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   

The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using ray tracing   总被引：1，自引：0，他引：1  

A. J. Stocker  N. F. Arnold  T. B. Jones 《Annales Geophysicae》1999,18(1):56-64

Characteristic signatures are often observed in HF radar range-time-intensity plots when travelling ionospheric disturbances (TIDs) are present. These signatures, in particular the variation of the F-region skip distance, have been synthesised using a ray tracing model. The magnitude of the skip variation is found to be a function of the peak electron density perturbation associated with the TID and radar frequency. Examination of experimental observations leads to an estimate of the peak electron density perturbation amplitude of around 25% for those TIDs observed by the CUTLASS radar system. The advantage of using the skip variation over the radar return amplitude as an indicator of density perturbation is also discussed. An example of a dual radar frequency experiment has been given. The investigation of the effect of radar frequency on the observations will aid the optimisation of future experiments.  相似文献   

Injection and acceleration of H+ and He2+ at Earth’s bow shock     

M. Scholer  H. Kucharek  K.-H. Trattner 《Annales Geophysicae》1999,17(5):583-594

We have performed a number of one-dimensional hybrid simulations (particle ions, massless electron fluid) of quasi-parallel collisionless shocks in order to investigate the injection and subsequent acceleration of part of the solar wind ions at the Earth’s bow shock. The shocks propagate into a medium containing magnetic fluctuations, which are initially superimposed on the background field, as well as generated or enhanced by the electromagnetic ion/ion beam instability between the solar wind and backstreaming ions. In order to study the mass (M) and charge (Q) dependence of the acceleration process He²⁺ is included self-consistently. The upstream differential intensity spectra of H⁺ and He²⁺ can be well represented by exponentials in energy. The e-folding energy E_c is a function of time: E_c increases with time. Furthermore the e-folding energy (normalized to the shock ramming energy E_p) increases with increasing Alfvén Mach number of the shock and with increasing fluctuation level of the initially superimposed turbulence. When backstreaming ions leave the shock after their first encounter they exhibit already a spectrum which extends to more than ten times the shock ramming energy and which is ordered in energy per charge. From the injection spectrum it is concluded that leakage of heated downstream particles does not contribute to ion injection. Acceleration models that permit thermal particles to scatter like the non-thermal population do not describe the correct physics.  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   

Reconfiguration and closure of lobe flux by reconnection during northward IMF: possible evidence for signatures in cusp/cleft auroral emissions     

M. Lockwood  J. Moen 《Annales Geophysicae》1999,17(8):996-1011

Observations are presented of the response of the dayside cusp/cleft aurora to changes in both the clock and elevation angles of the interplanetary magnetic field (IMF) vector, as monitored by the WIND spacecraft. The auroral observations are made in 630 nm light at the winter solstice near magnetic noon, using an all-sky camera and a meridian-scanning photometer on the island of Spitsbergen. The dominant change was the response to a northward turning of the IMF which caused a poleward retreat of the dayside aurora. A second, higher-latitude band of aurora was seen to form following the northward turning, which is interpreted as the effect of lobe reconnection which reconfigures open flux. We suggest that this was made possible in the winter hemisphere, despite the effect of the Earth’s dipole tilt, by a relatively large negative X component of the IMF. A series of five events then formed in the poleward band and these propagated in a southwestward direction and faded at the equatorward edge of the lower-latitude band as it migrated poleward. It is shown that the auroral observations are consistent with overdraped lobe flux being generated by lobe reconnection in the winter hemisphere and subsequently being re-closed by lobe reconnection in the summer hemisphere. We propose that the balance between the reconnection rates at these two sites is modulated by the IMF elevation angle, such that when the IMF points more directly northward, the summer lobe reconnection site dominates, re-closing all overdraped lobe flux and eventually becoming disconnected from the Northern Hemisphere.  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   

Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar   总被引：1，自引：0，他引：1  

G. Provan  T. K. Yeoman 《Annales Geophysicae》1999,17(7):855-867

A study has been performed on the occurrence of pulsed ionospheric flows as detected by the CUTLASS Finland HF radar. These flows have been suggested as being created at the ionospheric footprint of newly-reconnected field lines, during episodes of magnetic flux transfer into the terrestrial magnetosphere (flux transfer events or FTEs). Two years of both high-time resolution and normal scan data from the CUTLASS Finland radar have been analysed in order to perform a statistical study of the extent and location of the pulsed ionospheric flows. We note a great similarity between the statistical pattern of the coherent radar observations of pulsed ionospheric flows and the traditional low-altitude satellite identification of the particle signature associated with the cusp/cleft region. However, the coherent scatter radar observations suggest that the merging gap is far wider than that proposed by the Newell and Meng model. The new model for cusp low-altitude particle signatures, proposed by Lockwood and Onsager and Lockwood provides a unified framework to explain the dayside precipitation regimes observed both by the low-altitude satellites and by coherent scatter radar detection.  相似文献   

不同氢化反应条件下原子发射光谱同时测定锗锡砷锑铋   总被引：7，自引：0，他引：7  

吴列平  袁玄晖 《岩矿测试》1999,18(3):220-224

研究了不同氢化反应条件下电感耦合等离子体原子发射光谱同时测定锗,,锡,砷,锑和铋的方法。主要对锗,锡的氢化反应酸度,缓冲溶液的选择,动态线性范围,氧化剂的选择,共存元素的干扰及其消除进行实验。方法经国家一级标准物质分析验证,结果与标准值基本相符。  相似文献   

感耦等离子体发射光谱法测定原油中痕量铁镍铜钒   总被引：3，自引：0，他引：3  

吴建之  沈大可  沈尧汝 《岩矿测试》1999,(1)

系统地试验了用感耦等离子体发射光谱同时测定原油中痕量元素Ｆｅ、Ｎｉ、Ｃｕ和Ｖ的多种前处理方法,制定出Ｈ２ＳＯ４、ＨＮＯ３分步炭化,５００℃灰化,ＨＣｌ＋ＨＮＯ３（ＶＨＣｌ∶ＶＨＮＯ３＝１∶１）溶解灰分的最佳分解方案。该方法的检出限为１．０～６．０μｇ／Ｌ,精密度好,ＲＳＤ（ｎ＝４）＜４．６％,加标回收率为９６．２％～１１１％。方法已应用于大庆、苏北、惠州等原油样品的分析。  相似文献   

急性热应激对大菱鲆血液生化指标的影响   总被引：1，自引：0，他引：1  

孟振  张鸿丽  刘新富  贾玉东  刘滨  曲江波 《海洋科学》2020,44(1):122-131

为探讨大菱鲆(Scophthalmusmaximus)大规格幼鱼热耐受性和热应激过程中敏感指标的变化,本研究设定18℃、21℃、24℃和27℃4个温度梯度,采用1℃/h的升温速率,对驯化温度为18±1℃的苗种进行96 h急性胁迫实验,统计各温度组96 h成活率和测定血浆部分生化指标的变化情况。结果表明,在pH 7.85、盐度29.5和溶解氧高于6.5 mg/L的环境条件下,平均体质量183.65±15.99 g的大菱鲆幼鱼96h高起始致死温度(UILT50)为28.05℃;温度和胁迫时间对血浆肾上腺素(EPI)、皮质醇(Cortisol)、血糖(GLU)、还原型谷胱甘肽(GSH)、超氧化物歧化酶(SOD)和碱性磷酸酶(AKP)含量/活性都存在显著影响,除GSH外,温度和胁迫时间存在显著的交互影响作用;热应激组血浆EPI含量随胁迫时间延长呈逐渐上升趋势,同一胁迫时间以21℃组含量最高;热应激组Cortisol含量的响应时间随温度升高相应提前、随胁迫时间呈先升后降的趋势,均在48 h达最高值; 24℃和27℃组GLU含量随胁迫时间呈先升后降趋势,胁迫3h～6h即达最高值,上升幅度与温度正相关,21℃组则呈逐渐升高的趋势;热应激组GSH含量和SOD活性仅在胁迫初期(0 h～3 h)与对照组存在显著差异;热应激组AKP活性处理12 h显著低于对照组, 48 h后则显著高于对照组,且升高幅度与温度呈正相关。  相似文献