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Sometimes the ionospheric total electron content (TEC) is\udsignificantly enhanced during low geomagnetic activities before storms.\udIn this article, we investigate the characteristics of those interesting TEC\udenhancements using regional and global TEC data. We analyzed the low-latitude\udTEC enhancement events that occurred around longitude 120° E\udon 10 February 2004, 21 January 2004, and 4 March 2001, respectively. The\udTEC data are derived from regional Global Positioning System (GPS)\udobservations in the Asia/Australia sector as well as global ionospheric maps\ud(GIMs) produced by Jet Propulsion Laboratory (JPL). Strong enhancements\udunder low geomagnetic activity before the storms are simultaneously\udpresented at low latitudes in the Asia/Australia sector in regional TEC and\udJPL GIMs. These TEC enhancements are shown to be regional events with\udlongitudinal and latitudinal extent. The regions of TEC enhancements\udduring these events are confined at narrow longitude ranges around longitude\ud120° E. The latitudinal belts of maxima of enhancements locate around\udthe northern and southern equatorial ionization anomaly (EIA) crests, which\udare consistent with those low-latitude events presented by Liu et al. (2008). During\udthe 4 March 2001 event, the total plasma density <I>N<sub>i</sub></I> observed by the Defense\udMeteorological Satellite Program (DMSP) spacecraft F13 at 840 km altitude\udare of considerably higher values on 4 March than on the previous day in the\udTEC enhanced regions. Some TEC enhancement events are possibly due to\udcontributions from auroral/magnetospheric origins; while there are also\udquasi-periodic enhancement events not related to geomagnetic activity and\udassociated probably with planetary wave type oscillations (e.g. the 6\udJanuary 1998 event). Further investigation is warrented to identify/separate\udcontributions from possible sources

Case study on total electron content enhancements at low latitudes during low geomagnetic activities before the storms