Lower-Band "Monochromatic" Chorus Riser Subelement/Wave Packet Observations
Lower-Band "Monochromatic" Chorus Riser Subelement/Wave Packet Observations
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低频段“单色”合唱立管子元件/波包观测
DOI：
10.1029/2020ja028090
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发表时间：
2020-10-01
影响因子：
2.8
通讯作者：
Falkowski, Barbara J.
中科院分区：
文献类型：
--
作者：
Tsurutani, Bruce T.;Chen, Rui;Falkowski, Barbara J.
利用Van Allen探测器的数据，对在天边产生区探测到的三个低频段(f<；0.5FCE)合唱立管元件进行了详细的研究。每个立管内的两个亚元件/波包在7个连续的波周期内被检查其波“频率”的恒定性。七个波周期包含了亚元件/包的最大幅度。用最大方差B_1过零点来识别波周期的开始和停止时间。结果表明，频率恒定在3%以内(1个标准差)，在7个周期内没有向上扫频的迹象。7个周期内的连续小波功率谱证实了这一结论。其含义是，合唱立管单元由相干的近似单色阶跃组成，而不是在整个单元上以逐渐的频率扫频。与边带理论预测相反，在波幅最大的地方没有上行频率阶跃。结果表明，在L=5.8时，合唱提升管涉及回旋共振高能电子从类6到类40keV的不稳定性，即本质上是整个亚暴电子能谱。上述发现可能对可能的波浪产生机制产生重要影响。最后提出了一些新的机理设想。
Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave "frequency" constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within similar to 3% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately "monochromatic" steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from similar to 6 to similar to 40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.