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Photoelectrons are emitted from the surface of Mercury and take part in charge exchanges with the magnetosphere. We investigate the role of photoemission in closing field-aligned currents and in balancing the flow of magnetospheric electrons which precipitate to the surface. The conductance of the photoelectron sheath and sub-surface rock material are estimated and compared with that of the exosphere. It is shown that the loss cone angle is always larger than 30–40° on the dayside, and that significant electron precipitation takes place. It is concluded that the closure of field-aligned current is unlikely because the conductance of the surface environment is too low, but that photoemission may alter the isotropy of the magnetospheric electron energy distribution and induce plasma instabilities. 相似文献
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Magnetospheric substorms represent the basic dynamic process in the coupled solar wind -- magnetosphere -- ionosphere system. Recent satellite missions have considerably advanced our means to monitor this vast environment. These observations are interpreted in the context of a hierarchy of models: Global MHD simulations and various techniques of nonlinear physics are used to characterize the large-scale features, whereas microphysical models are used to study the small-scale processes. Empirical models are described in order to address questions that involve meso-scale or multi-scale phenomena. We discuss some of the recent observations and relate those to new advancements in various modeling techniques. 相似文献
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The degradation of organic wastes and the corrosion of metallic wastes and steel containers in low and intermediate level radioactive waste (LLW/ILW) repositories are important processes that affect repository geochemistry and the speciation and transport of radionuclides. Gas is generated in association with these degradation processes and this has the potential to overpressure the repository, which can promote transport of groundwater and gas, and consequently radionuclide transport. Microbial activity plays an important role in organic degradation, corrosion and gas generation through the mediation of reduction–oxidation reactions. 相似文献
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