Spontaneous axisymmetry breaking of the external magnetic field at Saturn

Spontaneous axisymmetry breaking of the external magnetic field at Saturn
复制标题

土星外部磁场的自发轴对称破缺

DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
A. Farmer
A. Farmer
中科院分区：
--
文献类型：
--
作者：
P. Goldreich;A. Farmer

文献摘要

被引文献

相似文献

土星的磁场是显著的轴对称。早期证据表明， 非轴对称性来自于土星公里级射电爆发（SKR）的周期性。 随后，发现SKR周期的水平变化发生在 年的时间尺度。最近的一个突破是直接检测到一种 场的非轴对称分量，其旋转周期接近SKR的旋转周期 它的大小随着与土星的距离变化很小。后者意味 它必须受到行星外部洋流的支持。我们探讨的假设， 离心驱动的对流自发地打破了外部的轴对称性， 土星的磁场靠近其源的流出等离子体的密度是 假设包含随coso变化并均匀旋转的实质部分。我们 证明了等离子流必须随着离行星的距离而变窄，而 将气流加入电离层的场向电流迅速增加。这些电流 产生大小变化的磁场的非轴对称分量 与行星赤道面的径向距离成反比对于血浆流出率 10^4牛顿10^5g s^（-1），该分量的强度与观测值一致。 此外，我们假设，SKR与窄范围的β-环糊精有关， 大电流沿着磁场线流过， 到极光电离层
Saturn’s magnetic field is remarkably axisymmetric. Early evidence for nonaxisymmetry came from the periodicity of Saturn’s kilometric radio bursts (SKR). Subsequently, percent-level variations of the SKR period were found to occur on timescales of years. A recent breakthrough has been the direct detection of a nonaxisymmetric component of the field that rotates with a period close to that of the SKR and whose magnitude varies only weakly with distance from Saturn. The latter implies that it must be supported by currents external to the planet. We explore the hypothesis that centrifugally driven convection spontaneously breaks the axisymmetry of the external magnetic field at Saturn. The density of the outflowing plasma close to its source is assumed to contain a substantial part that varies as coso and rotates uniformly. We demonstrate that the plasma stream must narrow with distance from the planet, while the field-aligned currents joining stream to ionosphere increase rapidly. These currents produce a nonaxisymmetric component of magnetic field whose magnitude varies inversely with radial distance in the planet’s equatorial plane. For a rate of plasma outflow 10^4 ≾ Ṁ ≾ 10^5g s^(-1), this component’s strength is compatible with that observed. Additionally, we postulate that the SKR is associated with the narrow range of longitudes over which large currents flow along magnetic field lines connecting the tip of the outflow to the auroral ionosphere.