Abstract:
Results are presented of a study of h-prime F data derived from interval ionograms recorded on the night of August 29-30, 1957 at Kodaikanal (10 deg 14 min N, 77 deg 29 min E, geomag. lat. 0.6 deg N) during a geomagnetic storm revealed clear-cut evidence for the occurrence of a transient electric field perturbation of a composite nature during a substorm, which occurred in the midnight-dawn period on that date. The perturbation is characterized by a sudden decrease in h-prime F, followed by a prominent increase over a 3-hr period. The decrease in h-prime F occurred around the onset of the substorm, and the subsequent increase took place during the substorm recovery phase. The observed F-region height disturbance is interpreted as a signature of a transient composite disturbance in the equatorial zonal electric field caused by the prompt penetration of high-latitude electric fields into the equatorial ionosphere.
