Numerical simulation of the formation of thin ionization layers at high latitudes

Abstract

A one‐dimensional simulation of high latitude sporadic‐E layers has been developed to investigate the role of electric field in layer formation. The simulation model computes the ion densities (O+, O2+, N+, N2+, NO+, Fe+) and temperatures as a function of altitude. The stationary state momentum equation and continuity equation is solved for each ion species. Then the energy equation is solved for electrons, neutrals, and a generic ion having the mean ion mass and velocity. The model does not include any photoionization or particle precipitation. Chemical production and loss are included for the five standard ion species, but not for the Fe+ ions. An initial altitude profile is assumed for the ions, and the model computes the altitude distribution as a function of time. The horizontal direction of the electric field is important for determining the layer structure and its altitude. An electric field directed between magnetic west and north results in convergent plasma flow and thus layer formation at about 120–130 km altitude. For fields directed to the west and south layers form at lower altitudes(100–115km). With an assumed dip angle of 75° the layers formed by the N‐W quadrant fields form quickly (<10min), are quite thin, and remain stationary in altitude. Layers formed by S‐W quadrant fields are initially thick but compress in time (15–20 min). Additionally they move down in altitude as they compress. The large perpendicular electric field (50 mV/m) used in the simulation leads to significant heating of the ions and to a smaller extent the electrons and neutrals. The layer formed by the field directed in the N‐W quadrant occurs in the region of significant heating, and the temperature profile shows some enhancement at the layer altitude.