Forecasting scintillation activity and equatorial spread F

When transionospheric radio waves propagate through an irregular ionosphere with plasma depletions or bubbles, they are subject to sporadic enhancement and fading, which is referred to as scintillation. Communication and navigation systems may be subject to these detrimental effects if the scintillation is strong enough. It is critical to have knowledge of the current ionospheric conditions so that system operators can distinguish between the natural radio environment and system-induced failures. In this paper we briefly describe the Forecasting Ionospheric Real-time Scintillation Tool UHF scintillation forecasting technique, which utilizes the observed characteristic parameter hF from a ground-based, ionospheric sounder near the magnetic equator. The prereversal enhancement in vertical ExB drift velocity after sunset is the prime driver for creating plasma depletions and bubbles. In addition, there exists a threshold in the hF value at 1930 LT, h'F-thr, such that, on any given evening, if hF is significantly above hF(thr), then scintillation activity is likely to occur, and if it is below h'F-thr, scintillation activity is unlikely to occur. We use this technique to explain the lack of scintillation activity prior to the Halloween storm in October 2003 in the Peruvian longitude sector. In addition, we have carried out a study which forecasts the occurrence or nonoccurrence of equatorial spread F (ESF), on a night-to-night basis, in five longitude sectors. The overall forecasting success is greater than 80% for each of the five longitude sectors.