Abstract
Abstract. A realistic fully time-dependent computer model, denominated LION (Low-latitude Ionospheric) model, that simulates the dynamic behavior of the low-latitude ionosphere is presented. The time evolution and spatial distribution of the ionospheric particle densities and velocities are computed by numerically solving the time-dependent, coupled, nonlinear system of continuity and momentum equations for the ions O+, O2+, NO+, N2+ and N+, taking into account photoionization of the atmospheric species by the solar extreme ultraviolet radiation, chemical and ionic production and loss reactions, and plasma transport processes, including the ionospheric effects of thermospheric neutral winds, plasma diffusion and electromagnetic E×B plasma drifts. The Earth's magnetic field is represented by a tilted centered magnetic dipole. This set of coupled nonlinear equations is solved along a given magnetic field line in a Lagrangian frame of reference moving vertically, in the magnetic meridian plane, with the electromagnetic E×B plasma drift velocity. The spatial and time distribution of the thermospheric neutral wind velocities and the pattern of the electromagnetic drifts are taken as known quantities, given through specified analytical or empirical models. The model simulation results are presented in the form of computer-generated color maps and reproduce the typical ionization distribution and time evolution normally observed in the low-latitude ionosphere, including details of the equatorial Appleton anomaly dynamics. The specific effects on the ionosphere due to changes in the thermospheric neutral winds and the electromagnetic plasma drifts can be investigated using different wind and drift models, including the important longitudinal effects associated with magnetic declination dependence and latitudinal separation between geographic and geomagnetic equators. The model runs in a normal personal computer (PC) and generates color maps illustrating the typical behavior of the low-latitude ionosphere for a given longitudinal region, for different seasons, geophysical conditions and solar activity, at each instant of time, showing the time evolution of the low-latitude ionosphere, between about 20° north and south of the magnetic equator. This paper presents a detailed description of the mathematical model and illustrative computer results.
Highlights
The distribution of ionization in the low-latitude ionosphere is characterized by the presence of the so-called Appleton anomaly or equatorial ionospheric anomaly
Different wind representations can be used in the LION model in order to analyze the wind effects on the low-latitude ionospheric ionization distribution at the various longitudes, and for different seasons and solar activity
Review articles on the equatorial ionospheric electric fields and low-latitude electrodynamic plasma drifts were published by Fejer (1981, 1991, 1997)
Summary
The distribution of ionization in the low-latitude ionosphere is characterized by the presence of the so-called Appleton anomaly or equatorial ionospheric anomaly. When measured values of the electron number density at the F2-peak are plotted as a function of magnetic latitude, for a given longitude and local time, a curve is obtained which shows a minimum (trough) over the magnetic dip equator, with two maxima (crests) at dip latitudes which may vary between 10◦ to 20◦ north and south of the dip equator, depending on local time and season This anomalous ionization distribution extends into the topside ionosphere where it gradually diminishes. A latitudinal asymmetry in the electron density, as well as in the F2-peak height, at the north-south crests has been observed, and it shows different behavior in the various longitudinal sectors, at the same local time This anomalous ionization distribution at low latitudes has been explained in terms of plasma transport processes that move the ionization to regions other than that of its production. A review on the electrodynamics of the equatorial ionosphere-thermosphere system was recently presented by Abdu (2005)
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