Modeling the formation of intermediate layers at Arecibo latitudes

Abstract

By using a modified version of the ionospheric model described by Bailey and Sellek (1990), we model the formation of intermediate ionization layers due to meridional neutral winds in the valley region between the E and F regions. The calculations are performed on a single field line with L = 1.4, in order to compare the results with observations of intermediate layers from the incoherent scatter radar at Arecibo. The winds are given a sinusoidal variation in altitude, and the effects of the wind amplitude and wavelength on layer formation are examined. Nighttime ionization rates are artificially specified to correspond with observed rates in the region. Our results show that tidal like meridional wind profiles act to deplete the apparent background ionospheric number density as well as enhance the number density in the intermediate layer. Thus the layer appears as an enhancement above a background that is much smaller than the background that would be present in the absence of a wind. In this way, layers with relatively high molecular ion concentrations can exist. Intermediate layers are seen to form at nulls in the neutral wind altitude profile, but in the altitude region above roughly 160 km this null need not coincide with a zero in the field‐aligned ion velocity.