Equatorial scintillations in relation to the development of ionization anomaly

Abstract

Abstract. The irregularities in the electron density distribution of the ionosphere over the equatorial region frequently disrupt space-based communication and navigation links by causing severe amplitude and phase scintillations of signals. Development of a specification and forecast system for scintillations is needed in view of the increased reliance on spacebased communication and navigation systems, which are vulnerable to ionospheric scintillations. It has been suggested

Characteristics of equatorial ionization anomaly (EIA) in relation to transionospheric satellite links around the northern crest in the Indian longitude sector

“…Similarly from Fig. 2b There are several studies relating the equatorward TEC gradient with the occurrence of post-sunset scintillations (Raghavarao et al, 1988;Ray et al, 2006). This is perhaps for the first time that efforts are being made to correlate occurrence of post-sunset scintillations with the poleward TEC gradient in the Indian longitude sector.…”

“…Several workers have studied the plausible causes and effects (Ray et al, 2006; , 2001, 2004Rama Rao et al, 2006;Ram et al, 2006;Nava et al, 2007) of such steep TEC gradients and have strived to develop a predictive mechanism for occurrence for post-sunset scintillations. These exercises have mostly been restricted to the region between the magnetic equator and the northern and southern crests of EIA.…”

“…The impact of a developed equatorial ionization anomaly (EIA) in the afternoon hours on the subsequent development of equatorial ionization density irregularities during postsunset hours was suggested by Raghavarao et al (1988) and validated by several workers (Valladares et al, 2001(Valladares et al, , 2004Ray et al, 2006;Rama Rao et al, 2006;Ram et al, 2006;Nava et al, 2007). However the majority of the validation exercise was performed at locations existing between the magnetic equator and the northern and southern crests of the EIA.…”

Thermospheric Meridional Wind Control on Equatorial Scintillations and the Role of the Evening F-Region Height Rise, E × B Drift Velocities and F2-Peak Density Gradients

“…However, during September the results show that the differences of the mean peak drift velocities are very marginal and not so significant between the three cases analyzed here, which suggests that other agents could be operating for the plasma instability to occur. Anderson et al (2004) investigated the night-to-night occurrence of post-sunset equatorial scintillation activity in the Peruvian/Chilean longitude sectors (years 1998-1999), and reported that a threshold velocity of 20 ms -1 for the E 9 B drift will determine whether the UHF scintillation index S 4 will be greater than 0.5 after 20:00 LT. Ray et al (2006) examined in the Indian sector the relationship between the maximum F-layer base height velocity and the post-sunset L-band scintillation, and found that the E 9 B drift velocity (dh 0 F/dt) is more reliable (80%) in forecast lower scintillation levels (S 4 \ 0.4) then their higher scintillations (43% for S 4 [ 0.4). Again, from Indian sector, Dabas et al (2007) showed that for the 4 GHz scintillation to be observed at a low latitude station the threshold in the E 9 B drift velocity should be approximately twice (*30 ms -1 ) the peak velocity in the situation of scintillation only near the magnetic equator.…”

“…As in the post-sunset hours the large electric field PRE causes the resurgence of the equatorial fountain effect, the ionosphere at latitudes surrounding the geomagnetic equator and adjacent to the enhanced anomaly crests tends to exhibit remarkable spatial gradients of the electron distribution (Ray et al 2006). Thus, a well-developed large scale bubble that expands/extends along the magnetic field lines may intersect those regions of increased background electron density and sharp ionospheric gradients and, consequently, set up at the walls of the bubbles a secondary instability processes that will create conditions favorable for the generation of smaller scale plasma irregularities (Muella et al 2010).…”