East-west and vertical spectral asymmetry associated with equatorial type I waves during strong electro jet conditions: 2. Theory

Abstract

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. Copyright 2006 by the American Geophysical Union.