East‐west and vertical spectral asymmetry associated with equatorial type I waves during strong electrojet conditions: 2. Theory

Abstract

[1] In order to explain vertical and east-west type I asymmetries uncovered in a companion paper and in references therein, we introduce the notion that the generating large-scale gradient drift waves break down first in elongated isolated enhancement and depletion regions (blobs and holes) that follow an asymmetric nonlinear evolution. The nonlinear evolution is accompanied by a rotation of the electric field inside the structures, be they blobs or holes. It is shown here that holes have a tendency to rotate more than blobs but that as a result the electric field inside holes is also weaker. These two features (contrasting rotations and contrasting field strengths) explain the predominant sign of the up-down and east-west asymmetries during weakly to moderately driven conditions. They also explain how the asymmetry is observed to disappear and even to reverse its sign under more strongly driven conditions. Citation: St.-Maurice, J.-P., and R. K. Choudhary (2006), East-west and vertical spectral asymmetry associated with equatorial type I waves during strong electrojet conditions: 2. Theory,

East‐west and vertical spectral asymmetry associated with equatorial type I waves during strong electrojet conditions: 1. Pohnpei radar observations

“…In turn, this points to a connection with the electrojet itself since the growth and saturation amplitude of the large‐scale gradient drift irregularities that drive the type I waves should depend on the vertical electric field (and, of course, on the ambient vertical density gradients). In paper 2 [ St.‐Maurice and Choudhary , 2006] we propose a mechanism that could be responsible for the dependence of the east‐west and up‐down asymmetries on driving conditions associated with the kilometer‐size gradient drift waves. The mechanism is based on a nonlinear description of the evolution of gradient drift instability.…”