Interplanetary magnetic field variations and the electromagnetic state of the equatorial ionosphere

Abstract

The effect of interplanetary magnetic field variations on the low‐latitude ionosphere has been studied by using the simultaneous occurrence of three phenomena—the disappearance of equatorial Esq, the reversal or decrease in intensity of the equatorial electrojet as implied from magnetogram signatures, and a northward turning of the z component of the interplanetary magnetic field Bz observed by the Explorer 43 satellite. The search for the simultaneous occurrence of these three phenomena is met with partial success because out of 20 events for which simultaneous data were available, 12 showed no significant change in the interplanetary field near the disappearance of the Esq. Four of the remaining eight showed only small variations. The four best cases are presented in detail. A possible explanation, for these events, is that the induced electric field imposed on the magnetosphere through the change in Bz and coupled to the high‐latitude ionosphere may affect the low‐latitude ionosphere by high‐latitude‐low‐latitude coupling. If the electric field is impressed to the low latitude, the resultant field may suppress cross‐field instability and cause the disappearance of the Esq.