ULF/ELF monochromatic oscillations observed by Prognoz-8 and -10 spacecrafts during quasiperpendicular supercritical shock crossings

The present paper analyses electromagnetic turbulence in the frequency range 0.1-75 Hz, associated with the supercritical quasiperpendicular crossings of the Earth’s bow shock recorded by the Prognoz-8 and -10 satellites. The quasimonochromatic waves are identified in the shock transition region. Their frequencies, lying in the range 2–5 Hz upstream from the shock ramp, shift to a value less than 1 Hz in the downstream region. The amplitudes of these narrow emissions are great enough to provide the primary dissipation in the flow of the solar wind plasma. Electromagnetic oscillations with such properties are likely to be generated during non-linear evolution of the shock front, rather than by the instabilities driven by ion and electron drifts. Emissions with frequencies higher than 5 Hz have much smaller amplitudes and may be driven by lower hybrid-like instabilities.     

ELF and VLF electric field measurements with the Interkosmos 10 satellite

Summary The ELF-VLF experiment onboard the Interkosmos 10 satellite consisted mainly of a broadband receiver covering the frequency range from 20 Hz to 22 kHz. The signal level in this broad band has also been measured, as well as the level in two narrow bands with centre frequencies of 720 Hz and 4 kHz. The electric component of the ELF-VLF fields has been measured by using an electric dipole antenna, 2.35 m in length. The purpose of this paper is to characterise the data obtained by the broadband RTT transmissions at the Panská Ves station during the seven-months active period of the satellite. The spectral analysis of all broad-band ELF-VLF recordings has been used. Examples of some typical phenomena, most frequently observed at different invariant latitudes are given.     

Observations of Pc5 micropulsation-related electric field oscillations in the equatorial ionosphere

A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5○N, 77○E, 0.5○N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (A_p=161). Simultaneous 100-nT-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6○N gm) and at Narsarsuaq, Greenland (70.6○N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730–1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV m⁻¹ and it increases with height, while it is about 1.0 mV m⁻¹ in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brorfelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the associated ionospheric electric field penetrating from high latitudes to the magnetic equator.     

ULF electric and magnetic anomalies accompanying the cracking of rock sample

The anomalies of electric-magnetic field and self-potential before earthquakes are important precursory phenom-ena.A simulating experiment study on the variations in ultra-low frequency(ULF)magnetic field and self-poten-tial during rock cracking was carried out in a magnetic field-free space.The results revealing in detail the whole process of the occurrences of electric and magnetic anomalises are significant for understanding the microscopic mechanism of ULF electric and magnetic signals.The experiment indicated that at the initial stage the slow changes in strain.self-potential and magnetic field with small amounts appeared firstly near the source of initial cracking,and then extended as the crack developed on.In the time domain,the self-potential anomaly emerged first and ULF magnetic field changes arose then.The shape of the ULF electric and magnetic anomaly varied ob-viously in early-,mid-and late-term of the test.The authors attributed the pulse-like changes of self-potential to the generationj and movement of the accumulated electric charges during the cracking caused by charge separation on the crack tips within the sample.While the magnetic pulses of shorter-period at the last stage of the test,may be induced by instantaneous electric current of the accumulated charege during the cracking acceleration.The technical method and the observational results of this experiment are given in detail and the microscopic mechanism of elec-tric and magnetic precursors before earthquake are discussd in the present paper as well.     

On the stationary electric field in the air surface layer

Summary The solution of the ionization balance equation is found in the surface air layer at horizontal homogeneity assuming an exponential law for the turbulent diffusion coefficient. Expressions describing the vertical distribution of the small ion concentration are found estimating on their basis the layer height by an electrode effect. A relation is found among the small ion concentration, the electric conductivity and the electric field in the surface layer.     

Excitation and absorption of ULF oscillations studied by high-latitude Doppler radar data

Maps for standard deviations of the drift velocity of E layer ionosphere electrons in the radar field of vision were constructed with the aid of narrowband and low-pass filtering based on STARE Doppler data. In these maps, narrowband filtering reveals the geometric configurations of the excitation of particular ultralow-frequency (ULF) oscillations. Such a configuration indicates nonresonant origins of these oscillations. Low-pass filtering of the Doppler data revealed specific absorption of background ULF signals; this absorption is attributed to the resonance of magnetic field lines. Quantitative estimates for minimum frequencies of the resonant ULF absorption occurring in the eigenfrequency continuum of magnetic field lines were found.     

On the connection between the atmospheric electric field measured at the surface and the ionospheric electric field in the Central Antarctica

Regular measurements of the atmospheric electric field made at Vostok Station (φ=78.45°S; λ=106.87°E, elevation 3500 m) in Antarctica demonstrate that extremely intense electric fields (1000–5000 V/m) can be observed during snow storms. Usually the measured value of the atmospheric electric field at Vostok is about 100–250 V/m during periods with “fair weather” conditions. Actual relation between near-surface electric fields and ionospheric electric fields remain to be a controversial problem. Some people claimed that these intense electric fields produced by snowstorms or appearing before strong earthquakes can re-distribute electric potential in the ionosphere at the heights up to 300 km. We investigated interrelation between the atmospheric and ionospheric electric fields by both experimental and theoretical methods. Our conclusion is that increased near-surface atmospheric electric fields do not contribute notably to distribution of ionospheric electric potential.     

强震前ELF/VLF磁场的扰动特征统计研究

本文利用DEMETER卫星记录的变化磁场数据统计研究了2005—2009年北半球7级以上强震前后空间磁场的扰动特征.在震中±10°范围内利用震前2个月至震后1个月的5年同期观测的ELF/VLF[370~897 Hz]频段磁场功率谱密度数据构建了背景场,定义了表征空间磁场在地震时段相对于背景场的扰动幅度指标.统计研究发现26个强震中42%的地震主要表现为震前磁场扰度幅度逐渐上升,超过3倍标准差,随后在扰度幅度下降过程中发震.35%强震在地震前10天内最大扰动幅度超过3倍标准差,在扰度幅度处于最高值期间发震,震后磁场扰动幅度逐渐回落.23%的强震在震前震后无明显规律.随机事件测试发现在空间天气平静且无强震条件下随机地点上空的磁场无明显的时空演化规律,且随机地点上空的空间磁场相对于背景场的平均扰度幅度很小,最大扰度幅度从未超过2倍标准差,并且没有明显的随时间变化特征.     

Some basic electromagnetic aspects of ULF field variations in the atmosphere

Recent analytical studies of ULF (ultra low frequency) electromagnetic fields in the atmosphere are reviewed. These fields have their origin in the discharging of thunderclouds and the interaction with the conductive atmosphere determines the resultant behavior. It is important that this interaction process be understood if observations are to be correctly interpreted in terms of the thunderstorm discharge process. Various theoretical approaches that have appeared in the literature are appraised and suggestions for further work are made.     

Phase variations of ULF magnetic field in the region of fault tectonics

The experiment on phase measurements of three components of a ULF magnetic field generated by a high-power controlled source in the region dominated by fault tectonics is described. The measurements were carried out along two orthogonal directions. It is established that the phase sharply varies by about 180° between some measurement points. The phase jumps are found to be confined to the conductive geological faults, which opens the possibility of locating the faults using the phases of ELF magnetic fields.     

Tidal effects in the controlled-source ULF electromagnetic field on the Baltic crystalline shield

The results of the experiment on studying the dynamics of the electromagnetic field (EM) generated by the stationary controlled ULF-band source during 30 days on the Baltic crystalline shield are presented. Diurnal variations in the EM fields and slow variations in the surface impedance with a period of about 14 days are revealed. The diurnal variations in the fields are mainly due to the fluctuations in the ionospheric parameters caused by the changes in the daytime ionization of the ionosphere by solar radiation. By comparing the harmonic component with a period of about 14 days, which was established in the time series of surface impedance, with the slow tidal deformations of the Earth’s crust, we revealed the correlation between the EM variations and tidal processes in the Earth. The estimates for the probable changes induced by tidal deformations in the structure and conductivity of the underlying medium are obtained by modeling.     

深井电极与地表电极的自然电场对比研究

通过对半无限空间和全无限空间电流密度的分布理论进行讨论,得出电流密度随电极埋设深度的增大而减小。因此,在电法观测中,当供电电极深埋后,人工电场和自然电场可减少地表各种噪声的干扰,提高视电阻率ρｓ和自然电位Ｖｓｐ的灵敏度,从而更好地捕捉地城常信息。从北京平谷台６年多来的观测结果分析认为,深井电极相对地表电极能降低诸如人为供电、雷击短路、冰冻期影响等各种干扰,经过宁河６．９级、６．５级和５．６级及离     

DEMETER卫星监测的极低频和超低频电磁场数据分析

分析了DEMETER卫星上测量的极低频(ELF, 3—30 Hz)和超低频(SLF, 30—300 Hz)水平磁场. 其统计变化规律与地面上实测的此频段大气噪声变化规律一致, 并且数值差异也符合电波传播规律, 说明卫星上监测的电磁场来源于地面. 同时对DEMETER卫星上测量的ELF和SLF归一化波阻抗进行了深入地分析, 由电子密度与离子密度计算出的归一化波阻抗与由实测电磁场计算出的归一化波阻抗均有差异. 现有观测资料并不完全“自洽”, 尚有问题需深入研究.     

Influence of a convective generator on the diurnal behavior of the electric field strength in the near-Earth atmosphere in Kamchatka

Diurnal variations in the electric field strength, electrical conductivity, and temperature in the near-Earth atmosphere under “fair-weather” conditions at the Paratunka observatory (Kamchatka) are considered. It is shown that the morning maximum in the electric field diurnal behavior is caused by air convection in the near-surface layer. The difference in the atmospheric temperatures near the Earth’s surface and at an altitude of 25 m is chosen as a measure of the convective air flow. A high correlation of the values of the temperature difference for these altitudes with the diurnal behavior of the electric field strength is obtained.     

地球电场与地球磁场的形成机理

为探讨地球磁场的形成机理,应用经典电磁理论以微分的思维方式建立起三种自激发电机模型,用球形自激发电机模型简明地描述地球磁场的形成和分布;从分析地轴参考系中相对于自转地球静止的电荷间洛仑兹力的特点以及地球上的电荷在地球电场和地球磁场作用下的漂移规律,阐述中心磁场的形成及反转机理;分析电荷相对于地球的漂移以阐述偏磁场的形成.理论分析表明:地球上每一点的磁场都可以看成是由该点的几个分磁场叠加而成;地球具有自身的电场;地球电场与地球磁场同时产生、同时变化,且都源自于地球的自转和地球上正负电荷的非对等分布.     

Synchronism of long-period oscillations of the magnetic field in sunspots

It is shown that long-period (T = 10?C20 h) oscillations of the magnetic field in sunspots, combined in bipolar groups, are excited synchronously in the main and tail spots of a group. At the same time, there is no correlation between long-period oscillations of the field of sunspots which are in different active regions, i.e., spaced sunspots oscillate independently. This fact eliminates the question about the apparatus nature of the oscillations of interest (if there is an artifact, oscillations of all sunspots on the visible solar hemisphere would be synchronous!). High-resolution (0.5 angular seconds per pixel) MDI(SOHO) data show a high correlation between long-period oscillations of the magnetic field at isolated points of the sunspot shadow. This points to the fact that the sunspot shadow participates in long-period oscillations as a quite integral physical formation.     

Global variation in the atmospheric electric field

Summary An analysis of the global nature of the atmospheric electric field is presented on the basis of comparison of measurements on the research vessel, Hakuho-Maru, on the Mid- and South-Pacific Ocean, with those at Syowa Station in Antartica and on two vessels on the Mid-Atlantic Ocean. The comparison of daily averages gave a different type of latitude dependence, which was characterized by a gradual decrease toward the antarctic region. Diurnal variations at these globally representative stations on the same day were checked with each other for the first time, and the correlation between them was found much higher than that between land stations. The regional effect, which might depend on the distance from the thunderstorm area, was not evidently detected. So the influence of the generator area was considered to propagate over the entire globe without significant attenuation.

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Zusammenfassung Auf der Grundlage von Vergleichen zwischen Messungen an Bord des Forschungsschiffes Hakohu-Maru im mittleren und südlichen Pazifischen Ozean, an der antarktischen Forschungsstation Syowa und an Bord von zwei Forschungsschiffen im mittleren Atlantik wird eine Analyse der weltweiten Natur des luftelektrischen Feldes vorgelegt. Der Vergleich von Tagesmitteln ergab eine spezielle Abhängigkeit von der geographischen Breite, gekennzeichnet durch eine allmähliche Abnahme in Richtung auf den antarktischen Bereich. Die Tagesgänge an diesen weltweitrepräsentativen Stationen wurden zum ersten Mal untereinander für jeweils die gleichen Tage verglichen. Es wurde gefunden, dass die Korrelation zwischen ihnen weitaus grösser war als sie zwischen Landstationen ist. Ein regionaler Effekt, vermutbar in der Form einer Abhängigkeit von der Entfernung zur Gewitterzone, wurde nicht sicher gefunden. Deswegen wird angenommen, dass die Auswirkungen des Generatorbereichs sich über die gesamte Erde ohne merkliche Verminderung erstrecken.

     

直流电场对沉水植物苦草(Vallisneria natans)生长的影响

沉水植物对维持湖泊生态系统平衡有重要作用,广泛应用在水体和沉积物污染修复领域.利用电场强化沉水植物修复过程是一种新的植物修复强化方法.本文研究了不同电压强度作用下沉水植物苦草的生长和生理响应,以期为应用电场强化沉水植物修复过程提供依据.结果表明:0.2~1.0 V电压可以促进苦草生长,而1.5~3.0 V电压则会抑制其生长.其中,0.5 V电压对苦草生长的促进效果最明显,生物量、平均株高、平均叶长、根尖数、新芽数和总叶绿素含量都比对照组显著增加;而3.0 V电压处理组的苦草在实验结束时出现萎蔫和凋亡,与对照组相比,叶绿素含量显著降低,丙二醛含量则极显著增加,表明苦草生长受到严重胁迫.系统上覆水的温度在不同处理组之间没有显著变化,上覆水的p H值在电压为1.0、1.5和3.0 V时显著下降,最终接近中性,上覆水的溶解氧浓度只在3.0 V电压处理组时表现显著下降;沉积物表层5 cm处的氧化还原电位随着电压增大显著下降,最终对苦草的生长形成胁迫.因此,本实验的结论是:0.2~1.0 V电压有助于沉水植物苦草的生长和强化植物修复过程,而1.5~3.0 V电压会破坏苦草组织,同时导致苦草生境变差,不利于沉水植物苦草的生长.