On the Assessment of Day‐To‐Day Occurrence of Equatorial Plasma Bubble

Abstract

AbstractIn this paper, we address the day‐to‐day variation in the development of equatorial plasma bubble (EPB) using simultaneous observations made by the 30 MHz Gadanki Ionospheric Radar Interferometer (GIRI) and ionosonde (DPS‐4D) from Gadanki and C/NOFS. We show that wave‐like variations with horizontal wavelengths of 200–660 km observed prior to sunset have a close connection with EPB spacings. We also show that the locations of EPB development at their origins, which varied on a day‐to‐day basis, were as large as 2600 km from Gadanki. A detailed analysis clearly reveals the cause of such variability and provides clue as to where the background ionospheric conditions led to the growth of the Rayleigh Taylor instability (RTI) generating EPB and where they failed. Results clearly show that while ionosonde observations show great potential for understanding day‐to‐day variation and predicting EPB development overhead (within ±1° longitude), they are inadequate to assess the growth potential of EPB at longitudes away from a longitude zone of about ±1° from overhead. A detailed analysis suggests that the day‐to‐day variability in EPB development is governed by large scale wave structures (LSWS) and it is inferred that the LSWS troughs (low electron density) are the sites for the EPB development. Results further suggest that LSWS with horizontal wavelength of 200–660 km acts as seed for the growth of the RTI resulting in EPBs with same spacing. While the sources of LSWS remain to be identified, it is suggested that observations with longitudinally distributed ground‐based sensor, viz., ionosonde, preferably separated by 250–300 km, would be an immediate step forward in this effort.