This contribution is the first of a two-part investigation into an unseasonal post-sunset
equatorial F-region irregularity (EFI) event over the Southeast Asian region on the evening
of 28 July 2014. Ground-based GPS scintillation data, space-based GPS radio occultation
(RO) data, and ionosonde data show the existence of EFIs shortly after sunset over a region
spanning 30° in longitude and 40° in latitude, centered on the geomagnetic equator. This
post-sunset EFI event was observed during a time of the year when post-sunset equatorial …

An unseasonal development of Equatorial Plasma Bubble (EPB)/Equatorial Spread-F (ESF)
activity in a wide longitudinal sector over India and Southeast Asia during the post-sunset
hours of 28 July 2014 has been investigated in detail using the multiple independent
observations in this paper and a companion paper by (Prog Earth Planet Sci 5: 10, 2018).
This post-sunset ESF/EPB event was preceded by a substantial elevation of the equatorial F-
layer due to strong pre-reversal enhancement (PRE) during the season which is …