The dynamics of equatorial irregularity patch formation, motion, and decay

Abstract

Using scintillation observations from a series of equatorial propagation paths as well as backscatter and airglow data, the development, motion, and decay of equatorial irregularity patches have been studied. Assembling the results of earlier studies in the field with our observations, we find the following: the patch has limited east‐west dimensions with a minimum of 100 km. Several patches may be melded together to reach an extent of 1500 km. Its magnetic north‐south dimensions are often greater than 2000 km; the most intense irregularities (as evidenced by the Jicamarca radar at the dip equator) are from 225 to 450 km in altitude, although irregularities are found as high as 1000 km. The patch initially has a westward expansion following the solar terminator, then, maintaining its integrity, moves eastward. Evidence over a limited series of experiments suggests that premidnight patches are formed within 1½ hours after ionospheric sunset in the absence of special magnetic conditions. From Ascension Island (∼16°S dip latitude) the individual patches can be clearly distinguished. The decay of patches in the midnight time period was studied, pointing to a rapid decrease in scintillation intensity in this time period.

Occurrence characteristics of low latitude ionosphere irregularities observed by impedance probe on board the Hinotori satellite.

“…Local time dependence of the occurrence of the plasma bubbles has been reported by many workers based on ground observations (RASTOGI, 1980a(RASTOGI, , 1980bAARONS et al, 1980;BASV et al, 1980aBASV et al, , 1980b. Since the locations of the ground stations are limited at several fixed positions, the data survey is not necessarily able to cover the whole global range.…”

Seasonal and solar cycle variations of spread F at the equatorial anomaly crest zone.

“…The equatorial spread Firregularities occur at regions of steep electron density gradients associated with plasma depletion or bubbles in the equatorial ionosphere (MCCLURE et al,1977) which is probably generated by Rayleigh-Tayler instability mechanism and, perhaps, also the gradient drift mechanism operating on an initial perturbation or seed in the ionosphere at the bottom side of F layer of the equatorial ionosphere (e.g. MCCLURE et al, 1977;AARONS et al,1980;TSUNODA et a!.,1982;CHEN et al,1983). It has been established that, after sunset, the equatorial irregularity regions develop from the bottom side of the ionosphere.…”

Diffusion of small‐scale density irregularities during equatorial spread F

“…On the other hand, large scale density irregularities (Ln 1 km) are observed to decay in several hours (Basu et al, 1980;Aarons et al, 1980) and this process cannot be explained by diffusion, even anomalous diffusion.…”