Numerical simulation of mid-latitude ionospheric E-region based on SEEK and SEEK-2 observations

Abstract. Observational campaigns of the mid-latitude ionospheric E-region with sounding rockets and ground-based instruments were conducted in 1996 (SEEK) and 2002 (SEEK-2). Both of them were successfully conducted to bring important findings about the mid-latitude E-region and quasi-periodic (QP) VHF radar echoes. The observational results in the SEEK and the SEEK-2 are compared with numerical simulations and discussed in this paper. While sporadic-E (E_s)-layers are actually formed by the observed neutral wind, it is difficult for the constant wind shear to produce the sharp E_s-layer gradient. However, once they are formed in the lower E-region, they cannot easily be dissipated by the simple diffusive motion. The polarization electric field, calculated under the condition at the rocket launch time, shows similar amplitude and structure to the measurement around the E_s-layer altitude. The structure of the plasma density and the electric field above the E_s-layer observed in the SEEK-2 showed a wave-like pattern up to an altitude of 150 km. Considering a mapping of the polarization electric field generated within the E_s-layers, gravity waves are the possible source of the wave-like structure of the measured electric fields and sub-peaks of the electron density above the main E_s-layers. Fluctuation of the measured magnetic field is reproduced by Hall or field-aligned current driven by the polarization electric field. The current theoretical models for QP echoes and the polarization electric field are basically verified by the discussion in this paper.

Keywords. Ionospheric irregularities – Mid-latitude ionosphere – Numerical simulation studies