Statistics of GNSS amplitude scintillation occurrences over Dakar, Senegal, at varying elevation angles during the maximum phase of solar cycle 24

Abstract

This study characterizes Global Navigation Satellite System amplitude scintillation over Dakar (14.75°N, 17.45°W, magnitude latitude: 5.88°N), Senegal. The data, which we arranged on daily and monthly scales, cover The data were further binned into three levels of scintillation using the S4 index: weak (0.3 ≤ S4 < 0.4), moderate (0.4 ≤ S4 < 0.7), and intense (S4 ≥ 0.7), over varying elevation angles (10°, 20°, and 30°). Daily occurrences of scintillation were most frequent around 22-02 LT. On a month-by-month basis, October recorded the highest occurrences of scintillations, while June recorded the least. Furthermore, contrary to Akala et al. (2014Akala et al. ( , 2015 who earlier reported January as off season for scintillation occurrences at some sites in Africa, namely, Lagos (Central West Africa), Nairobi, and Kampala (East Africa), the current study recorded some scintillation occurrences at Dakar (far west of West Africa) in January. It therefore implies that longitudinal variations do exist in the climatology of ionospheric scintillations over Africa. Consequently, detailed understanding of the climatology and daily distributions of ionospheric scintillations over equatorial Africa, which is our key objective in this study (from the perspective of Dakar), is the basic requirement for developing robust physics-based scintillation models for the African equatorial region. Finally, we noted that the conventional adoption of high-elevation masking angles during scintillation data processing, with a view to suppressing multipath effects usually hid important ionospheric-induced scintillation data.

Longitudinal Responses of the Equatorial/Low‐Latitude Ionosphere Over the Oceanic Regions to Geomagnetic Storms of May and September 2017

“…Generally, over the equatorial/low‐latitude region, postsunset eastward Pre‐Reversal Enhancement (PRE) of E × B drift supports the uplifting of F layer altitude to create conducive environment where irregularities can be generated through the Rayleigh Taylor Instability (RTI) process (Abdu et al, 1995; Akala et al, 2014, 2016). However, if the electric fields are westward during postsunset hours in the region, the uplifting of E × B drifts is prevented, consequently, irregularities generation is inhibited.…”

“…It has been reported that sharp and rapid variations in TEC are sine qua non to occurrences of ionospheric plasma‐density irregularities (Akala et al, 2011; Valladares et al, 1996). Ionospheric irregularities cause scintillations of radio waves (Kintner et al, 2007), and severe scintillations on the other hand can cause loss of signal and cycle slips to transionospheric radio systems (Akala et al, 2012, 2014, 2015, 2016, 2017).…”

Longitudinal and Seasonal Variability of Equatorial Ionospheric Irregularities and Electrodynamics

“…Although both of them implicate ionospheric density irregularities in the postsunset F layer and degrade electromagnetic signal propagation, ESF and EPB are not identical. While ESF describes irregular signatures, especially on ionosonde's ionograms due to backscatter echo from and above the bottomside of the nighttime F layer, EPB refers to irregular plasma density depletions observed by satellites and radar backscatter (Jin et al, ; Rodrigues et al, ; Woodman & LaHoz, ) as well as by GPS TEC (Akala et al, ; Valladares & Chau, ; Zakharenkova & Astafyeva, ) in the topside ionosphere.…”

Characterization of African Equatorial Ionization Anomaly During the Maximum Phase of Solar Cycle 24

“…Detailed knowledge of global variations of TEC under the EIA structure, particularly the African EIA structure whose variations have not been well documented, is needed for (i) designing robust transionospheric radio systems and (ii) developing effective forecasting tools for global TEC variations. Paradoxically, Africa has the largest landmass under the EIA, and many previous studies on global distributions of ionospheric equatorial irregularities have pointed out that African longitude is more susceptible to equatorial irregularities than other longitudes (Akala et al, 2016; Akala, Rabiu, et al, 2013; Burke et al, 2004; Gentile et al, 2011; Hei et al, 2005; Huang et al, 2012; Huang, de La Beaujardiere, et al, 2014; Huang & Hairston, 2015; Kil et al, 2009). Furthermore, Alken et al (2013) had also earlier reported that the magnitude of the eastward electric field was stronger in the African sector than in the American sector.…”