered from the viewpoint of registration of the electron beam synchrotron emission harmonics at ionospheric altitudes in the geomagnetic field. The model calculations of the frequency-time structure of ionospheric radio noise bursts drifting in frequency have been performed taking into account the measurement conditions. It has been indicated that the model electron radio noise bursts agree with the measured bursts reflecting from the ionosphere at altitudes of 100–180 km. The model of the monoenergetic beam of electrons precipitating from the radiation belt (L ～ 2.0–2.8) into the ionosphere has been proposed.  相似文献   

13.
The observations of the state of the midlatitude ionospheric D region during the March 29, 2006, solar eclipse, based on the measurements of the characteristics of partially reflected HF signals and radio noise at a frequency of f = 2.31 MHz, are considered. It has been established that the characteristic processes continued for 2–4 h and were caused mainly by atmospheric gas cooling, decrease in the ionization rate, and the following decrease in the electron density. An increase in the electron density on average by 200–250% approximately 70–80 min after the eclipse beginning at altitudes of 90–93 km and approximately 240 min after the end of the solar eclipse at altitudes of 81–84 km, which lasted about 3–4 h, has been detected experimentally. This behavior of N is apparently caused by electron precipitation from the magnetosphere into the atmosphere during and after the solar eclipse. Based on this hypothesis, the fluxes of precipitating electrons (about 107–108 m?2s?1) have been estimated using the experimental data.  相似文献   

14.
Disturbances produced by geomagnetic storms in the higher regions of the Earth’s atmosphere, such as in the ionospheric F2 region and in the lower ionosphere, are relatively better known than those produced at lower altitudes, where the effects of geomagnetic storms have been little studied. During magnetically perturbed conditions, some changes in pressure and temperature at high latitudes have been observed, from the surface level to heights of around 30 km, but there are no morphological studies and/or patterns of behavior. Moreover, the physical mechanisms are still unknown and what exists is a matter of controversy. Thus, the aim of this paper is to contribute to the vertical profile of the effects of geomagnetic storms as observed in the lower sectors of the atmosphere. For that, we study the variations of two atmospheric parameters (temperature and wind speed) during an intense geomagnetic storm (minimum Dst = −300 nT), at heights between about 6 km and 20 km. The data used were obtained from weather balloon flights carried out at low, mid and mid-high latitudes in different longitudinal sectors of the northern hemisphere, which took place twice per day: 00:00 and 12:00 UT. Small, but statistically significant changes in temperature and in zonal component of the neutral winds are observed at mid-high latitudes, which can be linked to short-term geomagnetic forcing. However, the results show different atmospheric response to the geomagnetic storm in the different longitudinal sectors at tropospheric and stratospheric levels, which suggests a regional character of the geomagnetic storms effects at tropospheric levels.  相似文献   

15.
Wave-like disturbances, caused by the launches of the Soyuz and Proton rockets from the Baikonur site, have been studied using the algorithm of the space-time accumulation of variations in the total electron content (TEC). Ionospheric TEC responses, observed on four GPS arrays at a distance of up to 4000 km from the launch site, represent a quasi-periodic oscillation with a period of 15–20 min, duration of 30–40 min, and amplitude of 0.1 TECU. The propagation velocity of wave-like disturbances is 300–1400 m/s, which corresponds to the range of sonic and supersonic velocities at an altitude of the ionospheric ionization maximum. Wave-like disturbances of TEC are caused by acoustic gravity waves (AGWs) propagating in the Earth’s atmosphere over large distances from a source. It has been established that the rocket launch region and rocket trajectory active legs, when a rocket moves under the action of the second and third operating stages of a propulsion device, are responsible for AGW generation.  相似文献   

16.
This paper is concerned with the study of the possibility of products of a meteoroid explosion in the atmosphere (meteoroid plume) to reach ionospheric altitudes. It has been shown that, in the case of meter-sized or larger space bodies entering the atmosphere, the plume is able to reach the lower ionosphere. The plume can be one of the sources of the formation of nacreous and noctilucent clouds. The aerosols ejected by the plume to lower ionospheric altitudes can lead to the formation of dust plasma, significantly changing the electrodynamic properties of the medium. The motion of the plume with a velocity of ~1 km/s is accompanied by the generation of a ballistic shock with a radius of 1–10 km. The relative excess pressure in the shock front can cause relative disturbances in the electron content at the altitudes of D, E, and F1 layers by ~10–100%. The geomagnetic effect of the plume and ballistic shock can reach ~1–10 nT.  相似文献   

17.
The field-aligned neutral oscillations in the F-region (altitudes between 165 and 275 km) were compared using data obtained simultaneously with two independent instruments: the European Incoherent Scatter (EISCAT) UHF radar and a scanning Fabry-Perot interferometer (FPI). During the night of February 8, 1997, simultaneous observations with these instruments were conducted at Tromsø, Norway. Theoretically, the field-aligned neutral wind velocity can be obtained from the field-aligned ion velocity and by diffusion and ambipolar diffusion velocities. We thus derived field-aligned neutral wind velocities from the plasma velocities in EISCAT radar data. They were compared with those observed with the FPI (=630.0 nm), which are assumed to be weighted height averages of the actual neutral wind. The weighting function is the normalized height dependent emission rate. We used two model weighting functions to derive the neutral wind from EISCAT data. One was that the neutral wind velocity observed with the FPI is velocity integrated over the entire emission layer and multiplied by the theoretical normalized emission rate. The other was that the neutral wind velocity observed with the FPI corresponds to the velocity only around an altitude where the emission rate has a peak. Differences between the two methods were identified, but not completely clarified. However, the neutral wind velocities from both instruments had peak-to-peak correspondences at oscillation periods of about 10–40 min, shorter than that for the momentum transfer from ions to neutrals, but longer than from neutrals to ions. The synchronizing motions in the neutral wind velocities suggest that the momentum transfer from neutrals to ions was thought to be dominant for the observed field-aligned oscillations rather than the transfer from ions to neutrals. It is concluded that during the observation, the plasma oscillations observed with the EISCAT radar at different altitudes in the F-region are thought to be due to the motion of neutrals.  相似文献   

18.
Slowness measurements on first and later arrivals from earthquakes in the Philippine and Taiwan regions recorded at the Warramunga array in Australia indicate abrupt decreases in slowness of the first arrival as well as triplications in the travel time curve at epicentral distances of about 38 and 43°. These results imply the presence of regions of rapid or discontinuous velocity increase at depths of about 900 and 1050 km, respectively. Between these regions of sharp velocity increases the dT/dΔ measurements indicate that the velocity gradients are lower than those determined by previous investigators. The observed extensions of the 650- and 770-km branches out to 50° can be explained in terms of the triplications if small negative velocity gradients of the order of 0.1 km/s per 100 km exist between 650–770 and 770–900 km depths. An alternative explanation of these observed extensions may be provided in terms of underside reflections from the bottom of the velocity discontinuities. Either of the two explanations require sharp velocity gradients at the depth of the velocity discontinuities. These observations are at variance with earth models where the P-wave velocity increases continuously with depth below a depth of 650 km.  相似文献   

19.
On 25th April, 2015 a hazardous earthquake of moment magnitude 7.9 occurred in Nepal. Accelerographs were used to record the Nepal earthquake which is installed in the Kumaon region in the Himalayan state of Uttrakhand. The distance of the recorded stations in the Kumaon region from the epicenter of the earthquake is about 420–515 km. Modified semi-empirical technique of modeling finite faults has been used in this paper to simulate strong earthquake at these stations. Source parameters of the Nepal aftershock have been also calculated using the Brune model in the present study which are used in the modeling of the Nepal main shock. The obtained value of the seismic moment and stress drop is 8.26 × 1025 dyn cm and 10.48 bar, respectively, for the aftershock from the Brune model .The simulated earthquake time series were compared with the observed records of the earthquake. The comparison of full waveform and its response spectra has been made to finalize the rupture parameters and its location. The rupture of the earthquake was propagated in the NE–SW direction from the hypocenter with the rupture velocity 3.0 km/s from a distance of 80 km from Kathmandu in NW direction at a depth of 12 km as per compared results.  相似文献   

20.
—More than 60 events recorded by four recently deployed seismic broadband stations around Scotia Sea, Antarctica, have been collected and processed to obtain a general overview of the crust and upper mantle seismic velocities.¶Group velocity of the fundamental mode of Rayleigh waves in the period between 10 s to 30–40 s is used to obtain the S-wave velocity versus depth along ten different paths crossing the Scotia Sea region. Data recorded by two IRIS (Incorporated Research Institutions for Seismology) stations (PMSA, EFI) and the two stations of the OGS-IAA (Osservatorio Geofisico Sperimentale—Instituto Antarctico Argentino) network (ESPZ, USHU) are used.¶The Frequency-Time Analysis (FTAN) technique is applied to the data set to measure the dispersion properties. A nonlinear inversion procedure, "Hedgehog," is performed to retrieve the S-wave velocity models consistent with the dispersion data.¶The average Moho depth variation on a section North to South is consistent with the topography, geological observations and Scotia Sea tectonic models.¶North Scotia Ridge and South Scotia Ridge models are characterised by similar S-wave velocities ranging between 2.0 km/s at the surface to 3.2 km/s to depths of 8 km/s. In the lower crust the S-wave velocity increases slowly to reach a value of 3.8 km/s. The average Moho depth is estimated between 17 km to 20 km and 16 km to 19 km, respectively, for the North Scotia Ridge and South Scotia Ridge, while the Scotia Sea, bounded by the two ridges, has a faster and thinner crust, with an average Moho depth between 9 km and 12 km.¶On other paths crossing from east to west the southern part of the Scotia plate and the Antarctic plate south of South Scotia Ridge, we observe an average Moho depth between 14 km and 18 km and a very fast upper crust, compared to that of the ridge. The S-wave velocity ranges between 3.0 and 3.6 km/s in the thin (9–13 km) and fast crust of the Drake Passage channel. In contrast the models for the tip of the Antarctic Peninsula consist of two layers with a large velocity gradient (2.3–3.0 km/s) in the upper crust (6-km thick) and a small velocity gradient (3.0–4.0) in the lower crust (14-km thick).  相似文献   

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