Equatorial spread-F occurrence statistics in the American longitudes: Diurnal, seasonal and solar cycle variations

Incorporation of equatorial spread-F (ESF) occurrence statistics into the IRI requires first a detailed characterization, as a function of longitude, of the spatial and temporal distribution of the different types of ESF irregularity activity indices based on data from the different available techniques, ionosondes/digisondes, scintillation and satellite in-situ measurements. In this paper we present and discuss the distribution statistics of ESF events, mainly from ionograms, using the long term data sets available from equatorial and low latitude stations in Brazil and Argentina. Significant longitudinal dependence in the ESF occurrence is observed. The results are discussed on the basis of the longitude dependent magnetic declination angle that characterizes this region and on relevant thermospheric parameters. (C) 1998 COSPAR. Published by Elsevier Science Ltd.