Magnetic hysteresis properties and rotational hysteresis losses of synthetic stress-controlled titanomagnetite (Fe_2.4Ti_0.6O₄) particles—II. Rotational hysteresis losses     

R. Keller  & E. Schmidbauer 《Geophysical Journal International》1999,138(2):334-342

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Concerning the generation of geomagnetic giant pulsations by drift-bounce resonance ring current instabilities     

K.-H. Glassmeier  S. Buchert  U. Motschmann  A. Korth  A. Pedersen 《Annales Geophysicae》1999,17(3):338-350

Giant pulsations are nearly monochromatic ULF-pulsations of the Earth’s magnetic field with periods of about 100 s and amplitudes of up to 40 nT. For one such event ground-magnetic observations as well as simultaneous GEOS-2 magnetic and electric field data and proton flux measurements made in the geostationary orbit have been analysed. The observations of the electromagnetic field indicate the excitation of an odd-mode type fundamental field line oscillation. A clear correlation between variations of the proton flux in the energy range 30–90 keV with the giant pulsation event observed at the ground is found. Furthermore, the proton phase space density exhibits a bump-on-the-tail signature at about 60 keV. Assuming a drift-bounce resonance instability as a possible generation mechanism, the azimuthal wave number of the pulsation wave field may be determined using a generalized resonance condition. The value determined in this way, m = −21±4, is in accord with the value m = −27±6 determined from ground-magnetic measurements. A more detailed examination of the observed ring current plasma distribution function f shows that odd-mode type eigenoscillations are expected for the case ∂f/∂W ≥ 0, much as observed. This result is different from previous theoretical studies as we not only consider local gradients of the distribution function in real space, but also in velocity space. It is therefore concluded that the observed giant pulsation is the result of a drift-bounce resonance instability of the ring current plasma coupling to an odd-mode fundamental standing wave. The generation of the bump-on-the-tail distribution causing ≥f/≥W ≥ 0 can be explained due to velocity dispersion of protons injected into the ring current. Both this velocity dispersion and the necessary substorm activity causing the injection of protons into the nightside magnetosphere are observed.  相似文献   

Spectral characteristics of waves and particles in the model of cyclotron wave-particle interactions near plasmapause     

D. L. Pasmanik  V. Y. Trakhtengerts 《Annales Geophysicae》1999,17(3):351-357

Further analysis of energetic electron precipitation at the evening sector of magnetosphere is performed. In the framework of the quantitative model of cyclotron wave-particle interactions developed in the previous Pasmanik et al. paper, the case of finite spread over energies of initial energetic electron distribution is studied. The solution for distribution function of energetic electron is found. The energetic spectrum of trapped and precipitating electrons and whistler wave spectrum are analysed.  相似文献   

A slow mode wave as a possible source of Pi 2 and associated particle precipitation: a case study     

O. Saka  O. Watanabe  K. Okada  D. N. Baker 《Annales Geophysicae》1999,17(5):674-681

An intensification of auroral luminosity referred to as an auroral break-up often accompanies the onset of geomagnetic pulsation (Pi 2) at the dip-equator. One such auroral break-up occurred at 2239 UT on 16 June, 1986, being accompanied by weak substorm activity (AE≈50 nT) which was recorded in all-sky image of Syowa Station, Antarctica (66.2°S, 71.8°E in geomagnetic coordinates). The associated Pi 2 magnetic pulsation was detected by a fluxgate magnetometer in the afternoon sector at the dip-equator (Huancayo, Peru; 1.44°N, 355.9° in geomagnetic coordinates; 12.1°S, 75.2°W in geographic coordinates; L = 1.00). In spite of the large separation of the two stations in longitude and latitude, the auroral break-up and subsequent luminosity modulation were seen to be correlated with the wave form of the ground Pi 2 pulsation. This occurred in such a way that the luminosity maximum was seen to occur at the phase of maximum amplitudes of Pi 2 wave form. We argue that the observed correlation could be interpreted as indicating a Pi 2-modulation of a field-aligned acceleration of the low energy electrons that may occur near the equator of the midnight magnetosphere.  相似文献   

Resonant enhancement of relativistic electron fluxes during geomagnetically active periods     

I. Roth  M. Temerin  M. K. Hudson 《Annales Geophysicae》1999,17(5):631-638

The strong increase in the flux of relativistic electrons during the recovery phase of magnetic storms and during other active periods is investigated with the help of Hamiltonian formalism and simulations of test electrons which interact with whistler waves. The intensity of the whistler waves is enhanced significantly due to injection of 10–100 keV electrons during the substorm. Electrons which drift in the gradient and curvature of the magnetic field generate the rising tones of VLF whistler chorus. The seed population of relativistic electrons which bounce along the inhomogeneous magnetic field, interacts resonantly with the whistler waves. Whistler wave propagating obliquely to the magnetic field can interact with energetic electrons through Landau, cyclotron, and higher harmonic resonant interactions when the Doppler-shifted wave frequency equals any (positive or negative) integer multiple of the local relativistic gyrofrequency. Because the gyroradius of a relativistic electron may be the order of or greater than the perpendicular wavelength, numerous cyclotron, harmonics can contribute to the resonant interaction which breaks down the adiabatic invariant. A similar process diffuses the pitch angle leading to electron precipitation. The irreversible changes in the adiabatic invariant depend on the relative phase between the wave and the electron, and successive resonant interactions result in electrons undergoing a random walk in energy and pitch angle. This resonant process may contribute to the 10–100 fold increase of the relativistic electron flux in the outer radiation belt, and constitute an interesting relation between substorm-generated waves and enhancements in fluxes of relativistic electrons during geomagnetic storms and other active periods.  相似文献   

Stratospheric background aerosol and polar cloud observations by laser backscattersonde within the framework of the European project “Stratospheric Regular Sounding”     

A. Adriani  F. Cairo  L. Pulvirenti  F. Cardillo  M. Viterbini  G. Di Donfrancesco  J. P. Pommereau 《Annales Geophysicae》1999,17(10):1352-1360

The Stratospheric Regular Sounding project was planned to measure regularly the vertical profiles of several tracers like ozone, water vapor, NO_x, ClO_x and BrO_x radicals, aerosol, pressure and temperature, at three latitudes, to discriminate between the transport and photochemical terms which control their distribution. As part of this project, the “Istituto di Fisica dell’Atmosfera” launched nine laser backscattersondes (LABS) on board stratospheric balloons to make observations of background aerosol and PSCs. LABS was launched with an optical particle counter operated by the University of Wyoming. Observations have been performed in the arctic, mid-latitudes and tropical regions in different seasons. Polar stratospheric clouds have been observed in areas inside and outside the polar vortex edge. A background aerosol was observed both in mid-latitudes and in arctic regions with a backscattering ratio of 1.2 at 692 nm. Very stratified aerosol layers, possibly transported into the lower stratosphere by deep convective systems, have been observed in the lower stratosphere between 20 and 29 km in the tropics in the Southern Hemisphere.  相似文献   

冲绳海槽浮岩中碳、氢同位素组成特征   总被引：4，自引：1，他引：3  

于增慧  翟世奎  赵广涛 《海洋学报》2004,26(6):58-64

利用分阶段热解释放气体质谱分析法研究了冲绳海槽浮岩热解释放气中CO₂和H₂O的碳、氢同位素组成,结果显示:浮岩中原生CO₂和H₂O主要释放于400～1 000℃,CO₂的碳同位素组成介于-6.7×10-3～-22.7×10-3,H₂O的氢同位素组成从-45×10-3变到-71×10-3,均落入幔源火山岩的变化范围,而且浮岩的氢同位素组成与海槽区玄武岩的氢同位素组成非常接近,这表明冲绳海槽浮岩与玄武岩之间具有密切的成因联系,浮岩岩浆和玄武岩岩浆是同源岩浆不同程度结晶分异的产物.另外,这些浮岩较洋中脊玄武岩要贫13C,并富集D,同时具有从洋中脊玄武岩向岛弧玄武岩变化的趋势,这表明浮岩岩浆在形成或上升过程中可能受到俯冲板块释放流体的影响.  相似文献   

Experimental study of the settling of twin spherical particles released side by side: The impact of particle size,fluid viscosity,initial spacing,and particle density     

Yang Xiao  Jieqing Liu  Pei Zhang  Jian Zhou  Dongfang Liang  Zhihao Wang  Taotao Zhang  Saiyu Yuan  Hongwu Tang 《国际泥沙研究》2023,38(1):83-96

The settling of solid particles in a fluid is an important process that needs to be considered in many fields of research. For example, the interactions among particles and between particles and the surrounding fluid are important topics in studying suspended sediment transport and water clarification. In this paper, the settling processes and interactions of twin spherical particles released side by side were experimentally studied. The Reynolds number varied in the range of 1-300, which is wit...  相似文献   

Effect of sediment particles on the velocity profile of sediment-water mixtures in open-channel flow     

Lei Zhang  Jianzhao Guan  Deyu Zhong  Yousheng Wang 《国际泥沙研究》2023,38(3):361-373

The presence of sediment particles in open-channel flow has an important effect on turbulence; thus, an empirical, turbulent eddy viscosity formula was established for application in the limit for low concentrations. The current study establishes a theoretical relation for the mixture viscosity based on the two-phase mixture model. The percentage contribution of the three mechanisms of mixture viscosity,namely, fluid turbulence(FT), particle turbulence(PT), and inter-particle collisions(IPCs), w...  相似文献   

Gravel dispersion on a granite pediment (East Mojave Desert,California): a short-term look at erosional processes     

S. B. Edinger-Marshall  L. J. Lund 《地球表面变化过程与地形》1999,24(4):349-359

Hypotheses about the influence of surface shape, landscape unit and vegetation cover on gravel dispersion were tested on a shallowly dissected portion of a low-sloping granite pediment in the East Mojave Desert of California. Painted gravels (2 to 20 mm diameter) were placed at 117 nodes on a 6m × 3m grid. Gravel movements were recorded after 9.7 cm of precipitation over a four-month period. Vectors indicating the magnitude and direction of gravel movement were longest for summits (24 cm, 34 nodes observed) and shortest for backslopes (14 cm, 27 nodes observed). Gravels beneath shrub canopies were protected significantly from rainsplash transport. To describe dispersion symmetry, eccentricity values were calculated using a ratio of variances of major and minor axes of an ellipse. Mean eccentricity values ranged from about 3 to 250 with dispersion on summits being the most symmetrical and dispersion in washes being the most elongated. Erosion is the most important soil- and pediment-modifying process at upper elevations of the Granite Cove Pediment which is cut off from sediment additions because of washes incised at the base of the mountain front. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献