Equatorial Plasma Bubbles: Variation of the Longitudinal Distribution with Altitude

Abstract

The equatorial plasma “bubbles” that form at the bottom-side of the F-layer are affected by zonal plasma drift when they rise to greater altitudes. Under the influence of the drift, the bubbles move eastward. Conversely, a plasma bubble that is “stretched” along a magnetic flux tube repeats its spatial course. For example, a change in the magnetic declination of a flux tube will result in a change in the longitudinal orientation of the bubble. Bubbles undergo an eastward shift in regions with an eastern magnetic declination and a westward shift in regions with a western magnetic declination. The character of the influence of these factors has been studied on the examples of the longitudinal distributions of the equatorial plasma bubbles calculated for the winter and spring periods. For this purpose, the data from the ISS-b, AE-E, OGO-6, ROCSAT-1, and Hinotori satellites obtained in the years of high solar activity at the different orbital altitudes were used. It was found that the bubbles detected at the altitudes of ~972–1220 km in the 0°–50° DIPLAT band follow the course of the magnetic declination of the flux tube, experiencing almost no influence of the zonal plasma drift. The bubbles detected at the altitudes of ~300–700 km within ±20° DIPLAT were found to be strongly influenced by the eastward zonal drift. The magnetic declination only controls the magnitude of their shift in the east direction.