The Equatorial F‐layer Irregularity Extent as Observed From Huancayo, Peru

Abstract

Simultaneous observations of propagation paths to two synchronous satellites transmitting at 137 MHz have revealed distinctive characteristics of the equatorial irregularity structure. Data were taken between July 1967 and February 1969. The abrupt onset of scintillations on a particular path within minutes led to the concept that a sharp boundary of about 10 km exists between quiet non‐scintillating regions and regions of irregularities. Once the scintillation has started, a region over 5000 km wide from east to west may contain irregularities. Within such a region there is strong localized control of irregularities. Comparison of scintillation onset on two paths spaced 1 to 2 hours apart at their subionospheric points reveals that, in the mean, scintillation onset is a function of local time. However, many days show nearly simultaneous onset on two paths that are 1 hour apart in local time. Other days show onset of scintillations on the westerly satellite path before onset at the eastern intersection; this variability is clearly a negation of the diurnal pattern. Maximum occurrence of scintillation has been observed in September, October, and November. A somewhat lower occurrence of high‐amplitude scintillation is noted in the December–January solstice period. A secondary maximum exists in March, according to other South American data. A very low occurrence of scintillation is observed in May, June, and July. The scintillation phenomenon is correlated in the mean with the downward motion of the F layer after 2100 local time at Huancayo. A hypothesis is advanced that after 2100 the westerly F‐layer maximum is higher in altitude and has a greater electron density than the easterly maximum. This west‐east gradient of electron density produces (either through electrodynamic forces or diffusion) the irregularities that show an apparent eastward drift. The diurnal pattern, with its nighttime maximum of scintillation occurrence, is a westward motion, but the irregularity drifts noted are clearly eastward in the direction of lower electron density profiles.