author = "Abdu, Mangalathayil Ali",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)}",
                title = "Precursor wave structure, polarization electric field and vertical 
                         drift as drivers for equatorial plasma bubble/spread F 
                 year = "2015",
         organization = "Annual Meetings Asia Oceania Geosciences Society (AOGS)",
             abstract = "The plasma bubble/spread F irregularities of the nighttime 
                         equatorial ionosphere typically develop in the post sunset hours, 
                         and often continue till sunrise. The irregularities develop from 
                         the R-T instability mechanism operating at the bottomside of an F 
                         layer in rapid rise under an enhanced evening prereversal zonal 
                         electric field (PRE). A precursor seed perturbation in electron 
                         density with polarization electric field, to be present at the 
                         steep density gradient region of the F layer bottomside, is an 
                         additional requirement, as per theoretical considerations and 
                         model studies. Recent results from both statistical as well as 
                         case studies bases have supported the presence of such 
                         perturbations in the form of wave structures, likely produced by 
                         upward propagating gravity waves. An important issue concerns the 
                         complementary/competing influences from the PRE and seed 
                         perturbation in the ESF development process. Of particular 
                         interest are the characteristics of the precursor wave structure 
                         in the hours preceding the post sunset ESF development, as 
                         diagnosed by different observational techniques. Analysis of the F 
                         layer heights at specific plasma frequencies as measured by 
                         Digisondes operated at equatorial and low latitude sites, 
                         including magnetic conjugate sites, in Brazil has revealed the 
                         characteristics of precursor wave structure in the form of gravity 
                         wave oscillations and their amplification in the afternoon hours 
                         leading to post sunset ESF development. In this talk we will 
                         present and discuss recent results on the characteristics of the 
                         precursor wave structure as seen by different techniques, and in 
                         particular the observations by Digisondes showing evidence on its 
                         sustenance and amplification in the afternoon hours, supported by 
                         model results, and the relationship to the PRE and post sunset ESF 
  conference-location = "Singapore",
      conference-year = "2-7 Aug.",
        urlaccessdate = "26 jan. 2021"