Self-consistent studies of two-dimensional large-scale (approx.100 m) electrojet irregularities

Two-dimensional structures of the cross-field instability are numerically studied in detail including self-consistent changes of vertical electric field and electron density profiles with the intention of studying type 2 electrojet irregularities of order 100 m. Many important results pertinent to nonlinear development of the irregularities are disclosed. The principal points are as follows. (1) The main stabilization mechanism is the density profile change due to the vertical nonlinear mass transport. (2) The saturation amplitude of density irregularities is almost independent of the electrojet speed but largely dependent on the density profile. (3) The electrojet speed is appreciably slowed down especially at the most unstable height. (4) The vertical profile of the irregularity amplitude is usually a double-peaked one, the peaks being bifurcated on both sides of the most unstable height at a distance of, say, a few hundred meters. (5) The power spectral shape of the density irregularities approaches k-3 in the horizontal direction as the electrojet speed increases. The vertical spectral shape cannot be expressed in a simple form but has a tendency to decrease as k-3, crudely speaking. On the other hand, the (power) spectral shape of the potential irregularities is always about k-6. (6) At the lower border of the unstable region, positive streaks (compression) are repeatedly generated and propagate upward, while at the upper border, negative streaks (rarefaction) are generated and propagate downward. They encounter at the most unstable height and then annihilate. Their speed is roughly 5 times as fast as the electrojet speed, the pulse width is roughly 100 m, and the amplitude can reach several percent. Comparison with nonlinear theories is also briefly made