共查询到20条相似文献，搜索用时 453 毫秒
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Robert F. Benson 《Journal of Atmospheric and Solar》1997,59(18):2281-2293
Ionospheric topside sounders can be considered to act as mobile ionospheric heating facilities. They stimulate a wide variety of plasma phenomena that suggests that significant plasma heating can be produced in the vicinity of the spacecraft following the short duration (0.1 ms) high-power (hundreds of watts) sounder pulse. Most of these phenomena are sensitive to the ambient plasma conditions, particularly to the ratio of the plasma frequency to the gyro frequency . Certain stimulated phenomena only occur, or are greatly enhanced, when where n is an integer. One example is a diffuse signal return that appears at a frequency just above the Z mode wave cutoff frequency (the L = 0 condition in the notation of Stix). This signal, which is the subject of the present paper, is present only for moderately large near-integer values for (e.g., n > 3). It is a relatively short-duration echo—usually less than about 10 ms. These characteristics are quite different from the Z mode echoes often observed between or (whichever is greater) and the upper hybrid frequency . These latter echoes occur for smaller values (not necessarily near-integer values) of and are received during the entire 30 ms listening time period following the sounder pulse. They have been attributed to the scattering of sounder Z mode signals from naturally occurring electron density fieldaligned irregularities (FAI). The short-duration echoes observed just above , on the other hand, are here attributed to the ducting of sounder-generated Z mode waves in sounder-stimulated (or sounderenhanced) FAI. These FAI are believed to be generated (or enhanced) on a very short time scale (? 1 s) by the efficient absorption of sounder energy when the plasma/gyro frequency ratio is nearly an integer value significantly greater than one. The most likely generation process is the filamentation instability driven by the ponderomotive force due to the high-power sounder pulse. 相似文献
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T. D. Borisova N. F. Blagoveshchenskaya V. A. Kornienko M. T. Rietveld 《Geomagnetism and Aeronomy》2007,47(1):76-84
The method for estimating the behavior of the ionospheric irregularity motion vector in the artificially disturbed HF ionospheric region has been proposed, and this behavior has been analyzed based on the simultaneous Doppler observations performed on several paths using the method of bi-static backscatter of diagnostic HF signals by small-scale artificial ionospheric irregularities. The Doppler measurements were performed during the modification of the auroral ionosphere by powerful HF radiowaves emitted by the EISCAT heating facility (Tromsø, Norway). It has been obtained that the dynamics of the ionospheric irregularity directions in the F region, calculated based on the Doppler measurements of the total vector of the ionospheric irregularity velocity above the Tromsø EISCAT radar at a frequency of 931 MHz, is in satisfactory agreement with such calculations performed using the three-position method. 相似文献
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V.L. Frolov L.M. Erukhimov S.A. Metelev E.N. Sergeev 《Journal of Atmospheric and Solar》1997,59(18):2317-2333
Features of artificial small-scale ionospheric irregularities (ASI) induced at F-region heights by powerful HF waves are discussed. The investigations presented here were performed during the past two decades at the Zimenki and Sura heating facilities, located at middle latitudes near Nizhniy Novgorod, Russia, as well as at the Gissar facility located at a lower latitude near Dushanbe, Tadzhikistan. The measurements were made by a variety of diagnostic methods employing artificial field-aligned scattering of HF and VHF radio waves, sounding of the disturbed region by means of low-power probing waves and testing of the artificial turbulence by means of stimulated electromagnetic emission (SEE). The dependence of ASI on such parameters as transverse scale length of the artificial irregularities, their location in the disturbed region, the power of the heating wave, the duration of HF radiation, geophysical conditions, aftereffects of the preceding modification, and the schedule of heater operation is considered for both the development stage after pump turn-on and the decay stage after pump turn-off. The temporal evolution of ASI spectral characteristics during the heater period is discussed. An empirical model for the ASI, based on the data available, was elaborated and verified by computer simulation of SEE generation. 相似文献
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Michael J. Rycroft Anna Odzimek Neil F. Arnold Martin Füllekrug Andrzej Ku&#x;ak Torsten Neubert 《Journal of Atmospheric and Solar》2007,69(17-18):2485
Several processes acting below, in and above thunderstorms and in electrified shower clouds drive upward currents which close through the global atmospheric electric circuit. These are all simulated in a novel way using the software package PSpice. A moderate negative cloud-to-ground lightning discharge from the base of a thunderstorm increases the ionospheric potential above the thundercloud by 0.0013%. Assuming the ionosphere to be an equipotential surface, this discharge increases the current flowing in the global circuit and the fair-weather electric field also by 0.0013%. A moderate positive cloud-to-ground lightning discharge from the bottom of a thunderstorm decreases the ionospheric potential by 0.014%. Such a discharge may trigger a sprite, causing the ionospheric potential to decrease by . The time scales for the recovery of the ionospheric potential are shown to be , which is of the same order as the CR time constant for the global circuit. Knowing the global average rate of lightning discharges, it is found that negative cloud-to-ground discharges increase the ionospheric potential by only 4%, and that positive cloud-to-ground discharges reduce it by 3%. Thus, overall, lightning contributes only 1%—an almost insignificant proportion—to maintaining the high potential of the ionosphere. It is concluded that the net upward current to the ionosphere due to lightning is only . Further, it is concluded that conduction and convection currents associated with “batteries” within thunderclouds and electrified shower clouds contribute essentially equally ( each) to maintaining the ionospheric potential. 相似文献
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T. D. Borisova N. F. Blagoveshchenskaya I. M. Ivanova M. T. Rietveld 《Geomagnetism and Aeronomy》2013,53(1):32-42
The interaction between the Earth’s ionosphere and magnetosphere in a situation when artificial disturbances are generated in the F region of the auroral ionosphere with the EISCAT/Heating facility is studied. An experiment was performed in the daytime when the facility effective radiated power changed in a stepwise manner. Wavelike disturbances with periods of (130–140) s corresponding to Pc4 pulsations were simultaneously registered by the method of bi-static backscatter and with ground magnetometers. The variations in the Doppler frequency shift were correlated with the changes in the facility power. Incoherent scatter radar measurements at a frequency of 930 MHz (Tromsö) and numerical calculations were used in an analysis. It has been indicated that the ionospheric drift of small-scale artificial ionospheric irregularities was modulated by magnetospheric Alfvén waves. The possible effect of powerful HF radioemission on the Alfvén wave amplitude owing to the modification of the magnetospheric resonator ionospheric edge reflectivity and the generation of an outgoing Alfvén wave above the region where the ionospheric conductivity is locally intensified has been considered. 相似文献
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N. V. Bakhmetieva V. D. Vyakhirev E. E. Kalinina G. P. Komrakov 《Geomagnetism and Aeronomy》2017,57(1):58-71
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
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