Structure of Disturbed Magnetosphere and Auroral Oval
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EMENTARY PARTICLES AND FIELDS Theory
Structure of Disturbed Magnetosphere and Auroral Oval L. L. Lazutin* Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia Received April 14, 2017
Abstract—A brief description of the structure of the magnetosphere—that is, permanent and temporary radiation belts, plasmasphere, and plasma layers—is presented. It is shown that the results of measurements of properties of energetic particles and plasma are sufficient for such a description. The outer night slope of the electron radiation belt is singled out as an individual domain where energetic particles do not complete a closed magnetic drift and where substorm processes develop. This region, which is referred to as an auroral magnetosphere, is often erroneously treated as only part of the radiation belt. In different domains of the magnetosphere, different mechanisms of the precipitation of particles causing Earth’s airglow in the form of auroras act independently. The properties and origin of these precipitated particles are different, and it is unreasonable to consider them as a unified formation—a ring or an auroral oval. It is equally erroneous to treat the oval as a kind of formation, a structure, or a domain of the magnetosphere and not as a manifestation of processes that proceed in domains. DOI: 10.1134/S1063778817060126
1. INTRODUCTION The questions of what the magnetosphere of the Earth is, what parts constitute it, and how their content and boundaries change, as well as some other allied questions, have been gradually clarified owing to the development of measurements performed on the Earth and in space. Relevant review articles and monographs have appeared concurrently. However, many points have thus far remained unclear, and there is even no consensus on the concepts of the magnetosphere. This article relies on the most recent results of investigations into the debated issues, but it is subjective to some extent, since it also reflects the ideas of the present author. Direct (satellite-borne) measurements of energetic particles and plasma, along with measurements of magnetic fields and terrestrial measurements of variations and pulsations of magnetic fields, the state of the ionosphere, ultralow-frequency radiation, and auroras, are the main sources of information about the structure of the magnetosphere. Measurements of particle and plasma properties play a dominant role since they are numerous: there are particle detectors on board each satellite—lowaltitude, geostationary, or going along an elliptic orbit; from these measurements, the magnetosphere structure becomes ever clearer. *
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Measurements of magnetic fields are sufficient for getting a general idea of the magnetosphere structure but are not sufficient for tracing the dynamics of structures and boundaries at various stages of magnetic disturbances. In particular, sets of terrestrial measurements and auroras reflect, first of all, characteristic episodes that are consequences of these disturbances; albeit being
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