Characteristics of travelling ionospheric disturbances observed in total electron content over Waltair

The diurnal and seasonal variations of travelling ionospheric disturbances (TIDs) have been studied using continuous data of total electron content (TEC) obtained at Waltair during the low sunspot activity period of 1983-1985. Results indicate that the level of occurrence is considerably higher in winter than in summer. The onset time of occurrence of TIDs is generally around 0800-0900 hrs LT in all the three different seasons.