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Found 2276 entries in the Bibliography.
Showing entries from 151 through 200
| 2021 |
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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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The changes in the ionosphere during geomagnetic disturbances is one of the prominent Space Weather effects on the near-Earth environment. The character of these changes can differ significantly at different regions on the Earth. We studied ionospheric response to five geomagnetic storms of March 2012, using data of Total Electron Content (TEC) and F2-layer critical frequency (foF2) along the meridian of 70° W in the Northern Hemisphere. There are few ionosondes along this longitudinal sector: in Thule, Sondrestrom, Millstone Hill and Puerto Rico. The lacking foF2 values between the ionosondes were determined by using the experimental latitudinal dependences of the equivalent ionospheric slab thickness and TEC values. During geomagnetic storms, the following features were characteristic: (a) two-hours (or longer in one case) delay of the ionospheric response to disturbances, (b) the more prominent mid-latitude trough and (c) the sharper border of the EIA northern crest. During four storms of 7–17 March, the general tendency was the transition from negative disturbances at high latitudes to intense positive disturbances at low latitudes. During the fifth storm, the negative ionospheric disturbance controlled by O/N2 change was masked by the overall prolonged electron density increase during 21–31 March. The multiple correlation analysis revealed the latitudinal dependence of dominant Space Weather parameters’ impacts on foF2. Sergeeva, Maria; Maltseva, Olga; Caraballo, Ramon; Gonzalez-Esparza, Juan; Corona-Romero, Pedro; Published by: Atmosphere Published on: feb YEAR: 2021 DOI: 10.3390/atmos12020164 foF2; geomagnetic storm; Ionospheric disturbance; ionospheric equivalent slab thickness; statistical analysis; TEC |
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Spread-F occurrence during geomagnetic storms near the southern crest of the EIA in Argentina This work presents, for the first time, the analysis of the occurrence of ionospheric irregularities during geomagnetic storms at Tucumán, Argentina, a low latitude station in the Southern American longitudinal sector (26.9°S, 294.6°E; magnetic latitude 15.5°S) near the southern crest of the equatorial ionization anomaly (EIA). Three geomagnetic storms occurred on May 27, 2017 (a month of low occurrence rates of spread-F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017 (a month of high occurrence rates of spread-F) are analyzed using Global Positioning System (GPS) receivers and ionosondes. The rate of change of total electron content (TEC) Index (ROTI), GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom side (h F) and the critical frequency of the F2 layer (foF2) are considered. Furthermore, each ionogram is manually examined for the presence of spread-F signatures. The results show that, for the three events studied, geomagnetic activity creates favorable conditions for the initiation of ionospheric irregularities, manifested by ionogram spread-F and TEC fluctuation. Post-midnight irregularities may have occurred due to the presence of eastward disturbance dynamo electric fields (DDEF). For the May storm, an eastward over-shielding prompt penetration electric field, (PPEF) is also acting. A possibility is that the PPEF is added to the DDEF and produces the uplifting of the F region that helps trigger the irregularities. Finally, during October and November, strong GPS L band scintillation is observed associated with strong range spread-F (SSF), that is, irregularities extending from the bottom-side to the topside of the F region. Published by: Advances in Space Research Published on: feb YEAR: 2021 DOI: 10.1016/j.asr.2020.10.051 Geomagnetic storms; ionospheric irregularities; space weather; Spread-F |
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Improved model of ionosphere variability and study for long-term statistical characteristics Ionospheric variability is influenced by many factors, such as solar radiation, neutral atmosphere composition, and geomagnetic disturbances. Mainly characterized by the total electron content (TEC) and electron density, the climatology of the ionosphere features temporal and spatial changes. Establishing a multivariant regression model helps substantially in better understanding the ionosphere characteristics and their long-term variability. In this paper, an improvement of the existing ionosphere multivariate linear fitting regression model is proposed and investigated using data from both the ionosonde and the global ionosphere map (GIM) derived from ground-based Global Navigation Satellite System (GNSS) observations. The proposed method gives more consideration to the impact of the solar activity and adds modeling of the annual periodic fluctuations and half-year periodic fluctuations for the F10.7 index. The improved model is verified to have a better correlation with the real observations and can help reduce the calculation uncertainty. Moreover, the proposed model is used to evaluate the fitting accuracy of the GIMs produced by five authorized data analysis centers from the International GNSS Service (IGS). The results show that there is a fixing hole in the North America region for the GIM model where the correlation between the GIM and the proposed model always returns lower values compared to other places. Published by: Chinese Journal of Aeronautics Published on: feb YEAR: 2021 DOI: 10.1016/j.cja.2020.03.018 total electron content; Analysis of anomalies; Long-term statistics; Regression model |
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This paper demonstrates and assesses the capability of the advanced three-dimensional (3-D) ionosphere tomography technique, during severe conditions. The study area is northeast Asia and quasi-Japan-centred. Reconstructions are based on total electron content data from a dense ground-based global navigation satellite system receiver network and parameters from operational ionosondes. We used observations from ionosondes, Swarm satellites and radio occultation (RO) to assess the 3-D picture. Specifically, we focus on St. Patrick’s day geomagnetic storm (17–19 March 2015), the most intense in solar cycle 24. During this event, the energy ingested into the ionosphere resulted in Dst and Kp and reaching values \textasciitilde − 223 nT and 8, respectively, and the region of interest, the East Asian sector, was characterized by a \textasciitilde 60\% reduction in electron densities. Results show that the reconstructed densities follow the physical dynamics previously discussed in earlier publications about storm events. Moreover, even when ionosonde data were not available, the technique could still provide a consistent picture of the ionosphere vertical structure. Furthermore, analyses show that there is a profound agreement between the RO profiles/in-situ densities and the reconstructions. Therefore, the technique is a potential candidate for applications that are sensitive to ionospheric corrections. Nicholas, Ssessanga; Mamoru, Yamamoto; Susumu, Saito; Published by: Earth, Planets and Space (Online) Published on: dec YEAR: 2021 DOI: 10.1186/s40623-021-01447-8 geomagnetic storm; Ground-GNSS-STEC tomography; Ionosonde data assimilation |
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Teleseismic measurements of upper mantle shear wave anisotropy in the Isthmus of Tehuantepec, Mexico Shear wave splitting measurements in the Isthmus of Tehuantepec (IT), southern Mexico, inferred from teleseismic core phases are presented. Measurements were made along a south-to-north profile across the IT. The results show a predominantly trench-normal pattern of fast polarization orientations with averaged delay times up to 2.2 s. Fast orientations near the trench suggest a corner flow in the mantle wedge and an entrained flow in the subslab region. Away the trench, fast orientations are parallel to the Absolute Plate Motion, suggesting that the anisotropy in that region is driven by a simple asthenospheric flow. A comparison with splitting measurements made in the Mexican subduction zone shows a 17° clockwise rotation of the fast orientations of between east and west Mexico. This is consistent with the observed change in orientation of 19° clockwise in the Middle American Trench (MAT). This suggests that the rotation of the fast orientations is controlled by the change of orientation in the MAT. León Soto, Gerardo; Valenzuela, Raúl; Arceo, R; Huesca-Pérez, Eduardo; Rosas, Ricardo; Published by: Geophysical Journal International Published on: dec YEAR: 2021 DOI: 10.1093/gji/ggab301 |
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The capability of IRI-2016 in reproducing the hemispheric asymmetry, the winter and semiannual anomalies has been assessed over the equatorial ionization anomaly (EIA) during quiet periods of years 2013–2014. The EIA reconstructed using Total Electron Content (TEC) derived from Global Navigation Satellite System was compared with that computed using IRI-2016 along longitude 25° − 40oE. These were analyzed along with hemispheric changes in the neutral wind derived from the horizontal wind model and the TIMED GUVI columnar O/N2 data. IRI-2016 clearly captured the hemispheric asymmetry of the anomaly during all seasons albeit with some discrepancies in the magnitude and location of the crests. The winter anomaly in TEC which corresponded with greater O/N2 in the winter hemisphere was also predicted by IRI-2016 during December solstice. The model also captured the semiannual anomaly with stronger crests in the northern hemisphere. Furthermore, it reproduced the variation trend of the asymmetry index (A) in December solstice and equinox during noon. However, in June solstice the model failed to capture the winter anomaly and misrepresented the variation of A. This was linked with its inability to accurately predict the pattern of the neutral wind, the maximum height of the F2 layer and the changes in O/N2 in both hemispheres. The difference between the variations of EUV and F10.7 fluxes was also a potential source of errors in IRI-2016. The results highlight the significance of the inclusion of wind data in IRI-2016 in order to enhance its performance over East Africa. Amaechi, Paul; Oyeyemi, Elijah; Akala, Andrew; Kaab, Mohamed; Younas, Waqar; Benkhaldoun, Zouhair; Khan, Majid; Mazaudier, Christine-Amory; Published by: Advances in Space Research Published on: aug YEAR: 2021 DOI: 10.1016/j.asr.2021.03.040 Equatorial ionization anomaly; hemispheric asymmetry; IRI-2016; Semiannual anomaly; Winter anomaly |
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The present paper reports magnetospheric-thermospheric-ionospheric interactions, observed during geomagnetically disturbed periods in 2015–2016 from mid-latitude stations located in the US-Pacific longitudes (\textasciitilde120°W geographic). These interactions have been analyzed for a series of Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storms during the moderate solar activity periods. The geomagnetically disturbed periods under consideration in this paper have an interesting feature of the occurrences of one or more HSSW events following an intense CME driven intense geomagnetic storm. Correlations were observed between the solar and geomagnetic parameters, hemispherically integrated Joule heating, changes in O/N2 ratio, corresponding changes in neutral wind velocities and mid-latitude Vertical Total Electron Content (VTEC) in most of the cases. Prolonged effects of neutral wind driven equatorward plasma transport process were noticed during the period of the summer solstice (June 23–26, 2015) which was correlated with the hemispherically integrated Joule heating and ionospheric conductivities. The effects of storm onset were observed during March 17–18, 2015. The influences of the ‘super-fountain effect’ in terms of Prompt Penetration Electric Field (PPEF) were seen during the main phases of the geomagnetic storms from these mid-latitude stations. This is correlated with the strength of Equatorial Electrojet (EEJ). Sur, Dibyendu; Ray, Sarbani; Paul, Ashik; Published by: Advances in Space Research Published on: aug YEAR: 2021 DOI: 10.1016/j.asr.2021.03.027 CME and HSSW storms; Joule heating; Meridional and zonal wind; O/N ratio; Plasma transport; VTEC |
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The results presented in this paper are obtained from low-latitude ionospheric total electron content (TEC) variation during the chosen geomagnetic storm events happening during the solar cycle 24. We include the four intense geomagnetic storms that occurred on 26 September 2011, 15 July 2012, 19 February 2014 and 20 December 2015, depending upon the availability of TEC data. For this, we have used the TEC data from low-latitude station Varanasi (geographic latitude 25°, 16′N, geographic longitude 82°, 59′E and geomagnetic latitude 16°, 24′N) and an equatorial station Bengaluru (geographic latitude 13°, 02′N, geographic longitude 77°, 34′E and geomagnetic latitude 04°, 68′N). The storm-induced TEC changes at chosen stations have been discussed in terms of local time, storm wind effect, neutral wind, composition changes and variation in the dawn–dusk component of the interplanetary electric field (IEF Ey). Singh, Abha; Rathore, Vishnu; Kumar, Sanjay; Rao, S.; Singh, Sudesh; Singh, A.; Published by: Journal of Astrophysics and Astronomy Published on: aug YEAR: 2021 DOI: 10.1007/s12036-021-09774-8 geomagnetic storm; Global positioning system; low latitude; total electron contents |
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This study investigates the ionospheric Total Electron Content (TEC) responses over 75°E longitude to the solar flares and geomagnetic storms of September 6–9, 2017. The results of this study provide the impacts of solely solar flares on the ionosphere and such impact when the effects of solar flares and geomagnetic storm are combined. On September 6, two X class solar flares, namely X2.2 at 0857 UT and X9.3 at 1153 UT, were recorded with quiet geomagnetic conditions. The EUV/X-ray intensity of X9.3 flare was significantly greater than that of X2.2 flare, and the recovery phase of both the flares was slower than their respective impulsive phase. The slower recovery rate in EUV/X-ray intensity is reflected as a delayed TEC response. A nearly 8\% higher crest to trough TEC change on flare day than the pre-flare day suggests an enhanced level of the equatorial electrojet. The overall weak TEC response to X9.3 solar flare is attributed to solar zenith angle dependency and shifting of solar flare location from disk center to west limb. The solar flares on September 7–8 were co-occurred with geomagnetic storms and observed large increments in TEC are additionally induced by prompt penetration electric field and the enhanced level of thermospheric compositional changes. On September 9, an increase in TEC is observed during M class solar flares under effect of solar flares and disturbed dynamo electric field. Chakraborty, Monti; Singh, A.; Rao, S.; Published by: Advances in Space Research Published on: aug YEAR: 2021 DOI: 10.1016/j.asr.2021.04.012 |
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The Dynamics of the Alfvénic Oval The auroral oval is a well-established concept, introduced more than five decades ago. The Alfvénic oval, on the other hand, is a very recent concept, which has been revealed in both observational and numerical studies. This is the first review of the global Alfvénic oval, while also defining primary, secondary and tertiary layers of the Alfvénic oval. The focus lies on the large-scale dynamic properties of the global Alfvénic oval in relation to the AE index, substorm phases, storm phases and solar wind/IMF conditions. Statistical data recorded above and below the nominal auroral acceleration region are reviewed, together with results from global simulation studies. The Alfvénic oval s relation to the auroral oval is also reviewed. This review demonstrates that the Alfvénic oval is well enough defined and investigated to give it its name, and it demonstrates that our understanding allows for the prediction of the Alfvénic oval under various conditions. Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: aug YEAR: 2021 DOI: 10.1016/j.jastp.2021.105616 AURORA; Alfven wave; Energy transport; geomagnetic activity; magnetosphere-ionosphere coupling; Wave-particle interaction |
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Ultraviolet Observations and a Theory of STEVE A search for ultraviolet (UV) emissions in satellite data during known STEVE (Strong Thermal Emission Velocity Enhancement) events found that simultaneous subauroral UV arcs (SUA) were usually, but not always present in the Southern Hemisphere despite coverage of the conjugate STEVE location. From 2005 to 2020 a systematic search for SUA found over 100 cases with a mean Magnetic Local Time (MLT) of 316°, standard deviation 13° and hemispheric asymmetry. Frequently coincident continuum UV and visible emissions, upwelling plasma flux, and downward Field Aligned Currents were observed. Occassionally coincident MeV protons were observed. A theory of solar MeV protons and comoving keV electrons following a Parker spiral can explain these phenomena. Published by: Earth and Space Science Open Archive ESSOAr Published on: apr YEAR: 2021 DOI: 10.1002/essoar.10504577.6 Atmospheric Sciences; Atmospheric Sciences / Airglow; Atmospheric Sciences / Aurora; Atmospheric Sciences / Ionosphere; Atmospheric Sciences / Magnetospheric Particles; Atmospheric Sciences / Precipitation Physics; Atmospheric Sciences / Solar Wind |
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Based on the observations of Ionospheric Bubble Index (IBI) data from the Swarm mission, the characteristics of plasma bubbles are investigated during different types of geomagnetic storms recorded from 2014 to 2020. The geometrical constellation of the Swarm mission enabled us to investigate the altitudinal profile of the IBIs during different activity levels in a statistical mean. Results show that the majority of IBIs associated with moderate storms are observed at low altitudes and the probability of observing IBIs at high altitudes (Swarm-B) increases with the increase in storm level. This is confirmed by observing the F2 layer peak height (hmF2) during super storm events at larger altitudes using COSMIC data. The maximum number of IBIs is recorded within the South Atlantic Anomaly (SAA) region with a long duration time and tends to increase only during dusk time. Both the large duration time and number of IBIs over the South Atlantic Anomaly (SAA) suggest that the gradient in the electron density and the depression in the magnetic field are the main factors controlling IBI events. Also, the IBIs at high altitudes are larger at sunset and at low altitudes pre-midnight. In addition, the occurrence of IBIs is always larger in the northern hemisphere than in the southern hemisphere irrespective of the type of storm, as well as during the summer months. Moreover, there is no correlation between the duration time of IBIs and both the altitudinal observation of the IBIs and the storm type. Seasonal occurrence of IBIs is larger during equinoxes and vice versa during solstices irrespective of both the type of storm and the altitude of the satellite. The large number of IBIs during equinoxes agrees with the previous studies, which expect that the large electron density is a developer of steeper ∇n. Large occurrences of super storm IBIs observed within the pre-midnight during summer and at sunset during equinoxes are a novel observation that needs further investigation. Also, the majority of IBIs are observed a few hours after geomagnetic substorms, which reflects the role of the Disturbance Dynamo Electric Field (DDEF) as a main driver of IBIs. Hussien, Fayrouz; Ghamry, Essam; Fathy, Adel; Published by: Universe Published on: apr YEAR: 2021 DOI: 10.3390/universe7040090 geomagnetic storm; ionospheric irregularity; plasma bubble; Swarm mission |
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Lower Thermospheric Material Transport via Lagrangian Coherent Structures We show that inter-model variation due to under-constraint by observations impacts the ability to predict material transport in the lower thermosphere. Lagrangian coherent structures (LCSs), indicating regions of maximal separation (or convergence) in a time-varying flow, are derived in the lower thermosphere from models for several space shuttle water vapor plume events. We find that inter-model differences in thermospheric transport manifest in LCSs in a way that is more stringent than mean wind analyses. LCSs defined using horizontal flow fields from the Specified Dynamics version of the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCMX) at 109 km altitude are compared to Global Ultraviolet Imager (GUVI) observations of the space shuttle main engine plume. In one case, SD-WACCMX predicts an LCS ridge to produce spreading not found in the observations. LCSs and tracer transport from SD-WACCMX and from data assimilative WACCMX (WACCMX + DART) are compared to each other and to GUVI observations. Differences in the modeled LCSs and tracer positions appear between SD-WACCMX and WACCMX + DART despite the similarity of mean winds. WACCMX + DART produces better tracer transport results for a July 2006 event, but it is unclear which model performs better in terms of LCS ridges. For a February 2010 event, when mean winds differ by up to 50 m/s between the models, differences in LCSs and tracer trajectories are even more severe. Low-pass filtering the winds up to zonal wavenumber 6 reduces but does not eliminate inter-model LCS differences. Inter-model alignment of LCSs improves at a lower 60 km altitude. Datta-Barua, Seebany; Pedatella, Nicholas; Greer, Katelynn; Wang, Ningchao; Nutter, Leanne; Harvey, Lynn; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028834 |
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Periodic Variations in Solar Wind and Responses of the Magnetosphere and Thermosphere in March 2017 TIMED/GUVI observed thermospheric column ∑O/N2 depletion in both hemispheres between March 1 and 21, 2017 which was caused by large periodic variations in interplanetary magnetic field (IMF) and a high solar wind speed, likely in a solar wind. The dominant periods seen in the solar wind and magnetosphere coupling function (CF) were around 1.9, 3.0, 4.7, 7.6, 14.0 and 22.0 h on March 1 and 2. The major AE variations were around 3.0, 4.7, 7.6, 10.7, 14.0 and 22.0 h. Auroral hemispheric power (HP) also showed periodic variations similar to that of AE, except for the absence of the 3.0 h variation due to a low sampling rate in HP data. SymH data didn t show the periodic variations seen in AE but a weak 12-h periodic variation which was seen in the solar wind dynamic pressure. A weak AE and HP variation at 10.7-h period was not observed in CF or any individual solar wind parameters or IMF components. These results suggest that (a) the oscillating IMF pumped energy and mass periodically into the magnetosphere and the polar ionosphere, creating a long lasting (20-days) storm and O/N2 depletion, (b) the high latitude AE and HP responded to the solar wind and IMF variations directly, (c) SymH did not show any direct periodic responses, likely due to the fact that the ring current response resulted from the cumulative effect of solar wind and IMF drivers, (d) the 10.7-h variations in AE and HP were likely due to magnetospheric internal processes. Zhang, Yongliang; Paxton, Larry; Wang, Wenbin; Huang, Chaosong; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029387 AE index; geomagnetic storm; hemispheric power; periodic variation; solar wind and magnetosphere coupling; thermospheric composition |
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Hemispheric asymmetries of the Vertical Total Electron Content (VTEC) were observed during the first recovery phase of the geomagnetic storm on September 7–8, 2017. These asymmetries occurred at the mid latitudes at two different local times simultaneously: In the European-African sector (early morning), the storm time VTEC in the southern/northern hemisphere was higher/lower than the quiet time value, suggesting the southern/northern hemisphere entered the positive/negative phase (N−S+). In the East Asian-Australian sector (afternoon), the storm time VTEC change was positive in the northern hemisphere, but negative in the southern hemisphere (N+S−). The electron density profiles from digisondes demonstrated that the asymmetries appeared in the F region density as well. The plasma drifts data from digisondes, the column-integrated [O]/[N2] ratio from GUVI onboard the TIMED satellite, and the detrended VTEC were utilized to study the drivers of the asymmetries. Traveling Ionospheric Disturbance (TID) signatures were identified in the digisonde drift and detrended VTEC data before the appearance of the asymmetry. The magnitude of TIDs was larger in the hemisphere where the negative phase occurred later. The storm time [O]/[N2] ratio change was positive in Africa (S+) and negative in Europe (N−). However, the [O]/[N2] measurements were not available in the East Asian-Australian sector during the focused period. The hemispheric differences in the vertical drifts were also observed in both sectors. Therefore, the observed hemispheric asymmetries in both sectors are suggested to be due to the hemispheric asymmetries in the thermospheric composition change, vertical drift, and TID activity. Wang, Zihan; Zou, Shasha; Liu, Lei; Ren, Jiaen; Aa, Ercha; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028829 |
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The Global-scale Observations of the Limb and Disk (GOLD) mission, launched in 2018, aims to investigate the low latitude ionosphere from a geostationary orbit at 47.5°W. It uses two identical spectrometers measuring the wavelength range from 134.0 to 163.0 nm. The configuration of the Earth s magnetic field shows that the largest offset between geographic and geomagnetic equators occurs in the longitude sectors sampled by GOLD. In an attempt to investigate the longitude dependence of the occurrence rate and time of onset of plasma bubbles, or plasma depletions, GOLD data were separated in three sectors: 65°-55°W, 50°-40°W, and 10°W–0°. Observations of the nighttime emissions in 135.6 nm on November 2018 and March 2019 show plasma depletions occurring very frequently at these longitudes. The growth rate of the Rayleigh-Taylor instability was computed at these longitudes under similar low solar activity conditions, assuming an empirical model of upward plasma drifts. The time and value of the maximum growth rates obtained cannot always explain the observations. On average, the observed occurrence rate of plasma depletions is high, with a maximum of 73\% (observed during November 2018 at ∼45°W). Most of the depletions observed in November at 45°W and 60°W occur within 1 h after sunset. When compared with the November 2018 observations, depletions in March 2019 occur at later times. Martinis, C.; Daniell, R.; Eastes, R.; Norrell, J.; Smith, J.; Klenzing, J.; Solomon, S.; Burns, A.; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028510 F region; longitude variability; plasma bubbles; Plasma depletions; upward drifts |
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The low-density cell structure in the high-latitude thermosphere is referred to as the density depletion with respect to the adjacent area. Based on Gravity Recovery and Climate Experiment (GRACE) accelerometer data during the September 2017 geomagnetic storms, the thermospheric mass density at about 350 km are estimated and further investigated especially in the high-latitude regions. At least two kinds of low-density cells over the Southern Hemisphere (SH) are observed along the GRACE orbit. To understand the low-density cell structures over the SH observed by GRACE, we investigate the underlying physical mechanism based on thermosphere-ionosphere numerical simulations using Thermosphere-Ionosphere Electrodynamic General Circulation Model and Global Ionosphere Thermosphere Model. According to the simulation results, the formation mechanism of the low-density cell is attributed to the storm-time vertical advection and horizontal velocity divergence driven by the auroral ion convection. The critical height of observable low-density cells is shown to be not less than 350 km. The meridional spatial scale of observed low-density cells over the SH are approximately or slightly larger than 1,500 km. Three low-density cells, including two in the dawn sector and one in the night sector were observed about 1 hour after the direction of interplanetary magnetic field BY component reversed. The occurrence of thermospheric low-density structure is essential to be included in the empirical model during geomagnetic storm time. Yuan, Liangliang; Jin, Shuanggen; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028915 |
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We present an investigation of the F-region electron temperature to an intense geomagnetic storm that occurred on 5 August 2011. The investigation is based on the incoherent scatter radar measurements at Arecibo Observatory, Puerto Rico (18.3°N, 66.7°W). The electron temperature exhibits a rapid and intensive enhancement after the commencement of the geomagnetic storm. The electron temperature increases by ∼800 K within an hour, which is seldomly reported at Arecibo. At the same time, a depletion of the electron density is also observed. The daytime perturbations of electron density and temperature are anticorrelated with the correlation coefficient, which is −0.88 and −0.91 on the day and the following day of the geomagnetic storm, respectively. According to the Global Ultraviolet Imager measurements, the ratio of atomic oxygen to molecular nitrogen concentration () decreases dramatically during the storm. Our analysis suggests that the enhancement of the electron temperature is due to the depletion of the electron density, which is likely associated with the decrease of . The reduction of maybe caused by a prompt upward plasma motion after the commencement of the geomagnetic storm. Lv, Xiedong; Gong, Yun; Zhang, ShaoDong; Zhou, Qihou; Ma, Zheng; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029836 Arecibo; F-region electron temperature; geomagnetic storm; incoherent scatter radar |
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The Empirical Canadian High Artic Ionospheric Model (E-CHAIM) provides the four-dimensional ionosphere electron density at northern high latitudes (\textgreater50° geomagnetic latitude). Despite its emergence as the most reliable model for high-latitude ionosphere density, there remain significant deficiencies in E-CHAIM s representation of the lower ionosphere (below ∼200 km) due to a sparsity of reliable measurements at these altitudes, particularly during energetic particle precipitation events. To address this deficiency, we have developed a precipitation component for E-CHAIM to be driven by satellite-based far-ultraviolet (FUV) imager data. Satellite observations of FUV emissions may be used to infer the characteristics of energetic particle precipitation and subsequently calculate the precipitation-enhanced ionization rates and ionosphere densities. In order to demonstrate the improvement of E-CHAIM s ionosphere density representation with the addition of a precipitation component, this paper presents comparisons of E-CHAIM precipitation-enhanced densities with ionosphere density measurements of three auroral region incoherent scatter radars (ISRs) and one polar cap ISR. Calculations for 29,038 satellite imager and ISR conjunctions during the years 2005–2019 revealed that the root-mean-square difference between E-CHAIM and ISR measurements decreased by up to 2.9 × 1010 ele/m3 (altitude dependent) after inclusion of the precipitation component at auroral sites, and by 2.6 × 109 ele/m3 in the polar cap. Improvements were most substantial in the winter season and during active auroral conditions. The sensitivity of precipitation-enhanced densities to uncertainties inherent to the calculation method was also examined, with the bulk of the errors due to uncertainties in FUV imager data and choice of distribution function for precipitation energy spectra. Watson, C.; Themens, D.; Jayachandran, P.; Published by: Space Weather Published on: YEAR: 2021 DOI: 10.1029/2021SW002779 auroral region; Ionosphere; ionosphere density; magnetosphere-ionosphere-thermosphere coupling; particle precipitation; polar cap |
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Wide-field aurora imager onboard Fengyun satellite: Data products and validation New observations of auroras based on the wide-field aurora imager (WAI) onboard Fengyun-3D (FY-3D) satellite are exhibited in this paper. Validity of the WAI data is analyzed by comparing auroral boundaries derived from WAI observations with results obtained from data collected by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) aboard the Defense Meteorological Satellite Program (DMSP F18). Dynamic variations of the aurora with the solar wind, interplanetary magnetic field (IMF) parameters, and the SYM-H index are also investigated. The comparison of auroral boundaries indicates that the WAI data are morphologically valid and suitable to the study of auroral dynamics. Effective responses to solar wind parameters indicate that the WAI data can be useful to monitor and predict the Earth s space weather. Since the configuration of aurora is a good indicator of the solar wind-magnetosphere-ionosphere (SW-M-I) coupling system, and can reflect the disturbance of the space environment, the WAI will provide important data to help us to study the physical processes in space. Ding, GuangXing; Li, JiaWei; Zhang, Xiaoxin; He, Fei; He, LingPing; Song, KeFei; Sun, Liang; Dai, Shuang; Liu, ShiJie; Chen, Bo; Yu, Chao; Hu, Xiuqing; Gu, SongYan; Yang, Zhongdong; Zhang, Peng; Published by: Earth and Planetary Physics Published on: YEAR: 2021 DOI: 10.26464/epp2021003 |
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The Earth’s Ionosphere and Thermosphere (IT) is a highly dynamic system persistently driven by variable forcings both from above (Solar EUV and the magnetosphere) and the lower atmosphere. The forcing from below accounts for the majority of the variability at low- and mid-latitude IT region during geomagnetic quiet times. The IT region is particularly sensitive to the composition, winds, and temperature of the Mesosphere and Lower Thermosphere (MLT) state. The goal of this dissertation is to help understand how the MLT region controls the upper atmosphere. This is achieved by using the IT model, Global Ionosphere Thermosphere Model (GITM) and altering its lower boundary (which is in the MLT) to allow a more accurate representation of the lower atmospheric physics within the model. At the beginning of this thesis, it is identified that recent solstitial observations of MLT atomic oxygen (O) from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument show larger densities in the summer hemisphere than in the winter hemisphere. This is opposite to what has been previously known and specified in the IT models, and its cause is still under investigation. The first study focuses on understanding the influence of this latitudinal distribution by using a more realistic specification of MLT [O] from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X), in GITM. This study shows that despite being a minor species throughout the lower thermosphere, reversing the [O] distribution affects the pressure gradients, winds, temperature, and N2 in the lower thermosphere. These changes then map to higher altitudes through diffusive equilibrium, improving the agreement between GITM O/N2 and Global Ultraviolet Imager (GUVI) measurements. Secondly, the importance of MLT variations on the thermospheric and ionospheric semiannual variation (T-I SAO) is investigated. This is done by analyzing the sensitivity of T-I SAO in GITM to different lower boundary assumptions. This study reveals that the primary driver of T-I SAO is the thermospheric spoon mechanism, as a significant T-I SAO is reproduced in GITM without an SAO variation in the MLT. However, using a more realistic MLT [O] from WACCM-X produces an oppositely-phased T-I SAO, maximizing at solstices, disagreeing with the observations. Since the MLT [O] distribution is correct in WACCM-X, the results hint at incomplete specification/physics for lower thermospheric dynamics in GITM that can drive the transition of the SAO to its correct phase. These mechanisms warrant further investigation and may include stronger winter-to-summer winds, and lower thermospheric residual circulation. The goal of the last study is to examine the effects of spatially non-uniform turbulent mixing in the MLT on the IT system. This is achieved by introducing latitudinal variation in the eddy diffusion parameter (Kzz) in GITM. The results reveal larger spatial variability in O/N2 and TEC. However, the net effect is small (within 2-4\%) on the globally averaged quantities and depends on the area of the turbulent patch. The results also show a different response between the summer and the winter IT region, with winter exhibiting larger changes. Overall, this thesis has highlighted some of the outstanding questions in the domain of lower atmosphere-IT coupling and have answered them through exhaustive comparisons of GITM simulations with different satellite observations, and extensive term analyses of the GITM equations, while laying out a framework for coupling of GITM with WACCM-X. Published by: Published on: YEAR: 2021 DOI: 10.7302/2811 |
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Near Real-Time Global Plasma Irregularity Monitoring by FORMOSAT-7/COSMIC-2 This study presents initial results of the ionospheric scintillation in the F layer using the S4 index derived from the radio occultation experiment (RO-S4) on FORMOSAT-7/COSMIC-2 (F7/C2). With the sufficiently dense RO-S4 observations at low latitudes, it is possible to construct hourly, global scintillation maps to monitor equatorial plasma bubbles (EPBs). The preliminary F7/C2 RO-S4 during August 2019 to April 2020 show clear scintillation distributions around American and the Atlantic Ocean longitudes. The RO-S4 near Jicamarca are compared with range-time-intensity (RTI) maps of the 50 MHz radar, and the results show that the occurrence of intense RO-S4 in the range 0.125–0.5 are co-located with the bottomside of the spread-F patterns. Increases in RO-S4 at the upward phase of bottom-side oscillations is theoretically consistent with large-scale wave seeding of the EPBs. The locations and occurrences of the RO-S4 greater than 0.5 are consistent with airglows depletions from the NASA GOLD mission. Climatology analyses show that monthly occurrences of RO-S4 \textgreater 0.5 agree well with the monthly EPB occurrences in GOLD 135.6 nm image, and show a similar longitudinal distribution to that of DMSP and C/NOFS in-situ measurements. The results suggest that the RO-S4 intensities can be utilized to identify EPBs of specific scales. Chen, Shih-Ping; Lin, Charles; Rajesh, Panthalingal; Liu, Jann-Yenq; Eastes, Richard; Chou, Min-Yang; Choi, Jong-Min; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028339 equatorial plasma bubbles; FORMOSAT-7/COSMIC-2; global observation of limb and disk; GNSS scintillation; radio occultation; S4 index |
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Accurate specification of the thermosphere states is crucial to the low Earth orbit satellite operation. In this work, the impact of different ionosphere and thermosphere observing systems on the improvement of neutral temperature of the data assimilation model has been investigated by a series of observing system simulation experiments. The selected observations include the Global Navigation Satellite System total electron content (e.g., MIT vertical total electron content [VTEC]) and the daytime Global-scale Observations of the Limb and Disk (GOLD) level-2 disk temperature (Tdisk). Such observations are ingested into the coupled ionosphere and thermosphere model based on our developed ensemble Kalman Filter data assimilation systems on the basis of the ensemble Kalman filter algorithm and the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model. The main findings are as follows: (a) A considerable improvement of the neutral temperature estimation of the physical-based model can be obtained in the global region by assimilating either the MIT VTEC or the GOLD Tdisk observations; (b) the assimilation of the GOLD can further contribute to temperature improvement in the lower thermosphere (\textless200 km), relative to the MIT VTEC assimilation; and (c) simultaneously assimilating both observation types can better improve the quality of neutral temperature estimation over the global area during the whole data assimilation process. The current results demonstrate that assimilating GOLD observations is important to improve the forecast capability of the physical-based model for the lower thermosphere states and can provide a possible reference for the joint assimilation of the ionosphere and thermosphere observations to better thermosphere specification. He, Jianhui; Yue, Xinan; Ren, Zhipeng; Published by: Space Weather Published on: YEAR: 2021 DOI: 10.1029/2021SW002844 |
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A method for retrieving temperature and composition from 150 to 350 km in Earth s thermosphere using total number density measurements made via extreme ultraviolet (EUV) solar occultations by the Project for OnBoard Autonomy 2/Large Yield Radiometer (PROBA2/LYRA) instrument is presented. Systematic and random uncertainties are calculated and found to be less than 5\% for the temperature measurements and 5\%–20\% for the composition measurements. Regression coefficients relating both temperature and the [O]/[N2] abundance ratio with EUV irradiance at 150, 275, and 350 km are reported. Additionally, it is shown that the altitude where [O] equals [N2] decreases with increasing solar EUV irradiance, an effect attributed to thermal expansion. Temperatures from 2010 to 2017 are compared with estimates from the MSIS empirical model and show good agreement at the dawn terminator but LYRA is markedly cooler at the dusk terminator, with the MSIS-LYRA temperature difference increasing with solar activity. Anthropogenic cooling can explain this discrepancy at periods of lower solar activity, but the divergence of temperature with increasing solar activity remains unexplained. LYRA measurements of the exospheric temperature sensitivity to EUV irradiance are compared with contemporaneous measurements made at Mars, showing that the exospheric temperature at Mars is approximately half as sensitive to EUV variability as that of Earth. Thiemann, Edward; Dominique, Marie; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029262 comparative planetology; EUV; occultations; space weather; thermosphere |
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The Thermospheric Column O/N2 Ratio More than 2 decades ago, D. J. Strickland and colleagues proposed use of the O/N2 column number density ratio as a new geophysical quantity to interpret thermospheric processes recorded in far ultraviolet (FUV) images of the Earth. This concept has enabled multiple advances in understanding the global behavior of Earth s thermosphere. Nevertheless, confusion remains about the conceptual meaning of the column density ratio, and in the application of this integral quantity. This is so even though it is now a key thermospheric measurement made by current and planned far ultraviolet remote sensing missions in pursuit of new understanding of thermospheric processes and variability. The intent here is to review the historical context of the O/N2 column density ratio, clarify its physical meaning, and resolve misunderstandings evident in the literature. Simple examples elucidate its original derivation for extracting column O/N2 ratios from measurements of the OI 135.6 nm/N2 Lyman-Birge-Hopfield (LBH) emission based on an algorithmic synthesis of model precomputations. These are organized in the form of a table lookup of column density ratio as a function of observed radiance ratios. To accommodate generalized solar-geophysical and viewing conditions, the table required to specify the number of needed parameters becomes large. Proposed as an alternative is a simplified, first principles approach to obtaining the column density ratio from the emission ratio. This new methodology is now being applied successfully to FUV measurements made from onboard the Ionospheric CONnection satellite and will be applied retrospectively to the Global Ultraviolet Imager data. Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA029059 disk algorithm; far UV remote sensing; GUVI; ICON; N2 LBH bands; Oxygen 135.6 nm |
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Transpolar Arcs During a Prolonged Radial Interplanetary Magnetic Field Interval Transpolar arcs (TPAs) are believed to predominantly occur under northward interplanetary magnetic field (IMF) conditions with their hemispheric asymmetry controlled by the Sun-Earth (radial) component of the IMF. In this study, we present observations of TPAs that appear in both the northern and southern hemispheres even during a prolonged interval of radially oriented IMF. The Defense Meteorological Satellite Program (DMSP) F16 and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellites observed TPAs on the dawnside polar cap in both hemispheres (one TPA structure in the southern hemisphere and two in the northern hemisphere) during an interval of nearly earthward-oriented IMF on October 29, 2005. The southern hemisphere TPA and one of the northern hemisphere TPAs are associated with electron and ion precipitation and mostly sunward plasma flow (with shears) relative to their surroundings. Meanwhile, the other TPA in the northern hemisphere is associated with an electron-only precipitation and antisunward flow relative to its surroundings. Our observations indicate the following: (a) the TPA formation is not limited to northward IMF conditions; (b) the TPAs can be located on both closed field lines rooted in the polar cap of both hemispheres and open field lines connected to the northward field lines draped over one hemisphere of the magnetopause. We believe that the TPAs presented here are the result of both indirect and direct processes of solar wind energy transfer to the high-latitude ionosphere. Park, Jong-Sun; Shi, Quan; Nowada, Motoharu; Shue, Jih-Hong; Kim, Khan-Hyuk; Lee, Dong-Hun; Zong, Qiu-Gang; Degeling, Alexander; Tian, An; Pitkänen, Timo; Zhang, Yongliang; Rae, Jonathan; Hairston, Marc; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029197 radial IMF; solar wind-magnetosphere-ionosphere coupling; transpolar arc |
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The Ionosphere at Middle and Low Latitudes Under Geomagnetic Quiet Time of December 2019 The ionospheric electron density shows remarkable day-to-day variability due to solar radiance, geomagnetic activity and lower atmosphere forcing. In this report, we investigated the ionospheric variations at middle and low latitudes during a period under geomagnetic quiet time (Kpmax = 1.7) from November 30 to December 8, 2019. During the quiescent period, the ionosphere is not undisturbed as expected in the Asian-Australian and the American sectors. Total electron content (TEC) has multiple prominent enhancements at middle and low latitudes in the two sectors, and TEC depletions also occur repeatedly in the Asian-Australian sector. The low-latitude electric fields vary significantly, which is likely to be modulated by the notably changing tides in the mesosphere and lower thermosphere region. It is worth noting that the variations of TEC and the electric fields are not consistent in the two sectors, particularly on December 4–6. Further investigation reveals that the increase in TEC depends on altitude. The TEC enhancements are mainly contributed by the altitude below 500 km in both two sectors, which indirectly reflects that the driving sources may come from the lower atmosphere. Especially, a mid-latitude band structure continuously appears at all local times in the North American sector on December 6–8, which is also mainly contributed by the altitude below 500 km. Kuai, Jiawei; Li, Qiaoling; Zhong, Jiahao; Zhou, Xu; Liu, Libo; Yoshikawa, Akimasa; Hu, Lianhuan; Xie, Haiyong; Huang, Chaoyan; Yu, Xumin; Wan, Xin; Cui, Jun; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028964 low-latitude electric fields; the ionosphere variations in solar minimum; the ionospheric day-to-day variations; the ionospheric disturbance; the ionospheric variations; topside ionosphere |
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Storm-Time Neutral Composition Changes in the Upper Atmosphere During geomagnetic storms, energy inputs, such as particle precipitation and Joule heating from the magnetosphere and solar wind, create significant disturbances in the upper atmosphere in the form of changes in the thermospheric density and temperature and, more important, composition, such as O/N 2 column density ratio, nitric oxide (NO) density, and atomic nitrogen (N) density. The composition changes control the ionosphere and have a feedback effect on thermospheric temperature and density due to a cooling effect of enhanced NO 5.3 μm radiation. We review the methods of deriving the composition information from far ultraviolet (FUV) observations as well as the signatures of the major features in the storm-time composition variations such as O/N 2 depletion and enhancement, NO and N enhancement, corotation of the O/N 2 depletion, seasonal and hemispheric asymmetry, traveling atmospheric disturbance (TAD) and its connection to traveling ionosphere disturbance (TID), and temperature increase in O/N 2 depleted regions and their interaction with TADs. A FUV spectrograph imager is a cost-effective instrument suitable for low Earth orbit missions and can monitor the response of the near-Earth space environment including the thermosphere, ionosphere, and aurora (magnetosphere) to solar wind forcing as well as forcing from low atmosphere. Zhang, Yongliang; Paxton, Larry; Published by: Published on: YEAR: 2021 DOI: 10.1002/9781119815631.ch7 far ultraviolet observations; storm-time neutral composition changes; thermospheric nitric oxide variations; traveling atmospheric disturbance; traveling ionosphere disturbance; upper atmosphere |
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The Northward IMF Magnetosphere The manner in which the Earth s magnetosphere responds to the solar wind is highly dependent upon the orientation of the interplanetary magnetic field (IMF), particularly the north–south (B Z ) component. As most auroral and geomagnetic activity occurs when the IMF is southward (or weakly northward, but dominated by the dawn–dusk [B Y ] component), it is perhaps unsurprising that these conditions have received the most attention. However, when the IMF is more strongly northward (B Z \textgreater 0 and B Z \textgreater \textbarB Y \textbar), magnetospheric dynamics (e.g. magnetic reconnection and auroral activity) move to higher latitudes; certain aspects of this activity are much more poorly understood than their southward IMF counterparts. In this chapter, we provide a review of the historical context and current understanding of the behavior of the Earth s magnetosphere during periods of northward IMF, and outline some current controversies and future directions of research. Published by: Published on: YEAR: 2021 DOI: 10.1002/9781119815624.ch19 auroral response; Earth s magnetosphere; geomagnetic activity; interplanetary magnetic field; magnetospheric dynamics; solar wind-magnetosphere coupling |
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In near-Earth space, variations in thermospheric composition have important implications for thermosphere-ionosphere coupling. The ratio of O to N2 is often measured using far-UV airglow observations. Taking such airglow observations from space, looking below the Earth s limb allows for the total column of O and N2 in the ionosphere to be determined. While these observations have enabled many previous studies, determining the impact of nonmigrating tides on thermospheric composition has proved difficult, owing to a small contamination of the signal by recombination of ionospheric O+. New ICON observations of far-UV are presented here, and their general characteristics are shown. Using these, along with other observations and a global circulation model, we show that during the morning hours and at latitudes away from the peak of the equatorial ionospheric anomaly, the impact of nonmigrating tides on thermospheric composition can be observed. During March–April 2020, the column O/N2 ratio was seen to vary by 3–4\% of the zonal mean. By comparing the amplitude of the variation observed with that in the model, both the utility of these observations and a pathway to enable future studies is shown. England, Scott; Meier, R.; Frey, Harald; Mende, Stephen; Stephan, Andrew; Krier, Christopher; Cullens, Chihoko; Wu, Yen-Jung; Triplett, Colin; Sirk, Martin; Korpela, Eric; Harding, Brian; Englert, Christoph; Immel, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029575 airglow; atmospheric composition; Atmospheric tides; thermosphere |
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Santa Maria Digisonde data are used for the first time to investigate the F region behavior during a geomagnetic storm. The August 25, 2018 storm is considered complex due to the incidence of two Interplanetary Coronal Mass Ejections and a High-Speed Solar Wind Stream (HSS). The F 2 layer critical frequency (f o F 2) and its peak height (h m F 2) collected over Santa Maria, near the center of the South American Magnetic Anomaly (SAMA), are compared with data collected from Digisondes installed in the Northern (NH) and Southern (SH) Hemispheres in the American sector. The deviation of f o F 2 (Df o F 2) and h m F 2 (Dh m F 2) are used to quantify the ionospheric storm effects. Different F region responses were observed during the main phase (August 25–26), which is attributed to the traveling ionospheric disturbances and disturbed eastward electric field during nighttime. The F region responses became highly asymmetric between the NH and SH at the early recovery phase (RP, August 26) due to a combination of physical mechanisms. The observed asymmetries are interpreted as caused by modifications in the thermospheric composition and a rapid electrodynamic mechanism. The persistent enhanced thermospheric [O]/[N2] ratio observed from August 27 to 29 combined with the increased solar wind speed induced by the HSS and IMF B z fluctuations seem to be effective in causing the positive ionospheric storm effects and the shift of the Equatorial Ionization Anomaly crest to higher than typical latitudes. Consequently, the most dramatic positive ionospheric storm during the RP occurred over Santa Maria (∼120\%). Moro, J.; Xu, J.; Denardini, C.; Resende, L.; Neto, P.; Da Silva, L.; Silva, R.; Chen, S.; Picanço, G.; Carmo, C.; Liu, Z.; Yan, C.; Wang, C.; Schuch, N.; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028663 Digisonde; Equatorial ionization anomaly; F-region; Ionospheric storm; SAMA; space weather |
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This study examines an unexpected and extreme positive ionospheric response to a minor magnetic storm on August 5, 2019 by using global ionosphere specification (GIS) 3D electron density profiles obtained by assimilating radio occultation total electron content (TEC) measurements of the recently launched FORMOSAT-7/COSMIC-2 satellites, and ground-based global navigation satellite system (GNSS) TEC. The results reveal ∼300\% enhancement of equatorial ionization anomaly (EIA) crests, appearing over 200–300 km altitudes, and a much intense localized density enhancement over the European sector. These are the most intense ionospheric response that has ever been detected for a small magnetic storm with Dst ∼ −53 nT (SYM-H ∼ −64 nT). The enhancements are validated by using global ionosphere map (GIM) TEC and ground-based GNSS TEC. The GIS vertical electron density structures during the storm are examined to understand the physical processes giving rise to such an intense ionosphere response during deep solar minimum conditions when the background electron density is very low. Altitude variations and poleward shifts of the locations of the EIA crests indicate that prompt penetration electric fields (PPEF) play an important role in producing the observed positive storm responses, with the storm-induced equatorward circulation supporting the plasma accumulation against recombination losses. Additional physical mechanisms are required to fully explain the unexpected electron density enhancements for this minor storm event. Rajesh, P.; Lin, C.; . Y. Lin, C; Chen, C.; . Y. Liu, J; Matsuo, T.; Chen, S.; Yeh, W.; . Y. Huang, C; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028261 FORMOSAT-7/COSMIC-2; Global Ionospheric Specification; ionospheric data assimilation; ionospheric response to magnetic storm; magnetosphere-ionosphere coupling; minor magnetic storm |
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Subauroral Flow Channel Structures and Auroral Undulations Triggered by Kelvin-Helmholtz Waves We investigate Kelvin-Helmholtz (K-H) waves on/near the magnetopause and surface waves near the plasmapause—in the outer region of the plasmasphere: in the hot zone—by utilizing multi-instrument/satellite observations. Our main aim is to study how the K-H waves and the K-H instability mechanisms impacted the subauroral and auroral regions during the geomagnetic storms of May 27–29 and July 16, 2017. For the subauroral region, we specify the structured flows as Sub-Auroral Polarization Streams Wave Structures (SAPS-WS) and the combined flows—created by Abnormal Sub-Auroral Ion Drifts (ASAID) and SAID or SAPS—as a complex equatorward-poleward ASAID-SAID or SAPS-ASAID. For the auroral zone, we identify the large auroral undulations appearing inside the auroral zone. The correlated observations of the K-H waves, the structured or complex subauroral flows and large auroral undulations, and the local geomagnetic field oscillations confirm the connections of both the subauroral flows and the auroral undulations with the K-H waves via the eigenfrequency of the Near-Earth Plasma Sheet (NEPS) resonator activated by the K-H waves. For the first time, we demonstrate the simultaneous detections of K-H waves near the magnetopause and surface waves near the plasmapause in the hot zone on July 16, 2017, and conclude their coupling via the NEPS resonator s eigenfrequency. Thus, the surface waves near the plasmapause were the manifestation of the undulating (or rippled) earthward inner boundary of the NEPS that led to the development of ASAID-SAID/SAPS-ASAID or SAPS-WS in the subauroral region and to the large auroral undulation inside the auroral zone. Horvath, Ildiko; Lovell, Brian; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029144 ASAID/SAPS/SAPS-WS; auroral undulations; hot zone; K-H instability |
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This study investigates the solar origins of August 26, 2018 geomagnetic storm and the responses of the interplanetary medium and equatorial/low-latitude ionosphere to it. We used a multiinstrument approach, with observations right from the solar surface to the Earth. Our results showed that the G3 geomagnetic storm of August 26, 2018 was initiated by a solar filament eruption of August 20, 2018. The storm was driven by an aggregation of weak Coronal Mass Ejection (CME) transients and Corotating Interaction Regions/High Speed Streams (CIR/HSSs). The solar wind energy which got transferred into the magnetosphere drove electrical currents, that penetrated down into the ionosphere to produce weak Prompt Penetration Electric Field (PPEF) (0.3 mV/m). For this reason, during the storm, at daytime, plasma densities of the Equatorial Ionization Anomaly (EIA) crests were localized within the inner flank of ±15° magnetic latitude strip. We attributed this to the extreme quietness of year 2018. There was a clear hemispherical asymmetry, with higher Total Electron Content (TEC) in the northern hemisphere. The major determining factors of the ionospheric responses during the various phases of this storm were the local time of the storm s onset, local time of storm s minimum SYM-H, and changes in thermospheric O/N2. Akala, A.; Oyedokun, O.; Amaechi, P.; Simi, K.; Ogwala, A.; Arowolo, O.; Published by: Space Weather Published on: YEAR: 2021 DOI: 10.1029/2021SW002734 |
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Conjugate Photoelectron Energy Spectra Derived From Coincident FUV and Radio Measurements We present a method for estimating incident photoelectrons energy spectra as a function of altitude by combining global scale far-ultraviolet (FUV) and radio-occultation (RO) measurements. This characterization provides timely insights important for accurate interpretation of ionospheric parameters inferred from the recently launched Ionospheric Connection Explorer (ICON) observations. Quantification of photoelectron impact is enabled by the fact that conjugate photoelectrons (CPEs) directly affect FUV airglow emissions but not RO measurements. We demonstrate a technique for estimation of photoelectron fluxes and their spectra by combining coincident ICON and COSMIC2 measurements and show that a significant fraction of ICON-FUV measurements is affected by CPEs during the winter solstice. A comparison of estimated photoelectron fluxes with measured photoelectron spectra is used to gain further insights into the estimation method and reveals consistent values within 10–60 eV. Urco, J.; Kamalabadi, F.; Kamaci, U.; Harding, B.; Frey, H.; Mende, S.; Huba, J.; England, S.; Immel, T.; Published by: Geophysical Research Letters Published on: YEAR: 2021 DOI: 10.1029/2021GL095839 airglow; conjugate photolectrons; COSMIC2; energy spectra; ICON |
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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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FTA: A Feature Tracking Empirical Model of Auroral Precipitation The Feature Tracking of Aurora (FTA) model was constructed using 1.5 years of Polar Ultraviolet Imager data and is based on tracking a cumulative energy grid in 96 magnetic local time (MLT) sectors. The equatorward boundary, poleward boundary, and 19 cumulative energy bins are tracked with the energy flux and the latitudinal position. With AE increasing, the equatorward boundary moves to lower latitudes everywhere, while the poleward boundary moves poleward in the 2300–0300 MLT region and equatorward in other MLT sectors. This results in the aurora getting wider on the nightside and becoming narrower on the dayside. The peak intensity of the aurora in each MLT sector is almost linearly related to AE, with the global peak moving from pre-midnight to post-midnight as geomagnetic activity increases. Ratios between the Lyman-Birge-Hopfield-long and -short models allow the average energy to be calculated. Predictions from the FTA and two other auroral models were compared to the measurements by the Defense Meteorological Satellite Program Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) on March 17, 2013. Among the three models, the FTA model specified the most confined patterns with the highest energy flux, agreeing with the spatial and temporal evolution of SSUSI measurements better and predicted auroral power (AP) better during higher activity levels (SSUSI AP \textgreater 20 GW). The Fuller-Rowell and Evans (1987) and FTA models specified very similar average energy compared with SSUSI measurements, doing slightly better by ∼1 keV than the OVATION Prime model. Wu, Chen; Ridley, Aaron; DeJong, Anna; Paxton, Larry; Published by: Space Weather Published on: YEAR: 2021 DOI: 10.1029/2020SW002629 Auroral Precipitation Model; cumulative energy bins; data-model comparisons; M-I coupling; statistical analyses |
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Exploring the Upper Atmosphere In this chapter, we describe how we can understand the state of the upper atmosphere (the ionosphere, thermosphere, and aurora) using optical observations and how one produces a global view of the Earth s upper atmosphere from optical remote sensing, especially using far ultraviolet (FUV) wavelengths, to advance our understanding of the near Earth space environment. We examine the choice of optical signatures, the basic science behind the signatures, and the techniques for observations. Examples of the technique as applied to key geophysical processes are described and discussed for tracing the physical processes that alter the state variables (in particular, density, composition, and temperature) in the upper atmosphere. Applications of optical remote sensing will be discussed in terms of the challenges inherent in establishing a predictive capability of the global upper atmosphere system, including the high-latitude regions (such as the Arctic) where the structures of the thermosphere and ionosphere are complicated by strong coupling among the polar ionosphere, magnetosphere, and solar wind. Paxton, Larry; Zhang, Yongliang; Kil, Hyosub; Schaefer, Robert; Published by: Published on: YEAR: 2021 DOI: 10.1002/9781119815631.ch23 Earth space environment; far ultraviolet wavelengths; high-latitude regions; optical remote sensing; solar wind; upper atmosphere |
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The global-scale observations of the limb and disk (GOLD) Mission images middle thermosphere temperature and the vertical column density ratio of oxygen to molecular nitrogen (O/N2) using its far ultraviolet imaging spectrographs in geostationary orbit. Since GOLD only measures these quantities during daylight, and only over the ∼140° of longitude visible from geostationary orbit, previously developed tidal analysis techniques cannot be applied to the GOLD data set. This paper presents a novel approach that deduces two specified non-migrating diurnal tides using simultaneous measurements of temperature and O/N2. DE3 (diurnal eastward propagating wave 3) and DE2 (diurnal eastward propagating wave 2) during October 2018 and January 2020 are the focus of this paper. Sensitivity analyses using TIE-GCM simulations reveal that our approach reliably retrieves the true phases, whereas a combination of residual contributions from secondary tides, the restriction in longitude, and random uncertainty can lead to ∼50\% error in the retrieved amplitudes. Application of our approach to GOLD data during these time periods provides the first observations of non-migrating diurnal tides in measurements taken from geostationary orbit. We identify discrepancies between GOLD observations and TIE-GCM modeling. Retrieved tidal amplitudes from GOLD observations exceed their respective TIE-GCM amplitudes by a factor of two in some cases. Krier, Christopher; England, Scott; Greer, Katelynn; Evans, Scott; Burns, Alan; Eastes, Richard; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029563 |
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The local, regional, and global morphology of the ionospheric response of the March 2015 geomagnetic storm has been investigated by different studies. However, the spatio-temporal evolution of the drivers of the global ionospheric response to this storm has not yet been investigated, using multi-data sources, in detail. Therefore, in this study drivers of the ionospheric response to the March 17–18, 2015 storm are investigated. Spatial and temporal variations of deposition of solar wind energy are found to be the cause for hemispherical asymmetry of the response of the ionosphere; the American-Canada-Greenland sector, Northern Hemisphere high-latitude ionosphere responded about 12 h earlier than the Southern Hemisphere (SH) high-latitude ionosphere, resulted from hemispherical energy imbalance as detected from Hemispherical Power. The positive ionospheric storm observed in the high-latitude regions is found to be due to solar wind energy deposition at high latitudes. Interestingly, it is found that the Northern hemisphere ionospheric positive storm shifted to the mid-latitude and disappeared there whereas the SH ionospheric positive storm shifted to mid-latitude and then farther to the low-latitude with time; this spatio-temporal evaluation of positive ionospheric storm is found to be due to the spatio-temporal enhancement of the O/N2 ratio. Also, the mid (Europe-African)and low (Brazilian) latitudes positive ionospheric storms prevailed due to prompt penetration electric fields, disturbance dynamo electric fields, and enhancement of the O/N2 ratio. Moreover, the negative ionospheric storm, observed at the NH high and mid-latitudes in the American and Asian sectors, is linked to the reduction of the O/N2 ratio. Terefe, Dejene; Nigussie, Melessew; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029348 |
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Lee, Woo; Kil, Hyosub; Paxton, Larry; Published by: Journal of Geophysical Research: Space Physics Published on: |
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Space Physics and Aeronomy, Upper Atmosphere Dynamics and Energetics Published by: Published on: |
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The Wind Imaging Interferometer (WINDII) Empirical Model, which provides the characteristics of the O(1D) 630.0 nm atomic oxygen dayglow emission from the upper atmosphere has been reviewed and updated. It now includes the Integrated Emission Rate, the peak Volume Emission Rate, the Altitude of that peak and the Full Width at Half Maximum as functions of the F10.7 cm Solar Radio Flux and the solar zenith angle (SZA). The model employs 98,617 WINDII observations obtained between the years 1992 and 1996, and the model and observations of the Integrated Emission Rate agree well with one another within 2 standard deviations of 588.7 Rayleigh (R) (106 photons cm−2 sec−1). It is also demonstrated that the impact of latitude, longitude and day of year, independently of their contribution to the SZA, is very small. The WINDII Empirical Model is also shown to agree with results from the TRANSCAR photochemical model. The dayglow is challenging to measure with ground-based instruments, as the solar scattered light from the daytime sky must be accurately subtracted from the data. Ground-based measurements of the integrated emission rate have been made by others, with good agreement for observations from Hyderabad during the 2015 summer and winter, but mixed agreement with measurements made over Boston in 2003. The latter results are reviewed and assessed. Shepherd, Gordon; Cho, Young-Min; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA028715 dayglow; empirical model; O(1D) Emission; solar radio flux; solar zenith angle; upper atmosphere |
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Mlynczak, Martin; Yee, Jeng-Hwa; Paxton, Larry; Ridley, Aaron; Published by: Published on: |
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Carter, Jennifer; Samsonov, AA; Milan, Stephen; Branduardi-Raymont, Graziella; Ridley, Aaron; Paxton, Larry; Anderson, Brian; Waters, Colin; Edwards, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: |
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The spatial distribution of aurora intensity is an important manifestation of solar wind-magnetosphere-ionosphere energy coupling process, and it oscillates with the change of space environment parameters and geomagnetic index. It is of great significance to establish an appropriate aurora intensity model for the prediction of space weather and the study of magnetosphere dynamics. Based on Ultraviolet Imager (UVI) data of Polar satellite, we constructed two auroral models by using two different neural networks, that is, the generalized regression neural network (GRNN), and the conditional generation adversarial network (CGAN). Input parameters of the models include interplanetary magnetic field, solar wind velocity and density, and the geomagnetic AE index. Output result is the spatial distribution of auroral intensity in altitude adjusted corrected geomagnetic (AACGM) coordinates. The structural similarity index (SSIM) of image quality is used as an evaluation standard of detail similarity between the prediction results of auroral intensity model and corresponding UVI images (complete similarity is 1, dissimilarity is 0, SSIM is generally considered to have good similarity if it is greater than 0.5). Based on the respective training datasets of GRNN and CGAN models, the evaluating results showed that the mean values (standard deviation) of SSIM were 0.5409 (0.0912) and 0.5876 (0.0712), respectively, so the prediction results from both models can restore the auroral intensity distribution of the original images of UVI. In addition, the value of SSIM can increase with the increase of the number of training data. Therefore, more training data will help improve the effectiveness of these models. Hu, Ze-Jun; Han, Bing; Zhang, Yisheng; Lian, Huifang; Wang, Ping; Li, Guojun; Li, Bin; Chen, Xiang-Cai; Liu, Jian-Jun; Published by: Space Weather Published on: YEAR: 2021 DOI: 10.1029/2021SW002751 conditional generation adversarial network; generalized regression neural network; interplanetary and geomagnetic parameters; neural networks; ultraviolet auroral intensity model |
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Inhibition of F3 Layer at Low Latitude Station Sanya During Recovery Phase of Geomagnetic Storms A special F2 layer stratification structure named F3 layer occurs frequently in equatorial and low latitude ionosphere during summer daytime. In this study, a new phenomenon of decreasing occurrence of the F3 layer, and narrowing differences of virtual heights between the F3 and F2 layers in the recovery phase of geomagnetic storms is reported. We named this phenomenon as the inhibition of F3 layer event (IFLE). Using the ionosonde observations during summer of 2012–2015 at Sanya (18.3°N, 109.6°E, dip latitude 12.6°N), we found that IFLE occurred during 14 geomagnetic storms (−127 nT ≤ Dstmin ≤ −22 nT), which was accompanied by the thinning and lowering bottom ionosphere, and decreasing the crest-to-trough ratio of total electron content (TEC). Together with the ion drift data measured by Defense Meteorological Satellite Program F18, we suggest that the IFLE is mainly caused by the westward disturbance dynamo electric field (DDEF; downward drift velocity), taking disadvantage of the formation of the F3 layer. The observed decrease in the crest-to-trough ratio of TEC also indicates that the westward DDEF should prompt IFLE by providing less plasma from the equatorial region to the low latitude. Hence, IFLE then can be a good indicator to show how the magnetosphere-ionospheric coupling process affects the low and equatorial ionosphere. Notably, the results also indicate that even a very weak geomagnetic storm can generate significant changes in ionospheric state at low latitude. Jin, Yuyan; Zhao, Biqiang; Li, Guozhu; Li, Zishen; Zhou, Xu; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029850 F3 layer; Geomagnetic storms; westward disturbance dynamo electric field |
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Yu, Tingting; Wang, Wenbin; Ren, Zhipeng; Cai, Xuguang; Yue, Xinan; He, Maosheng; Published by: Journal of Geophysical Research: Space Physics Published on: |
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Far Ultraviolet Hyperspectral Imager: NASA's TIMED/GUVI and DMSP SSUSI Paxton, Larry; Zhang, Yongliang; Schaefer, Robert; Kil, Hyosub; Wolven, Brian; Romeo, Giuseppe; Yonker, Justin; Published by: Published on: |