On merging empirical models for the lower ionosphere of auroral and non-auroral latitudes

The quiet ionosphere at high latitudes should in principle behave in a similar manner as the non-auroral ionosphere, i.e. controlled by the solar zenith angle, solar activity and season. Independent empirical models for auroral-zone and non-auroral latitudes have been developed over many years based on different sets of data; notably at high latitudes the small number of data from rocket borne wave propagation experiments was recently complemented by a much larger number of incoherent scatter data (EISCAT). The discontinuities between the two models are interpreted in terms of differences in the composition of the neutral atmosphere in the two latitude regions. Procedures are suggested to merge the non-auroral model which is defined up to 60degrees with the auroral model established with data taken at 70degrees. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.