{"title":"Total electron content at an equatorial station during low solar activity: Geomagnetic activity effects emphasis","authors":"Sarvesh Kumar , Sushil Kumar","doi":"10.1016/j.jastp.2024.106415","DOIUrl":null,"url":null,"abstract":"<div><div>The initial results of Total Electron Content (TEC) data from September 2017 to November 2018 recorded over an equatorial station, Tarawa (geographic: 1.33°N, 173.01°E, geomagnetic: 2.68°S, 114.26°W) are presented which showed diurnal TEC maxima between 15:00–14:00 LT. The seasonal and semi-annual variations in the VTEC are clear, along with the less occurring winter anomalies and TEC bite-outs. The VTEC on magnetically disturbed days was higher than on quiet days. VTEC response to seven geomagnetic storms (5 moderate and 2 intense) showed positive ionospheric effect by all storms during their main phase. The VTEC response to two selected geomagnetic storms of 7–8 November 2017 (moderate strength, <em>Dst</em> = −72 nT) and 25–26 August 2018 (intense strength, <em>Dst</em> index = −174 nT) has been presented. During the November storm, TEC decreased by about 25.6% during the first step development of the main phase and increased by approximately 26.2% during the second step of main phase development. A long duration (>24 h) increase in VTEC of about 47.3% was found during the main phase of the August storm. VTEC changes during the main phase of both storms are due to the storm-time auroral prompt penetrating electric field, while the disturbance dynamo electric field produced negative ionospheric effects during their recovery phases as indicated by changes in equatorial electrojet values obtained from SWARM A, B, and C satellites and <em>AE</em> index, respectively. The global O/N<sub>2</sub> gas data from the Global Ultraviolet Imager (GUVI) onboard TIMED spacecraft show that O/N<sub>2</sub> changes, to a lesser extent, were also responsible for the geomagnetic storm effects observed at our station.</div></div>","PeriodicalId":15096,"journal":{"name":"Journal of Atmospheric and Solar-Terrestrial Physics","volume":"267 ","pages":"Article 106415"},"PeriodicalIF":1.8000,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Atmospheric and Solar-Terrestrial Physics","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1364682624002438","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
The initial results of Total Electron Content (TEC) data from September 2017 to November 2018 recorded over an equatorial station, Tarawa (geographic: 1.33°N, 173.01°E, geomagnetic: 2.68°S, 114.26°W) are presented which showed diurnal TEC maxima between 15:00–14:00 LT. The seasonal and semi-annual variations in the VTEC are clear, along with the less occurring winter anomalies and TEC bite-outs. The VTEC on magnetically disturbed days was higher than on quiet days. VTEC response to seven geomagnetic storms (5 moderate and 2 intense) showed positive ionospheric effect by all storms during their main phase. The VTEC response to two selected geomagnetic storms of 7–8 November 2017 (moderate strength, Dst = −72 nT) and 25–26 August 2018 (intense strength, Dst index = −174 nT) has been presented. During the November storm, TEC decreased by about 25.6% during the first step development of the main phase and increased by approximately 26.2% during the second step of main phase development. A long duration (>24 h) increase in VTEC of about 47.3% was found during the main phase of the August storm. VTEC changes during the main phase of both storms are due to the storm-time auroral prompt penetrating electric field, while the disturbance dynamo electric field produced negative ionospheric effects during their recovery phases as indicated by changes in equatorial electrojet values obtained from SWARM A, B, and C satellites and AE index, respectively. The global O/N2 gas data from the Global Ultraviolet Imager (GUVI) onboard TIMED spacecraft show that O/N2 changes, to a lesser extent, were also responsible for the geomagnetic storm effects observed at our station.
期刊介绍：
The Journal of Atmospheric and Solar-Terrestrial Physics (JASTP) is an international journal concerned with the inter-disciplinary science of the Earth''s atmospheric and space environment, especially the highly varied and highly variable physical phenomena that occur in this natural laboratory and the processes that couple them.
The journal covers the physical processes operating in the troposphere, stratosphere, mesosphere, thermosphere, ionosphere, magnetosphere, the Sun, interplanetary medium, and heliosphere. Phenomena occurring in other "spheres", solar influences on climate, and supporting laboratory measurements are also considered. The journal deals especially with the coupling between the different regions.
Solar flares, coronal mass ejections, and other energetic events on the Sun create interesting and important perturbations in the near-Earth space environment. The physics of such "space weather" is central to the Journal of Atmospheric and Solar-Terrestrial Physics and the journal welcomes papers that lead in the direction of a predictive understanding of the coupled system. Regarding the upper atmosphere, the subjects of aeronomy, geomagnetism and geoelectricity, auroral phenomena, radio wave propagation, and plasma instabilities, are examples within the broad field of solar-terrestrial physics which emphasise the energy exchange between the solar wind, the magnetospheric and ionospheric plasmas, and the neutral gas. In the lower atmosphere, topics covered range from mesoscale to global scale dynamics, to atmospheric electricity, lightning and its effects, and to anthropogenic changes.
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