A total electron content space weather study of the nighttime Weddell Sea Anomaly of 1996/1997 southern summer with TOPEX/Poseidon radar altimetry

This paper reports on a total electron content space weather study of the nighttime Weddell Sea Anomaly, overlooked by previously published TOPEX/Poseidon climate studies, and of the nighttime ionosphere during the 1996/1997 southern summer. To ascertain the morphology of spatial TEC distribution over the oceans in terms of hourly, geomagnetic, longitudinal and summer-winter variations, the TOPEX TEC, magnetic, and published neutral wind velocity data are utilized. To understand the underlying physical processes, the TEC results are combined with inclination and declination data plus global magnetic field-line maps. To investigate spatial and temporal TEC variations, geographic/magnetic latitudes and local times are computed. As results show, the nighttime Weddell Sea Anomaly is a large (similar to 1,600(degrees)(2); similar to 22 million km(2) estimated for a steady ionosphere) space weather feature. Extending between 200 degrees E and 300 degrees E (geographic), it is an ionization enhancement peaking at 50 degrees S-60 degrees S/250 degrees E-270 degrees E and continuing beyond 66 degrees S. It develops where the spacing between the magnetic field lines is wide/medium, easterly declination is large-medium (20 degrees-50 degrees), and inclination is optimum (similar to 55 degrees S). Its development and hourly variations are closely correlated with wind speed variations. There is a noticeable (similar to 43%) reduction in its average area during the high magnetic activity period investigated. Southern summer nighttime TECs follow closely the variations of declination and field-line configuration and therefore introduce a longitudinal division of four (Indian, western/eastern Pacific, Atlantic). Northern winter nighttime TECs measured over a limited area are rather uniform longitudinally because of the small declination variation. TOPEX maps depict the expected strong asymmetry in TEC distribution about the magnetic dip equator.