EQUATORIAL SCINTILLATION AND SYSTEMS SUPPORT

The need to nowcast and forecast scintillation for the support of oper ational systems has been recently identified by the interagency Nation al Space Weather Program. This issue is addressed in the present paper in the context of nighttime irregularities in the equatorial ionosphe re that cause intense amplitude and phase scintillations of satellite signals in the VHF/UHF range of frequencies and impact satellite commu nication, Global Positioning System navigation, and radar systems. Mul tistation and multifrequency satellite scintillation observations have been used to show that even though equatorial scintillations vary in accordance with the solar cycle, the extreme day-to-day variability of unknown origin modulates the scintillation occurrence during all phas es of the solar cycle. It is shown that although equatorial scintillat ion events often show correlation with magnetic activity, the major co mponent of scintillation is observed during magnetically quiet periods , In view of the day-to-day variability of the occurrence and intensit y of scintillating regions, their latitude extent, and their zonal mot ion, a regional specification and short-term forecast system based on real-time measurements has been developed. This system, named the Scin tillation Network Decision Aid, consists of two latitudinally disperse d stations, each of which uses spaced antenna scintillation receiving systems to monitor 250-MHz transmissions from two longitudinally separ ated geostationary satellites. The scintillation index and zonal irreg ularity drift are processed on-line and are retrieved by a remote oper ator on the Internet. At the operator terminal the data are combined w ith an empirical plasma bubble model to generate three-dimensional map s of irregularity structures and two-dimensional outage maps for the r egion.