Generation of periodic signatures at Saturn through Titan's interaction with the centrifugal interchange instability
Generation of periodic signatures at Saturn through Titan's interaction with the centrifugal interchange instability
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通过泰坦与离心交换不稳定性的相互作用在土星上产生周期性特征
DOI：
10.1002/jgra.50397
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
D. Snowden
中科院分区：
文献类型：
--
作者：
R. Winglee;A. Kidder;E. Harnett;N. Ifland;C. Paty;D. Snowden
土星的无线电、等离子体和磁场的周期性的起源一直存在争议。由于土星的偶极与其自转轴高度一致，因此预计不会有很强的自转周期。然而，卡西尼号的数据表明，这种周期性的存在不仅在土星的公里无线电发射（SKR），但在等离子体和磁场签名。结果表明，发展的离心交换不稳定性，起源于质量加载从土卫二环面包含有关行星自转周期的信息。然而，行星周期被不稳定性的高频分量所掩盖。土卫六的存在抑制了高频分量，并使行星旋转频率附近的基频以高频分量为代价增长。因此，交换不稳定性被认为是从一个五到七个大的交换指占主导地位的一个有大约三个，导致调制的磁层参数附近的行星周期。这种调制包括磁层顶的运动，高能粒子注入到内磁层和高纬度的等离子体密度，这两者都控制着SKR。频率上的控制因素包括土卫六对等离子体片的阻力，这会产生北方和南半球之间的不对称，太阳风条件和土卫二等离子体环的密度。由此产生的磁扰动的大小和频率与卡西尼号的数据相似。
The origin of the periodicities in the radio, plasma, and magnetic fields of Saturn has long been debated. Given the high degree of alignment of Saturn's dipole with its rotation axis, no strong rotational periodicities are expected. However, Cassini data demonstrated the existence of such periodicities not only in Saturn's kilometric radio emissions (SKR) but in the plasma and magnetic field signatures. It is shown that the development of the centrifugal interchange instability that originates from mass loading from the Enceladus torus contains information about the planetary rotation period. However, the planetary period is masked by high‐frequency components of the instability. The presence of Titan is shown to damp the high‐frequency components and enables the fundamental frequency near the planetary rotation frequency to grow at the expense of the high‐frequency components. As a result, the interchange instability is seen to change from one where five to seven large interchange fingers dominate to one where there are about three which cause the modulation of magnetospheric parameters near the planetary period. This modulation includes the movement of the magnetopause, the injection of energetic particles into the inner magnetosphere and the plasma density at high latitudes, both of which control SKR. Controlling factors on the frequency include Titan's drag on the plasma sheet which produces asymmetries between the Northern and Southern Hemispheres, solar wind conditions, and the density of the Enceladus plasma torus. The resultant magnetic perturbations are shown to have similar size and frequency as that seen in Cassini data.