Equatorial spread F echo and irregularity growth processes from conjugate point digital ionograms

Spread F irregularity signatures in the form of range spreading F layer traces are examined in Digisonde ionograms from dip equatorial and conjugate sites in Brazil, to determine the dominant process/mechanism of echo returns from the irregularity structures. A significant component of the ESF echo structures is found to be consistent with them originating from coherent back-scattering at field line perpendicular directions. The spread range of the echoes is found to increase linearly with the top frequency of the echo trace. Further, the irregularity strength is asymmetric at conjugate sites.