Nonlinear evolution of the temperature gradient instability in the midlatitude ionosphere

Abstract

The midlatitude Super Dual Auroral Radar Network radars frequently observe quiet time decameter‐scale irregularities in the nightside subauroral ionosphere. Since opposed temperature and density gradients are a persistent feature in the vicinity of the ionospheric projection of the plasmapause, the temperature gradient instability (TGI) is proposed to explain the observed irregularities. In this paper, modeling of the TGI is extended into the kinetic regime appropriate for HF radar frequencies and analyzed as the cause of these irregularities. The nonlinear evolution of the TGI is investigated utilizing gyrokinetic particle‐in‐cell simulation techniques with Monte Carlo collisions for the first time. The purpose of this investigation is to identify the mechanism responsible for the nonlinear saturation as well as the associated anomalous transport. It is found that the saturation amplitude level and the associated diffusion are greatly enhanced as a result of electron collisions. The simulation results indicate that the nonlinear E×Bconvection (trapping) of the electrons is the dominant TGI saturation mechanism. The spatial power spectra of the electrostatic potential and density fluctuations associated with the TGI are also computed, and the results show wave cascading of TGI from kilometer scales into the decameter‐scale regime of the radar observations. This implies that the E region may be responsible for shorting out the F region TGI electric fields before and around sunset. This also suggests that the observed midlatitude decameter‐scale ionospheric irregularities may be produced directly by the TGI or by turbulent cascade from primary longer‐wavelength irregularity structures produced from this instability.

Investigation of the role of plasma wave cascading processes in the formation of midlatitude irregularities utilizing GPS and radar observations

“…Unfortunately, the data available to this study are not sufficient to investigate the power spectral densities for much smaller decameter-scale irregularities. However, the spectra calculations of TGI and GDI density irregularities [e.g., Eltrass and Scales, 2014;Keskinen and Huba, 1990] along with ground GPS measurements are in reasonable agreement with DMSP satellite measurements for several disturbed time events in the nightside subauroral ionosphere [e.g., Foster and Rich, 1998;Mishin et al, 2003;Mishin and Blaunstein, 2008]. Also, the growth times for the disturbed midlatitude irregularities are on the order of several minutes [e.g., Mishin and Blaunstein, 2008;Keskinen et al, 2004], which is consistent with the TGI and GDI simulation results.…”

“…However, a kinetic model is required in the short wavelength regime when k ⊥ ρ c i ≥1 ( λ ≤15 m). The observations discussed in this paper examine wavelengths of around 10–15 m, which is where kinetic effects begin to play a role and the fluid theory looses validity [ Eltrass and Scales , ; Eltrass et al , ]. The TGI electrostatic dispersion relation has been solved with full kinetic effects including Landau damping, finite gyroradius, temperature anisotropy, and electron collisions appropriate for SuperDARN HF radar frequencies by Eltrass et al [2014].…”

“…However, as will be discussed subsequently, the linear theory results in conjunction with simulation results show that TGI and GDI irregularities are initially generated at kilometer scale with large amplitudes, become unstable, and dissipate their energy by generating decameter‐scale irregularities. The decameter‐scale irregularities do not reach large amplitude because they are involved in the TGI/GDI cascading process [ Eltrass and Scales , ].…”

“…Basu et al [] and Ledvina et al [] reported intense midlatitude UHF and L1 band scintillations within structured SAPS over the eastern continental United States. Mishin et al [] showed that strong SAPS wave structures and irregular plasma density troughs are associated with strong opposite temperature and density gradients, which represent the precise conditions required for the development of the F region temperature gradient instability (TGI) [e.g., Hudson and Kelley , ; Eltrass et al , , ; Eltrass and Scales , ].…”

The Wave Energy Up Conversion of Plasma Wave in Inhomogeneous Ionosphereic Plasma

“…Kelly [5] observed in inhomogeneous ionospheric region at the mid altitude, different entities like gravity waves, shear effects, drift waves and lower hybrid waves are contributing in turbulence processes. In several studies investigations on instabilities in an inhomogeneous magnetised plasma system associated with density and temperature gradients from nonlinear wave-particle interaction approach in both open and laboratory plasma environment as well as in homogeneous and inhomogeneous magnetised plasma system are carried on [10][11][12][13][14][15][16][17]. Deka [18] investigated on the amplification of Langmuir wave in presence of ion acoustic turbulence in inhomogeneous plasma in presence of magnetic field gradients through plasma maser effect.…”