A z mode electron‐cyclotron maser model for bottomside ionospheric harmonic radio emissions
A z mode electron‐cyclotron maser model for bottomside ionospheric harmonic radio emissions
复制标题
用于底侧电离层谐波无线电发射的 z 模式电子回旋脉塞模型
DOI：
10.1029/97ja03601
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发表时间：
1998
影响因子：
--
通讯作者：
Z. Kuncic
中科院分区：
文献类型：
--
作者：
A. J. Willes;S. Bale;Z. Kuncic
提出了一个模型，用于最近的地面观测极光轰鸣发射，检测到2Ωe和3Ωe，其中Ωe是本地电子回旋频率的源区，在200和500公里以上的地球表面。电子回旋脉塞辐射是解释这些辐射的一种可能机制，因为它自然地产生了Ωe谐波的相干辐射。极光轰鸣发射的理论已经被提出，据此，脉泽产生的第二（X2）和第三（X3）谐波x模式辐射在源区被产生它们的密度腔壁的多次反射放大。在多次反射之后，X2和X3波沿着密度空腔传播到地面观测者。然而，它表明，在这里与射线跟踪计算，这是非常可能的微波激射器产生的X2和X3辐射被重吸收在较低的高度，因此不能在地面上检测到。提出了一种间接的脉泽机制，即脉泽产生的z模波在源区增长到高水平，然后经历重复的非线性波-波聚结，产生直接传播到地面的二次和三次谐波。z模式波必须满足必要的运动学约束，以产生可观测的二次和三次谐波辐射。讨论了z模脉泽对温度和不稳定电子分布的函数形式的依赖关系，沿着讨论了聚结过程进行和产生所观察到的辐射水平所需的条件。
A model is proposed for recent ground-based observations of auroral roar emissions, detected at 2Ωe and 3Ωe, where Ωe is the local electron cyclotron frequency in the source region, between 200 and 500 km above the Earth's surface. Electron cyclotron maser emission is a likely mechanism to account for these emissions because it naturally produces coherent radiation at harmonics of Ωe. A theory for auroral roar emissions has already been proposed, whereby maser-generated second (X2) and third (X3) harmonic x mode radiation is amplified in the source region by multiple reflections off the walls of the density cavity in which they are produced. After many reflections the X2 and X3 waves propagate along the density cavity to a ground-based observer. However, it is demonstrated here with ray-tracing calculations that it is highly probable that maser-generated X2 and X3 radiation is reabsorbed at lower altitudes and thus cannot be detected at the ground. An indirect maser mechanism is proposed instead, where maser-generated z mode waves at Ωe grow to high levels in the source region and then undergo repeated nonlinear wave-wave coalescence to produce second- and third-harmonic waves that propagate directly to the ground. The z mode waves must satisfy the necessary kinematic constraints to produce observable second- and third-harmonic radiation. The dependence of the z mode maser on the temperature and functional form of the unstable electron distribution is discussed, along with the conditions required for the coalescence processes to proceed and produce the observed levels of radiation.