Multiscale equatorial electrojet turbulence:Baseline 2‐D model

Abstract

The spatial and spectral characteristics of the turbulent plasma density, electric fields, and ion drift in ionospheric E region are studied using a new set of nonlinear plasma fluid equations. The fluid model combines both Farley-Buneman (Type-I) and Gradient-Drift (Type-II) plasma instabilities in the equatorial electrojet. In our unified model of the plasma instabilities, we include the ion viscosity in the ion momentum equation and electron inertia in the electron momentum equation. These two terms play an important role in stabilizing the growing modes in the linear regime and in driving the Farley-Buneman instability into the saturation state. The simulation results show good agreements with a number of features of rocket and radar observations, such as (1) saturation of plasma density perturbations depends on the solar condition and reaches 7-15% relative to the background, (2) fluctuation of the horizontal secondary electric field reaches 8-15 mV/m, (3) stabilization of the phase velocity of the perturbed density wave around the value of the ion-acoustic speed inside the electrojet, (4) "up-down" asymmetry in the vertical fluxes of the plasma density, (5) "east-west" asymmetry of the plasma zonal drifts, and (6) generation of small scale of the order of meter scale lengths irregularities embedded in large-scale structures. Spectral analysis of the density fluctuations reveals the energy cascade due to the nonlinear coupling between structures of different scales. The break-up of the large-scale structures into small-scale structures explains the disappearance of Type-II echoes in the presence of Type-I instabilities.

Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2‐D fluid model

“…Moreover, the Doppler shift of Type I irregularities supports the previous observations by Pfaff et al [, ], Kudeki et al [], and Hysell and Burcham [] about the limit of small structure drifts to the ion‐acoustic speed ( C s ). The simulation results of the unified fluid model presented in the previous work [ Hassan et al , and Hassan , ] and the present work show a very good agreement with these radar measurements.…”

“…As noted above, in the previous work of Hassan et al [] the 2‐D unified fluid model that unifies the Farley‐Buneman and gradient‐drift instabilities was derived. There it was shown that this model has linear results that are comparable to the kinetic treatment of the Farley‐Buneman plasma instability by Schmidt and Gary [], and simulation results also showed good agreement with the radar measurements and sounding rocket observations.…”

“…Simultaneously, a backscattering radar measurement taken at Jicamarca, Peru, showed a strong Type I echo of 3 m wavelength which is modified by long‐scale horizontally propagating Type II waves [ Kudeki et al , ]. In Hassan et al [, ] the linear growth‐rate profile in the vertical direction of the ionosphere was seen to have three distinct regions in the equatorial electrojet: The lower region (90–103 km) being dominated by the gradient‐drift instability, the higher region (108–115 km) being dominated by the Farley‐Buneman instability, and the middle region (103–108) showing a strong coupling between the two types of plasma instabilities. Under varying ionospheric conditions, linear and nonlinear simulation results that reproduce many of the radar and rocket observations were described in that paper and light was shed on the physical mechanisms that drive these instabilities and are responsible for the coupling between them.…”

Plasma turbulence in the equatorial electrojet: A two-dimensional Hamiltonian fluid model

“…2, where the phase velocity is calculated at different altitudes using nonlocal magnitudes of the ionospheric background. 18,19 We still can see the three distinct regions of the equatorial electrojet with the exchange dominance and coupling between unstable waves of different scale-sizes that are generated as a result of the gradient-drift and Farley-Buneman instabilities. The maximum phase velocity is found at the core of the electrojet around 105 km has the same magnitude of the E × B drift velocity (400 m/s).…”

“…4 to unify Farley-Buneman and gradient-drift instabilities in the equatorial electrojet. In that model, the plasma dynamics in the ion viscosity-tensor and electron polarization drifts were considered to play an important role in stabilizing the evolving fields.…”