Simulation of Es Layer Modulated by Nonlinear Kelvin–Helmholtz Instability. Issue 8 (24th August 2022)

• Record Type: Journal Article
• Authors: Wu, Jinnan; Zhou, Chen; Wang, Geng; Liu, Yi; Jiang, Chaowei; Zhao, Zhengyu
• Is Part Of: Journal of geophysical research. Volume 127:Issue 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-24
• Subjects: middle and low latitude E region irregularities -- Kelvin–Helmholtz instability (KHI) -- QP echoes -- polarization electric field; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2021JA030065
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: In this study, a two‐dimensional numerical model of the nonlinear Kelvin–Helmholtz (KH) instability is used to investigate the nonlinear evolution processes of the ion layer, which is associated with the middle and low latitude E region irregularities. Based on simulation results, the two‐stage process in the evolution of the nonlinear KH instability is found in KH vortex morphology. The simulated nonlinear KH instability process presents multiple striation structures, including horizontal structures of the primary ion layer vortex with a size of a few kilometers and the secondary KH vortex with a size of 2 km. The polarization electric field is induced in the horizontal structure of the sporadic E (Es) layer associated with the vortex structure of neutral wind. The polarization electric field presents a similar tendency to the quasi‐periodic vortex structure. The horizontal distorted Es layer structure and anomalously large polarization electric field can provide the initial condition and lead to plasma instability, which can further develop to meter‐scale irregularities of QP echoes. Plain Language Summary: Low and middle latitude sporadic E layer is generated by the wind shear theory at the height of vertical wind shear convergence nodes which are provided by the zonal and meridional winds. Es layer can develop into field‐aligned irregularities (FAIs) and can be observed by very high frequency (VHF) coherent radar as quasi‐periodic (QP) echoes. However, the generation of these QP echoes of FAIs remains an open question. Previous studies indicate that the polarization electric field is significant for generating E region FAIs. This study investigates the Kelvin–Helmholtz (KH) instability in a neutral atmosphere induced by strong wind shear. The Es layer can be modulated by the neutral wind and evolve into KH billows. The KH reaches the maximum and then collapses to trigger the formation of small‐scale structures and the formation of large structures during the vortex pair process. The distorted horizontal structures of the Es layer and polarization electric field are presented in our simulation. We infer that the plasma instability (e.g., Es layering instability or gradient drifting instability) can be further triggered, which controls the generation of QP echoes of FAIs. Key Points: The nonlinear KHI process presented the multiscale structures, including structures of primary and secondary KH vortex ion layer Polarization electric field presents a similar tendency to the quasi‐periodic vortex structure The horizontal distorted Es layer structure and polarization electric field provide the initial condition and lead to plasma instability