Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities
<p>The relation between the occurrence of ionospheric irregularities and the spatial gradient of total electron content (TEC) derived from two closely located stations (ASAB: 4.34<span class="inline-formula"><sup>∘</sup></span> N, 114.39<span cla...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-12-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/37/1161/2019/angeo-37-1161-2019.pdf |
| Summary: | <p>The relation between the occurrence of ionospheric irregularities and the spatial gradient of total electron content (TEC) derived from two closely located
stations (ASAB: 4.34<span class="inline-formula"><sup>∘</sup></span> N, 114.39<span class="inline-formula"><sup>∘</sup></span> E and DEBK: 3.71<span class="inline-formula"><sup>∘</sup></span> N, 109.34<span class="inline-formula"><sup>∘</sup></span> 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 (<span class="inline-formula">ΔTEC∕Δlong</span>) and its standard deviation over 15 min, <span class="inline-formula"><i>σ</i>(ΔTEC∕Δlong</span>), were used in this study. The
rate of change of TEC-derived indices (ROTI, ROTI<span class="inline-formula"><sub>ave</sub></span>) were also utilized. Our results revealed that most of the maximum enhancement and reduction values in
<span class="inline-formula">ΔTEC∕Δlong</span> 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 <span class="inline-formula"><i>σ</i>(ΔTEC∕Δlong)</span> observed after postsunset show
similar trends with ROTI<span class="inline-formula"><sub>ave</sub></span>, and was stronger (weaker) during equinoctial (solstice) months. The observed enhancement of <span class="inline-formula"><i>σ</i>(ΔTEC∕Δlong)</span>
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 ROTI<span class="inline-formula"><sub>ave</sub></span> observed during the evening time period show similar trends with EEF with a
delay of about 1–2 h between them. The relationship between <span class="inline-formula"><i>σ</i>(ΔTEC∕Δlong)</span> and ROTI<span class="inline-formula"><sub>ave</sub></span> correlate linearly with correlation
coefficient of <span class="inline-formula"><i>C</i>=0.7975</span> and <span class="inline-formula"><i>C</i>=0.7915</span> 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.</p> |
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| ISSN: | 0992-7689 1432-0576 |