第32回 ESCセミナー
Trying to Understand Solar Luminosity Variations with the Virial Theorem
- 日時
- 2007年11月21日(水) 13:30-14:30
- 場所
- 横浜研究所 シミュレータ研究棟1階 大会議室
- 講演者
- Antonio Ferriz-Mas (Departamento de Fisica Aplicada Facultad de Ciencias de Orense Universidad de Vigo, Spain)
- 使用言語
- 英語
要旨
The variability of solar radiance over a solar cycle is probably the result of a delicate balance between the radiative deficit of sunspots and the extra contribution of plage and network regions: Sunspots are cooler than the surrounding photosphere and block part of the outgoing radiation. On the other hand, faculae are magnetic flux bundles that lead to a depression of the solar surface at their location; in regions where they are abundant (plage and network), they increase the "roughness" of the solar surface, thus increasing the effective surface from where radiation can escape. While Spiegel & Weiss (1981) suggested that the cause of luminosity variations was in the magnetic field at the base of the solar convection zone, conventional wisdom nowadays is that it is the direct result of surface magnetism. In this contribution we try to show how solar luminosity variability might be connected to a deeply seated flux-tube dynamo and how the connection with the surface is established on a hydrodynamical time scale. We make use of the virial theorem for a continuum (Chandrasekhar & Fermi, 1953), which is basically a global statement of momentum balance. Some energy estimates are considered. The physical picture underlying our approach is that the toroidal flux system responsible for the sunspot cycle is stored in the form of flux tubes with field strength close to 105 Gauss at the bottom of the solar convection zone. The process of flux-tube rise and flux-tube explosion can be interpreted as a magnetoconvective mixing-length transport, similar to, but more efficient than the regular hydrodynamic convection. By this process, the convection zone can find a more efficient means of transporting energy across it, limited only by the number of available magnetic flux tubes.
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地球シミュレータセンター連結階層シミュレーション研究開発プログラム
草野 完也
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