Low-Latitude Ionospheric Density Irregularities and Associated Scintillations Investigated by Combining COSMIC RO and Ground-Based Global Positioning System Observations Over a Solar Active Period

This study for the first time presents a locally integrated analysis of occurrences of ionospheric E and F region irregularities/scintillations in southeast China, by employing radio occultation (RO) profile data retrieved from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites and observations from a ground-based Global Navigation Satellite System receiver over a solar active period from 2014 to 2015. Their occurrences in both nighttime and daytime were examined by using both amplitude scintillation index (S4) and the rate of change of total electron content index. It is found that (1) F region irregularities occurred predominantly during 20–03 local time (LT) and exhibited maximum (minimum) during equinoxes (solstices) and equinoctial (solstice) asymmetry. Their geographic mapping reveals the maximum occurrence in the westward tilted structure of equatorial plasma bubbles. In addition, the altitude-time variations indicate that their occurrences at higher altitudes were prevailing at 20–22 LT. (2) The E region irregularities were found prominently during 15–00 LT at altitudes of 90–110 km with an even geographic distribution. Their occurrences with maximum in summer (May–August) were distinctly detected by RO observations but insignificantly by ground-based observations. (3) By examining simultaneous observations of E and F region irregularities, it is found that they appeared absent during 21–00 LT and predominant after midnight. This could be related to the weakening/disruption of sporadic E (Es) layers during the development of equatorial plasma bubbles. A sign of coupling of E and F regions during nighttime is likely revealed from RO profile data.