A simplified theory of ELF propagation in the Earth-ionosphere transmission line

An approximate theory of ELF propagation in the Earth-ionosphere transmission line is developed by combining the reflection theory of Booker and Lefeuvre (1977) with Greifinger and Greiferinger's (1978, 1979) treatment of the effect of ionization below the level of reflection. The theory allows for the influence of the Earth's magnetic field, for reflection from the gradient on the underside of the D region (or, at night, of a ledge below the E region), for reflection from the gradient on the underside of the E region, and for reflection from the gradient on the topside of the E region. The procedure is to compare local vertical gradient with local wavelength, thereby classifying altitude into intervals where the gradient is high and ones where it is low. Where the gradient is low, the phase-integral treatment is adequate. An interval where the gradient is high may, to a first approximation, be replaced by a discontinuity. The amount of the discontinuity is the difference between the refractive indices at the top and bottom of the interval of high gradient, judged in relation to local wavelength. It is then a matter of combining reflections from the several discontinuities. This requires calculation of the complex phase-changes between the discontinuities. But these are the intervals where the phase-integral treatment is available. To a beter approximation, there is a non-zero phase-change associated with an interval of high gradient. The method for incorporating this is described.     

Schumann Resonances as a Means of Investigating the Electromagnetic Environment in the Solar System

The propagation of extremely low frequency (ELF, 3 Hz to 3 kHz) radio waves and resonant phenomena in the spherical Earth-ionosphere cavity has been studied for almost fifty years. When such a cavity is excited by naturally occurring broadband electromagnetic radiation, resonances can develop if the equatorial circumference is approximately equal to an integral number of wavelengths of the propagating electromagnetic waves; these are termed Schumann resonances. They provide information not only about thunderstorm and lightning activity on the Earth, and their relation to climate, but also on the properties of the low ionosphere. Similar investigations can be performed for any other planet or satellite, provided that it has an ionosphere. There are important differences between the Earth and other celestial bodies regarding, for example, the surface conductivity, the atmospheric conductivity profile, the geometry of the ionospheric cavity, and the sources of excitation. To a first approximation, the size of the cavity defines the fundamental resonant frequency, the atmospheric electron density profile controls the wave attenuation, the nature of the sources influences the electromagnetic field distribution in the cavity, and the body surface conductivity indicates to what extent the subsurface can be explored. The frequencies and attenuation rates of the principal eigenmodes depend upon the electrical properties of the cavity. Instruments that monitor the electromagnetic environment in the ELF range on the surface, on balloons, or on descent probes provide unique information on the cavity. In this paper, we present Schumann resonance models for selected inner planets, some gaseous giant planets and a few of their satellites. We review the crucial parameters of ELF electromagnetic waves in their atmospheric cavities, namely the electric and magnetic field spectra, their eigenfrequencies, and the associated Q-factors (damping factors). Then we present important information on theoretical developments, on a general model that uses the finite element method and on the parameterization of the cavity. Next we show the distinctiveness of each planetary environment, and discuss how ELF radio wave propagation can contribute to an assessment of the major characteristics of those planetary environments.     

Plasma-maser effects in plasma astrophysics

The role of a new mode coupling effect (plasma-maser) in space plasma physics is reviewed. The new maser effect, the idea that the resonant electrons with the low-frequency mode can amplify the high-frequency mode, does not require population inversion of electrons. The generation mechanisms of ULF modulated ELF emissions, auroral kilometric radiation, chorus related electrostatic bursts, whistler mode in the solar wind, and type III solar radio bursts are studied based on plasma-maser effect. The forced plasma-maser interaction model reduces to a conservative Lotka-Volterra system. A chaotic behavior of the forced Lotka-Volterra system is obtained. The new mode coupling process has potential importance in attempting to interpret numerous astrophysical radio phenomena.     

Geomagnetic pulsations

Conclusion In writing this review paper the author has been aware that although the present international classification on geomagnetic pulsations (see Table I) had been really useful for several years since the Berkeley Meeting, it seems unsuitable for the up-to-date pulsation study. This is mainly due to the fact that it depends only on the period and waveform of the pulsations. For example, (1) occurrence of PP type of Pc1 even in the international Pc3 range (Heacock, 1966), (2) PP and CE getting mixed in a common period band (cf. 2.7), (3) similar mixing tendency of Pc3 with Pc4 (cf. 3.3 or Figure 21), (4) subtypes of Pi pulsations having common period ranges but different source mechanisms, (5) existence of various types of pulsations which can be classified neither to Pc nor to Pi (cf. Section 6), and so on. Hence the author feels that a new pulsation classification based on physical image on the occurrence models is really needed now.According to the international definition which has a period range of pulsations from 0.2 (5 Hz) to 600 sec, a part of the following electromagnetic field fluctuations called ELF emissions and ELF whistlers should belong to geomagnetic pulsations. ELF emissions are at times observed near 4 Hz and 9 Hz. They are so termed because of the difference between these frequencies and the Schumann resonance frequencies of 8 and 14 Hz (Yanagihara and Shimizu, 1969; Polk, 1969). Another type, ELF whistlers, exhibit either rising, falling or fluctuating tones from about 2 Hz to probably a few tens of Hz (Duffus, Nasmyth et al., 1958; Yamashita, 1967; Glangeaud, 1967; Yanagihara and Shimizu, 1969). In this review paper, however, both ELF emissions and whistlers have not been reviewed, since most of these seem to be out of the international frequency range so far as present observational knowledge is concerned. Some of the Pc6 and Dp2, involved in the international period range of pulsations, have also not been commented on, but the reader is advised to refer to Herron (1967) and Nishida (1968), respectively, for more detail.It has been frequently pointed out in this paper that latitudinal dependence of pulsation amplitude is one of the most important clues for seeking the model of excitation and propagation of HM and EM waves, but that this dependence has not been precisely obtained so far owing to the difference in geomagnetic longitude of the pulsation stations (for example, see Figure 40). Cooperative observations based on standardized magnetometers are eagerly desired at stations which are densely arranged along the same magnetic meridian, even if the observation is temporal.As already reviewed, various conflicting models have been proposed for each type of pulsation. On the occurrence of pc's, for example, there are two main conflicting models. In the first model, Pc2, 3, and 4 (Troitskaya, 1967; Patel and Hastings, 1968; and others) or Pc3 and 4 (Radoski and Carovillano, 1966) are related to one and the same resonance system and the difference in the type of these pc's is attributed to an effect of geomagnetic activity on the size of this system. In the second model, Pc2, 3, 4 and 5 are related to three or four different resonant systems (Jacobs and Sinno, 1960b; Hirasawa and Nagata, 1966; Kato, Mori et al., 1968; and others). Most of the conflict among such models seems to be removable by combining more thorough theoretical studies and correct dynamic spectrum analyses of the data at the polar region, auroral zone, sub-auroral zone, and middle and low latitudes, for various geomagnetic disturbance conditions.     

Non-linear resonant excitation of whistler mode waves in the Earth's ionosphere

We examine the resonant non-linear interaction in the Earth's ionosphere of two powerful high frequency radio beams with frequencies f ₁ and f ₂ (both larger than the plasma frequency at F2_max) and wave numbers k ₁ and k ₂ such that a whistler mode wave can be excited with a frequency f ₃ = f ₁ — f ₂ and a wave number k ₃ = k ₁ – k ₂. The feasibility of an effective ground based installation, sited at low latitudes, is discussed and the field strength of the wave emerging from a 10 km wide ionospheric region illuminated by the beams is evaluated for a range of transmitted frequencies, beam orientations and plasma frequencies in the interaction region. It is suggested that the longitude dependence of the enhancement of VLF noise bands detected by the Ariel 3 satellite may be due to a non-linear interaction of this type between any two or more medium wavelength signals from areas where there is a high concentration of commercial broadcasting stations, such as the NE region of the U.S.A.     

Kinetic Models for Whistler Wave Scattering of Electrons in the Solar Corona and Wind

Kinetic models are necessary to describe the physical processes associated with non-Maxwellian velocity distribution functions (VDFs) of electrons or ions in the solar corona and wind. It is shown that pitch-angle scattering of electrons in the solar wind needs to be considered in kinetic solar wind models. Coulomb collisions are not efficient enough to provide this scattering, but resonant interaction with whistler waves is. A solar wind model for undisturbed fast wind is presented, and the influence of scattering on flare electron propagation is investigated. Furthermore, it is found that resonant interaction of electrons with whistler waves is capable of producing suprathermal tails of electron distributions even under quiet conditions without flare activity.     

Ground-based ELF/VLF observations at high latitudes during passes of GEOS-1 and ISEE-1 and -2

Recordings of ELF/VLF radio signals were made, as a contribution to the International Magnetospheric Study, in Iceland (17 August to 5 September 1977) and Norway (21 October to 15 December 1977; and 11 January to 27 February 1978) by the Space Radio Physics group. The equipment used at each of three sites was a goniometer (direction finding) receiver. As an example of the results obtained, recordings of risers, occurring at a rate up to 10 min^-1 and with frequencies (1.0 to 1.5 kHz) just greater than those of simultaneous hissy chorus signals, made between 10:20 and 11:00 UT on 31 August 1977, are discussed. These risers (downcoming whistler mode signals) are shown to have well defined exit points from the ionosphere which are located, to within an uncertainty of typically ±40 km, by triangulation. The observations are broadly consistent with there being a single exit point which, on this occasion, happens to be almost on the flux tube through the geomagnetic observatory at Leirvogur. Simultaneous ground-based magnetometer observations, and also wave and energetic charged particle observations made aboard GEOS-1, have been studied. The electron spectra and pitch angle distributions are as required for the operation of the electron cyclotron instability in which whistler mode signals are amplified.     

Unsteady analysis of jet impingement under vibration conditions

The vibration of thermodynamic machinery will affect its cooling system. In this research, a high-resolution simulation of jet impingement was performed to quantify the unsteady turbulent convection under vibration conditions. A newly developed Self-Adaptive Turbulence Eddy Simulation(SATES) method was used. The Reynolds number was Re = 23000, the jet-towall distance was fixed at H/D = 2, and the vibrating frequency of the impinging wall f varied from 0 to 200 Hz. Compared with the static wall c...     

Power-line harmonic radiation and the electron slot

World maps of the occurrence of VLF emissions obtained by the satellites Ariel 3 and 4 reveal maxima above industrial regions of high power consumption in North America and Euro-Asia. A study of the generation and radiation of power line harmonics indicates that these may be a major source of the observed signals. The latter propagate in the whistler mode into the geomagnetically conjugate regions in the southern hemisphere. A particularly prominent zone of emission is obtained at VLF (3.2 kHz) over North America where frequent magnetospheric wave amplification/stimulated emission, up to 50 dB and typically 10 to 20 dB above a baseline level that we ascribe to power harmonic radiation (PLHR), is obtained at invariant latitudes 45 to 55° (2 < L < 3) centred on the electron slot. It appears that PLHR may be responsible for pitch angle diffusion of energetic electrons (E 100 keV) at large pitch angles by first-order resonance and thereby contribute to the formation of the electron slot. There is a strong seasonal variation in wave-amplification/stimulated emission which we suggest may be due to a variation in the ability of the waves to become entrapped in ducts where wave-amplification occurs through a phase-bunching process. There is a strong correlation between D _ST and signal intensity, the latter lagging by 1–5 hr in the morning and 10 hr in the evening; here again wave-amplification appears to depend on duct formation and wave trapping therein. One or two (or multi) hop emissions occur with about equal probability at 3.2 kHz; at 9.6 kHz one hop are predominant.Paper presented at the Fifth International Wrocaw Symposium on Electromagnetic Compatibility, Wroclaw (Poland), 17–19 September, 1980. Sci. Rpt. 1978 (1), Sheffield Univ. Space Physics Grp.     

某涡轮级转静干涉噪声数值研究

通过采用结合相位延迟方法的非定常数值计算,得到真实叶片数下某高压涡轮级叶片通过频率及其倍频下的脉动压力.然后在转子后管道中利用模态匹配方法,摒除了管道末端非物理反射及其非声压脉动的影响,从而获得转子后管道中向下游传播的转静干涉噪声分量.结果分析表明:该涡轮级在叶片通过频率下,周向模态m=3未被截止,且为主要转静干涉噪声源;在2倍叶片通过频率下,周向模态m=6,-64未被截止.      

Midlatitude Sporadic E. A Typical Paradigm of Atmosphere-Ionosphere Coupling

This paper provides a comprehensive update on sporadic E layers that is placed in the context of atmosphere-ionosphere coupling, exemplified here by the fundamental windshear theory processes that govern sporadic E layer formation and variability. Some basics of windshear theory are provided first, followed by a summary of key experimental results, their interpretation and physical understanding. The emphasis is placed on the wind shear control of the diurnal and sub-diurnal variability and altitude descent of sporadic E layers and the key role behind these properties of the diurnal and semidiurnal tides. Furthermore, the paper summarizes recent observations that establish a role also for the planetary waves in sporadic E layer occurrence and long-term variability. The possible mechanisms behind this interaction are examined and evidence is presented which shows that planetary waves affect sporadic E layers indirectly though the amplitude modulation of tides at lower altitudes in the MLT region. Only a brief mention is made about gravity wave effects on sporadic E, which apparently exist but cannot be as crucial in layer forming as thought in the past. There is now enough evidence to suggest that mid- and low-latitude sporadic E is not as “sporadic” as the name implies but a regularly occurring ionospheric phenomenon. This may suggest that the sporadic E layer physics can be incorporated in large-scale atmosphere-ionosphere coupling models.     

Chaotic Temporal Variability of Magnetospheric Radio Emissions

Nonthermal magnetospheric radio emissions provide the radio signatures of solar-terrestrial connection and may be used for space weather forecasting. A three-wave model of auroral radio emissions at the fundamental plasma frequency was proposed by Chian et al. (1994) involving resonant interactions of Langmuir, whistler and Alfvén waves. Chaos can appear in the nonlinear evolution of this three-wave process in the magnetosphere. We discuss two types of intermittency in radio signals driven by temporal chaos: the type-I Pomeau-Manneville intermittency and the interior crisis-induced intermittency. Examples of time series for both types of intermittency are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wave motions in the atmosphere and related ionospheric phenomena

We review important studies in the field of stratosphere-ionosphere coupling, including recent studies of wave motions of planetary waves, atmospheric tides and internal gravity waves in the atmosphere. The interrelation between stratospheric sudden warmings and winter anomaly of radio absorption, a dynamical model of stratospheric sudden warmings and some production mechanisms of intensified electron density in the D region are discussed. Other topics presented are atmospheric tides in the lower thermosphere including dynamo action, and internal gravity waves, by which we intend to explain travelling ionospheric disturbances in the F ₂ region and sporadic E layer at midlatitude (wave-enhanced sporadic E). Thermospheric winds are also reviewed and wind effects on the F ₂ layer are discussed. For each atmospheric event systematic observations of suitable physical quantities with proper time and spatial intervals are desirable.     

Aircraft with outboard horizontal stabilizers,history, current status,development potential

The potential of using outboard horizontal stabilizers (OHS) to reduce aircraft drag, and hence improve fuel economy, was investigated historically, experimentally and theoretically. The feasibility of OHS configurations on the basis of the structural stress levels expected was also studied. The findings of the work showed that from simple, low Reynolds number, wind-tunnel tests, at a wing-chord-based Reynolds number of approximately 6×10⁴ and also from theoretical analyses for a higher Reynolds number of 9×10⁶, lift/drag (L/D) value increases in the region of 40–50% for wing and tail surfaces can be expected relative to corresponding values for conventional aircraft. When account is taken of fuselage and tail-support boom drag, the expected overall L/D increase is in the region of 30–35%. The analytical stress-level work showed that contrary to what, on a first thought basis, might be expected, there were no major stress problems. Flight tests at the University of Calgary, and by others elsewhere, employing radio-controlled, powered, model aircraft (i.e. UAVs) showed that aircraft of the OHS type were easily controlled in flight and were stable. An examination was made of additional areas that may contribute yet further to the development of the OHS concept.     

高频高速流体振荡器工作特性

设计了一种新型高频高速流体振荡器,并采用热线风速仪、高频动态压力传感器等测量手段,对其频率-压力响应特性、速度-压力响应特性及内部压力传播特性进行了实验研究。结果表明:设计的流体振荡器工作频率约为900 Hz,进出口压比为2时,其出口射流速度范围为75~239 m/s。建立了振荡周期/频率与内部尺寸的关系式,验证了振荡器内部的压力传播与反射机制,并用压力的作用机制解释了射流偏转的两个阶段,为今后设计不同流动条件下所需的流体振荡器提供了设计思路。      

Effects of Superthermal Particles on Waves in Magnetized Space Plasmas

Distributions with excess numbers of superthermal particles are common in space environments. They are well modelled by the isotropic kappa distribution, or, where magnetic effects are important, the kappa-Maxwellian. This paper presents a review of some studies of electrostatic and electromagnetic waves in such plasmas, based on the associated generalized plasma dispersion functions, Z _κ and Z _κM. In particular, the effects of low values of κ are considered, i.e. strongly accelerated distribution functions. Recently the full susceptibility tensor for oblique propagation of electromagnetic waves in a kappa-Maxwellian magnetoplasma has been established and has been applied to the study of whistler waves.     

冷气喷射法控制激波强度的数值研究

对冷气喷射时激波受到的影响进行了多方案数值研究.在高压级静叶吸力面反射激波生成点前后5个不同位置上采用相同总压及相同温度的冷气喷射,分析了不同位置的冷气喷射对激波强度和方向影响.结果表明:在吸力面激波折射点附近喷射冷气是一种行之有效的控制激波强度的方法.冷气喷射位置位于激波折射点附近时能够对激波的强度产生影响,在接近激波折射点前部位置注入冷气对流动有积极作用,减弱了激波.      

Substorm-associated injections of energetic ions observed by GEOS-1 and ATS-6 in and near synchronous altitude

Energetic ion measurements of GEOS-1 and ATS-6 are analysed for the period of geomagnetic activity following the arrival of a solar wind shock at 0027 UT on July 29, 1977. GEOS crossed the magnetopause at 6.9 R _E and 0027 UT (1312 LT). Although the difference in local time to ATS at 6.6 R _E is only 2 h ATS seems to remain well inside the magnetopause. During the second orbital pass on this day GEOS crossed the geostationary orbit at the onset time of a major substorm developing at 1120 UT. At this time the local time difference of GEOS and ATS was 12 h. The considerably different energy dispersions are discussed. An azimuthal anisotropy of approximately 20% observed in the GEOS data is interpreted to be the result of a particle density gradient.NOAA-SEL, Boulder, Colo., U.S.A.     

The Search Coil Magnetometer for THEMIS

THEMIS instruments incorporate a tri-axial Search Coil Magnetometer (SCM) designed to measure the magnetic components of waves associated with substorm breakup and expansion. The three search coil antennas cover the same frequency bandwidth, from 0.1 Hz to 4 kHz, in the ULF/ELF frequency range. They extend, with appropriate Noise Equivalent Magnetic Induction (NEMI) and sufficient overlap, the measurements of the fluxgate magnetometers. The NEMI of the searchcoil antennas and associated pre-amplifiers is smaller than 0.76 pT $/\sqrt{\mathrm{Hz}}$ at 10 Hz. The analog signals produced by the searchcoils and associated preamplifiers are digitized and processed inside the Digital Field Box (DFB) and the Instrument Data Processing Unit (IDPU), together with data from the Electric Field Instrument (EFI). Searchcoil telemetry includes waveform transmission, FFT processed data, and data from a filter bank. The frequency range covered depends on the available telemetry. The searchcoils and their three axis structures have been precisely calibrated in a calibration facility, and the calibration of the transfer function is checked on board, usually once per orbit. The tri-axial searchcoils implemented on the five THEMIS spacecraft are working nominally.     

On ULF Signatures of Lightning Discharges

Recent works on magnetic signatures due to distant lightning discharges are reviewed. Emphasis is laid on magnetic signatures in the ULF range (in the old definition from less than 1 mHz up to 1 Hz), that is in the frequency range below the Schumann resonance. These signatures are known to be of importance for the excitation of the ionospheric Alfvén resonator (IAR) which works only at night time conditions. This emphasizes the difference between night and day time ULF signatures of lightning. The IAR forms a link between the atmosphere and magnetosphere. Similarities and differences of this link in the VLF (Trimpi effect) and ULF range are worked out. A search for a unique signature of sprite-associated positive cloud-to-ground (⁺CG) lightning discharges ended with a negative result. In this context, however, a new model of lightning-associated induced mesospheric currents was built. Depending on mesospheric condition it can produce magnetic signatures in the entire frequency range from VLF, ELF to ULF. In the latter case it can explain signatures known as the Ultra Slow Tail of ⁺CG lightning discharges. A current problem on the magnetic background noise intensity has been solved by taking more seriously the contribution of ⁺CG lightning discharges to the overall background noise. Their low occurrence rate is more than compensated by their large and long lasting continuing currents. By superposed epoch analysis it could be shown that the ULF response to ^?CG is one to two orders smaller that in case of ⁺CG with similar peak current values of the return stroke.