Morphological studies of rising equatorial spread <i>F</i> bubbles

Abstract

Analytical electrodynamic morphological studies of rising equatorial spread F bubbles, within the context of the collisional Rayleigh‐Taylor regime, are presented. The analogy between bubbles (plasma density depletions) and barium clouds (plasma density enhancements) is noted. Bubbles tend to steepen on their tops and elongate in the vertical direction, and they narrow horizontally as they rise through the equatorial F region ionosphere. Linear and nonlinear models of constant shape bubbles are presented. It is shown for these models that the vertical bubble rise velocity V B = (g/ν in ) f (δ n / n 0 ), where ν in is the ion‐neutral collision frequency and f is an increasing function of δ n / n 0 (fractional density depletion), depending on the shape of the bubble. Consequently, high altitudes and/or large percentage plasma depletions yield large vertical bubble rise velocities. The models are extended to include arbitrary electric fields in addition to the gravitational force.