Comment on “A new approach to Saturn's periodicities” by J. F. Carbary
Comment on “A new approach to Saturn's periodicities” by J. F. Carbary
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对 J. F. Carbary 的“土星周期性的新方法”的评论
DOI：
10.1002/2015ja021996
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
D. Andrews
中科院分区：
文献类型：
--
作者：
S. Cowley;P. Zarka;G. Provan;L. Lamy;D. Andrews
土星磁层中的“行星周期振荡”现象最早是由旅行者号宇宙飞船通过在千米波长的无线电发射强度中的行星旋转周期附近的调制观测到的[沃里克等人，一九八一年; Desch和Kaiser，1981年]，以及磁层内原位粒子和磁场的相关振荡[Carbary和Krimigis，1982年;埃斯皮诺萨和Doughnos，2000年]。随后由土星天文台的航天器对土星千米辐射（SKR）进行的远程观测表明，周期可以在每年的间隔内变化约1%，因此调制不能直接与行星的旋转联系起来[Galopeau和Lecacheux，2000]。卡西尼号最近的一个发现是，在SKR数据中通常存在两种这样的变量调制，在任务早期的土星南部夏季条件下，周期为~10.6和~10.8小时[Kurth等人，2008; Gurnett等人，2009 a]，虽然后来变得更接近，更可变，并且只有一个可检测的间隔期postquinox [Provan等人，2014; Fischer等人，2014; Cowley和Provan，2015]。如下文所述，在随后的讨论中，这两个周期通常被认为对应于与行星的北方和南半球相关的行星周期振荡（PPO）现象。然而，在最近的一篇论文中，Carbary [2015]对这些发现提出了一种“新方法”，通过一些基本的演示指出了一个简单的事实，即如果单个正弦振荡在振幅，频率或相位上进行调制，则其频谱不再是单色的，并且可能会分裂成靠近主周期的许多峰值，建议对应于观察到的双PPO调制。最简单的说明性示例是由频率为ω2的“载波”组成的信号S（t），其幅度由频率为ω1的正弦曲线调制，对于该正弦曲线，可以通过初等三角学示出：
The phenomenon of “planetary period oscillations” in Saturn’s magnetosphere was first observed by the Voyager spacecraft via modulations near the planetary rotation period in the intensity of radio emissions at kilometer wavelengths [Warwick et al., 1981; Desch and Kaiser, 1981], together with related oscillations in particles and magnetic fields in situ within the magnetosphere [Carbary and Krimigis, 1982; Espinosa and Dougherty, 2000]. Subsequent remote observations of Saturn kilometric radiation (SKR) by the Ulysses spacecraft showed that the period can change by of order ~1% over yearly intervals, such that the modulations cannot be connected directly to the rotation of the body of the planet [Galopeau and Lecacheux, 2000]. A more recent Cassini discovery has been that two such variable modulations are generally present in SKR data, with periods of ~10.6 and ~10.8 h during Saturn southern summer conditions early in themission [Kurth et al., 2008; Gurnett et al., 2009a], though later becoming closer together, more variable, and with intervals of only one detectable period postequinox [Provan et al., 2014; Fischer et al., 2014; Cowley and Provan, 2015]. As will be indicated below, in subsequent discussions these two periods have generally been taken to correspond to planetary period oscillation (PPO) phenomena associated with the Northern and Southern Hemispheres of the planet. In a recent paper, however, Carbary [2015] has suggested a “new approach” to these findings, pointing out the simple fact via a number of elementary demonstrations that if a single sinusoidal oscillation is modulated in amplitude, frequency, or phase, its frequency spectrum is no longer monochromatic andmay become split into a number of peaks near that of the principal period, suggested to correspond to the observed dual PPO modulations. The simplest illustrative example is that of a signal S(t) consisting of a “carrier” of frequency ω2 whose amplitude is modulated by a sinusoid of frequency ω1, for which it can be shown by elementary trigonometry that
土星磁层中的行星周期振荡：赤道磁场振荡与土星千米辐射调制的相位关系
DOI：
10.1029/2007ja012937
发表时间：
2008
期刊：
Space Physics
影响因子：
--
作者：
Andrews D
通讯作者：
Andrews D
土星磁层周期振荡：赤道和高纬度磁场周期与南北土星千米辐射周期的比较
DOI：
10.1029/2010ja015666
发表时间：
2010
期刊：
Space Physics
影响因子：
--
作者：
Andrews D
通讯作者：
Andrews D