Equatorial ionospheric responses in relation to the occurrence of main phase of intense geomagnetic storms in the local dusk sector

During five intense geomagnetic storms with main phases occurring around local dusk sector, equatorial ionosonde and electrojet data, VHF/UHF scintillation data of Calcutta, and several solar wind parameters are investigated to ascertain the polarity of prompt penetration electric field (PPEF). Abrupt increases in AE, ASY-H and/or sharp decreases in Dst/SYM-H with strong southward IMF Bz may symbolize eastward PPEF to equatorial latitude leading to evolution of density irregularities if the period is associated with arrival and sustenance of large magnetospheric shock compression. On the contrary, westward PPEF is more feasible if the shock reduces suddenly or fluctuates with small values.

► Feasibility conditions for storm induced equatorial irregularities are studied.
► For dusk sector MPO southward IMF Bz and dDst/dt≤−50 nT/h are not useful proxies.
► Persistence of large magnetospheric shock for ≥6 h may indicate eastward PPEF.
► Inhibition of irregularities is more probable for sudden shock reduction.