Characterization of the Low Latitude Plasma Density Irregularities Observed using C/NOFS and SCINDA Data.

Abstract

Abstract Complex electrodynamic processes over the low latitude region often result in post sunset plasma density irregularities which degrade satellite communication and navigation. In order to forecast the density irregularities, their occurrence time, duration and location need to be quan- tified. Data from the Communication/Navigation Outage Forecasting System (C/NOFS) satel- lite was used to characterize the low latitude ion density irregularities from 2011 to 2013. This was supported by ground based data from the SCIntillation Network Decision Aid (SCINDA) receivers at Makerere (Geographic coordinate 32.6oE, 0.3oN, and dip latitude -9.3oN) and Nairobi (Geographic coordinate 36.8oE, -1.3oN, and dip latitude -10.8oN). The results show that irregularities in ion density have a daily pattern with peaks from 20:00-24:00 Local Time (LT). Scintillation activity at L band and VHF over East Africa peaked in 2011 and 2012 from 20:00-24:00 LT, though in many cases scintillation at VHF persisted longer than that at Lband. A longitudinal pattern in ion density irregularity occurrence was observed with peaks over 135-180oE and 270-300oE. The likelihood of ion density irregularity occurrence decreased with increasing altitude. Analysis of C/NOFS zonal ion drift velocities showed that the largest nighttime and daytime drifts were in 270-300oE and 300-330oE longitude regions respectively. Zonal irregularity drift velocities over East Africa were for the first time estimated from L-band scintillation indices. The results show that the velocity of plasma density irregularities in 2011 and 2012 varied daily, and hourly in the range of 50-150 m s−1. The zonal drift velocity estimates from the L-band scintillation indices had good positive correlation with the zonal driftvelocities derived from VHF receivers by the spaced receiver technique.