Short‐wavelength electrostatic waves in the Earth's magnetosheath
Short‐wavelength electrostatic waves in the Earth's magnetosheath
复制标题
地球磁鞘中的短波长静电波
DOI：
10.1029/ja090ia02p01435
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发表时间：
1982
影响因子：
--
通讯作者：
D. Gallagher
中科院分区：
文献类型：
--
作者：
D. Gallagher
最近对ISEE 1号航天器的观测发现，向阳面磁鞘中的电场发射，其频谱调制为航天器自旋周期的两倍。发射的频率-时间谱中的上频率截止具有特征抛物线形状或“花彩”形状。低频截止范围为100至400 Hz，而高频极限范围为约1至4 kHz。带宽被发现，以尽量减少天线方向平行的波矢量。波矢似乎与局部磁场、等离子体流速或航天器-太阳方向无关。航天器观测到的频谱是航天器天线对等离子体中多普勒频移波矢谱响应的结果。对等离子体静止帧波矢量和频率施加的约束表明，发射发生在约150 Hz至1 kHz的频率范围内，波长在约40和600 nm之间。这些限制强烈表明，花彩状的发射是离子声波。小的群速度和k方向的离子声模式是一致的波生成上游的弓形激波和对流下游的位置内的外部昼侧磁鞘。
Recent observations with the ISEE 1 spacecraft have found electric field emissions in the dayside magnetosheath whose frequency spectrum is modulated at twice the spacecraft spin period. The upper frequency cutoff in the frequency-time spectrum of the emission has a characteristic parabola shape or “festoon” shape. The low-frequency cutoff ranges from 100 to 400 Hz, while the high-frequency limit ranges from about 1 to 4 kHz. The bandwidth is found to minimize for antenna orientations parallel to the wave vectors. The wave vector does not appear to be related to the local magnetic field, the plasma flow velocity, or the spacecraft-sun directions. The spacecraft observed frequency spectrum results from the spacecraft antenna response to the Doppler-shifted wave vector spectrum which exists in the plasma. Imposed constraints on the plasma rest frame wave vectors and frequencies indicate that emissions occur within the frequency range from about 150 Hz to 1 kHz, with wavelengths between about 40 and 600 m. These constraints strongly suggest that the festoon-shaped emissions are ion-acoustic waves. The small group velocity and k direction of the ion-acoustic mode are consistent with wave generation upstream at the bow shock and convection downstream to locations within the outer dayside magnetosheath.