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

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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.