Some aspects of electrostatic coupling between E and F regions relevant to plasma irregularities: A review based on recent observations

This paper provides a review on some of the electrostatic coupling effects relevant for generating/modifying plasma irregularities during nighttime in the low latitude ionosphere based on recent observations. Emphasis is given to the role of large polarization electric field associated with an unstable region affecting another region remotely located. Recent radar observations on valley region and E region irregularities from low latitudes show convincing evidence in support of effective electrostatic field coupling along the magnetic field line for their manifestation. Interestingly, the low latitude observations clearly show the ineffectiveness of plasma bubble related fringe fields in generating low latitude valley region irregularities unlike that over the dip equator. Velocity perturbations associated with the unstable low latitude E region relevant for studying the seeding of equatorial spread F are also shown. These new observations have been critically examined in the light of existing experimental knowledge and current understanding of the electrostatic coupling effects for the generation/modification of plasma irregularities in a remote region.