Nonlinear growth, bifurcation, and pinching of equatorial plasma bubble simulated by three‐dimensional high‐resolution bubble model

Abstract A new three‐dimensional high‐resolution numerical model to study equatorial plasma bubble (EPB) has been developed. The High‐Resolution Bubble (HIRB) model is developed in a magnetic dipole coordinate system for the equatorial and low‐latitude ionosphere with a spatial resolution of as fine as 1 km. Adopting a higher‐order numerical scheme than those used in the existing models, the HIRB model is capable of reproducing the bifurcation, pinching, and turbulent structures of EPB. From a seeding perturbation resembling large‐scale wave structure (LSWS), EPB grows nonlinearly from the crest of LSWS upwelling, bifurcates at the top of EPB, then becomes turbulent at the topside of the F region. One of the bifurcated EPB is pinched off from the primary EPB and stops growing after pinching. The narrow channel of EPB tends to have a wiggle due to the secondary instability along the wall of EPB. Because of the fringe field effect above and below the EPB, upward drifting low‐density plasma converges toward the F peak altitude, forming a narrow‐depleted channel, and diverges above the peak, forming a flattened top of the EPB. The flattened top which has a steep upward density gradient is so unstable that bifurcation can easily occur even from a very small thermal perturbation. A higher density region between the bifurcated EPB moves downward due to westward polarization electric field. The EPB is pinched off when it reaches the wall of the primary EPB. It is concluded that turbulent plume‐like irregularities can be spontaneously generated only from large‐scale perturbation at the bottomside F region.