Energetic particles in the environment of the Earth's magnetosphere

This review summarizes the work in the field of magnetospheric energetic particles during the years 1987–1989. Out of a wealth of contributions it concentrates on a few topics. First it follows the path of ions extracted out of the polar ionosphere and their acceleration parallel and perpendicular to the magnetic field, as well as their subsequent transport into the equatorial magnetosphere and tail region. Then it focuses on acceleration of ions in the magnetotail and the related characteristics in the boundary layers including consequences for current substorm modeling. In the ring current region, the AMPTE and VIKING missions have made possible detailed studies of charge state and pitch-angle distributions as well as their variations during magnetospheric storms and substorms, from which conclusions on the transport and loss processes can be drawn. Recently, observations of energetic particles from orbiting nuclear reactors in the magnetosphere, which can be used as tracers for these satellites, have been made public. However, this may also constitute a serious background problem for future γ-astronomy missions with an increased sensitivity of the instrumentation. Finally, leading beyond the boundaries of the magnetosphere, attention is drawn to the still ongoing debate on the source of energetic particles upstream of the Earth's bow-shock and the respective importance of particle leakage and/or acceleration at the magnetospheric boundaries.     

The theory of radio windows in the ionosphere and magnetosphere

Radio waves in a stratified plasma can sometimes penetrate through a region where, according to a simple ray theory, they would be evanescent. They emerge on the far side in a different magnetoionic mode. This occurs when the incident wave normal is within a small cone of angles, called a radio window. The best known example is the Ellis window, used to explain the Z-trace in ionosonde records. Other phenomena where windows may be important have recently been studied. Simple approximate formulae are given for the transmission coefficient of a window and for its angular widths. These show the dependence on frequency, electron concentration gradient and direction of the ambient magnetic field. Comparison with more accurate calculations shows that these formulae are likely to be reliable in practical applications. The tracing of rays near a window is discussed, and the properties of a second kind of window are described.     

Global dynamics of the magnetosphere for northward IMF conditions

Ground-based and spacecraft observations of polar cap geophysical phenomena during periods of northward interplanetary magnetic field (IMF) show specific patterns of electric fields, field-aligned currents, aurora and particle precipitation. These are basically different from those when the IMF is southward. The total combination of observational data for northward IMF indicates rather a closed magnetosphere. This topology has led to the formation of a specific convection pattern in the distant plasma sheet. As different theoretical studies show, the connection of the IMF to geomagnetic flux tubes poleward of the cusp region may serve as the driving mechanism for plasma sheet convection and as the dynamo of current systems. Unfortunately, the direct observations of processes in the distant magnetosphere are too scarce either to accept or reject the concept of a closed magnetosphere. There are also some experimental data that are inconsistent with the closed magnetosphere topology. Definitive open or closed models must await future measurements.     

Penetration of solar wind plasma elements into the magnetosphere

Assuming that the solar wind is unsteady and non-uniform, it is suggested that field aligned plasma elements dent the magnetopause surface. This indentation makes the magnetopause boundary convex and therefore locally unstable with respect to flute instabilities. The intruding element is slowed down and stopped within 1 or 2 Earth radii from the magnetopause. Its excess convection kinetic energy is dissipated in the lower polar cusp ionosphere after ~ 50–500 s, depending on the value of the integrated Pedersen conductivity. Once the plasma element has been engulfed, keeping its identity, the warm plasma content is dissipated by precipitation and by drifting. The magnetosheath particles with large pitch angles are mirrored, and feed the plasma mantle flow.Several consequences of this penetration mechanism are pointed out:Ionospheric heating beneath the polar cusp;Birkeland currents on the eastward and westward edges of the plasma element;Diamagnetic field fluctuations within 1–2 R_E from the magnetopause (multiple magnetopause crossings);Oscillation of the magnetopause surface after a new element has penetrated;Exit of energetic particles out of the magnetosphere, and entry of energetic solar wind particles into the magnetosphere along the magnetic field lines of the intruding element;Subtraction of magnetic flux from the dayside magnetosphere and its addition to the geomagnetic tail when the magnetic field of the element has a southward component.     

A static-state field-line reconnection model for the Earth's magnetosphere

A magnetostatic boundary value problem has been solved within the magnetospheric cavity and in the interplanetary space in order to incorporate the interplanetary magnetic field in a quantitative magnetospheric vacuum-B-field model. The boundary condition for the closed model, B_⊥ = 0 at the magnetopause, is replaced by the condition that the normal component of the total field penetrates the boundary continuously. Penetration of the B-field depends on a ‘merging-constant’ C₀, which is assumed to be independent of position on the magnetopause. C₀ = 0 indicates the closed model and C₀ = 1 describes, the complete interconnection between the magnetospheric and the interplanetary field.The model is valid for the field-line topology on the dayside including the polar cusp region. The position of the polar cusp's equatorial edge depends on the actual value of the merging constant C₀ and the orientation of the interplanetary magnetic field. Plasma-physical effects enter the model implicitly by the fact that a magnetopause shields the solar wind from the magnetospheric cavity. The static model neglects the hydrodynamic behaviour of the field-line merging process.     

Broad-band auroral VLF hiss and inverted-V electron precipitation in the polar magnetosphere

A polar map of the occurrence rate of broad-band auroral VLF hiss in the topside ionosphere was made by a criterion of simultaneous intensity increases more than 5 dB above the quiet level at 5, 8, 16 and 20 kHz bands, using narrow-band intensity data processed from VLF electric field (50 Hz–30 kHz) tapes of 347 ISIS passes received at Syowa Station, Antarctica, between June 1976 and January 1983.The low-latitude contour of occurrence rate of 0.3 is approximately symmetric with respect to the 10–22 MLT (geomagnetic local time) meridian. It lies at 74° around 10 MLT, and extends down to 67° around 22 MLT. The high-latitude contour of 0.3 lies at invariant latitude of about 82° for all geomagnetic local times. The polar occurrence map of broad-band auroral VLF hiss is qualitatively similar to that of inverted-V electron precipitation observed by Atmospheric Explorer.(AE-D) (Huffman and Lin, 1981, American Geophys. Union, Geophysics Monograph, No. 25, p. 80), especially concerning the low-latitude boundary and axial symmetry of the 10–22 h MLT meridian.The frequency range of the broad-band auroral VLF hiss is discussed in terms of whistler Aode Cerenkov radiation by inverted-V electrons (1–30 keV) precipitated from the boundary plasma sheet. High-frequency components, above 12 kHz of whistler mode Cerenkov radiation from inverted-V electrons with energy below 40 keV, may be generated at altitudes below 3200 km along geomagnetic field lines at invariant latitudes between 70 and 77°. Low-frequency components below 2 kHz may be generated over a wide region at altitudes below 6400 km along the same field lines. Thus, the frequency range of the downgoing broad-band auroral hiss seems to be explained by the whistler mode Cerenkov radiation generated from inverted-V electrons at geocentric distances below about 2 R_E (Earth's radius) along polar geomagnetic field lines of invariant latitude from 70 to 77°, since the whistler mode condition for all frequencies above 1 kHz of the downgoing hiss is not satisfied at geocentric distance of 3 r_e on the same field lines.     

The suppressing effect of field-aligned currents on VLF emissions in the magnetosphere

The growth rate of whistler-mode waves is calculated analytically for a bi-Maxwellian plasma in the presence of a beam of cool electrons. This beam is moving in the same direction as the gyroresonant electrons and in the opposite direction to the waves which are considered to propagate parallel (or anti-parallel) to the imposed geomagnetic field. A somewhat surprising result is found. This is that even if the anisotropy is greater than a critical value, which is strongly frequency dependent, the beam reduces the growth of the waves near half the electron gyrofrequency. For a field-aligned current density ~ 1 μA m⁻², this mechanism can explain the lack of signals near 1.4 kHz on auroral (return current) flux tubes. It can also explain the observed absorption of signals at half the electron gyrofrequency, around 7 kHz on L = 4 flux tubes, near the equatorial plane and just outside the plasmapause.     

Interactions between whistler-mode waves and energetic electrons in the coupled system formed by the magnetosphere,ionosphere and atmosphere

The physical mechanism of a cyclotron resonance interaction between trapped energetic electrons and whistler-mode waves in the magnetosphere is discussed. Not only do the electrons have their pitch angles reduced in this interaction, so that they may be precipitated into the upper atmosphere, but also the waves can be amplified. Such a flux of precipitating electrons can, either by direct ionisation or via bremsstrahlung radiation, cause a pimple to be produced on the bottom of the ionosphere. That can significantly modify the amplitude and/or phase of very low frequency radio signals propagating in the Earth-ionosphere waveguide. Various experimental observations that demonstrate the reality of such effects are reviewed. The conditions necessary for a positive feedback situation are discussed, and some evidence for its existence assessed.     

Ionospheric modification experiments in northern Scandinavia

The heating facility at Ramfjordmoen near Tromsø, Norway, is briefly described, and a survey is given of the experiments performed with this facility until now. These experiments comprise D-region modification, polar electrojet modulation at VLF, ELF and ULF, HF absorption and backscatter due to short-scale field-aligned irregularities, stimulated radio wave emission of the modified ionospheric plasma, short-time scale HF absorption due to the parametric decay instability, airglow modification, excitation of large-scale irregularities, and F-region cross modulation.     

Incisions,breakages and charring,some probably man-made,in fossil bones from Mammoth Cave,Western Australia

Two small patches of richly fossiliferous deposit in Mammoth Cave, excavated early this century, yielded tooth-bearing and post-cranial material. We have studied a notched tibia, various broken femurs and charred bones, many of which are attributable to extinct taxa, and have concluded that deliberate action by Aboriginals is the most probable explantation for their condition.

The age of one of the deposits, and probably also of the other, is in excess of 37,000 years.     

An alternative interpretation of auroral precipitation and luminosity observations from the DE,DMSP, AUREOL,and Viking satellites in terms of their mapping to the nightside magnetosphere

We present an interpretation, which differs from that commonly accepted, of several published case studies of the patterns of auroral electron precipitation into the high-latitude upper atmosphere in the near-midnight sector based on their mapping to the nightside magnetosphere. In our scheme bright discrete auroral structures of the oval and respective precipitation are considered to be on the field lines of the Central, or Main, Plasma Sheet at distances from 5–10 to 30–50 R_E, depending on activity. This auroral electron precipitation pattern was discussed in detail by Feldstein and Galperin [(1985) Rev. Geophys.23, 217] and Galperin and Feldstein [(1991) Auroral Physics, p. 207. Cambridge University Press. It is applied and shown to be consistent with the results of case studies based on selected transpolar passes of the DE, DMSP, AUREOL-3 and Viking satellites.A diagram summarising the polar precipitation regions and their mapping from the magnetospheric plasma domains is presented. It can be considered as a modification of the Lyons and Nishida (1988) scheme which characterizes the relationship between the gross magnetospheric structure and regions of nightside auroral precipitation. The modification takes into account non-adiabatic ion motions in the tail neutral sheet, so that the ion beams characteristic of the Boundary Plasma Sheet (BPS) originate on closed field lines of the distant Central Plasma Sheet (say, at distances more than ~30 R_E).     

Ionospheric plasma modification in the vicinity of a spacecraft by powerful radio pulses in topside sounding

A mechanism of strong turbulence is proposed for interpretation of the resonances observed by a wide-band receiver during topside sounding. The turbulence is created in the vicinity of the spacecraft due to the striction modulation instability. Experimental results obtained with the aid of a wide-band receiver on board the Intercosmos-19 satellite are discussed in terms of strong wave-wave and/or wave-particle interaction, namely electron acceleration in Langmuir cavitons and non-linear generation of the electron Langmuir plasma waves and Tonks-Dattner resonances.     

An empirical study on the modification of China's current urban social security system

This study challenges the conventional correlation between economic performance and the level of the development of social security systems. By focusing on China's urban areas, we provide an overview of the components and benefits, from a comparative perspective, of China's current social security system. We also create a comprehensive and generally applicable method using factors such as economics and population, among others, as standards to evaluate the efficacy of China's system. In order to demonstrate our primary hypothesis – that the Chinese Communist Party government has to modify its social security system to adapt to or bring about changes in the basis of its legitimacy – we analyse Chinese social security records and other related data after 1949 by statistical methods. The formula we provide in this study can be used to forecast China's expenditure on its urban social security system, and other scholars can apply our methods to countries in which conditions are broadly similar.     

Middle atmospheric electrodynamic modification by particle precipitation at the South Atlantic Magnetic Anomaly

Evidence for a localized middle atmospheric electrodynamic modification at low latitudes (southern Brazilian coast) of the South Atlantic Magnetic Anomaly (SAMA), in association with enhanced geomagnetic activity, are presented in a unified way combining recent observational efforts and related numerical studies. They involve a distortion effect in the fair weather electric field at balloon altitudes. This effect is attributed to a local intensification of energetic electron precipitation through a related middle atmospheric ionization enhancement and is elucidated by numeric simulation. From the electric field measurements and the numeric simulation, the intensification of precipitation is considered to occur in fairly narrow regions at the observed low L values (around L = 1.13) of the SAMA, with horizontal extensions of the order of a few hundred kilometers. A physical mechanism that could be responsible for this sort of intensification is suggested. Furthermore, a comparison of the phenomenon of middle atmospheric electrodynamic modification at the SAMA with a similar one at auroral latitudes, in response to enhanced solar and geomagnetic activity, is also given.     

Travelling ionospheric disturbances and the effectiveness of powerful HF transmitters in ionospheric modification and radio location of the Moon

Using ray tracing we investigate, on a qualitative level and in the linear approximation, the effects of medium-scale travelling ionospheric disturbances (MS TIDs) arising when powerful HF radio transmitters are operated in conjunction with antenna arrays designed for ionospheric modification (heating) and for radio location of the Moon. It is shown that the HF radio wave focusing effect, arising during the movement of the MS TIDs, can give rise to a strong inhomogeneous and nonstationary modulation of the space-time distribution of the field intensity of a powerful radio transmitter both at heights near the reflection region (in heating experiments) and at the exit from the ionosphere (in radio location of the Moon). The excess of intensity over an unperturbed value for typical parameters of MS TIDs in experiments on ionospheric modification can reach values of hundreds of percent: a ‘spot’ of increased intensity of the wave field can have the size of about 1–10 km, and can move with a velocity close to the MS TID phase velocity.In the case of lunar radio location, the inhomogeneity and nonstationarity of the wave field intensity distribution at the exit from the ionosphere substantially complicates the evaluation of the corresponding distribution on the Moon's surface and the interpretation of the Moon-reflected radio signal characteristics.     

The classification of distorted-mirror reflections and its ionospheric modification due to the underlying ionization

A systematic classification of reflections from a sinusoidally distorted-mirror has led to the identification of three classes of rays: direct simple rays which hit the mirror once on reflection; direct complex rays which hit the mirror several times before reflection; indirect rays which leave from and return to the source at different angles. The conditions on the distortion amplitude, wavelength and height for the different classes to exist are obtained. A comparison of results is made with those from a Chapman layer with a sinusoidally varying height of peak density, in the absence of any magnetic field. The broad classification of solutions is preserved, but direct and indirect rays are no longer independent and at large scale heights the presence of underlying ionization removes some solutions. The construction of ionograms of these profiles shows that indirect and complex direct rays contribute significantly to the traces observed.     

Some effects in the middle atmosphere due to lightning

A brief review is given of some of the electrodynamic responses of the middle atmosphere to lightning. Attention is focused on the precipitation of energetic electrons from the magnetosphere, due to whistler mode electromagnetic waves. The secondary ionisation and bremsstrahlung radiation created, and some of the ways in which such effects can be detected, are also considered. Finally, the possibilities of positive feedback mechanisms operating between the atmosphere and the magnetosphere are investigated.     

聚丙烯纤维、偏高岭土和细砂对水硬石灰改性的研究

为改善水硬石灰的力学性能,适当提高其抗压与抗折强度,本工作设计并制备了添加不同配比的聚丙烯纤维、偏高岭土和细砂的水硬石灰,并对其力学强度,矿物成分和微观形貌进行试验研究。结果表明,单独添加30%偏高岭土、0.1%聚丙烯纤维或者50%石英砂的水硬石灰抗压强度相对较高。在偏高岭土-水硬石灰中,单独添加0.1%短长度聚丙烯纤维或者共同加入0.1%聚丙烯纤维和50%石英砂可以提高其长期抗压强度。添加聚丙烯纤维还可以提高水硬石灰抗折强度。钙铝水合物不稳定和长期抗压强度下降有关,添加1%聚丙烯纤维可以提高碳酸化反应。聚丙烯纤维还能够增大水硬石灰内部的摩擦力和锚固力。在南京市罗廊巷太平天国建筑壁画保护中,对于地仗层脱落部位的修补采用改性水硬石灰进行了局部应用,效果良好。     

Electrodynamic effects of metal ions in the noon equatorial E-region

The observations of metal ions in significant concentrations and in layer formation in the lower E-region are briefly reviewed. It is expected that a metal ion layer may alter the electro-conductivity of the ionosphere and modify the distribution of ionospheric dynamo current. The variation in the electroconductivity is theoretically calculated, and it is shown that the Pedersen conductivity is reduced by less than 14%. In the equatorial ionosphere, field line integration of metal ion effects is likely to be large. A metal ion layer, similar to those observed, is numerically modelled in the equatorial region and its electrodynamic effects on the equatorial electrojet (EEJ) are numerically examined using our self-consistent model of the ionospheric dynamo. The effects are found to be significant on the amplitude of the EEJ, but not effectively large on its peak altitude.