Intensities and spatiotemporal variability of equatorial noise emissions observed by the Cluster spacecraft
Intensities and spatiotemporal variability of equatorial noise emissions observed by the Cluster spacecraft
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DOI：
10.1002/2014ja020814
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
F. Němec;O. Santolík;Z. Hrbackova;N. Cornilleau-Wehrlin
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作者：
F. Němec;O. Santolík;Z. Hrbackova;N. Cornilleau-Wehrlin
赤道噪声(EN)辐射是在内磁层赤道区域观察到的频率介于质子回旋频率和较低混合频率之间的电磁波。我们给出了2001-2010年集群航天器的场起伏时空分析(STAFF)实验数据中确定的2229个EN事件的分析。使用偏振分析来区分EN发射，并且其强度是基于对坡印亭磁通的评估而不是仅基于电场/磁场强度的评估来确定的。分析了En事件的强度与频率、航天器在等离子体层内外的位置、磁当地时和地磁活动的函数关系。等离子体槽中的辐射比等离子体层中的辐射频率更高、强度更强。在等离子体槽中观测到的EN事件在接近当地中午时最为强烈，而在等离子体层中观测到的EN事件几乎与磁当地时间(MLT)无关。无论是在等离子体层内还是在等离子体槽内，EN事件的强度在扰动期间都是增强的。几个星团航天器对相同事件的观测使我们能够估计它们的时空变异性。在所分析的空间尺度上(ΔMLT<；0.2h，Δr<；0.2RE)，在等离子体层中观测到的EN发射没有变化，但在大约一小时的时间尺度上它们发生了显著变化。在等离子体槽中观察到的EN事件似乎也是如此，尽管等离子体槽相关性不太清楚。
Equatorial noise (EN) emissions are electromagnetic waves observed in the equatorial region of the inner magnetosphere at frequencies between the proton cyclotron frequency and the lower hybrid frequency. We present the analysis of 2229 EN events identified in the Spatio‐Temporal Analysis of Field Fluctuations (STAFF) experiment data of the Cluster spacecraft during the years 2001–2010. EN emissions are distinguished using the polarization analysis, and their intensity is determined based on the evaluation of the Poynting flux rather than on the evaluation of only the electric/magnetic field intensity. The intensity of EN events is analyzed as a function of the frequency, the position of the spacecraft inside/outside the plasmasphere, magnetic local time, and the geomagnetic activity. The emissions have higher frequencies and are more intense in the plasma trough than in the plasmasphere. EN events observed in the plasma trough are most intense close to the local noon, while EN events observed in the plasmasphere are nearly independent on magnetic local time (MLT). The intensity of EN events is enhanced during disturbed periods, both inside the plasmasphere and in the plasma trough. Observations of the same events by several Cluster spacecraft allow us to estimate their spatiotemporal variability. EN emissions observed in the plasmasphere do not change on the analyzed spatial scales (ΔMLT<0.2h, Δr<0.2 RE), but they change significantly on time scales of about an hour. The same appears to be the case also for EN events observed in the plasma trough, although the plasma trough dependencies are less clear.