A Three Dimensional Model for Equatorial Ionospheric Bubbles

Previous models of equatorial plasma bubbles have been two-dimensional, describing the structure of the bubbles/plumes strictly perpendicular to the geomagnetic field in the equatorial plane or describing field-line integrated quantities. Our goal is to introduce the third dimension, and describe the variations along the direction of the geomagnetic field. Plasma transport within the three-dimensional structure is described using the perpendicular transport code of our previous two-dimensional bubble model along with a parallel transport code. The resulting plasma densities are then used to evaluate the field-line integrals of conductivity and current density in the current-continuity equation to provide self-consistent electric fields. In runs of the model, we find that the three-dimensional plasma exhibits the same upwelling instability found in two dimensions, with a similar tendency for the plumes to bifurcate in the plane perpendicular to the geomagnetic field. In new results, we find that the uplifting flux tubes of low plasma density tend to remain depleted from end to end, at least until they rise to the equatorial heights that map to the equatorial ionization anomalies. The anomalies tend to be structured on the inside (low latitude), smooth on the outside. These three-dimensional structures will be illustrated with computer animations. Images of equatorial bubbles as depletions of airglow emission are a useful diagnostic of bubble structure. We compare the predictions of the bubble model with some of the common views of airglow images of equatorial features. In-situ measurements of plasma density in the vicinity of the bubbles give us a set of constraints on the bubble extent. Another important diagnostic of bubble structure is the extent of radio scintillation measured by ground-based receivers. As an application of the model, this parameter is pursued with the goal of making forecasts of the scintillation.