Three‐dimensional polarization characteristics of high‐latitude Pc 5 geomagnetic micropulsations
Three‐dimensional polarization characteristics of high‐latitude Pc 5 geomagnetic micropulsations
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高纬度Pc 5 地磁微脉动三维极化特征
DOI：
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发表时间：
1972
期刊：
影响因子：
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通讯作者：
J. Samson
中科院分区：
文献类型：
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作者：
J. Samson
1969年和1970年，在加拿大西部58.5°至77.7°北纬校正地磁纬度和302°东经校正地磁经度2°范围内建立了一条磁力计站线。本文研究了这些台站记录的pc5低频（f250秒）地磁微脉冲的三维极化特征。这些脉动的活动中心全天跟随极光椭圆。清晨（0200-1000地磁时）的脉动次数最多，在水平面上几乎呈圆极化，而下午通常在磁北方向上的正弦脉动很少，几乎呈线性极化。在地磁地方时1130到1230之间出现的水平面极化意义上的反转表明，pc5事件的能量来源于磁层顶的开尔文-亥姆霍兹不稳定性。极化意义上的纬向变化，发生在峰值强度的纬度附近，表明脉动的能量可能在地球内部偶极子场内以共振磁模式分布，或者高纬度（λ > 70°）的场线可能进入磁鞘。Pc事件的垂直分量可能是由与脉动相关的电离层电流的空间梯度引起的。在脉动周期的一部分，电离层中有强的切变流向东和向西流动，在水平分量强度峰值的纬度附近产生一个大的垂直磁场。
In 1969 and 1970, a line of magnetometer stations was operated in western Canada between 58.5° and 77.7°N corrected geomagnetic latitude and within 2° of 302°E corrected geomagnetic longitude. This paper deals with the three-dimensional polarization characteristics of low-frequency (f 250 sec) Pc 5 geomagnetic micropulsations recorded at these stations. The center of activity of these pulsations follows the auroral oval during the whole day. The early morning (0200–1000 local geomagnetic time) has the greatest number of pulsations, with almost circular polarization in the horizontal plane, whereas the afternoon normally has few sinusoidal pulsations and almost linear polarization in the direction of magnetic north. A reversal in the sense of polarization in the horizontal plane, occurring between 1130 and 1230 local geomagnetic time, suggests that the Pc 5 events derive their energy from a Kelvin-Helmholtz instability at the magnetopause. A latitudinal change in the sense of polarization, occurring near the latitude of the peak intensity, indicates that the energy of the pulsations may be distributed in a resonant hydromagnetic mode within the earth's inner dipole field or that field lines at high latitudes (λ > 70°) may pass into the magnetosheath. The vertical components of the Pc events are likely caused by spatial gradients in the ionospheric currents associated with the pulsations. During part of the pulsation cycle, strong shear currents flow to the east and the west in the ionosphere, giving a large vertical magnetic field near the latitude of the peak in the intensity of the horizontal components.