• Fulltext


        Click here to view fulltext PDF

      Permanent link:

    • Keywords


      Equatorial ionosphere; equatorial spread F; F-region drift; plasma density irregularities.

    • Abstract


      The equatorial ionosphere often shows the occurrence of plasma-density irregularities and velocity fluctuations with a broad range of scale sizes and amplitudes. These irregularities in the F-region are commonly referred to as the equatorial spread F (ESF) and they are predominantly a night-time phenomenon. The vertical drift of ionisation to higher altitudes post-sunset hours has been suggested to be responsible for the occurrence of these irregularities. We have therefore used all the available ionograms at Ilorin, Nigeria (latitude = 8.48$^{\circ}$N, longitude= 4.67$^{\circ}$W and dip= 4.1$^{\circ}$S) to study the occurrence of ESF and the effect of the F-region drift on the occurrence of ESF. The available data at Ilorin, though not continuous, cover a period of 6 yrs (i.e., 2002, 2005, 2006, 2007, 2008 and 2010). The F-region vertical drift velocity was estimated starting from around local sunset until the onset of ESF, and the maximum value for a night ($V_{Z,\rm{max}}$) is used to represent the strength of the $E \times B$ drift for that night. Results obtained showed that the percentage occurrence of ESF increases with the increase in solar activities. A seasonal trend is also observed in the occurrence frequency; occurrence seems to be more frequent during and around the equinox periods. The onset time or the time of commencement (TOC) of ESF was observed to vary from day to day. Also, $V_{Z,\rm{max}}$ seems to increase with the increase in solar activities, which in turn influences the TOC of ESF. It was found that the higher the $V_{Z,\rm{max}}$, the closer the TOC was found to be to the local time $V_{Z,\rm{max}}$. In a few cases, there was no noticeable movement of ionisation prior to the commencement of the ESF, and this might be pointing to the fact that the drifting of ionisation to a higher altitude is not the only condition for the occurrence of ESF. Other conditions that have been identified to play a role in ESF occurrence are thermospheric neutral dynamics, equatorial thermodynamic meridional winds and the post-sunset base height of the F-layer ($h^{\prime}F$).

    • Author Affiliations


      Oladipo O A1 Adeniyi J O2 Adimula I A1 Olawepo A O1 Olowookere A1 Salifu F U1 Radicella S M3 Reinisch B W4

      1. Physics Department, University of Ilorin, P.M.B. 1515, Ilorin, Nigeria.
      2. Faculty of Science and Engineering, Department of Physical Sciences (Physics Programme), Landmark University, P.M.B. 1001, Omu Aran, Nigeria.
      3. Aeronomy and Radiopropagation Laboratory, The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34014 Trieste, Italy.
      4. Lowell Digisonde International, LLC, 175 Cabot Street, Suite 200, Lowell, MA 01854, USA.
    • Dates

  • Journal of Earth System Science | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.