Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities

Dugassa, Teshome; Bosco Habarulema, John; Nigussie, Melessew

The relation between the occurrence of ionospheric irregularities and the spatial gradient of total electron content (TEC) derived from two closely located stations (ASAB: 4.34inline-formula N, 114.39inline-formula E and DEBK: 3.71inline-formula N, 109.34inline-formula E, geomagnetic), located within the equatorial region, over Ethiopia, during the postsunset hours was investigated. In this study, the Global Positioning System (GPS)-derived TEC during the year 2014 obtained from the two stations were employed to investigate the relationship between the gradient of TEC and occurrence of ionospheric irregularities. The spatial gradient of TEC (inline-formulaΔTEC∕Δlong) and its standard deviation over 15 min, inline-formulaσ(ΔTEC∕Δlong), were used in this study. The rate of change of TEC-derived indices (ROTI, ROTIinline-formulaave) were also utilized. Our results revealed that most of the maximum enhancement and reduction values in inline-formulaΔTEC∕Δlong are noticeable during the time period between 19:00 and 24:00 LT. In some cases, the peak values in the spatial gradient of TEC are also observed during daytime and postmidnight hours. The intensity level of inline-formulaσ(ΔTEC∕Δlong) observed after postsunset show similar trends with ROTIinline-formulaave, and was stronger (weaker) during equinoctial (solstice) months. The observed enhancement of inline-formulaσ(ΔTEC∕Δlong) in the equinoctial season shows an equinoctial asymmetry where the March equinox was greater than the September equinox. During the postsunset period, the relation between the spatial gradient of TEC obtained from two closely located Global Navigation Satellite System (GNSS) receivers and the equatorial electric field (EEF) was observed. The variation in the gradient of TEC and ROTIinline-formulaave observed during the evening time period show similar trends with EEF with a delay of about 1–2 h between them. The relationship between inline-formulaσ(ΔTEC∕Δlong) and ROTIinline-formulaave correlate linearly with correlation coefficient of inline-formulaC=0.7975 and inline-formulaC=0.7915 over ASAB and DEBK, respectively. The majority of the maximum enhancement and reduction in the spatial gradient of TEC observed during the evening time period may be associated with ionospheric irregularities or equatorial plasma bubbles. In addition to latitudinal gradients, the longitudinal gradient of TEC has contributed significantly to the TEC fluctuations.

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Dugassa, Teshome / Bosco Habarulema, John / Nigussie, Melessew: Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities. 2019. Copernicus Publications.

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