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New observations of energetic helium ion fluxes in the Earth’s radiation belts have been obtained with the CAMMICE/HIT instrument on the ISTP/GGS POLAR spacecraft during the extended geomagnetically low activity period April through October 1996. POLAR executes a high inclination trajectory that crosses over both polar cap regions and passes over the geomagnetic equator in the heart of the radiation belts. The latter attribute makes possible direct observations of nearly the full equatorial helium ion pitch angle distributions in the heart of the Earth’s radiation belt region. Additionally, the spacecraft often re-encounters the same geomagnetic flux tube at a substantially off-equatorial location within a few tens of minutes prior to or after the equatorial crossing. This makes both the equatorial pitch angle distribution and an expanded view of the local off-equatorial pitch angle distribution observable. The orbit of POLAR also permitted observations to be made in conjugate magnetic local time sectors over the course of the same day, and this afforded direct comparison of observations on diametrically opposite locations in the Earth’s radiation belt region at closely spaced times. Results from four helium ion data channels covering ion kinetic energies from 520 to 8200 KeV show that the distributions display trapped particle characteristics with angular flux peaks for equatorially mirroring particles as one might reasonably expect. However, the helium ion pitch angle distributions generally flattened out for equatorial pitch angles below about 45°. Significant and systematic helium ion anisotropy difference at conjugate magnetic local time were also observed, and we report quiet time azimuthal variations of the anisotropy index. 相似文献
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在用计算机断层成像方法由EUV观测图像重建等离子体层全球密度分布时,地球的遮挡和有限角度都会导致投影数据不完备,从而无法精确重建出等离子体层的密度分布.本文针对该问题,提出一种基于图像总变差极小化的代数迭代算法.通过重建等离子体层投影数据缺失最为严重的中心子午面,证明该算法能够显著提高重建图像的质量. 并且在IMAGE卫星仅能达到90°的有限投影角度下,此算法重建图像的相关系数可达0.760,而代数迭代算法的相关系数仅为0.696. 相似文献
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本文是利用计算机断层成像(CT)方法中的滤波反投影法(FBP)和代数迭代法(ART),根据等离子体层的仿真模型,重建其全球密度分布.在重建过程中,地球遮挡是一个很重要的问题.计算结果表明两种方法都可以使用,但ART比FBP重建的效果好.ART重建图像的相关系数可达0.98,而FBP重建图像的相关系数仅为0.86.FBP重建的偏差是由地球遮挡引起,向阳面靠近地球区域的密度会减小.从定量分析中可以进一步看出地球遮挡所引起的偏差变化. 相似文献
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Extremely low frequency (ELF)/Very low frequency (VLF) hiss is whistler mode wave that interacts with energetic electrons
in the magnetosphere. The characteristics features of ELF/VLF hiss observed at low latitude ground station Jammu (Geomag.
lat. 22°16′ N, L=1.17) are reported. It is observed that most of hiss events first propagate in ducted mode along higher L-values (L = 4–5), after reaching lower edge of ionosphere excite the Earth-ionosphere waveguide and propagate towards equator to be
received at low-latitude station Jammu. To understand the generation mechanism of ELF/VLF hiss, incoherent Cerenkov radiated
power from the low-latitude and mid-latitude plasmasphere are evaluated. Considering this estimated power as an input for
wave amplification through wave–particle interaction, the growth rate and amplification factor is evaluated which is too small
to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of
ELF/VLF hiss. 相似文献
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The coupled ionosphere–thermosphere–plasmasphere system is very complex. The study of its interrelationships during geomagnetically disturbed conditions is an especially challenging task.Significant progress has been achieved during the last few years in developing comprehensive theoretical models to describe its global behaviour.Moreover, more simple, specialized numerical modelling of some specialaspects of storm behaviour and/or regional models have contributedto the progress in this field.This paper summarizes recent developments in upper ionosphereand plasmasphere storm studies and modelling.From an observational point of view the upper ionosphere/plasmasphereregion is well reflected in radio beacon measurements providing the totalelectron content (TEC). The development of space-based radio navigation systems such as GPS offersnew opportunities to derive TEC on both regional and global scale.Combining TEC with ionosonde data enables the variability of the shape of the electron density distribution during storms to be studied.We present some examples of co-ordinated investigation,made during the CEDAR storm study intervals. 相似文献
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Tamara L. Gulyaeva 《Acta Geophysica》2007,55(2):253-266
Variations of the upper boundary of the ionosphere (UBI) are investigated based on three sources of information: (i) ionosonde-derived
parameters: critical frequency foF2, propagation factor M3000F2, and sub-peak thickness of the bottomside electron density profile; (ii) total electron content (TEC) observations from signals
of the Global Positioning System (GPS) satellites; (iii) model electron densities of the International Reference Ionosphere
(IRI*) extended towards the plasmasphere. The ionospheric slab thickness is calculated as ratio of TEC to the F2 layer peak electron
density, NmF2, representing a measure of thickness of electron density profile in the bottomside and topside ionosphere eliminating the
plasmaspheric slab thickness of GPS-TEC with the IRI* code. The ratio of slab thickness to the real thickness in the topside ionosphere is deduced making use of a similar ratio
in the bottomside ionosphere with a weight Rw. Model weight Rw is represented as a superposition of the base-functions of local time, geomagnetic latitude, solar and magnetic activity.
The time-space variations of domain of convergence of the ionosphere and plasmasphere differ from an average value of UBI
at ∼1000 km over the earth.
Analysis for quiet monthly average conditions and during the storms (September 2002, October–November 2003, November 2004)
has shown shrinking UBI altitude at daytime to 400 km. The upper ionosphere height is increased by night with an ‘ionospheric
tail’ which expands from 1000 km to more than 2000 km over the earth under quiet and disturbed space weather. These effects
are interposed on a trend of increasing UBI height with solar activity when both the critical frequency foF2 and the peak height hmF2 are growing during the solar cycle. 相似文献
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Martin J. Jarvis 《Surveys in Geophysics》2001,22(2):155-174
Within the global context, Antarctica has a key role to play in understanding long-term change in the upper atmosphere, both because of its isolation from the rest of the world and because of its unique geophysical attributes. Antarctic upper atmosphere data can provide global change observations regarding the mesosphere, thermosphere, ionosphere, plasmasphere and magnetosphere. It will not only provide trend estimates but, just as importantly, it will define the background variability which exists in the upper atmosphere and against which these trends must be resolved. Upper atmospheric change can be driven both from within the Earth's near environment primarily through changing atmospheric composition, dynamics or geomagnetic field, or it can be driven externally, predominantly by the Sun. Recent observations are discussed in the light of increasing interest in global change issues and sun-weather relationships. 相似文献
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The nighttime winter anomaly (NWA) effect was observed during solar minimum conditions at the American sector by means of ionospheric electron content and vertical sounding measurements in Havana (Cuba). An effective interhemispheric transport of plasma is suggested to explain enhanced northern nighttime ionization during winter solstice. To elucidate this effect, an adequate physicalnumerical model of the coupled system ionosphere-plasmasphere is presented and applied to a corotating tube of plasma at L=1.5 in the American sector. The NWA can be explained by theoretically derived higher tube content during the December solstice and accordingly by more intense nighttime fluxes from the plasmasphere, compared to the June solstice. 相似文献
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E. E. Titova T. A. Yahnina A. G. Yahnin B. B. Gvozdevsky A. A. Lyubchich V. Yu. Trakhtengets A. G. Demekhov J. L. Horwitz F. Lefeuvre D. Lagoutte J. Manninen T. Turunen 《Annales Geophysicae》1997,16(1):25-33
Specific type of energetic electron precipitation accompanied by a sharp increase in trapped energetic electron flux are found in the data obtained from low-altitude NOAA satellites. These strongly localized variations of the trapped and precipitated energetic electron flux have been observed in the evening sector near the plasmapause during recovery phase of magnetic storms. Statistical characteristics of these structures as well as the results of comparison with proton precipitation are described. We demonstrate the spatial coincidence of localized electron precipitation with cold plasma gradient and whistler wave intensification measured on board the DE-1 and Aureol-3 satellites. A simultaneous localized sharp increase in both trapped and precipitating electron flux could be a result of significant pitch-angle isotropization of drifting electrons due to their interaction via cyclotron instability with the region of sharp increase in background plasma density. 相似文献