V. A. Troitskaya: the Founder of the Russian School of Geomagnetic Pulsations

A thorough investigation of short-period oscillations in the Earth’s magnetic field as a fundamental natural process of the magnetospheric plasma began in Russia after V.A. Troitskaya established two oscillatory regimes in the geomagnetic field, namely, the regimes of continuous (Pc) and irregular pulsations (Pi). For studying these pulsations, 19 stations recording the telluric currents were installed during the International Geophysical Year (IGY, 1957–1959) on Troitskaya’s initiative. One of these stations was the Borok station. Subsequently, Borok has become the basic site for investigating geomagnetic pulsations and the main center for studying the short-period pulsations (SPPs) in the Earth’s magnetic field. This is the Borok scientific station where the key fundamental regularities of different types of geomagnetic pulsations were established. Troitskaya led and actively participated these works. Troitskaya organized and conducted the first complex geomagnetic observations in the world at the conjugate points Sogra (Arkhangelsk region, Russia) and Kerguelen (Indian Ocean). These studies were initially tested at the Borok observatory, where it was established that the wave packets of Pc1 geomagnetic pulsations are alternately observed in the northern and southern hemispheres in contrast to the other pulsation types which simultaneously occur in both hemispheres. The studies carried out at Borok promoted the establishment of a new direction in geophysics—diagnostics of the state of the magnetosphere based on the ground observations of geomagnetic pulsations. The analysis of simultaneous observations of the geomagnetic pulsations at polar latitudes of the Arctic and Antarctic was also for the first time conducted at the Borok observatory. This analysis revealed the main characteristics of wave phenomena at the geomagnetic poles and in the vicinity of the projection of the dayside polar cusp. Thus, for the first time in the world, Troitskaya and her Borok colleagues established the key patterns of the oscillatory regimes in the geomagnetic field of the Earth. This laid the basis for the further experimental and theoretical investigations which have shown that SPPs play a leading role in the dynamics of the magnetospheric plasma. In this paper we also list of 60 of Troitskaya’s main publications.     

An Overview of Thunderstorm-Related Research on the Atmospheric Electric Field, Schumann Resonances, Sprites, and the Ionosphere at Sopron, Hungary

This paper gives a resume of the papers written in English which (a) describe some of the recording instruments in use at the Nagycenk Observatory (NCK) since the International Geophysical Year (IGY 1957–1958) and up to the present time, (b) summarise the most important and different types of observations associated with thunderstorms which have been made there, and (c) discuss their various geophysical interpretations. The paper describes the main results which have been obtained in four areas of thunderstorm associated atmospheric and geospace science within the context of Earth system science. These relate to the following parameters of atmospheric electricity: the vertical electric potential gradient just above the Earth’s surface and the air–Earth current as well as the point discharge current, Schumann resonance (SR) signals of the Earth-ionosphere cavity at 8, 14 and 20 Hz, transient luminous events (TLEs), and some aspects of the behaviour of the ionosphere. Deductions from these data sets are concerned with the global lightning activity and the conductivity of the air, with diurnal, seasonal, annual and long-term variations of the SR amplitudes and resonant frequencies in terms of migrating thunderstorm centres, with transient SR excitations and with sprites and other TLEs, and with ionospheric disturbances. The paper closes with some thoughts on future research directions based on the observations at NCK and Sopron and the results achieved since the IGY.     

Results of Crust and Mantle Soundings in Central and Northern Europe in the 21st Century (Review)

The first decade of 21st century is characterized by the appearance of new approaches to deep induction soundings. The theory of magnetovariation and magnetotelluric soundings was generalised or corrected. Spatial derivatives of response functions (induction arrows) were obtained for the ultra-long periods. New phenomena have been detected by this method: secular variations of the Earth’s apparent resistivity and the rapid changes of induction arrows over the last 50 years. The first one can be correlated with the number of earthquakes, and the second one–with geomagnetic jerks in Central Europe. The extensive studies of geoelectrical structure of the crust and mantle were realized in the frame of a series of international projects. New information about geoelectrical structures of the crust in Northern Europe and Ukraine was obtained by deep electromagnetic soundings involving controlled powerful sources. An influence of the crust magnetic permeability on the deep sounding results was confirmed.     

Planetary features of aurorae: Results of the IGY (a review)

In the period of the International Geophysical Year (IGY), almost the entire planet was covered for the first time by ground-based geophysical observations. Their analysis led to two fundamental results: the existence of the auroral oval and auroral (magnetospheric) substorm. At the final stage of the IGY, satellite explorations of the near-Earth space began. The auroral luminosity appeared to be related to the plasma structure of the magnetosphere. That opened new possibilities for parameters diagnostics of the Earth’s magnetosphere on the basis of ground-based aurora observations. The concepts of auroral oval and magnetospheric substorm became paradigms of the new science of solar-terrestrial physics.     

Water resources and the sustainable development of humankind: International cooperation in the rational use of freshwater-lake resources: Conclusions from materials of foreign studies

The current and future state of the Earth’s water resources under present-day trends in water use is discussed. The activity of international institutions in the organization of management of lake ecosystems and drainage basins was analyzed from the viewpoint of sustainable development. The work of International Committee on Lake Environment, International Joint Commission (USA and Canada), International Commission on Lake Constance Protection, Autonomous Bilateral Management of Lake Titicaca, Commission on Chad Lake Basin, and Fishery Organization of Lake Victoria. Recommendations are proposed for the organization of international management of water bodies and their drainage basins.     

Geoelectromagnetic Oscillations

A hundred years have passed since the outstanding scientist Professor V.A. Troitskaya was born. This paper is dedicated to her centenary. It discusses her scientific contributions to studying ultralow frequency oscillations of the Earth’s electromagnetic field. The discussion covers permanent and sporadic oscillations, “pearl necklace,” pulsations of increasing frequency, specific oscillations observed in the Arctic and Antarctic. The paper also describes the current state of the scientific problems that were Professor Troitskaya’s focus of interest. Particular attention is given to the key role of the interplanetary magnetic field in forming the spatial-temporal structure of oscillations.     

Integration of space geodesy: A US National Geodetic Observatory

In the interest of improving the performance and efficiency of space geodesy a diverse group in the US, in collaboration with IGGOS, has begun to establish a unified National Geodetic Observatory (NGO). To launch this effort an international team will conduct a multi-year program of research into the technical issues of integrating SLR, VLBI, and GPS geodesy to produce a unified set of global geodetic products. The goal is to improve measurement accuracy by up to an order of magnitude while lowering the cost to current sponsors. A secondary goal is to expand and diversify international sponsorship of space geodesy. Principal benefits will be to open new vistas of research in geodynamics and surface change while freeing scarce NASA funds for scientific studies. NGO will proceed in partnership with, and under the auspices of, the International Association of Geodesy (IAG) as an element of the Integrated Global Geodetic Observation System project. The collaboration will be conducted within, and will make full use of, the IAG's existing international services: the IGS, IVS, ILRS, and IERS. Seed funding for organizational activities and technical analysis will come from NASA's Solid Earth and Natural Hazards Program. Additional funds to develop an integrated geodetic data system known as Inter-service Data Integration for Geodetic Operations (INDIGO), will come from a separate NASA program in Earth science information technology. INDIGO will offer ready access to the full variety of NASA's space geodetic data and will extend the GPS Seamless Archive (GSAC) philosophy to all space geodetic data types.     

The influence of the participation in the igy/igc programmes on present-day czechoslovak geophysics

Conclusion The present paper was written on the occasion of the 20th anniversary of the world-wode scientific venture called the International Geophysical Year and the International Geophysical Cooperation. The participation of Czechoslovakia was active and successful. The two following decades were, so to say, stigmatized in this country by the spirit of the IGY, the spirit of devotion and skill, as Sydney Chapman said. The quantitative growth of the staff, laboratories and working teams was, of course, significant. More significant, however, was the change in the minds of the geophysicists toward a deeper understanding of the difficult problems of the Earth. This understanding requires a closer co-operation in many fields, a gradual amalgamation along the contacts of the individual disciplines of the Earth's sciences. Ten years ago, for the first time, man touched the Moon and opened a new epoch. Geophysics will continue to develop in the new epoch, too. The author wishes the human generations, who will be living in the new epoch, good luck.     

Manifestation of the Lunar–Solar Tide and Free Oscillations of the Earth in the Variations of the Magnetic Field

The results of processing and analyzing the instrumental observations of the Earth’s magnetic field at the Geophysical Observatory Mikhnevo of the Institute of Geosphere Dynamics of the Russian Academy of Sciences (IGD RAS) for 2010–2015 are presented. Quasi-harmonic components with the periods close to the lunar–solar tidal waves are revealed in the spectra of geomagnetic variations over a period of 0.4 to 30 days. The elliptical S₁ tidal wave which is detected in the geomagnetic variations has modulations with periods of 1/3, 1/2, and 1 year. The spectra of the geomagnetic variations contain peaks corresponding to the free oscillations of the Earth. The analysis of the time series of the magnetic field for the period of the strong earthquakes in the absence of geomagnetic disturbances revealed the fine structure of the Earth’s fundamental spheroidal mode ₀S₂, which splits into five singlets. The established features of the spectrum of geomagnetic variations are helping the development of the new method for studying the deep structure of the Earth and the properties of the inner geospheres for estimating the viscosity of the Earth’s outer core and dynamics of the current systems in the outer (liquid) core, as well as for exploring, with the use of empirical data, the general regularities governing the regimes of energy exchange processes in the geospheres.     

Portable generator for deep electromagnetic soundings and monitoring of seismically active zones with the use of industrial power transmission lines

The structure and a possible practical application of the portable generator with extremely and super low frequency (ELF-SLF) range (0.1–200 Hz) and power of 2 kW are described. The generator is designed for deep sounding of the Earth’s crust for the purposes of mineral exploration and electromagnetic monitoring of source zones of earthquakes in seismically active regions. Computational and theoretical works, as well as numerical simulation for optimizing the generator’s parameters and element base, are carried out. The main constructive elements of the generator, namely, the power factor corrector, the driver control circuit for power transistors, the inverter of the high-frequency decoupling converter, the multichannel pulse power converter, the output inverter, and etc., are consistently described. The generator’s weight does not exceed 10 kg, and, therefore, the generator may be easily delivered to a testing site using any kind of transport, including planes. The generator is powered by the single-phase network with a voltage of 220 V. The full-scale testing of the generator is performed at the territory of the Yamalo-Nenets autonomous okrug via the connection to the high-voltage transmission line Urengoi-Pangody with a length of 114 km. The maximum current in the line is 12 A. The maximum distance of reliable signal recording is 110 km.     

Surface Wave Tomography of the Arctic from Rayleigh and Love Wave Group Velocity Dispersion Data

Izvestiya, Physics of the Solid Earth - The results of studying the deep structure of the Earth’s crust and upper mantle of the Arctic from surface wave data are presented. For this purpose,...     

Deep electrical conductivity features in the transition zone from the Pacific to Eurasia

Understanding the processes that occur in the transition from the Pacific Ocean to Eurasia is key to constructing the tectonic models of the Earth’s shells and the convection models of the upper mantle. The electromagnetic methods permit estimating the temperature and fluid content (and/or carbon (graphite) content) in the Earth’s interior. These estimates are independent of the traditionally used estimates based on seismic methods because the dependence of electrical conductivity on the physical properties of the rock is based on different principles than the behavior of the elastic waves. The region is characterized by a complicated geological structure with intense three-dimensional (3D) surface heterogeneities, which significantly aggravate the retrieval of the information about the deep horizons in the structure of the Earth’s mantle from the observed electromagnetic (EM) fields. The detailed analysis of the nature of the deep electrical conductivity and structural features of the transition from the Pacific to Eurasia included numerical modeling of the typical two- and three-dimensional models has been carried out. Based on this analysis, the approaches that increase the reliability of the interpretation of the results of the EM studies are suggested.     

The State of the Art in Studying the Deep Structure of the Earth’s Crust and Upper Mantle beneath the Baikal Rift from Seismological Data

Izvestiya, Physics of the Solid Earth - Abstract—This review discusses the major milestone results yielded by the regional seismological studies of the deep structure of the Earth’s...     

Tutorial review of seismic surface waves’ phenomenology

In recent years, surface wave seismology has become one of the leading directions in seismological investigations of the Earth’s structure and seismic sources. Various applications cover a wide spectrum of goals, dealing with differences in sources of seismic excitation, penetration depths, frequency ranges, and interpretation techniques. Observed seismic data demonstrates the great variability of phenomenology which can produce difficulties in interpretation for beginners. This tutorial review is based on the many years’ experience of authors in processing and interpretation of seismic surface wave observations and the lectures of one of the authors (ALL) at Workshops on Seismic Wave Excitation, Propagation and Interpretation held at the Abdus Salam International Center for Theoretical Physics (Trieste, Italy) in 1990–2012. We present some typical examples of wave patterns which could be encountered in different applications and which can serve as a guide to analysis of observed seismograms.     

金星:认识早期地球的窗口

无论在行星大小、质量还是轨道速度等方面,金星都是太阳系中与地球最相似的行星.自1960年代初期开始,金星一直是人类深空探测的重要目标.本文简要地回顾了人类探索金星的历史,总结了对金星已有的认识,梳理了金星的主要科学问题,最后介绍了未来的国际探测计划,并建议了我国的金星探测目标.早期对金星的探测以苏联的金星计划(Венера)和美国的水手系列(Mariner)为代表,后期的探测器以欧盟、日本等国家的“金星快车(Venus Express)”、“拂晓号(Akatsuki)”为代表.这些探测结果为我们认识金星大气成分、地表地形和内部结构提供了重要的数据.金星的大气组成以CO₂为主,含少量N2,与现在地球的大气组成显著不同,类似早期地球的大气组成.虽然金星地表目前没有液态水,但部分理论模拟工作表明金星地表可能曾经有液态水.一系列探测器对金星地表成分的分析表明,金星地表主要由玄武岩组成.在地形地貌方面,由于金星特殊的地表环境,金星表面风化作用对地表地貌影响很小.金星的地表主要受控于比较年轻的火山作用,发育了许多不同于地球的地貌特征,主要包括区域平原、盾状火山平原、冕状地形以及瓦片状地形等,其动力学机制可能是地幔柱—岩石圈相互作用或地幔对流,至今未发现与板块构造相关的地貌.现阶段金星没有太多大型的、活跃的火山热点,虽然无法估测准确的火山活动速率,但相比地球来说火山活动速率小很多.在内部结构方面,金星具有与地球类似的核幔壳结构.金星的内部组成也与地球类似,例如金星地幔很可能是与地球相似的橄榄岩成分.不存在内部磁场和缺乏板块构造是金星区别于地球的两个重要特征.关于金星为什么没有自身磁场,主流观点是金星地核缺乏对流,无法演化出磁场.而针对金星为什么没有演化出板块构造,目前认为主要有三个可能的原因:地表温度过高,没有软流圈,金星缺乏液态水,其中液态水的缺乏接受度最广.从大气组成、地表岩石组合、构造作用等角度来看,金星都与早期地球非常相似,是我们理解类地行星演化的天然实验室.研究金星和地球为什么会朝不同方向演化,是深入理解包括系外行星在内的行星的宜居性形成与演变的重要途径。因此,金星一直是优先级别最高的深空探测目标之一.近几年,美国、俄罗斯以及欧洲等国家和地区分别针对金星目前主要的科学问题,例如金星是否存在早期海洋、金星的宜居性以及结构和重力场等,先后提出各自的金星探测计划.我国在新的国际竞争中应该、也必然有所作为.     

The discovery and the first studies of the auroral oval: A review

The auroral oval concept radically changed the view that existed for a century in geophysics on the patterns in aurora planetary spatial–temporal distributions. The auroral zone, which is located around the geomagnetic pole as a continuous ring at a constant angular distance of ~23°, was replaced by the auroral oval in 1960. The auroral oval spatial position reflects the shape of the Earth’s magnetosphere, which is compressed by the solar wind on the dayside and stretches into the magnetotail on the nightside. The oval is fixed relative to the direction toward the Sun and is located around the geomagnetic pole at altitudes of the upper atmosphere at an angular distance of ~12° at noon and ~23° at midnight. After an animated discussion over several subsequent years, the existence of the auroral oval was accepted by the scientific community as a paradigm of a new science, i.e., solar–terrestrial physics. The oval location indicates the zone where electron fluxes with energies varying from ~100 eV to ~20 keV precipitate into the upper atmosphere and is related to the structure of plasma domains in the Earth’s magnetosphere. The paper describes the scientific studies that resulted in the concept of the auroral oval existence. It has been shown how this concept was subsequently justified in the publications by Y.I. Feldstein and O.B. Khorosheva. The issue of the priority of the auroral oval concept introduction into geophysics has been considered. The statement that the concept of the oval is an archaic paradigm of solar–terrestrial physics has been called into question. Some scientific fields in which the term auroral oval or simply oval was and is the paradigm have been listed.     

Cyclic variations in the Earth’s flattening and questions of seismotectonics

For more than a decade, the global network of GPS stations whose measurements are part of the International GPS Service (IGS) have been recording cyclic variations in the radius vector of the geodetic ellipsoid with a period of one year and amplitude of ~10 mm. The analysis of the figure of the Earth carried out by us shows that the observed variations in the vertical component of the Earth’s surface displacements can induce small changes in the flattening of the Earth’s figure which are, in turn, caused by the instability of the Earth’s rotation. The variations in the angular velocity and flattening of the Earth change the kinetic energy of the Earth’s rotation. The additional energy is ~10²¹ J. The emerging variations in the flattening of the Earth’s ellipsoid lead to changes in the surface area of the Earth’s figure, cause the development of deformations in rocks, accumulation of damage, activation of seismotectonic processes, and preparation of earthquakes. It is shown that earthquakes can be caused by the instability of the Earth’s rotation which induces pulsations in the shape of the Earth and leads to the development of alternating-sign deformations in the Earth’s solid shell.     

Energetic Charged Particles Above Thunderclouds

The French government has committed to launch the satellite TARANIS to study transient coupling processes between the Earth’s atmosphere and near-Earth space. The prime objective of TARANIS is to detect energetic charged particles and hard radiation emanating from thunderclouds. The British Nobel prize winner C.T.R. Wilson predicted lightning discharges from the top of thunderclouds into space almost a century ago. However, new experiments have only recently confirmed energetic discharge processes which transfer energy from the top of thunderclouds into the upper atmosphere and near-Earth space; they are now denoted as transient luminous events, terrestrial gamma-ray flashes and relativistic electron beams. This meeting report builds on the current state of scientific knowledge on the physics of plasmas in the laboratory and naturally occurring plasmas in the Earth’s atmosphere to propose areas of future research. The report specifically reflects presentations delivered by the members of a novel Franco-British collaboration during a meeting at the French Embassy in London held in November 2011. The scientific subjects of the report tackle ionization processes leading to electrical discharge processes, observations of transient luminous events, electromagnetic emissions, energetic charged particles and their impact on the Earth’s atmosphere. The importance of future research in this area for science and society, and towards spacecraft protection, is emphasized.