Multi‐Source Perturbations in the Evolution of a Low‐Latitudinal Equatorial Plasma Bubble Event Occurred Over China

Abstract

AbstractIn this paper, multi‐source perturbations during the evolution of an equatorial plasma bubble (EPB) event at low latitudes in China are studied by means of multi‐ground‐based instruments, including an all‐sky airglow imager, a very high frequency (VHF) radar and eight digisondes. We found that EPB event initially evolved from bottom perturbations (∼600 km scale) seeded by atmospheric gravity waves in a form of large‐scale wave‐like structure, accompanying smaller‐scale perturbations (∼150 km scale) mostly by collision‐shear instability (CSI); once formed, those seed perturbations further evolved into the ionospheric topside by the plasma instability. Observed and analyzed are two different instabilities: one is the Rayleigh‐Taylor instability (RTI) driven by a prereversal enhancement of the zonal electric field (PRE) occurred near sunset; the other is an equatorward wind‐induced secondary E × B gradient drift instability (GDI) around midnight. Accompanying the PRE‐induced RTI are freshly‐generated depletions with larger poleward (upward) velocities. The PRE‐driven RTI could elevate the bottom perturbations directly to form fast‐moving depletions/structures at the ionospheric topside. The E × B GDI was trigged by a vertical upward plasma jet caused by a seasonal equatorward wind in regions as far as 10°N (20°N) from the geomagnetic (geographic) equator. This equatorward wind‐induced E × B GDI continuously forced topside structures of those drifting‐type EPB depletions to extend poleward more slowly, resulting in active 3.2‐m irregularities around midnight. Besides, we present evidence that a westward polarization electric field generated in an adjacent trough region of the faster‐growing cluster‐type depletions inhibited the neighboring slower‐growing cluster‐type depletions.