On the propagation of electrostatic wave modes in the inhomogeneous ionospheric plasma of Venus
On the propagation of electrostatic wave modes in the inhomogeneous ionospheric plasma of Venus
复制标题
金星非均匀电离层等离子体中静电波模式的传播
DOI：
10.1063/5.0050039
复制
发表时间：
2021
影响因子：
2.2
通讯作者：
W. Moslem
中科院分区：
文献类型：
--
作者：
A. Fayad;I. Elkamash;H. Fichtner;M. Lazar;S. El;W. Moslem
研究了等离子体中数密度梯度、磁场梯度和流速梯度对低频静电波传播的影响。为此，我们假设一个无碰撞的非均匀等离子体模型，包括两个正离子物种，氢H+和氧O+，以及中和电子。线性色散关系预测两种类型的等离子体模式，即离子声学模式和漂移模式。结果发现，这些模式具有相对较长的波长，可延伸至10 km，频率约为10−3−10−2 Hz。这些模式的特性表现出强烈的依赖于等离子体参数的梯度，数值分析表明，这些模式的耦合可能会导致非线性不稳定性。然而，不稳定的模式只发生时，场向剪切流被引入。这些结果有助于解释金星电离层中低频静电模式及其基本特征的存在，并将使未来的研究扩展到其他行星甚至彗星条件的建模。
The influence of gradients of number density, magnetic field, and flow velocity in a plasma on the propagation of low-frequency electrostatic waves is investigated in plasma conditions relevant for the Venusian ionosphere (vicinity of Venus terminator). For this purpose, we assume a collisionless inhomogeneous plasma model consisting of two positive ion species, hydrogen H+ and oxygen O+, as well as neutralizing electrons. Linear dispersion relations predict two types of plasma modes, namely, ion-acoustic mode and drift mode. It is found that these modes have relatively long wavelengths, extending to 10 km and frequencies on the order of ∼10−3−10−2 Hz. The characteristics of these modes show a strong dependence on the gradients of plasma parameters, and numerical analysis reveals that the coupling of these modes may lead to nonlinear instabilities. However, unstable modes occur only when the field-aligned shear flows are introduced. These results help explain the presence of low-frequency electrostatic modes and their basic features in the Venusian ionosphere, and will allow future studies to extend modeling to other planetary or even cometary conditions.