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Found 37 entries in the Bibliography.
Showing entries from 1 through 37
| 2022 |
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Accurate representation of ionospheric equivalent slab thickness (τ) and scale height (Hm) plays a crucial role in characterizing the complex dynamics of topside and bottomside ionospheric constituents. In the present work, we examined the corresponding morphologies of ionospheric profile parameters with collocated global positioning system (GPS) and Digisonde Portable Sounder (DPS) setups at an equatorial location in west Africa Ilorin (8.50°N, 4.68°E), during a low solar activity year 2010. The extracted τ from GPS and DPS in selected quiet periods confirm it to be a first-order measure of Hm over Africa. The seasonal analysis of τ shows substantial enhancement in the magnitude during the post-sunset and solstice seasons, of which December solstice manifests relatively higher values than June solstice. This result could be associated with the elevation of the meridional wind and drift in the parameters, which are more substantial during the post-noon and solstices. Therefore, at solstices, the post-night increase could indicate solar cycle dynamics during HSA (high solar activity) and LSA (low solar activity). However, the extracted Hm from its relationship with τ did not show visible effects of dynamics in E × B plasma drift and the meridional wind. In our study, a decline in morphologies of Hm and τ from December solstice to June solstice through the equinox is not consistent with the existing observations at mid-latitude. The results would complement the relationships between bottomside and topside profile peak parameters and dynamics of ionospheric constituents for a realistic representation and modeling of the ionosphere over African equatorial and low latitude regions. Thus, it also contributes to the global effort of improving ionospheric prediction and forecasting models. Odeyemi, Olumide; Adeniyi, Jacob; Oyeyemi, Elijah; Panda, Sampad; Jamjareegulgarn, Punyawi; Olugbon, Busola; Oluwadare, Esholomo; Akala, Andrew; Olawepo, Adeniji; Adewale, Adekola; Published by: Advances in Space Research Published on: jan YEAR: 2022 DOI: 10.1016/j.asr.2021.10.030 Global positioning system; Digital portable sounder; Equatorial latitude; Equivalent slab thickness; scale height |
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Scintillation due to ionospheric plasma irregularities remains a challenging task for the space science community as it can severely threaten the dynamic systems relying on space-based navigation services. In the present paper, we probe the ionospheric current and plasma irregularity characteristics from a latitudinal arrangement of magnetometers and Global Navigation Satellite System (GNSS) stations from the equator to the far low latitude location over the Indian longitudes, during the severe space weather events of 6–10 September 2017 that are associated with the strongest and consecutive solar flares in the 24th solar cycle. The night-time influence of partial ring current signatures in ASYH and the daytime influence of the disturbances in the ionospheric E region electric currents (Diono) are highlighted during the event. The total electron content (TEC) from the latitudinal GNSS observables indicate a perturbed equatorial ionization anomaly (EIA) condition on 7 September, due to a sequence of M-class solar flares and associated prompt penetration electric fields (PPEFs), whereas the suppressed EIA on 8 September with an inverted equatorial electrojet (EEJ) suggests the driving disturbance dynamo electric current (Ddyn) corresponding to disturbance dynamo electric fields (DDEFs) penetration in the E region and additional contributions from the plausible storm-time compositional changes (O/N2) in the F-region. The concurrent analysis of the Diono and EEJ strengths help in identifying the pre-reversal effect (PRE) condition to seed the development of equatorial plasma bubbles (EPBs) during the local evening sector on the storm day. The severity of ionospheric irregularities at different latitudes is revealed from the occurrence rate of the rate of change of TEC index (ROTI) variations. Further, the investigations of the hourly maximum absolute error (MAE) and root mean square error (RMSE) of ROTI from the reference quiet days’ levels and the timestamps of ROTI peak magnitudes substantiate the severity, latitudinal time lag in the peak of irregularity, and poleward expansion of EPBs and associated scintillations. The key findings from this study strengthen the understanding of evolution and the drifting characteristics of plasma irregularities over the Indian low latitudes. Vankadara, Ram; Panda, Sampad; Amory-Mazaudier, Christine; Fleury, Rolland; Devanaboyina, Venkata; Pant, Tarun; Jamjareegulgarn, Punyawi; Haq, Mohd; Okoh, Daniel; Seemala, Gopi; Published by: Remote Sensing Published on: jan YEAR: 2022 DOI: 10.3390/rs14030652 space weather; equatorial plasma bubbles; ionospheric irregularity; global navigation satellite system; magnetometer; poleward drift; rate of change of TEC index; scintillations; storm-time electric currents |
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The ionosphere around the Equatorial Ionization Anomaly (EIA) region exhibits complex dynamics and responds markedly to the solar-magnetospheric energy and momentum. In this paper, the hourly total electron content (TEC) variations in response to the EIA structure in Africa to the 2013 and 2015 St. Patrick’s Day storms is investigated using data obtained from a chain of GPS receivers located in the Africa region. The TEC variations are characterized based on the convective magnetospheric dynamo fields, neutral wind circulation, and zonal electric fields. Generally, the result indicates that the TEC variations are consistent with the different directions of the interplanetary fields during the different phases of the storms. We observed reverse EIA structures in the main phase of the March 2015 storm, likely to be related to the intense PPEF and strong equatorward wind, which imposed a westward zonal electric field at the equator. A similar equatorial peak observed during the recovery phase is associated with DDEF, poleward wind and plasma convergence. Furthermore, the TEC variations also indicate hemispheric asymmetries during the storms. During the main phase of the storm, the TEC variation is more enhanced in the Northern Hemisphere in March 2013 and reverses during March 2015. We observed an equatorial peak during the SSC period in March 2013, while EIA structures are generally weak in March 2015 event. This posit that ionospheric pre-storm behaviour in the EIA region can be better understood when the IMF-Bz and E-field are not significant. The observed distinctive response avowed the peculiarity of the electrodynamics intricacy in the Africa sector. Bolaji, Olawale; Adekoya, Bolarinwa; Adebiyi, Shola; Adebesin, Babatunde; Ikubanni, Stephen; Published by: Astrophysics and Space Science Published on: jan YEAR: 2022 DOI: 10.1007/s10509-021-04022-5 |
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This paper investigates the diurnal variations of modelled and observed Vertical Total Electron Content (VTEC) over the African region (40oN to+ 40oS, 25oW to 65oE) obtained from Devanaboyina, Venkata; , others; Published by: Published on: YEAR: 2022 DOI: 10.21203/rs.3.rs-1695991/v1 |
| 2021 |
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Assessment of the predictive capabilities of NIGTEC model over Nigeria during geomagnetic storms The Nigerian Total Electron Content (NIGTEC) is a regional neural network-based model developed by the Nigerian Centre for Atmospheric Research to predict the Total Electron Content (TEC) at any location over Nigeria. The addition of the disturbance storm time (Dst) index as one of NIGTEC s input layer neurons raises a question of its accuracy during geomagnetic storms. In this paper, the capability of NIGTEC in predicting the variability of TEC during geomagnetic storms has been assessed. TEC data predicted by NIGTEC is compared with those derived from Global Navigation Satellite System (GNSS) over Lagos (6.5oN, 3.4oE) and Toro (10.1oN, 9.12oE) during the intense storms in March 2012 and 2013. The model s predictive capability is evaluated in terms of Root Mean Square Error (RMSE). NIGTEC reproduced a fairly good storm time morphology in VTEC driven by the prompt penetration electric field and the increase in thermospheric O/N2. Nevertheless, it failed to predict the increase in TEC after the intense sudden impulse of 60 nT on 8 March 2012. And it could not capture the changes in VTEC driven by the storm time equatorward neutral wind especially during 18:00–24:00 UT. Consequently, the RMSEs were higher during this time window, and the highest RMSE value was obtained during the most intense storm in March 2012. Amaechi, Paul; Humphrey, Ibifubara; Adewoyin, David; Published by: Geodesy and Geodynamics Published on: nov YEAR: 2021 DOI: 10.1016/j.geog.2021.09.003 geomagnetic storm; global navigation satellite system; Nigerian Total Electron Content (NIGTEC); total electron content |
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Recent studies revealed that the long-lasting daytime ionospheric enhancements of Total Electron Content (TEC) were sometimes observed in the Asian sector during the recovery phase of geomagnetic storms (e.g., Lei (J Geophys Res Space Phys 123: 3217–3232, 2018), Li (J Geophys Res Space Phys 125: e2020JA028238, 2020). However, they focused only on the dayside ionosphere, and no dedicated studies have been performed to investigate the nighttime ionospheric behavior during such kinds of storm recovery phases. In this study, we focused on two geomagnetic storms that happened on 7–8 September 2017 and 25–26 August 2018, which showed the prominent daytime TEC enhancements in the Asian sector during their recovery phases, to explore the nighttime large-scale ionospheric responses as well as the small-scale Equatorial Plasma Irregularities (EPIs). It is found that during the September 2017 storm recovery phase, the nighttime ionosphere in the American sector is largely depressed, which is similar to the daytime ionospheric response in the same longitude sector; while in the Asian sector, only a small TEC increase is observed at nighttime, which is much weaker than the prominent daytime TEC enhancement in this longitude sector. During the recovery phase of the August 2018 storm, a slight TEC increase is observed on the night side at all longitudes, which is also weaker than the prominent daytime TEC enhancement. For the small-scale EPIs, they are enhanced and extended to higher latitudes during the main phase of both storms. However, during the recovery phases of the first storm, the EPIs are largely enhanced and suppressed in the Asian and American sectors, respectively, while no prominent nighttime EPIs are observed during the second storm recovery phase. The clear north–south asymmetry of equatorial ionization anomaly crests during the second storm should be responsible for the suppression of EPIs during this storm. In addition, our results also suggest that the dusk side ionospheric response could be affected by the daytime ionospheric plasma density/TEC variations during the recovery phase of geomagnetic storms, which further modulates the vertical plasma drift and plasma gradient. As a result, the growth rate of post-sunset EPIs will be enhanced or inhibited. Wan, Xin; Xiong, Chao; Gao, Shunzu; Huang, Fuqing; Liu, Yiwen; Aa, Ercha; Yin, Fan; Cai, Hongtao; Published by: Satellite Navigation Published on: nov YEAR: 2021 DOI: 10.1186/s43020-021-00055-x Equatorial plasma irregularity; Geomagneitc storm; Ionospheric response; longitudinal variations; Storm recovery phase |
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Latitudinal Dependence of Ionospheric Responses to Some Geomagnetic Storms during Low Solar Activity The Latitudinal dependence in the response of the Ionospheric F2-layer electron density (NmF2) and peak height (hmF2) to three geomagnetic storms of May and August 2010 has been examined. The data-sets used for the study were obtained from Ilorin, Nigeria (1.87° S/76.67° E), San Vito, Italy (34.68° N/90.38° E), Hermanus, South Africa (42.34° S/82.15° E), and Pruhonice, Czech Republic (45.66° N/90.38° E) geomagnetic coordinates. The quiet time result shows that the rise in NmF2 began earlier at San Vito, followed by Pruhonice. The rate of ionization was observed to be highest in Ilorin, while, the rate of decay in NmF2 is faster at Hermanus. For disturbed NmF2 condition, remarkable similarities in the NmF2 responses during geomagnetic storms were recorded from Hermanus in the mid-latitude and Ilorin, an equatorial station. NmF2 enhancements (\textgreater6 hours) that is consistent with the increase in hmF2 were observed at all the mid-latitude stations during the main phase of the 02 May, 2010 storm, without any noticeable change over ILN. Similarly, 12 hours of positive phase was observed at ILN and HMN, with 30 hours of NmF2 depletions at PRN and SVT during the recovery phase. ILN is in the equatorial Trough, so most of the NmF2 produced at this region is lifted to the higher latitudes by the fountain effect during the main phase. The suppression of the zonal electric field at ILN is responsible for the NmF2 enhancement during the recovery phase, while the mid-latitude responses have been attributed to the effect of the thermospheric winds and neutral composition changes. Joshua, B.; Adeniyi, J.; Olawepo, A.; Rabiu, Babatunde; Daniel, Okoh; Adebiyi, S.; Adebesin, B.; Ikubanni, S.; Abdurahim, B.; Published by: Geomagnetism and Aeronomy Published on: may YEAR: 2021 DOI: 10.1134/S0016793221030063 Electric field; Electron density; Geomagnetic storms; magnetosphere; peak height |
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Latitudinal Dependence of Ionospheric Responses to Some Geomagnetic Storms during Low Solar Activity The Latitudinal dependence in the response of the Ionospheric F2-layer electron density (NmF2) and peak height (hmF2) to three geomagnetic storms of May and August 2010 has been examined. The data-sets used for the study were obtained from Ilorin, Nigeria (1.87° S/76.67° E), San Vito, Italy (34.68° N/90.38° E), Hermanus, South Africa (42.34° S/82.15° E), and Pruhonice, Czech Republic (45.66° N/90.38° E) geomagnetic coordinates. The quiet time result shows that the rise in NmF2 began earlier at San Vito, followed by Pruhonice. The rate of ionization was observed to be highest in Ilorin, while, the rate of decay in NmF2 is faster at Hermanus. For disturbed NmF2 condition, remarkable similarities in the NmF2 responses during geomagnetic storms were recorded from Hermanus in the mid-latitude and Ilorin, an equatorial station. NmF2 enhancements (\textgreater6 hours) that is consistent with the increase in hmF2 were observed at all the mid-latitude stations during the main phase of the 02 May, 2010 storm, without any noticeable change over ILN. Similarly, 12 hours of positive phase was observed at ILN and HMN, with 30 hours of NmF2 depletions at PRN and SVT during the recovery phase. ILN is in the equatorial Trough, so most of the NmF2 produced at this region is lifted to the higher latitudes by the fountain effect during the main phase. The suppression of the zonal electric field at ILN is responsible for the NmF2 enhancement during the recovery phase, while the mid-latitude responses have been attributed to the effect of the thermospheric winds and neutral composition changes. Joshua, B.; Adeniyi, J.; Olawepo, A.; Rabiu, Babatunde; Daniel, Okoh; Adebiyi, S.; Adebesin, B.; Ikubanni, S.; Abdurahim, B.; Published by: Geomagnetism and Aeronomy Published on: may YEAR: 2021 DOI: 10.1134/S0016793221030063 Electric field; Electron density; Geomagnetic storms; magnetosphere; peak height |
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\textlessp\textgreaterTopside ionospheric background distribution and its seasonal variations over China and its adjacent areas, e.g. 0°-54°N and 70°-140°E, are studied using the in situ electron density (Ne) measurements obtained by the LAP payload on board the ZH-1 (CSES) satellite. Results are as followings:(1) Regularities consistent with results from previous studies are shown on the latitudinal extension, longitudinal distribution, and seasonal variations of the EIA (Equatorial Ionization Anomaly) phenomenon in the study area. (2) In the mid-latitude regions, there is a relative low-value zone for the daytime Ne, which shows relative high-value data during nighttime. Nighttime Ne enhancement is shown in all the mid-latitudes for all the seasons when comparing the nighttime and daytime Ne together. The equatorward extension of this phenomenon is in contrast to the poleward extension of the EIA phenomenon; when this phenomenon extends, the EIA shrinks, and vice versa. (3) For the daytime Ne, semiannual anomaly demonstrates a regular pattern, in which the two peaks start in spring and autumn equinoxes at the Equator, then evolve toward the summer solstice with increasing latitude, and finally combine into one summer time peak in mid-latitudes; seasonal anomaly only appears within latitude 4° of the Equator. While for the nighttime Ne, semiannual anomaly appears between latitude 22° and 50°, and seasonal anomaly appears below latitude 22°. (4) The monthly average background of the ionosphere generally shows that the nighttime Ne varies more dramatically than the daytime Ne. For the daytime Ne, observations in both equinoxes and summer solstice vary more violently than that in winter solstice, and observations in EIA regions vary more violently than that in mid-latitude regions. And for the nighttime Ne, observation variations are roughly similar in all seasons and latitudes. (5) Features of the ionospheric background, which fluctuates with time and space in the study area, are relatively complicated, therefore it is necessary to pay attention to the ionosphere background and its fluctuations when conducting studies on ionosphere related scientific problems. Based on the above results and comparisons with other simultaneous observations, we believe that the relative variations of the in situ Ne measurements from the ZH-1 satellite are in consistent with that from other datasets. Besides the well-known ionosphere features, some features which were not found in previous studies are found from the ionosphere background in the study area. The in situ Ne measurements from the ZH-1 satellite are a good data source for systematic studies on ionosphere-related scientific problems due to the similar local times and locations of the observations.\textless/p\textgreater XiuYing, Wang; DeHe, Yang; ZiHan, Zhou; Jing, C.; Na, Zhou; XuHui, Shen; Published by: Chinese Journal of Geophysics Published on: feb YEAR: 2021 DOI: 10.6038/cjg2021O0152 |
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On the dayside of August 25–26, 2018 (main phase, MP of the storm), we unveiled the storm time effects on the latitudinal distribution of ionospheric total electron content (TEC). We used 17 and 19 Global Positioning System receivers in American and Asian-Australian sectors, respectively. Also, we employed a pair of magnetometers in each sector to unveil storm time effects on vertical E × B upward directed inferred drift velocity in the F region ionosphere. Also used is NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite airglow instrument to investigate storm time changes in neutral composition, O/N2 ratio. In this investigation, we corrected the latitudinal offset found in the works of Younas et al. (2020, https://doi.org/10.1029/2020JA027981). Interestingly, we observed that a double-humped increase (DHI) seen at a middle latitude station (MGUE, ∼22°S) after the MP on the dayside in American sector (Younas et al., 2020, https://doi.org/10.1029/2020JA027981) did straddle ∼23.58°N and ∼22°S. On August 25, 2018, storm commencement was evident in Sym-H (∼−8 nT) around 18:00 UT. It later became intensified (∼−174 nT) on August 26 around 08:00 UT. During storm s MP (after the MP), fountain effect operation was significantly enhanced (inhibited) in Asian-Australian (American) sector. Middle latitude TEC during MP got reduced in American sector (13:00 LT–15:40 LT) compared to those seen in Asian-Australian sector (13:00 LT–15:40 LT). The northern equatorial peak (∼25 TECU) seen at IHYO (14:00 LT) after MP in the American sector is higher when compared with that (∼21 TECU) seen at PPPC (11:40 LT) during MP in Asian-Australian sector. Bolaji, O.; Fashae, J.; Adebiyi, S.; Owolabi, Charles; Adebesin, B.; Kaka, R.; Ibanga, Jewel; Abass, M.; Akinola, O.; Adekoya, B.; Younas, W.; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA029068 double-humped increase (DHI); equatorial ionization anomaly (EIA); prompt penetrating electric field (PPEF); storm time equatorward wind |
| 2020 |
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Adebiyi, Shola; Adimula, Isaac; Oladipo, Olushola; Published by: Journal of the Nigerian Society of Physical Sciences Published on: |
| 2019 |
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Research Progress on On-Orbit Calibration Technology for Far Ultraviolet Payload Li-ping, Fu; Nan, Jia; Xiu-qing, Hu; Tian, Mao; Fang, Jiang; Yun-gang, Wang; Ru-yi, Peng; Tian-fang, Wang; Da-xin, Wang; Shuang-tuan, Dou; , others; Published by: Published on: |
| 2018 |
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Response of GPS-TEC in the African equatorial region to the two recent St. Patrick s day storms The 2015 St. Patrick’s Day storm is one of the most intense geomagnetic storm in this present solar cycle (SYM-H=-213nT). In this paper, we investigate the response of the African low Ikubanni, SO; Adebiyi, SJ; Adebesin, BO; Dopamu, KO; Joshua, BW; Bolaji, OS; Adekoya, BJ; Published by: International Journal of Civil Engineering and Technology Published on: |
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Heliophysics Science enabled by Lunar Orbiting Platforms Spann, James; Giles, Barbara; Spence, Harlan; Savage, Sabrina; Paxton, Larry; Kasper, Justin; Horanyi, Mihaly; DeLuca, Edward; Collado-Vega, Yaireska; Clark, Pamela; Published by: 2018 Triennial Earth-Sun Summit (TESS Published on: |
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Photo-counting detector for ionosphere far ultraviolet night airglow remote sensing Far ultraviolet earth night airglow is related to total electron content(TEC) of Ionosphere. Observing the night airglow nadir at OI 135.6nm emission produced by ionospheric O+ and e recombination can get the distribution of ionosphere TEC. In this paper, a compact of ionospheric FUV photometer developed for micro satellite will be introduced. The instrument works in photo-counting mode to achieve high sensitivity for weak night airglow radiation detection. The design of this photo-counting detector will be described in detail. Peng, Jilong; Wang, Shanshan; Yu, Qian; Yi, Zhong; Tian, Dongbo; Published by: Published on: YEAR: 2018 DOI: 10.1117/12.2315060 |
| 2017 |
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of TIMED/GUVI to derive the O/N2 [14], and the data of TIMED/GUVI which are recorded by as the data of Polar BEAR/AIRS and TIMED/GUVI. This method uses the intensity ratio of OI Zhang, Yongchao; Zhu, Jun; Yin, Huan; Zhang, Xiaoxin; Published by: Published on: |
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QUASI-BIENNIAL VARIATIONS IN IONOSPHERIC TIDAL/SPW AMPLITUDES: OBSERVATIONS AND MODELING Loren, Cheewei; Yan-Yi, Sun; Jack, Chieh; Shih-Han, Chien; Rung, Tsai-Lin; Jia, Yue; Published by: Published on: |
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Zhang, Yongchao; Zhu, Jun; Yin, Huan; Zhang, Xiaoxin; Published by: Published on: |
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Zhang, Yongchao; Zhu, Jun; Yin, Huan; Zhang, Xiaoxin; Published by: Published on: YEAR: 2017 DOI: 10.1007/978-3-319-49184-410.1007/978-3-319-49184-4_29 |
| 2016 |
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Ionospheric effects of magnetospheric and thermospheric disturbances on March 17--19, 2015 Using vertical and oblique radio-sounding data, we analyze the ionospheric and thermospheric disturbances during the magnetic storm that occurred in northeastern Russia on March 17\textendash19, 2015. We consider the heliospheric sources that induced the magnetic storm. During the main and early recovery phases, the midlatitude stations are characterized by extremely low values of electron density at the F2 layer maximum. Using oblique sounding data, we recorded signals that propagated outside the great circle arc. In evening and night hours, no radio signals were found to pass along the Norilsk\textendashIrkutsk and Magadan\textendashIrkutsk paths. The observed ionospheric effects are shown to be caused by a sharp shift of the boundaries of the main ionospheric trough to the invariant latitude 46\textdegree N during the main phase of the magnetic storm. The negative ionospheric disturbance during the recovery phase of the storm, which was associated with significant variations in the composition of the neutral atmosphere, led to a change in the mode composition of received radio signals and a decline in observed maximal frequencies in daytime hours of March 18, 2015 by more than 2 times. Polekh, N.; Zolotukhina, N.; Romanova, E.; Ponomarchuk, S.; Kurkin, V.; Podlesnyi, A.; Published by: Geomagnetism and Aeronomy Published on: 09/2016 YEAR: 2016 DOI: 10.1134/S0016793216040174 |
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Ionospheric effects of magnetospheric and thermospheric disturbances on March 17—19, 2015 Using vertical and oblique radio-sounding data, we analyze the ionospheric and thermospheric disturbances during the magnetic storm that occurred in northeastern Russia on March Polekh, NM; Zolotukhina, NA; Romanova, EB; Ponomarchuk, SN; Kurkin, VI; Podlesnyi, AV; Published by: Geomagnetism and Aeronomy Published on: |
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Ionospheric Space Weather: Longitude Dependence and Lower Atmosphere Forcing This monograph is the outcome of an American Geophysical Union Chapman Conference on longitude and hemispheric dependence of ionospheric space weather, including the Fuller-Rowell, Timothy; Yizengaw, Endawoke; Doherty, Patricia; Basu, Sunanda; Published by: Published on: |
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Using a three-dimensional nonhydrostatic general circulation model, we investigate the response of the thermosphere–ionosphere system to the 5–6 August 2011 major geomagnetic Yi\ugit, Erdal; Frey, Harald; Moldwin, Mark; Immel, Thomas; Ridley, Aaron; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: YEAR: 2016 DOI: 10.1016/j.jastp.2015.10.002 |
| 2015 |
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Waves in Terrestrial and Planetary Atmospheres First, a brief introduction to wave processes in nature is presented, summarizing basic wave parameters. The main types of atmospheric internal waves, such as gravity waves, solar Published by: Published on: YEAR: 2015 DOI: 10.1007/978-3-319-21581-5_5 |
| 2014 |
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Geomagnetic control of equatorial plasma bubble activity modeled by the TIEGCM with Kp Describing the day-to-day variability of Equatorial Plasma Bubble (EPB) occurrence remains a significant challenge. In this study we use the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM), driven by solar (F10.7) and geomagnetic (Kp) activity indices, to study daily variations of the linear Rayleigh-Taylor (R-T) instability growth rate in relation to the measured scintillation strength at five longitudinally distributed stations. For locations characterized by generally favorable conditions for EPB growth (i.e., within the scintillation season for that location), we find that the TIEGCM is capable of identifying days when EPB development, determined from the calculated R-T growth rate, is suppressed as a result of geomagnetic activity. Both observed and modeled upward plasma drifts indicate that the prereversal enhancement scales linearly with Kp from several hours prior, from which it is concluded that even small Kpchanges cause significant variations in daily EPB growth. Carter, B.; Retterer, J.; Yizengaw, E.; Groves, K.; Caton, R.; McNamara, L.; Bridgwood, C.; Francis, M.; Terkildsen, M.; Norman, R.; Zhang, K.; Published by: Geophysical Research Letters Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014GL060953 |
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GPS derived TEC and foF2 variability at an equatorial station and the performance of IRI-model The ionosphere induces a time delay in transionospheric radio signals such as the Global Positioning System (GPS) signal. The Total Electron Content (TEC) is a key parameter in the mitigation of ionospheric effects on transionospheric signals. The delay in GPS signal induced by the ionosphere is proportional to TEC along the path from the GPS satellite to a receiver. The diurnal monthly and seasonal variations of ionospheric electron content were studied during the year 2010, a year of extreme solar minimum (F10.7\ =\ 81 solar flux unit), with data from the GPS receiver and the Digisonde Portable Sounder (DPS) collocated at Ilorin (Geog. Lat. 8.50\textdegreeN, Long. 4.50\textdegreeE, dip -7.9\textdegree). The diurnal monthly variation shows steady increases in TEC and F2-layer critical frequency (foF2) from pre-dawn minimum to afternoon maximum and then decreases after sunset. TEC show significant seasonal variation during the daytime between 0900 and 1900\ UT (LT\ =\ UT\ +\ 1\ h) with a maximum during the March equinox (about 35 TECU) and minimum during the June solstice (about 24 TECU). The GPS-TEC and foF2 values reveal a weak seasonal anomaly and equinoctial asymmetry during the daytime. The variations observed find their explanations in the amount of solar radiation and neutral gas composition. The measured TEC and foF2 values were compared with last two versions of the International Reference Ionosphere (IRI-2007 and IRI-2012) model predictions using the NeQuick and CCIR (International Radio Consultative Committee) options respectively in the model. In general, the two models give foF2 close to the experimental values, whereas significant discrepancies are found in the predictions of TEC from the models especially during the daytime. The error in height dependent thickness parameter, daytime underestimation of equatorial drift and contributions of electrons from altitudes above 2000\ km have been suggested as the possible causes. Adebiyi, S.J.; Odeyemi, O.O.; Adimula, I.A.; Oladipo, O.A.; Ikubanni, S.O.; Adebesin, B.O.; Joshua, B.W.; Published by: Advances in Space Research Published on: 08/2014 YEAR: 2014 DOI: 10.1016/j.asr.2014.03.026 |
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Ionospheric response to magnetic activity at low and mid-latitude stations The F2-layer response to the moderate storm of 5\textendash7 April 2010 was investigated using data from two equatorial stations (Ilorin: lat. 8.5\textdegreeN, 4.5\textdegreeE; Kwajalein: lat. 9\textdegreeN, long. 167.2\textdegreeE) and mid-latitude (San Vito: lat. 40.6\textdegreeN, long. 17.8\textdegreeE; Pruhonice: lat. 50\textdegreeN, long. 14.6\textdegreeE). Before storm commencement, enhancement, and depletion of NmF2 values were observed in the equatorial and mid-latitude stations, respectively, indicating the latitudinal dependence of the pre-storm event. All the stations with the exception of Kwajalein show positive phase in NmF2 response at the storm onset stage. Positive phase in NmF2 continues over Ilorin and appears on the daytime ionosphere of Kwajalein on 6 April, whereas negative phase suppressed the positive feature in Pruhonice and San Vito until the recovery condition. The differences in the response of F2-layer to the storm for the two equatorial stations were attributed to their longitudinal differences. On the average, both theAE and D st indices revealed poor correlation relationship. More studies are required to ascertain this finding. Adebiyi, Shola; Adimula, Isaac; Oladipo, Olusola; Joshua, Benjamin; Adebesin, Babatunde; Ikubanni, Stephen; Published by: Acta Geophysica Published on: 08/2014 YEAR: 2014 DOI: 10.2478/s11600-014-0205-x Electric field; equatorial station; Ionosphere; mid-latitude; moderate storm; positive phase |
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Gravity wave activity and dissipation in the height range from the low stratosphere to the low thermosphere (25\textendash115 km) covering latitudes between 50\textdegreeS and 50\textdegreeN are statistically studied by using 9-year (January 22, 2002\textendashDecember 31, 2010) SABER/TIMED temperature data. We propose a method to extract realistic gravity wave fluctuations from the temperature profiles and treat square temperature fluctuations as GW activity. Overall, the gravity wave activity generally increases with height. Near the equator (0\textdegree\textendash10\textdegree), the gravity wave activity shows a quasi-biennial variation in the stratosphere (below 40 km) while from 20\textdegree to 30\textdegree, it exhibits an annual variation below 40 km; in low latitudes (0\textdegree\textendash30\textdegree) between the upper stratosphere and the low thermosphere (40\textendash115 km), the gravity wave activity shows a semi-annual variation. In middle latitudes (40\textdegree\textendash50\textdegree), the gravity wave activity has a clear annual variation below 85 km. In addition, we observe a four-monthly variation with peaks occurring usually in April, August, December in the northern hemisphere and in February, June, October in the southern hemisphere, respectively, above 85 km in middle latitudes, which has been seldom reported in gravity wave activity. In order to study the dissipation of gravity wave propagation, we calculate the gravity wave dissipation ratio, which is defined as the ratio of the gravity wave growth scale height to the atmosphere density scale height. The height variation of the dissipation ratio indicates that strong gravity wave dissipation mainly concentrates in the three height regions: the stratosphere (30\textendash60 km), the mesopause (around 85 km) and the low thermosphere (above 100 km). Besides, gravity wave energy enhancement can be also observed in the background atmosphere. Shuai, Jing; Zhang, ShaoDong; Huang, ChunMing; YI, Fan; Huang, KaiMing; Gan, Quan; Gong, Yun; Published by: Science China Technological Sciences Published on: 05/2014 YEAR: 2014 DOI: 10.1007/s11431-014-5527-z climatology; dissipation; gravity wave; middle and high atmosphere; SABER; TIMED |
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Presented is an analysis of the occurrence of postsunset Equatorial Plasma Bubbles (EPBs) detected using a Global Positioning System (GPS) receiver at Vanimo. The three year data set shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The Vanimo ionosonde station is used with the GPS receiver in an analysis of the day-to-day EPB occurrence variability during the 2000 equinox period. A superposed epoch analysis (SEA) reveals that the altitude, and the change in altitude, of the F layer height is \~1 standard deviation (1σ) larger on the days for which EPBs were detected, compared to non-EPB days. These results are then compared to results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), which show strong similarities with the observations. The TIEGCM is used to calculate the flux-tube integrated Rayleigh-Taylor (R-T) instability linear growth rate. A SEA reveals that the modeled R-T growth rate is 1σ higher on average for EPB days compared to non-EPB days, and that the upward plasma drift is the most dominant contributor. It is further demonstrated that the TIEGCM\textquoterights success in describing the observed daily EPB variability during the scintillation season resides in the variations caused by geomagnetic activity (as parameterized by Kp) rather than solar EUV flux (as parameterized by F10.7). Geomagnetic activity varies the modeled high-latitude plasma convection and the associated Joule heating that affects the low-latitude F region dynamo, and consequently the equatorial upward plasma drift. Carter, B.; Yizengaw, E.; Retterer, J.; Francis, M.; Terkildsen, M.; Marshall, R.; Norman, R.; Zhang, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.410.1002/2013JA019570 |
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Kuzmin, AK; Merzlyi, AM; Shadrin, DG; Yu, Potanin; Banshchikova, MA; Chuvashov, IN; Published by: Published on: |
| 2013 |
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Is Space Weather Different Over Africa, and If So, Why? An AGU Chapman Conference Report With the increasing reliance on technology, the impact of space weather on engineered systems will certainly increase unless suitable protective measures are taken. Understanding the physics behind space weather impacts and improving the forecasting are the major objectives of the space science community. It is well recognized that many space weather impacts, especially on communications systems, arise from structures in the ionosphere. The equatorial ionosphere, in particular, is one of the most complex and is host to numerous instabilities and interactions, with many unresolved questions regarding its dynamics and variability. Radio waves, either transmitted through the ionosphere, for satellite communication and navigation, or reflected off the ionosphere for HF and radar applications, are all impacted by ionospheric variability and structure. Ionospheric irregularities or plasma \textquotedblleftbubbles\textquotedblright occurring at low latitudes are one such source of interference. These irregularities cause scintillations on satellite radio transmissions, resulting in information loss in communications, as well as degradation in positioning and navigation used in aviation and maritime industries. Yizengaw, Endawoke; Doherty, Patricia; Fuller-Rowell, Tim; Published by: Space Weather Published on: 07/2013 YEAR: 2013 DOI: 10.1002/swe.20063 atmosphere ionosphere interactions; ionospheric irregularities; space weather |
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One important characteristic of longitudinal variability of the ionosphere is the global wavenumber-4 signature. Recent investigations have focused mainly on the climatological pattern during daytime and evening sectors. We investigate the day-to-day variability of the wavenumber-4 structure of the longitudinal ionospheric density distribution using the global total electron content (TEC) measurements from Global Positioning Systems receivers on the ground. The quiet time (Kp <= 3) day-to-day occurrence of the wavenumber-4 is obtained during periods of low solar flux conditions for the years 2008 and 2009. We find that the wavenumber-4 structure occurs at all local time sectors; however, the daytime TEC wavenumber-4 structures are clearer and can persist until the midnight hours. The most significant occurrence is observed during the 1000\textendash2400 LT sector while the minimum number of wavenumber-4 structure is observed between the 0400 and 0600 LT sector. Around the nighttime sector, more wavenumber-4 occurrence is observed during the premidnight sector than the postmidnight hours. The seasonal occurrence probability of the wavenumber-4 pattern is at a maximum during the March\textendashApril equinox and June\textendashJuly solstice. December\textendashJanuary is the period when the wavenumber-4 occurrence is less dominant than the rest of the year. Published by: Journal of Geophysical Research: Space Physics Published on: 04/2013 YEAR: 2013 DOI: 10.1002/jgra.50241 day-to-day; Ionosphere; longitudinal variability; TEC; wavenumber-4 |
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Determination of the Ionospheric Electron Density Profile from FUV Remote Sensing Measurements A limb viewing model is established in this paper based on GUVI measurements of OI 135.6 nm nightglow and a method with Chapman function describing the distribution of ionospheric electron density is presented to obtain the ionospheric electron density profile. We apply the regularization and Newton iteration method to calculate ionospheric peak electron density and peak height with GUVI measurements, eliminating the ill condition of the weighted matrix. The ionospheric electron density profile is obtained using the calculated peak electron density and peak height as inputs. To evaluate the fidelity of the proposed algorithm in this paper, the retrieved electron density profiles are compared with those from ground-based observations. The results show that the retrieved electron density profiles agree well with those from ISR. Afterwards, the effects of magnetic storms on EDP are studied with the retrieved EDPs of the period between Sep 29 and Oct 3, 2002. Jing, Wang; Yi, TANG; Zhi-Ge, ZHANG; Xu-Li, ZHENG; Guo-Qiang, NI; Published by: Chinese Journal of Geophysics Published on: 03/2013 YEAR: 2013 DOI: 10.1002/cjg2.20011 Electron density profile; Far ultraviolet spectrum remote sensing; GUVI; Ionosphere |
| 2012 |
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Global Longitudinal Dependence Observation of the Neutral Wind and Ionospheric Density Distribution Published by: International Journal of Geophysics Published on: Jan-01-2012 YEAR: 2012 DOI: 10.1155/2012/342581 |
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Longitudinal differences of ionospheric vertical density distribution and equatorial electrodynamics Accurate estimation of global vertical distribution of ionospheric and plasmaspheric density as a function of local time, season, and magnetic activity is required to improve the operation of space-based navigation and communication systems. The vertical density distribution, especially at low and equatorial latitudes, is governed by the equatorial electrodynamics that produces a vertical driving force. The vertical structure of the equatorial density distribution can be observed by using tomographic reconstruction techniques on ground-based global positioning system (GPS) total electron content (TEC). Similarly, the vertical drift, which is one of the driving mechanisms that govern equatorial electrodynamics and strongly affect the structure and dynamics of the ionosphere in the low/midlatitude region, can be estimated using ground magnetometer observations. We present tomographically reconstructed density distribution and the corresponding vertical drifts at two different longitudes: the East African and west South American sectors. Chains of GPS stations in the east African and west South American longitudinal sectors, covering the equatorial anomaly region of meridian \~37\textdegreeE and 290\textdegreeE, respectively, are used to reconstruct the vertical density distribution. Similarly, magnetometer sites of African Meridian B-field Education and Research (AMBER) and INTERMAGNET for the east African sector and South American Meridional B-field Array (SAMBA) and Low Latitude Ionospheric Sensor Network (LISN) are used to estimate the vertical drift velocity at two distinct longitudes. The comparison between the reconstructed and Jicamarca Incoherent Scatter Radar (ISR) measured density profiles shows excellent agreement, demonstrating the usefulness of tomographic reconstruction technique in providing the vertical density distribution at different longitudes. Similarly, the comparison between magnetometer estimated vertical drift and other independent drift observation, such as from VEFI onboard Communication/Navigation Outage Forecasting System (C/NOFS) satellite and JULIA radar, is equally promising. The observations at different longitudes suggest that the vertical drift velocities and the vertical density distribution have significant longitudinal differences; especially the equatorial anomaly peaks expand to higher latitudes more in American sector than the African sector, indicating that the vertical drift in the American sector is stronger than the African sector. Yizengaw, E.; Zesta, E.; Moldwin, M.; Damtie, B.; Mebrahtu, A.; Valladares, C.; Pfaff, R.; Published by: Journal of Geophysical Research Published on: 07/2012 YEAR: 2012 DOI: 10.1029/2011JA017454 |
| 2010 |
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Mordovskaya, V.; textquoterightev, A.; Boldyrev, S.; Boldyrev, S.; Ivanov-Kholodnyi, G.; Kolomiitsev, O.; Published by: Geomagnetism and Aeronomy Published on: Jan-10-2010 YEAR: 2010 DOI: 10.1134/S0016793210050154 |
| 2008 |
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Multi-instrument observations of the ionospheric and plasmaspheric density structure Published by: Published on: |
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