Observation of TEC Depletions during the Storm Sudden Commencement

For the study of night time TEC depletion during the disturbed geomagnetic conditions, the TEC data over the low latitude stations QUI1, Quito (Geog. Lat. 0.21°S, Geog. Long. 281.50°E, Geomag. Lat. 9.60°N) located in the Ecuador, South America have been analyzed for the event of 15 May 2005 geomagnetic storm. Since the IGS receivers do not provide the amplitude scintillation index (S4 index) hence rate of TEC index (ROTI) have been calculated and is presented along with TEC variation. These observations may be used to infer that the nighttime TEC depletions at low latitudes could be observed before the storm main phase.