Using JULIA long dataset to find preconditioning evidence of ESF in bottom-type layers

Abstract

Recently Hysell et al. [2005] has suggested that the periodic structuring observed in the bottomtype (BT) scattering layers might be used to determine the occurrence or not of full-blown equatorial spread F (ESF) on a given day. The seed or precursor waves may be generated by a collisional shear instability. Preliminary observations at Jicamarca and AL TAIR have shown that such structures present wavelengths of the order of tens or hundreds of kilometers. At Jicamarca periodic structures have been observed using in-beam radar imaging techniques, however such observations are limited to few days in the last five years. On the other hand, routine observations using the JULIA system at Jicamarca have been done since 1996 on approximately 100 days per year on average, using interferometric and dual-beam observations with very narrow beams. Since the bottom-type irregularities drift ata relatively constant speed in the westward direction, using the JULIA narrow beams (～1o), the spatial periodicities might be observed as temporal periodicities in typical range-time intensity maps. In this initial work we present the statistics of the observed bottom-type periodicities and the occurrence of ESF plumes as detected with the JULIA system for years 2006-2008. Besides we presenta time occurrence statistics of a weak bottom-type layer that took place previously to bottom-type layers.