Electrostatic and electromagnetic turbulence associated with the earth's bow shock
Electrostatic and electromagnetic turbulence associated with the earth's bow shock
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与地球弓形激波相关的静电和电磁湍流
DOI：
10.1029/ja080i001p00019
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发表时间：
1975
影响因子：
--
通讯作者：
D. Gurnett
中科院分区：
文献类型：
--
作者：
P. Rodriguez;D. Gurnett
利用Imp 6航天器上的两台16通道频谱分析仪，在20 Hz至200 kHz频率范围内测量了地球弓激波中等离子体波的电场和磁场频谱密度。弓激波中的电场谱由两个不同的分量组成：一个分量具有通常以 200 到 800 Hz 为中心的宽峰，峰值处的平均（5.12-s 时间常数）谱密度约为 10−9 V² m−2 Hz−1，另一个分量随着频率的降低单调增加，大约为 f−(2.0±0.5)，平均谱密度约为 3.0 × 10−9 V² m−2 36.0 Hz 时 Hz−1。激波中的磁场谱只有一个随着频率大约为 f−(4.0±0.5) 降低而单调增加的分量，并且具有接近局部电子陀螺频率的上限截止频率。该磁场谱似乎与电场谱的单调分量相关。该噪声的电磁能量密度比 ϵE/ϵB 约为 10−3 至 10−4，这与弓激波中电磁哨声模式波的预期能量密度比一致。 200 至 800 Hz 之间的电场谱中的宽峰具有很大的电磁能量密度比，约 10² 至 10³，表明该分量几乎纯粹由静电波组成。在激波下游的整个磁鞘区域中观察到静电噪声，其频谱与激波中的湍流相似，但强度较低。这种磁鞘电场湍流通常包括许多在几秒的时间尺度上具有明显“抛物线”频率-时间变化的爆发。电场方向的自旋调制测量表明，激波过渡区域和磁鞘区域中的电场矢量优先定向为平行于静磁场方向。上游电子等离子体振荡的电场也平行于静磁场定向。
The electric and magnetic field spectral densities of plasma waves in the earth's bow shock have been measured in the frequency range 20 Hz to 200 kHz by using two 16-channel spectrum analyzers on the Imp 6 spacecraft. The electric field spectrum in the bow shock consists of two distinct components: one component has a broad peak typically centered between 200 and 800 Hz with an average (5.12-s time constant) spectral density at the peak of about 10−9 V² m−2 Hz−1, and the other component increases monotonically with decreasing frequency approximately as f−(2.0±0.5) and has an average spectral density of about 3.0 × 10−9 V² m−2 Hz−1 at 36.0 Hz. The magnetic field spectrum in the shock has only one component that increases monotonically with decreasing frequency approximately as f−(4.0±0.5) and has an upper cutoff frequency near the local electron gyrofrequency. This magnetic field spectrum appears to be associated with the monotonic component of the electric field spectrum. The electric to magnetic energy density ratio ϵE/ϵB of this noise is about 10−3 to 10−4, which is consistent with the energy density ratio expected for electromagnetic whistler mode waves in the bow shock. The broad peak in the electric field spectrum between 200 and 800 Hz has a large electric to magnetic energy density ratio, ∼10² to 10³, indicating that this component consists of almost purely electrostatic waves. Electrostatic noise with a spectrum similar to the turbulence in the shock but with lower intensities is observed throughout the magnetosheath region downstream of the shock. This magnetosheath electric field turbulence often includes many bursts with a distinct ‘parabolic’ frequency-time variation on a time scale of a few seconds. Spin modulation measurements of the electric field direction show that the electric field vectors in both the shock transition region and the magnetosheath region are preferentially oriented parallel to the static magnetic field direction. The electric field of upstream electron plasma oscillations also is oriented parallel to the static magnetic field.