The role of the ring current in the generation or inhibition of equatorial F layer irregularities during magnetic storms

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Abstract
For the equatorial ionosphere in years of high solar flux the F layer parameters are such that irregularities are produced almost every night in specific months. The question that has emerged is why are there nights in these months without irregularities. The hypothesis advanced is that for this period, one must look not for external seeding mechanisms but for inhibiting factors. The ring current during magnetic storms appears to play a leading role directly or indirectly in establishing the conditions necessary for equatorial F layer irregularity generation and inhibition. The hypothesis advanced is that for a particular ionospheric propagation intersection, the local time when the peak excursion of the ring current occurs (its decay from maximum negative values), affects the equatorial electric field and therefore the height of the F layer. Using data from a number of magnetic storms with dates ranging from December 1971 to November 1981 primarily in years of high solar flux, the following categories were found. If the maximum ring current energy as shown by Dst occurred during the midnight to postmidnight time period, irregularities were generated. If the maximum Dst, the period before recovery set in, occurred in the early afternoon, irregularities were inhibited. If the maximum occurred around sunset or shortly after sunset, then there was no effect on the generation of irregularities that night. While the ideas on positive and negative correlation with magnetic indices have been shown in many early references, the importance of local time and its relationship with the maximum ring current energy have not been emphasized. The use of widely spaced equatorial data from Manila and Huancayo allowed for contrasting reactions for the same storm and for validation of the hypothesis for the months and solar conditions stated. For other periods, when occurrence of irregularities is lower, the effect on layer height may be only one factor in setting conditions for the generation of irregularities.

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