A statistical investigation of polar auroras

Summary The magnetosphere depends on the astronomical orientation of the geomagnetic field with respect to the solar wind. The statistical distribution of polar auroras must therefore depend on the orientation of the geomagnetic field with respect to the ecliptic plane. We have investigated this peculiar feature of auroras that we call auroral astronomical geometry. We give here some preliminary results concerning a limited set of pre-IGY auroras. The criteria that we have chosen to prepare the auroral collection are also briefly summarized. The results conform to the hypothesis of the auroral origin from the magnetospheric neutral sheet. Auroral particles are found to impinge over the earth with low angles with respect to the ecliptic plane (40°). Only in a 4-hours interval around midnight they are found to impinge with angles up to 70°. Definite evidence of these facts requires further investigation with a larger amount of data. — We have also prepared a complex code for recording the morphological features of each aurora, namely: standard information, movement. intensity, color, sunlight illumination, period of pulsation, location in the sky among stars and planets, time evolution, duration and general features of the auroral display. It is well known in fact that the auroral morphology affects auroral heights and latitudes, etc.; presumably it should also affect its astronomical geometry, which we will investigate later.Presented at the Inter-Union Symposium on Solar-Terrestrial Physics — Belgrade 1966.     

Oceanic electromagnetic studies: A review

The review covers the main results of the oceanic electromagnetic studies presented during last 4–5 years. Seafloor electromagnetic observations are dedicated to studies in solid Earth geophysics and oceanography. Thus, a large range of objectives and targets are under investigation. Technological and theoretical advances provide an increase of quantity and quality of the collected seafloor data. The host conductivity models for oceanic crust and mantle are being developed; the possibility of obtaining useful structural constraints in heterogeneous environment are discussed. Significant oceanographic results were derived from electromagnetic field observations; these appeared to be a new powerful method for study of long-term large-scale ocean variability.     

A search for coastline effects on the auroras

A camera on board the Polar spacecraft has provided an unique opportunity to search for coastline effects on the spatial distributions of auroral emissions. This study is motivated by a ground-based report of such shoreline effects on auroral emissions during the Russian Polar Expedition of almost a century ago. This Polar camera, the Low-Resolution Visible Camera of the Visible Imaging System, is capable of obtaining auroral images of the Northern Hemisphere with high spatial and temporal resolutions for extended continuous periods of time, i.e., tens of km, one to several minutes, and many hours, respectively. The entire set of 8588 auroral images at OI 557.7 nm which were gathered during January 1997 were examined for three types of coastal effects, (1) diversion of the auroral arc at the shore, (2) increase of intensity as the arc is followed from sea to land, and (3) decrease of intensity from sea to land. A null test of the results of this auroral survey was conducted by a search of the entire set of images for random coincidences of auroral features in rotated maps of the coastlines. This null test provides support for the occasional transient existence of coastline effects during the onset and early expansion phases of auroral substorms and some auroral intensifications.     

Geochemistry and tectonic setting of alkaline volcanic rocks in the Antarctic Peninsula: A review

The numerous Miocene-Recent alkaline volcanic outcrops in the Antarctic Peninsula form a substantial volcanic province, the least well-known part of a major belt of alkaline volcanism that extends between South America and New Zealand. The outcrops consists mainly of aa and pahoehoe lavas and hyaloclastites which locally contain accidental nodules of spinel lherzolite and other mantle-derived lithologies. The province is predominantly basaltic with two major differentiation lineages: (1) a sodic series of olivine and alkali basalt, hawaiite, mugearite, trachy-phonolite and trachyte; and (2) a relatively potassic, highly undersaturated series of basanite, tephrite and phono-tephrite. All the lavas show varying effects of fractionation by crystallization of olivine and clinopyroxene, joined by plagioclase in the hawaiites to trachytes. Fractional crystallization can probably explain most of the chemical variation observed within each outcrop, but variable partial melting is necessary to account for the differences in incompatible element enrichment between the two series, and between the individual outcrops. The degree of partial melting may not have exceeded 3%, as is the case for many other alkaline magmas.The volcanism is an intraplate phenomenon but there is no correlation in timing between the cessation of subduction and the inception of alkaline volcanism. The activity cannot be related to the passage of the coupled Pacific-Antarctic plate over a stationary mantle hot-spot. Although the precise causal relationship with tectonic setting is unknown, regional extension was a prerequisite for giving the magmas rapid access to the surface.     

Features of morning-time auroras during SC

The optical observations on Heiss Island and the ion drift measurements on the DMSP F8 satellite were used to study the aurora characteristics and ionospheric convection before and after SC registered at 2330 UT on January 13, 1988. It has been indicated that two zones of luminosity can be distinguished in morning-time auroras during the quiet period before SC: the soft zone with auroral arcs and the harder diffuse auroral zone (equatorward of the first zone). After SC, a gradual smooth activation of auroras in both zones was followed (4–5 min later) by a more abrupt intensification of diffuse luminosity and by the appearance of numerous bright discrete auroras throughout the sky. In the diffuse auroral zone, the variations in the luminosity intensity with a period of 6–7 min were observed after SC. Auroral and geomagnetic field pulsations are closely correlated. During the quiet period before SC, sunward convection was concentrated in the soft precipitation region in the form of jets located in the vicinity of auroral arcs. After SC, considerable sunward convection was observed in the diffuse auroral zone. Peaks of the upward ion drift velocity were registered in the vicinity of auroral arcs.     

Low-latitude auroras: The great aurora of 4 February 1872

The aurora of 4 February 1872 was comparable to, and perhaps even greater than, that of 1/2 September 1859. In this paper we show that the aurora of 4 February 1872 was seen worldwide, and that in the Caribbean, Egypt, Southern Africa, the Indian Ocean, the Indian subcontinent, and China these observations extended as low as 20° magnetic latitude. Observations are also available in the north to as far as the vicinity of the north magnetic pole. This aurora is then comparable to, or greater than, in geographical extent, and in equatorward closeness, to that of 2 September 1859. Both must now be included as the only known members in the class of greatest auroras of the past few hundred years. For the 1859 aurora, however, there is no accepted observation at a lower magnetic latitude than about 20°. By contrast, several observations for the aurora of 4 February 1872 are reported at magnetic latitudes of the order of 10°, and one probable observation at an even lower magnetic latitude of about 3°. This paper presents a survey and discussion of these observations.     

Theoretical and numerical studies of chorus waves: A review

Theoretical and numerical models of chorus waves are reviewed in this paper. Specifically, we focus on the nonlinear wave particle interactions and the current understanding of the frequency chirping of rising tone chorus waves. Various other related topics, such as the optimal excitation condition of chorus, the formation of subpackets, and the non-adiabaticity of the nonlinear interaction are also discussed. We end this review paper with a short list of questions of chorus waves that are still under research and debate.     

Regional induction studies: A review of methods and results

The geomagnetic skin-effect is specified by setting three length scales in relation to each other: L₁ for the overhead source. L₂ for the lateral non-uniformity of the subsurface conductor, L₃ for the depth of penetration of a quasi-uniform transient field into this conductor. Relations for the skin-effect of a quasi-uniform source in layered conductors are generalized to include sources of any given geometry by introducing response kernels as functions of frequency and distance. They show that only those non-uniformities of the source which occur within a distance comparable to L₃ from the point of observation are significant. The skin-effect of a quasi-uniform source in a laterally non-uniform earth is expressed by linear transfer functions for the surface impedance and the surface ratio of vertical/horizontal magnetic variations. In the case of elongated structures and E-polarisation of the source, a modified apparent resistivity is defined which as a function of depth and distance gives a first orientation about the internal distribution of conductivity. The skin-effect of a non-uniform source in a non-uniform earth is considered for stationary and “running” sources. Recent observations on the sea floor and on islands indicate a deep-seated change of conductivity at the continent—ocean transition, bringing high conductivity close to the surface, a feature which may not prevail, however, over the full width of the ocean. There is increasingly reliable evidence for high conductivities (0.02 to 0.1 micro ^?1 m^?1) at subcrustal or even at crustal depth beneath certain parts of the continents, in some cases without obvious correlation to geological structure.     

Ground-based observations of auroras under the sunlit conditions

The results of the ground-based optical observations of sunlit auroras, performed at Lovozero and Apatity observatories on April 10 (event 1) and April 27, 2007(event 2), are presented. The observations were performed in the (OI) 557.7 nm emission, using a new equipment based on a Fabry-Pérot interferometer connected to a PhotonMAX CCD camera. During event 1, the observations were performed in the Harang discontinuity region at a low magnetic disturbance. It has been indicated that an auroral arc was located in the polar part of the eastward electrojet, and the arc position coincides with the equatorward boundary of structured precipitation (b2e). During event 2, auroras were observed within the average statistical boundaries of the auroral oval and the region of structured precipitation under the conditions of rather high geomagnetic activity. However, during the period of low geomagnetic activity, discrete auroras were registered at a geomagnetic latitude of ~64° on that day, which is 3°—4° equatorward of the structured precipitation region. Such a low latitudinal position of auroras can be explained by the effect of a high solar wind velocity, which was ~580 km/s during the period of observations.     

Numerical electromagnetic modeling including studies of characteristic dimensions: A review

Recent activity in important approximate methods used in numerical electromagnetic (EM) modeling is reviewed. Comparisons between the results obtained by different numerical methods and between analytical and numerical solutions are presented. The importance of 3D modeling and thin sheet approximations are pointed out.This review also considers and summarizes studies of characteristic dimensions in three topics: source fields, numerical modeling and physical phenomena in the earth and interpretation. The skin depth (i.e., generally the attenuation) of the EM energy is considered to be the most important and fundamental characteristic dimension.     

Interplanetary magnetic field By control of dayside auroras

The effect of the interplanetary magnetic field (IMF) By component on the dayside auroral oval from Viking UV measurements for March–November 1986 is studied. Observations of dayside auroras from Viking UV images for large positive (15 cases) and negative (22 cases) IMF By (∣By∣>4 nT), suggest that: (1) the intensity of dayside auroras tends to increase for negative IMF By and to decrease for positive By, so that negative IMF By conditions seem preferable for observations of dayside auroras; (2) for negative IMF By, the auroral oval tends to be narrow and continuous throughout the noon meridian without any noon gap or any strong undulation in the auroral distribution. For positive IMF By, a sharp decrease and spreading of auroral activity is frequently observed in the post-noon sector, a strong undulation in the poleward boundary of the auroral oval around noon, and the formation of auroral forms poleward of the oval; and (3) the observed features of dayside auroras are in reasonable agreement with the expected distribution of upward field-aligned currents associated with the IMF By in the noon sector.     

Magnetometer array studies: A review of the interpretation of observed fields

A magnetometer array study consists of a number of variometers recording simultaneously across a two-dimensional area. Data recorded by an array should satisfy certain criteria, showing that transient magnetic events have been thoroughly monitored on the plane of observation. Interpretation of such data in terms of solid-earth geophysics involves two separate classes of problem. In the first the local geoelectric structure changes over a shorter lateral distance than does the inducing field. The observed response of the local structure is modelled numerically, taking the inducing field to be uniform. The parameters modelled are relationships between regional and anomalous horizontal and vertical field components. Operation of many instruments in an array should give better estimates of these parameters than operation of instruments singly, or in small groups. Numerical models constructed to fit observed data are non-unique, though the wide frequency range of geomagnetic events may perhaps be used to greater advantage in distinguishing between conductors in the upper crust, lower crust, and upper mantle. In constructing models a further complication arises in distinguishing between conductors simply concentrating current induced elsewhere, and conductors in which the induction is itself taking place.The second class of problem comprises determination of conductivity as a function of depth, utilizing non-uniformity in inducing fields. Here a large array of instruments should enable estimation of field gradients more accurately than is possible with fewer instruments. Interpretations published to date have perhaps not exploited this aspect of array information as fully as might prove possible.Some miscellaneous comments are: (1) daily-variation data in particular could resolve some depth ambiguity problems; (2) there is confusion in the literature between two possible definitions of phase; (3) ideas on optimum station spacing are still evolving; (4) it is not easy to decide an optimum ratio for time spent collecting data to time spent interpreting data; (5) array data have relevance to the study of electric currents in the ionosphere.     

Simultaneous optical and satellite observations of auroras in the mantle: Case study

The all-sky camera data obtained in Barentsburg (Spitsbergen Archipelago) are compared with specific features of electron and ion precipitations on the DMSP F18 satellite during its flight within the camera field of view on December 15, 2012. Before arriving at the cusp from the mantle side, the satellite detects two outbursts of precipitating particles. The burst of mantle precipitations far from the cusp is observed simultaneously in both ionic and electronic components. In the ionosphere related to the satellite, no auroras are detected, which is likely due to the low intensity of the flux of precipitating electrons and their low energy (80 eV). Near the cusp, a more intensive burst of precipitations of higher-energy electrons (140 eV) is accompanied by an almost complete “locking” of ions. This burst of mantle precipitations is related to the faint luminous structure in the ionosphere. The ion locking is indicative of the accelerating potential difference in the force tube, which is based on the glowing region. The luminous structure is an element of the so-called “polewar moving auroral forms,” which is related in the literature to the reconnection in the daytime magnetopause. The possible relation of the observed phenomena to the reconnected magnetic force tubes, which drift from the cusp in the antisolar direction, is also confirmed by the dispersion of ionic precipitations, i.e., an increase in ion energy as the satellite approaches to the cusp.     

Spatial-temporal dynamics of auroras during the magnetic storm main phase

The structure and dynamics of auroras in the midnight sector during substorms, which develop during the magnetic storm main phase as compared to the characteristics of a typical auroral substorm, have been studied using the ground-based and satellite observations. It has been found out that a difference from the classical substorm is observed in auroras during the magnetic storm main phase. At the beginning of the storm main phase, the series of pseudobreakups with the most pronounced jump-like motion toward the equator shifts to lower latitudes. The substorm expansion phase can be observed not only as arc jumps to higher latitudes but also as an explosive expansion of a bright diffuse luminosity in all directions. During the magnetic storm main phase, auroras are mainly characterized by the presence of stable extensive rayed structures and by the simultaneous existence of different auroral forms, typical of different substorm phases, in the TV camera field of view.     

元谋盆地河湖相沉积物磁性地层学研究综述

元谋盆地河湖相沉积物分布广泛，沉积连续性好，富含古人类和哺乳动物化石，是进行磁极性地层学研究和探讨西南季风演化与转型、早期人类迁徙、哺乳动物扩散与交流的理想材料.本文对已有的磁性地层学研究作了较系统的总结与分析，发现造成对元谋人生活年代和盆地形成与演化过程的争议，主要是由于过去的磁性地层学研究所涉及的采样间隔太大和实验室测试条件不足等诸多因素的影响.这是未来元谋盆地研究必须注意的问题.     

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.     

泥河湾层磁性地层学研究回顾

泥河湾盆地以富含哺乳动物化石和古人类遗址而引起了古人类学家和地贡学家的广泛关注,泥河湾层是该盆地中发育的一套晚新生代河湖相沉积物．磁性地层学研究结果表明泥河湾层的形成始于高斯正极性世,经历了松山反向极性世,结束于布容正极性世．本文回顾了针时泥河湾层的磁性地层学研究工作,选取了小长梁、东谷坨、郝家台、洞沟、红崖、虎头粱及许家窑等七个剖面作详细介绍,并进行了横向时比．     

A review of analogue model studies of the coast effect

This work reviews electromagnetic analogue model studies of the coast effect, dealing particularly with a vertical interface model, a thin conducting sheet model, a wedge model, and a wedge underlain by a conducting block simulating an upwelling in a conducting zone beneath the coast. The vertical interface model results and the infinitely conducting thin sheet model results show good agreement with calculated values. It is concluded that a sloping sea-land interface alone cannot account for the experimentally observed coast effect, but that a sloping sea-land interface underlain by a conducting step could produce the observed coast effect.     

卫星大地测量用于东亚大陆地球动力学与地震学研究回顾

王仁先生是中国地球动力学研究的开创者,他所引领的有关潮汐和板块运动造成的地壳应力场演化研究使得有关活动构造、断层形变和地震危险性的研究从定性走向定量,并在过去半个世纪中不断丰富发展.卫星大地测量方法从20世纪80年代开始用于精密定位和运动测量,为地球动力学和地震学研究提供了不可缺少的观测资料,极大促进了相关学科的发展.本文结合本人研究经历回顾卫星大地测量方法用于东亚大陆地球动力学、地震构造学和地震物理过程研究带来的一些重要发现,作为对王仁先生在相关领域开创性贡献的纪念.

     

Some early Russian studies of subsurface storm‐flow processes

Subsurface flow is an important component of the catchment hydrological cycle. Various mechanisms of this process and their role in storm‐flow generation attracted the attention of many researchers throughout the twentieth century. The results of most of these studies are well documented. However, similar studies conducted in the past by many Russian hydrologists have never been made available to the English speaking hydrological community. This paper attempts to fill this gap and briefly review some of these investigations, focusing on their main results. It starts with the review of the early experimental studies (after 1930s–1950s), which allow the main characteristics of subsurface storm flow to be established. This is followed by a review of the research conducted in 1960s, which resulted in some conceptualization of the subsurface flow mechanisms. The paper also draws some parallels between this, mostly unknown, subsurface flow research in Russia and the better‐known contemporary studies of this process. Copyright © 2002 John Wiley & Sons, Ltd.