Zonal/meridional wind and disturbance dynamo electric field control of the low-latitude ionosphere based on the SUNDIAL/ATLAS 1 campaign

We present an evaluation of global-scale equatorial and low latitude ionospheric disturbances in response to the weak-to-moderate disturbed conditions that marked the SUNDIAL/ATLAS1 twelve-day campaign of Match 22 to April 2, 1992. Ionosonde data from South American and Indian-Asian longitudes are analyzed to examine first the climatological (the average) pattern of the critical F region parameters (the layer peak density and height) in comparison with the empirical International Reference Ionospheric model, and then to characterize the day-to-day variabilities aiming at identifying potential causal contributions from either disturbance zonal and meridional winds or magnetospheric and disturbance dynamo electric fields. Included in this analysis are data from South American midlatitude locations which are used to determine meridional winds using an adaptation of the servo analysis technique in the Field Line Integrated Plasma (FLIP) model. We have made an assessment of the causal mechanism of the day-to-day variabilities as arising from latitude dependent disturbance meridional winds, and from electric fields produced by disturbance zonal winds and disturbance dynamo. While the contribution from disturbance meridional winds decreases from middle to equatorial latitudes, that of the electric fields maximizes : around the equator. In particular, first-time evidence based on ionosonde data is provided for a disturbance dynamo electric field in the equatorial ionosphere. It is found that there are two time intervals of maximum ionospheric variability resulting from the weak to moderate magnetospheric disturbance conditions that prevailed during the campaign: one near the evening/postsunset hours and the other in the postmidnight-sunrise hours over low latitudes. At midlatitudes a broad maximum of the response occurs from premidnight to morning hours. We provide a comparison of results for the South American and Indian-Asian longitudes and a discussion of the competing roles of the disturbance zonal and meridional winds; and magnetospheric and disturbance dynamo electric fields as a function OI latitude.