Formation of the electron density layers in the equatorial E-region

Ion convergence rates at various latitudes are calculated and discussed in relation to the formation of electron density layers in the equatorial E region. A three-dimensional model of gravity wave winds is used to obtain an expression for ion velocity which is in turn used in the derivation of an expression for the ion convergence rates due to the interaction of the winds with the ionospheric plasma. Calculations show that the convergence rate increases with decreasing wavelength in the vertical direction and is at a maximum at the equator below 120 km and a minimum at the equator above 185 km. In addition, the convergence rate is found to be very small when the wavelength along the magnetic field direction is very large, and ion convergence in the lower E region is due to vertical shear in the east-west wind while in the F region it is due to field-aligned shears in the field-aligned wind. The rates obtained, together with estimates of daytime and nighttime electron densities in the 100-km region, are shown to imply that the formation of ionization layers through ion convergence is only possible at night