Ionospheric effects near the magnetic equator and the anomaly crest of the Indian longitude zone during a large number of intense geomagnetic storms

► Storm time evolution of ionospheric irregularity depends on local times of MPO/EMP. ► For premidnight scintillation near the EIA crest dDst/dt≤∼−25 nT/h may be a proxy. ► Sharp increase in Dst and northward turning of Bz favor postmidnight scintillation. ► Scintillation occurrence depends on amplitude and initiation time of TEC deviation. ► h′F thresholds for irregularity are lower on disturbed times than quiet times.