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Found 13 entries in the Bibliography.
Showing entries from 1 through 13
| 2022 |
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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 |
| 2021 |
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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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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 |
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MLT science enabled by atmospheric lidars With the pioneering development and deployment of different types of narrowband sodium fluorescence lidars in Europe (1985) and North America (1990) along with subsequent potassium and iron lidars, temperature and wind profilers have been observed to investigate atmospheric dynamics in the mesosphere and lower thermosphere (MLT) in midlatitude, polar and equatorial regions. Their achieved resolution allows investigation ranging from small-scale gravity waves to long-term global change. This chapter highlights MLT science enabled by resonance fluorescence lidars in the past 30 years, divided into sections on climatology and long-term change of the atmospheric (background) state; MLT responses to external forcings that lead to atmospheric tides, the global-scale impacts of sudden stratospheric warming as well as geomagnetic storms; gravity wave dynamics and their fluxes; synergistic campaigns with lidars serving as a central instrument, and lidar observation of metal layers in the thermosphere at ever-higher altitudes. Recent advances in maintenance-free resonance lidars will increase the time and duration of lidar observation as well as their ease of operation. These should lead to more coherent multiple-day continuous observations of the MLT. Continued efforts to increase lidar signal/noise and to extend measurements from the main metal layers (80–110 km) into the lower thermosphere (up to 150 km) are ongoing. Further technology developments will also enable more lidar deployment on airplanes and in space to study the MLT over the oceans and other remote areas. She, Chiao-Yao; Liu, Alan; Yuan, Tao; Yue, Jia; Li, Tao; Ban, Chao; Friedman, Jonathan; Published by: Published on: YEAR: 2021 DOI: 10.1002/9781119815631.ch20 Geomagnetic storms; atmospheric stabilities; atmospheric state; climatology; clustered instrumentation; gravity wave dynamics; MLT science; resonance fluorescence lidars; sporadic metal layers; thermospheric metal layers |
| 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: |
| 2016 |
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We present an analysis of a regional ionospheric response during six strong storms (-200\ nT\ <=Dst<=-100\ nT) that occurred in 2012 for the geographic latitudinal coverage of 10\textdegreeS\textendash40\textdegreeS within a longitude sector of 10\textdegreeE\textendash40\textdegreeE. Although these storms occurred during the same solar activity period and were all coronal mass ejection driven, their impacts and associated features on the ionosphere have been found different due to different contributing factors to their driving mechanisms. With the exception of one case, the rest of the storm periods were characterized by positive storm effects during the main and (or) recovery phases with varying physical mechanisms including low-latitude electrodynamics, neutral composition changes, and traveling ionospheric disturbances (TIDs). The common result to all the analyzed strong storms was the presence of large-scale TIDs during the storm main phases. Using total electron content data derived from the Global Navigational Satellite System (GNSS) observations and radio occultation (RO) electron density data on a regional scale, we have attempted to investigate meridional and vertical propagation of TIDs simultaneously during the strong storms. We have showed that it is possible to identify vertical motion of TIDs using RO data in cases when equatorward TIDs, as revealed by GNSS total electron content data, are present. RO results were compared to ionosonde data, and both data sources gave vertical velocities below 100\ m/s of the associated TIDs. Habarulema, John; Katamzi, Zama; Sibanda, Patrick; Matamba, Tshimangadzo; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2016 YEAR: 2016 DOI: 10.1002/jgra.v122.110.1002/2016JA023066 |
| 2014 |
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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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Space shuttle exhaust plumes in the lower thermosphere: Advective transport and diffusive spreading The space shuttle main engine plume deposited between 100 and 115\ km altitude is a valuable tracer for global-scale dynamical processes. Several studies have shown that this plume can reach the Arctic or Antarctic to form bursts of polar mesospheric clouds (PMCs) within a few days. The rapid transport of the shuttle plume is currently not reproduced by general circulation models and is not well understood. To help delineate the issues, we present the complete satellite datasets of shuttle plume observations by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument and the Sub-Millimeter Radiometer instrument. From 2002 to 2011 these two instruments observed 27 shuttle plumes in over 600 limb scans of water vapor emission, from which we derive both advective meridional transport and diffusive spreading. Each plume is deposited at virtually the same place off the United States east coast so our results are relevant to northern mid-latitudes. We find that the advective transport for the first 6\textendash18\ h following deposition depends on the local time (LT) of launch: shuttle plumes deposited later in the day (~13\textendash22 LT) typically move south whereas they otherwise typically move north. For these younger plumes rapid transport is most favorable for launches at 6 and 18 LT, when the displacement is 10\textdegree in latitude corresponding to an average wind speed of 30\ m/s. For plumes between 18 and 30\ h old some show average sustained meridional speeds of 30\ m/s. For plumes between 30 and 54\ h old the observations suggest a seasonal dependence to the meridional transport, peaking near the beginning of year at 24\ m/s. The diffusive spreading of the plume superimposed on the transport is on average 23\ m/s in 24\ h. The plume observations show large variations in both meridional transport and diffusive spreading so that accurate modeling requires knowledge of the winds specific to each case. The combination of transport and spreading from the STS-118 plume in August 2007 formed bright PMCs between 75 and 85\textdegreeN a day after launch. These are the highest latitude Arctic PMCs formed by shuttle exhaust reported to date. Stevens, Michael; Lossow, Stefan; Siskind, David; Meier, R.R.; Randall, Cora; Russell, James; Urban, Jo; Murtagh, Donal; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 02/2014 YEAR: 2014 DOI: 10.1016/j.jastp.2013.12.004 Atmospheric dynamics; Lower thermosphere; Polar mesospheric clouds; Space shuttle exhaust |
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A study on ionospheric scintillation near the EIA crest in relation to equatorial electrodynamics Equatorial electrojet (EEJ) data, which are considered as a proxy index of equatorial electric field, are analyzed in conjunction with equatorial ionosonde, total electron content (TEC) and scintillation data near the equatorial ionization anomaly (EIA) crest for the equinoctial months of high solar activity years (2011\textendash2012) to identify any precursor index of postsunset evolution of equatorial electron density irregularities and subsequent occurrence of scintillation near the northern EIA crest. Only geomagnetically quiet and normal electrojet days are considered. The diurnal profiles of EEJ on the scintillation days exhibit a secondary enhancement in the afternoon to presunset hours following diurnal peaks. A series of electrodynamical processes conducive for generation of irregularities emerge following secondary enhancement of EEJ. Latitudinal profile of TEC exhibits resurgence in EIA structure around the postsunset period. Diurnal TEC profile near the EIA crest resembles postsunset secondary enhancement on the days with afternoon enhancement in EEJ. Occurrence of equatorial spread F and postsunset scintillation near the EIA crest seems to follow the secondary enhancement events in EEJ. Both the magnitude and duration of enhanced EEJ are found to be important for postsunset intensification of EIA structure and subsequent occurrence of equatorial irregularities. A critical value combining the two may be considered an important precursor for postsunset occurrence of scintillation near the EIA crest. The results are validated using archived data for the years 1989\textendash1990 and explained in terms of modulation effects of enhanced equatorial fountain. Chatterjee, S.; Chakraborty, S.; Veenadhari, B.; Banola, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013JA019466 |
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Kuzmin, AK; Merzlyi, AM; Shadrin, DG; Yu, Potanin; Banshchikova, MA; Chuvashov, IN; Published by: Published on: |
| 2009 |
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Plasma probe data from DMSP-F13, DMSP-F15 and DEMETER satellites were used to examine longitudinal structures in the topside equatorial ionosphere during fall equinox conditions of 2004 year. Since the launch of DEMETER satellite on 29 June 2004, all these satellites operate close together in the topside ionosphere. Here, data taken from\ Special Sensor-Ion, Electron and Scintillations\ (SSIES) instruments on board DMSP-F13, F15 and\ Instrument Analyser de Plasma\ (IAP) on DEMETER, are used. Longitudinal variations in the major ions at two altitudes (~730 km for DEMETER and ~840 km for DMSP) are studied to further describe the recently observed "wavenumber-four" (WN4) structures in the equatorial topside ionosphere. Different ion species H+, He+\ and O+\ have a rather complex longitudinal behavior. It is shown that WN4 is almost a regular feature in O+\ the density distribution over all local times covered by these satellites. In the evening local time sector, H+\ ions follow the O+\ behavior within WN4 structures up to the pre-midnight hours. Near sunrise H+\ and later in the daytime, He+longitudinal variations are out of phase with respect to O+\ ions and effectively reduce the effect of WN4 on total ion density distribution at altitudes 730\textendash840 km. It is shown that both a WN4\ E\texttimesB\ drift driver and local F-region winds must be considered to explain the observed ion composition variations. Bankov, L.; Heelis, R.; Parrot, M.; Berthelier, J.-J.; Marinov, P.; Vassileva, A.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009 DOI: 10.5194/angeo-27-2893-2009 |
| 2007 |
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Altamimi, Z; Appleby, G; Aquino, M; Banyai, L; Bar-Sever, YE; Barlier, F; Bettadpur, S; Biancale, R; Boomkamp, H; Bruinsma, S; , others; Published by: Advances in Space Research Published on: |
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