共查询到20条相似文献，搜索用时 46 毫秒
1.
Manoranjan Rao 《Planetary and Space Science》1975,23(6):923-927
On certain occasions, whistler rate occurrences at Gulmarg (24°N geomagnetic) and Naini Tal (19°N geomagnetic) are found to exhibit some periodicity. Power spectrum analyses of the occurrence rates yield a dominant period of about 1 hr. It is suggested that this period is an indication of the duct-life times at low L-values. Dispersion analyses of the whistlers have qualitatively confirmed the existence of separate ducts during the period of observation. It is pointed out that power spectrum analyses may not be applicable to whistler data corresponding to high L-values. 相似文献
2.
Using the results from special observations, the storm-time effects on whistler characteristics at low latitudes were examined and found to agree with previous statistical studies. A short discussion is made on the link between spread-F irregularities and magnetospheric whistler ducts. The enhanced whistler activity is explained as a consequence of the stable whistler duct region during spread-F conditions. 相似文献
3.
Morphological features of whistlers recorded at low latitude ground station Gulmarg (geomag. lat., 24 26N) are studied to deduce information about ducts. The morphological characteristics of low latitude whistlers are discussed and compared with the characteristics of middle and high latitude whistlers. The maximum electron density (N
m
) at the height of the ionosphere obtained from whistler dispersion comes out to be higher than that of the background, which is in accordance with the characteristics of the whistler duct. The equivalent width of the whistler duct at the maximum height of its path is found to be close to the value obtained from satellite observations. The characteristics of whistler ducts in low latitude ionosphere are similar to those in middle and high latitude ionosphere. The width of ducts estimated from the diffuseness of the whistler track observed during magnetic storm is found to lie in the range of 50–200 km. 相似文献
4.
Whistler components received by the VLF goniometer at Halley, Antarctica, have been scaled for nose frequency and direction of arrival. The data were taken from two separate one hour periods on either side of local midnight (0023–0133 UT and 0340–0450 UT, 5 June 1975). Because of the high whistler occurrence rate at this time and the rapid processing facilitated by the Sheffield semi-automated whistler analyser, it has been possible to scale 1850 whistler components and hence obtain high resolution mapping of the whistler duct structure. The number of observable ducts increased from 4 at 0030 UT to about 15 at 0130 UT and had reached about 31 by 0400 UT. This increasing number of ducts together with an observed clustering of ducts in the second one hour period, provides evidence for duct formation. The observations have been compared with the various duct generation mechanisms which have been proposed. The duct formation process may have been associated with a negative change in Dst which occurred at the same time, and this possibility is discussed. 相似文献
5.
T. Takakura 《Solar physics》1982,75(1-2):277-292
It is demonstrated by a numerical simulation that both the whistler waves and plasma waves are excited by a common solar electron beam. The excitation of the whistler waves is ascribed to the loss-cone distribution which arises at a later phase of the passage of the beam at a given height due to a velocity dispersion in the electron beam with a finite length. It is highly probable that the fundamental of type III bursts are caused by the coalescence of the whistler waves and the plasma waves excited by a common electron beam, although the plasma waves must suffer induce scatterings by thermal ions to have small wave numbers before the coalescence to occur. 相似文献
6.
The observed periodicity in the whistler occurrence rate recorded at our low latitude ground station at Varanasi (geomagnetic latitude, 14°55'N) is interpreted in terms of duct life time at lowL values. Power spectrum analysis of the whistler data yields a period of about 50 min for the growth and decay of ducts. Further dispersion analysis of the whistlers has qualitatively confirmed the existence of separate ducts during the period of observations. 相似文献
7.
In this paper, the nonlinear dispersion relation for whistlers in the ionosphere has been derived and then the group travel time for an ion-cyclotron whistler from its source to an observer at the satellite has been theoretically calculated. It is seen that the nonlinear effect has some important contribution in the expression of group travel time. Our present analysis gives a more correct result than that obtained by Gurnett and others. From numerical estimations, it is found that the group travel time of whistler may be changed reasonably due to nonlinear interaction of the wave and the plasma of ionosphere. 相似文献
8.
E. M. Poulter J. K. Hargreaves G. J. Bailey R. J. Moffett 《Planetary and Space Science》1981,29(12):1281-1286
Recent satellite beacon derived measurements of the recovery of protonospheric ionization following periods of increased geomagnetic activity show that the recovery takes longer than is indicated by whistler measurements. Realistic plasmasphere models have been used to determine whether satellite beacon measurements are reliable indicators of this recovery. It is found that the recovery time of the protonospheric content is similar to that of the minimum L-value flux tube intersected by the slant raypaths. Satellite beacon results are therefore useful indicators of protonospheric recovery after a storm provided any unrepresentative diurnal variations are eliminated. 相似文献
9.
A.D.M. Walker 《Planetary and Space Science》1978,26(4):375-379
A theory of whistler duct formation is presented. By means of order of magnitude calculations it is shown that, when the ring current overlaps the outer plasmasphere, irregularities will cause field-aligned currents to flow, which are below the threshold sensitivity of satellite-borne magnetometers. These currents must be continuous with horizontal ionospheric currents, which produce horizontal electric fields. These fields map up to the equatorial plane and are large enough to produce flux tube interchange and hence the formation of whistler ducts in the outer plasmasphere. 相似文献
10.
Close temporal correlation between high-frequency Langmuir waves and low-frequency electromagnetic whistler waves has been observed recently within magnetic holes of the solar wind. In order to account for these observations, a theory is formulated to describe the nonlinear coupling of Langmuir waves and whistler waves. It is shown that a Langmuir wave can interact nonlinearly with a whistler wave to produce either right-hand or left-hand circularly polarized electromagnetic waves. Nonlinear coupling of Langmuir waves and whistler waves may lead to the formation of modulated Langmuir wave packets as well as the generation of circularly polarized radio waves at the plasma frequency in the solar wind. Numerical examples of whistler frequency, nonlinear growth rate and modulation frequency for solar wind parameters are calculated. 相似文献
11.
Considering the presence of electric field parallel to geomagnetic field in the magnetosphere, the problem of wave-particle interaction has been considered. Dispersion equation of whistler mode wave in presence of parallel electric field has been derived. Using the effective dispersion equation, the wave-particle interaction has been reformulated to account for the effect of parallel electric field. Using charged particle energy spectrum and magnetospheric field and plasma models, the flux of electron precipitation has been computed. It is shown that the parallel electric field plays an important role and may work in simultaneity with other processes known for enhancement of electron precipitation. 相似文献
12.
The work attempts to give a theoretical explanation of the triggering of VLF emissions by magnetospheric whistler morse pulses. First studied is the behaviour of resonant particles in a whistler wave train in an inhomogeneous medium. It is found that second order resonant particles become stably trapped in the wave. After 1–2 trapping periods such particles dominate the resonant particle distribution function, and produce large currents that are readily estimated. 相似文献
13.
The effect of parallel electrostatic field on the amplification of whistler mode waves in an anisotropic bi-Maxwellian weakly ionized plasma for Jovian magnetospheric conditions has been carried out. The growth rate for different Jovian magnetospheric plasma parameters forL = 5.6R
j has been computed with the help of general dispersion relation for the whistler mode electromagnetic wave of a drifted bi-Maxwellian distribution function. It is observed that the growth or damping of whistler mode waves in Jovian magnetosphere is possible when the wave vector is parallel or antiparallel to the static magnetic field and the effect of this field is more pronounced at low frequency wave spectrum. 相似文献
14.
On 26 July 1967, a magnetically quiet day (ΣKp = 12?) with high whistler activity at Halley Bay, it was found possible, by measurement of whistler nose-frequency and dispersion and the bearings of the whistler exit points, to make a detailed study of the magnetospheric structure associated with the whistler ducts.During the period 0509–2305 UT most of the exit points of whistlers inside the plasmasphere were situated along a strip about 100km wide passing through Halley Bay in an azimuthal direction 30°E of N between 57° and 62° invariant latitude. A mechanism which can give rise to such a well-defined locus which co-rotates with the Earth is not clear. Nevertheless, it does appear that the locus coincides with the contour of solar zenith angle 102° at 1800 UT 25 July. This was also the time of occurrence of a sub-storm and it is suggested that the magnetospheric structure was initiated by proton precipitation along the solar zenith angle 102° contour.At mid-day knee-whistlers observed outside the plasmapause had exit points which were closely aligned along an L-shell at an invariant latitude of 62.5°. They exhibited a marked variation (~ 3:1) in electron tube content over about 12° of invariant longitude and a drift of about 8 msec?1 to lower L-shells.Throughout the period of observation the plasmapause lay about 2° polewards of the mean position found by Carpenter (1968) for moderately disturbed days. 相似文献
15.
A theoretical study is made of the whistler mode cyclotron instability both in linear and nonlinear regimes in conjunction with the generation of VLF emissions in the magnetosphere. For the nonlinear treatment, a well-established quasilinear method is used and some physical processes of the cyclotron instability viz. energy conservation, mechanism of instability and frequency change of the excited emissions are clarified. The results are applied to some types of the triggered VLF emissions; whistler triggered emissions and artificially stimulated emissions (ASE). It is found that whistler triggered emissions excited around the upper cutoff frequencies of whistlers may be explained by the whistler mode cyclotron instability by a model distribution function inferred from satellite data. In order to see a nonlinear evolution of the whistler mode cyclotron instability, computer simulations were carried out and it is shown that the change of frequency with time of whistler triggered emissions as well as characteristics of ASE are well explained by resonant nonlinear behaviour of whistler mode cyclotron instability considered in the present paper. 相似文献
16.
Direct observations or deduced analysis indicate clearly that formation of intense fluxes of relativistic electrons is an important ingredient in the evolution of numerous active magnetized plasma systems. Examples of relativistic electron energization include the recovery phase of a planetary magnetic storm, post solar flare coronal activity and the afterglow of gamma ray bursts. It is suggested that there exists a universal mechanism, which may explain electron energization at the vastly different magnetized plasma environments. The favorite configuration consists of an inhomogeneous magnetic field anchored at a given magnetic structure and excitation of whistler waves due to external injection of low-energy non-isotropic electrons. The energization proceeds as a bootstrap process due to interaction with the propagating whistler waves along the inhomogeneous magnetic field. 相似文献
17.
R.N. Singh 《Planetary and Space Science》1974,22(2):333-339
The VLF wave generation by ?erenkov process from weakly ionized plasma has been considered. The effect of collisions on ?erenkov power spectrum and on propagation of VLF waves in whistler mode has been studied. The radiated power is shown to depend on the collisional parameter. The presence of collisions is found to modify the refractive index surfaces. It is shown that the focussing of VLF waves is less probable in the presence of collisions. 相似文献
18.
Fiber – or intermediate drift – bursts are a continuum fine structure in some complex solar radio events. We present the analysis of such bursts in the X17 flare on 28 Oct. 2003. Based on the whistler wave model of fiber bursts we derive the 3D magnetic field structures that carry the radio sources in different stages of the event and obtain insight into the energy release evolution in the main flare phase, the related paths of nonthermal particle propagation in the corona, and the involved magnetic field structures. Additionally, we test the whistler wave model of fiber bursts for the meter and the decimeter wave range. Radio spectral data (Astrophysikalisches Institut Potsdam, Astronomical Observatory Ond?ejov) show a continuum with fibers for ≈?6 min during the main flare phase. Radio imaging data (Nançay Radio Heliograph) yield source centroid positions of the fibers at three frequencies in the spectrometer band. We compare the radio positions with the potential coronal magnetic field extrapolated from SOHO/MDI data. Given the detected source site configuration and evolution, and the change of the fiber burst frequency range with time, we can also extract those coronal flux tubes where the high-frequency fiber bursts are situated even without decimeter imaging data. To this aim we use a kinetic simulation of whistler wave growth in sample flux tubes modeled by selected potential field lines and a barometric density model. The whistler wave model of fiber bursts accurately explains the observations on 28 Oct. 2003. A laterally extended system of low coronal loops is found to guide the whistler waves. It connects several neighboring active regions including the flaring AR 10486. For varying source sites the fiber bursts are emitted at the fundamental mode of the plasma frequency over the whole range (1200?–?300 MHz). The present event can be understood without assuming two different generation mechanisms for meter and decimeter wave fiber bursts. It gives new insight into particle acceleration and propagation in the low flare and post-CME corona. 相似文献
19.
Dastgeer Shaikh 《Monthly notices of the Royal Astronomical Society》2009,395(4):2292-2298
Non-linear, three-dimensional, time-dependent fluid simulations of whistler wave turbulence are performed to investigate role of whistler waves in solar wind plasma turbulence in which characteristic turbulent fluctuations are characterized typically by the frequency and length-scales that are, respectively, bigger than ion gyrofrequency and smaller than ion gyroradius. The electron inertial length is an intrinsic length-scale in whistler wave turbulence that distinguishably divides the high-frequency solar wind turbulent spectra into scales smaller and bigger than the electron inertial length. Our simulations find that the dispersive whistler modes evolve entirely differently in the two regimes. While the dispersive whistler wave effects are stronger in the large-scale regime, they do not influence the spectral cascades which are describable by a Kolmogorov-like k −7/3 spectrum. By contrast, the small-scale turbulent fluctuations exhibit a Navier–Stokes-like evolution where characteristic turbulent eddies exhibit a typical k −5/3 hydrodynamic turbulent spectrum. By virtue of equipartition between the wave velocity and magnetic fields, we quantify the role of whistler waves in the solar wind plasma fluctuations. 相似文献
20.
A whistler study has been made of plasma convection within the plasmasphere during a transition from steady moderate geomagnetic activity to quiet conditions. Continuous whistler data recorded at Sanae, Antarctica (L= 3.98) for the period 0400 UT, 10 July to 0400 UT, 11 July 1973 have been analyzed in 15 min intervals.This study has revealed two distinct bulges in the plasmasphere centred on 1700 and 0100 UT. The bulges appear to result from the outward flow of plasma rather than the addition of new plasma. We tentatively interpret the late bulge at 0100 UT as being the duskside bulge of earlier studies rotated into the midnight region. In this bulge, plasma above L = 3.8 appears to convect outwards to form the bulge whereas plasma at lower L-values is relatively undisturbed. For the early bulge (1700 UT) the plasma convection pattern is similar over all observable L-values and closely reflects the shape of the estimated plasmapause in that region. Comparison of the bulges, with those obtained by Carpenter (1966) suggests that the onset of quiet conditions results in a general displacement of the bulges in an eastward direction by about 3 hr. 相似文献