Characterization of ionospheric irregularities at different longitudes during quiet and disturbed geomagnetic conditions

This paper investigates the plasma irregularities at different longitudes in the month of March 2015; a period that consists of both quiet and disturbed geomagnetic conditions. The average rate of change of TEC index (ROTI_ave), derived from Global Positioning System (GPS) measurements obtained at South America, Africa, Asia and Oceania equatorial regions, was used as indicator. The observations revealed significant longitudinal differences for both quiet and disturbed conditions. The quiet-time observations indicate that irregularities were most frequent in the American and African sectors, it is rarely observed in the Asian sector and mostly absent in the Oceania longitudes. The strength is however observed to decrease eastward i.e. it is most prominent in the American sector (up to ∼1.6 TECU/min.) and absent in the Oceania longitudes. The results of the investigation of the 17 March, 2015 storm event revealed that the storm appeared not to hinder the development of irregularities in all the stations in the America sector during the night following the main phase. However, significant longitudinal variation is observed within the sector on the first night following the storm's recovery. In the African sector, the storm inhibits the development of irregularities in all the stations during the storm days considered: a development that is fundamentally different from the America sector. Generally, no significant storm effect is observed in the Asian and Oceania stations considered. The storm-time longitudinal variations of irregularities have been partly attributed to the storm timing and significant longitudinal difference in the action of storm-induced related drivers.