不稳定性
物理
电离层
计算物理学
电子
非相干散射
离子
雷达
光电效应
原子物理学
散射
F区域
地球物理学
光学
机械
电信
核物理学
量子力学
计算机科学
作者
A. Green,M. M. Oppenheim,William Longley
摘要
Abstract One Hundred and Fifty kilometer echoes are a type of strong radar echo observed in the valley region of the equatorial ionosphere, whose origin was long standing mystery. Recently, a new upper hybrid (UH) instability theory, driven by high energy photoelectrons, has been proposed to explain most features of 150 km echoes. However, this instability excites high frequency electron modes, whereas radars observe low frequency ion modes. To explain 150 km echoes, the UH instability must ultimately excite ion acoustic modes. This paper describes a set of particle‐in‐cell simulations used to study how photoelectrons interacting with a cold background plasma generate UH waves, and how these drive ion acoustic waves measured by radars. We implement a new electron‐N 2 collision algorithm to better model the bump on tail features of the photoelectron distribution in the valley region. These simulations show that photoelectrons drive unstable UH waves that strongly enhance ion acoustic waves. We also show a strong frequency dependence on power in the ion line, which explains observational differences between radars, most notably the lack of echoes at ALTAIR. The photoelectron driven UH instability successfully reproduces most features of 150 km echoes associated with naturally enhanced incoherent scattering.
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