University of Crete Island of Crete

Approaches to the study of non-electrodynamical sources of
ionospheric variability at equatorial and low latitudes

M. Mendillo1, H. Rishbeth1,2, R. Roble3, J. Wroten1 and B. Foster3
  1. Boston University, Boston, MA 02215, USA
  2. University of Southampton, Southampton, UK
  3. National Center for Atmospheric Research, Boulder, CO, USA

Over the span of the full set of ISEA meetings, participant attention has most often been focused upon topics of plasma disturbances---morphologies, sources, mechanisms and effects.  These included both F-layer and E-layer perturbations that range from small scale, non-storm-time, plasma instabilities, to the large-scale modification of the entire ionosphere’s total electron content (TEC) during major geomagnetic storms. Consistent with the very nature of the regime defined by the equatorial ionization anomaly (EIA), electrodynamical processes are often seen to be the foremost driver of disturbed behavior.  In addition to locally-induced electric field effects, well known magnetosphere-ionosphere interactions penetrate to low latitudes as well.  Attention is now being given to the important sources of vertical coupling from below and, in particular, to non-electrodynamical mechanisms, or at least processes initiated by non-electrical effects.  In this paper, we review the broad context of ionospheric variability over time scales of day-to-night, day-to-day and month-to-month.  We do this using the TIME-GCM model run for each day of 2002, and compare the predictions for variability with the patterns observed at three low latitude ionosonde stations. These are Jicamarca (near the geomagnetic equator), Ascension Island (near a crest of the EIA), and Darwin (poleward of the EIA).  As with midlatitude effects, observed variability for the F-layer peak density is typically 15-25% for all seasons, while model results fall short of that level.  Variabilities observed during geomagnetic disturbances versus quiet periods do not differ appreciably, as found also in model calculations using input parameters for each of those days.

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