Forcasting Equatorial Spread-F on a Night to Night Basis in 5 Longitude Sectors

Abstract:

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 present and describe a proven technique for forecasting UHF scintillation activity in the equatorial region after sunset and compare these forecasts with observed Equatorial Spread-F (ESF) on a night-to-night basis. The UHF scintillation forecasting technique described in Redmon et al. (Space Weather, Vol 8, 2010) utilizes the observed characteristic h’F from a ground-based, ionospheric sounder near the magnetic equator. This paper demonstrated that there exists an excellent correlation (R² ~ 0.91) between h’F (1930LT) and the pre-reversal enhancement in vertical ExB drift velocity after sunset which is the prime driver for creating plasma depletions and bubbles. In addition, there exists a “threshold” in the h’F value at 1930 LT, h’F_thr, which can be used to predict post-sunset scintillation activity. A digital sounder near the magnetic equator provides the h’F values and the observations of ESF. The digital sounders are located at Jicamarca, Peru; Sao Luis, Brazil; Ilorin, Nigeria; Guam and the Kwajalein Atoll. The years that are covered are in 2010, 2011 and 2013. A previous study carried out at Jicamarca for 2013 which correlated the forecast of scintillation activity and the occurrence or non-occurrence of ESF achieved an overall forecasting success of 90%. The important aspect of this study is to determine if this high success rate can be achieved in different longitude sectors.