Equatorial ionospheric responses to magnetospheric storm/substorm-associated electric fields are investigated for a few intense events of the equinoctial months of solar maximum years 1978--1979. All the magnetic storms considered here are the result of the transit at Earth of interplanetary magnetic clouds. The interplanetary magnetic field data Bz from the ISEE 3 satellite, the auroral electrojet activity index AE, and the ring current index Dst are used as indicators of the disturbed magnetospheric conditions, and the ionospheric response features are analyzed using the F layer critical parameters h'F, h'F3, hpF2, and f0F2. Focus is given to identify, when a large number of sequential substorms occurs, (1) the responses to prompt penetration electric field (from individual substorm events) as different from the delayed effect from the disturbance dynamo electric field and (2) the verification of local time dependences of the disturbance electric field polarity as predicted from the existing theoretical models. We have found evidence of near-midnight polarity reversal of prompt penetration disturbance electric field during the course of a developing substorm. Evidence is provided also on the near-midnight polarity reversal for the disturbance dynamo electric field. The prereversal enhancement electric field at sunset, produced by the F layer dynamo, is found to undergo drastic day-to-day variations in the course of a disturbed interval. However, the competing influences of the prompt versus delayed electric fields after a series of substorms could result at times in partial, or even complete, cancellation of the effects, so that the prereversal enhancement in the vertical drift could appear unaffected by the disturbances. There are indications that the disturbance dynamo electric field effects on the equatorial ionosphere last for one more day past the end of the substorm recovery.¿ 1997 American Geophysical Union