Abstract:
The unusual evolution of fresh and intense field-aligned irregularities (FAI) near sunrise terminator
which further sustained for more than 90min of postsunrise period was observed by Equatorial Atmosphere
Radar at Kototabang during a minor geomagnetic storm period. These FAI echoes were initially observed
around 250–350 kmaltitudes, growing upward under eastward polarization electric fields indicating the plasma
bubbles that are fully depleted along the flux tube. The background low-latitude F layer dynamics that lead to
the development of these dawn time FAI have been investigated from two ionosondes at near magnetic
conjugate low-latitude locations. A minor geomagnetic storm was in progress which did not appear to cause
any large electric field perturbations at preceding postsunset to midnight period over Indonesian sector.
However, the prompt penetration of overshielding electric fields associated with sudden northward turning of
interplanetary magnetic field Bz caused spectacular ascent of F layer and development of fresh, intense, and
upward evolutionary plasma bubbles near sunrise terminator.
