Bibliography
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Found 2276 entries in the Bibliography.
Showing entries from 401 through 450
| 2020 |
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Investigating Ionospheric Heat Sources and Resultant Thermospheric Responses During this project, the team conducted detailed investigations on various complex geophysical processes occurring in the coupled system of solar wind, magnetosphere, ionosphere Published by: Published on: |
| 2019 |
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Dayside aurora is related to processes in the dayside magnetosphere and especially at the dayside magnetopause. A number of dayside aurora phenomena are driven by reconnection between the solar wind interplanetary magnetic field and the Earth\textquoterights internal magnetic field at the magnetopause. We summarize the properties and origin of aurora at the cusp foot point, High Latitude Dayside Aurora (HiLDA), Poleward Moving Auroral Forms (PMAFs), aurora related to traveling convection vortices (TCV), and throat aurora. Furthermore we discuss dayside diffuse aurora, morning side diffuse aurora spots, and shock aurora. Frey, Harald; Han, Desheng; Kataoka, Ryuho; Lessard, Marc; Milan, Stephen; Nishimura, Yukitoshi; Strangeway, Robert; Zou, Ying; Published by: Space Science Reviews Published on: 11/2019 YEAR: 2019 DOI: 10.1007/s11214-019-0617-7 |
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Klimenko, V.V.; Klimenko, M.V.; Bessarab, F.S.; Sukhodolov, T.V.; Rozanov, E.V.; Published by: Advances in Space Research Published on: 11/2019 YEAR: 2019 DOI: 10.1016/j.asr.2019.06.029 |
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Effects of the interplanetary magnetic field y component on the dayside aurora A dawn\textendashdusk asymmetry in many high-latitude ionospheric and magnetospheric phenomena, including the aurora, can be linked to the east\textendashwest (y) component of the interplanetary magnetic field (IMF). Owing to the scarcity of observations in the Southern Hemisphere, most of the previous findings are associated with the Northern Hemisphere. It has long been suspected that if the IMF By component also produces a dawn\textendashdusk asymmetry and/or a mirror image in the Southern Hemisphere as predicted by some theories. The present study explores the effect of the IMF By component on the dayside aurora from both hemispheres by analyzing the auroral emission data from the Global UltraViolet scanning spectrograph Imager on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission spacecraft from 2002 to 2007. The data set comprises 28,774 partial images of the northern hemispheric oval and 29,742 partial images of the southern hemispheric oval, allowing for a statistical analysis. It is found that even though auroras in different regions of the dayside oval respond differently to the orientation of the IMF By component, their responses are opposite between the two hemispheres. For example, at ~ 1400\textendash1600\ MLT in the Northern Hemisphere, where the so-called 1500\ MLT auroral hot spots occur, peak auroral energy flux is larger for negative IMF By comparing to positive IMF By. The response is reversed in the Southern Hemisphere. The present study also suggests that the total energy flux does not change with the IMF By orientation change. This result is consistent with a larger (smaller) convection vortex in the postnoon sector for IMF By \< 0 (By \> 0) resulting from anti-parallel merging. Published by: Geoscience Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1186/s40562-019-0141-3 |
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Radiative cooling due to NO at 5.3 The effect of geomagnetic storms on the peak emission of NO Volume Emission Rate (NO VER) at 5.3 m, in mesosphere and lower thermosphere (MLT) region, is studied over the Asian sector during 26\textendash29 September 2011 (storm 1) and 18\textendash21 February 2014 (storm 2). The data for peak emission of NO VER is obtained from SABER instrument onboard the NASA\textquoterights TIMED satellite. The SABER retrieved data along with the neutral densities obtained from NRLMSISE-00 model have been used to study the latitudinal and longitudinal variation of peak NO VER during the storm period. The variations induced in the peak emission of NO VER is understood with the help of fluctuations in neutral species and the resulting changes in chemistry. It has been found that the peak emission of NO VER is strongly influenced by the storm conditions. The peak emission of NO VER at 5.3 m is found to be maximum at higher latitudes during the storms. However, the magnitude of peak NO VER gradually decreases towards the equator during the storms. The modeled atomic oxygen number density shows depletion at the higher latitudes corresponding to peak altitude of NO VER. There is a negative correlation between the peak emission of NO VER and Dst index during the main phase of the storm. The peak emission of NO VER and modeled atomic oxygen number density shows the positive correlation at the equator region, while negative correlation at the higher latitudes. At higher latitudes modeled atomic oxygen number density shows positive correlation with Dst index, while negative correlation at the equator. The correlation factors obtained between various parameters related to the storm time radiative cooling strongly support the existing understanding of the variation of NO VER during extreme space weather events. Bharti, Gaurav; Krishna, M.V.; Singh, Vir; Published by: Advances in Space Research Published on: 11/2019 YEAR: 2019 DOI: 10.1016/j.asr.2019.07.016 |
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The characteristics of global electron density variations in the ionosphere during a geomagnetic storm on November 7 and 8, 2004, were investigated using total electron content (TEC) obtained from the global navigation satellite system (GNSS). The regions of enhanced TEC over North America, Europe, and Japan first appeared in the mid-latitude regions. The TEC enhancements over North America showed a rapid longitudinal expansion and reached a wide longitudinal extent during the initial and main phases of the geomagnetic storm. TEC enhancements were simultaneously observed in both North America and Japan at 05:00 UT on November 8. Observation data from the Defense Meteorological Satellite Program showed a slight enhancement of electron density at 850 km below the equatorward boundary of the mid-latitude trough (45\textendash48\textdegreeN in geomagnetic latitude) over the Pacific Ocean. This electron density variation may correspond to the TEC enhancements observed in both Japan and North America. These results imply that an enhanced TEC region existed between North America and Japan. The TEC enhancement in Japan appeared with a magnetic conjugacy in the Southern hemisphere, indicating one of the characteristics of storm-enhanced density (SED). Moreover, TEC enhancements simultaneously appeared from Japan to Central Asia at 11:00 UT on November 8, corresponding to the early recovery phase of the geomagnetic storm. From the above results, it is suggested that SED phenomena can be simultaneously generated over a wide longitudinal width (~100\textdegree). The longitudinal extent of this SED event is 2.5\textendash5.0 times longer than those reported by previous studies. Sori, T.; Shinbori, A.; Otsuka, Y.; Tsugawa, T.; Nishioka, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026713 |
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The ionospheric response of two geomagnetic storms of 2016 occurred during spring equinox (5-8 March, 2016) and autumn equinox (12-15 October, 2016) is investigated using the total electron content (TEC) data derived from Global Positioning System (GPS) receivers located in the equatorial ionization anomaly (EIA) crest regions at northern hemisphere (Tripura University, Agartala, India) and southern hemisphere (Karratha, Australia). While in southern EIA station ionospheric responses for the two storms are found to be symmetric but in northern EIA station the responses are completely asymmetric. The observations are explained by the contribution of storm-time prompt penetration electric fields (PPEFs), disturb dynamo electric fields (DDEFs), disturbed meridional (equatorward) winds as well as the neutral compositional changes over low latitudes. Patari, Arup; De, Barin; Guha, Anirban; Paul, Bapan; Published by: Journal of Physics: Conference Series Published on: 10/2019 YEAR: 2019 DOI: 10.1088/1742-6596/1330/1/012004 |
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This paper presents the response of the ionosphere during the intense geomagnetic storms of October 12\textendash20, 2016 and May 26\textendash31, 2017 which occurred during the declining phase of the solar cycle 24. Total Electron Content (TEC) from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dips varying from 32.23\textdegreeN, 32\textdegreeN and 39.49\textdegreeN respectively and at the International GNSS Service (IGS) stations at Lucknow (beyond anomaly crest), Hyderabad (between geomagnetic equator and northern crest of EIA) and Bangalore (near magnetic equator) in the Indian longitude zone have been used for the storms. Prominent peaks in diurnal maximum in excess of 20\textendash45 TECU over the quiet time values were observed during the October 2016 storm at Lucknow, Indore, Hyderabad, Bangalore and 10\textendash20 TECU for the May 2017 storm at Siliguri, Indore, Calcutta and Hyderabad. The GUVI images onboard TIMED spacecraft that measures the thermospheric O/N2 ratio, showed high values (O/N2 ratio of about 0.7) on October 16 when positive storm effects were observed compared to the other days during the storm period. The observed features have been explained in terms of the O/N2 ratio increase in the equatorial thermosphere, CIR-induced High Speed Solar Wind (HSSW) event for the October 2016 storm. The TEC enhancement has also been explained in terms of the Auroral Electrojet (AE), neutral wind values obtained from the Horizontal Wind Model (HWM14) and equatorial electrojet strength from magnetometer data for both October 2016 and May 2017 storms. These results are one of the first to be reported from the Indian longitude sector on influence of CME- and CIR-driven geomagnetic storms on TEC during the declining phase of solar cycle 24. Chakraborty, S.; Ray, S.; Sur, D.; Datta, A.; Paul, A.; Published by: Advances in Space Research Published on: 10/2019 YEAR: 2019 DOI: 10.1016/j.asr.2019.09.047 |
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Isolated Auroral Spots Observed by DMSP/SSUSI This work reports auroral spots event observed by the SSUSI instruments on board the DMSP spacecraft between 22 and 23 July 2009 during the recovery phase of a moderate magnetic storm. The spots were observed between 18:00 and 02:00 magnetic local time and stayed at ~60\textdegree magnetic latitude. They lasted for ~10 hr and corotated with ~64\% of the Earth\textquoterights rotational speed. In situ observations indicate that the isolated auroral spots were produced by energetic ions at energies between 10 and 240 keV, with significantly anisotropic electron (30\textendash300 keV) precipitations. It is expected that the energetic ions originate from the ring current and can be scattered by the EMIC waves through cyclotron resonance. The energetic electrons can be precipitated by the nonresonant interaction between the electrons and EMIC waves, which is suggested by previous works. Zhou, Su; Luan, Xiaoli; Pierrard, Viviane; Han, Desheng; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026853 |
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Morphological features of the quiet/disturbed time variations in the Total Electron Content (TEC) at the polar cusp station Bharati (76.69\textdegreeS MLAT) during a period of 5 years starting from February 2013 to December 2017 has been studied using GPS TEC measurements. The TEC at Bharati follows a diurnal pattern with its peak appearing close to local noon/magnetic noon during the summer/winter months. A nighttime enhancement in the TEC is seen around the magnetic midnight during winter. The plasma density at Bharati also exhibits semi-annual variation and a strong dependence on solar activity. A comparison of the IRI 2016 model derived TEC and the GPS TEC at Bharati shows significant differences with large underestimation of TEC especially during the nighttime period of the winter months. A two fold difference in magnitude between the GPS and modeled TEC is also observed in the summer months of the high solar activity period of 2013\textendash2015. The response of the TEC to geomagnetic storms is found to depend on the onset time of the storm. We show that the morphological features in the temporal evolution of the plasma density at Bharati vary as the location of Bharati changes from being inside the polar cap, to the auroral region, and to the polar cusp in quick succession in a day. Our results highlight the fact that the dynamic nature of the location of Bharati with respect to the position of the polar cap plays an important role in deciding the plasma distribution at the polar cusp station. Shreedevi, P.R.; Choudhary, R.K.; Yu, Yiqun; Thomas, Evan; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1016/j.jastp.2019.105058 |
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We propose a new method to derive the nightside thermsopheric density by extending GUVI dayside limb observations using empirical orthogonal function (EOF) analysis. First, we acquire the GUVI dayside total mass density during 2002-2005 to construct a preliminary empirical model (EM). Simultaneously, we decompose the background thermospheric density from US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended (NRLMSISE-00) model into different empirical orthogonal functions (EOFs). The decomposed EOFs are then used to fit the continuous density from EM, to develop a new nightside extended model (NEM). The preliminary EM and developed NEM are further evaluated with CHAMP satellite observations. Higher correlation coefficients and smaller relative standard errors (RSE) between CHAMP observations and the NEM results are obtained than those between CHAMP observations and the EM results, and the NEM results are in good agreement with the CHAMP observations in time series during both daytime and nighttime, which all prove the NEM method is effective to the reproduction and extension of GUVI original dayside observations. Furthermore, the NEM reveals two typical seasonal variation features, the semiannual variation and equinoctial asymmetry of thermospheric density. The model provides an effective tool to derive the nightside thermospheric density and explore the thermospheric intrinsic structure, and needs the further development to achieve more widespread application of the thermosphere. Yu, Tingting; Ren, Zhipeng; Yu, You; Wan, Weixing; Published by: Space Weather Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019SW002304 |
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Measurements of the limiting escape rate of atomic hydrogen (H) atoms at Earth, and the relative significance of thermal evaporation and non-thermal escape mechanisms, such as charge exchange and polar wind, have long been lacking. Our recent development of sophisticated radiative transport analysis techniques now enables the reliable interpretation of remotely-sensed measurements of optically-thick H emission, such as those acquired along the Earth\textquoterights limb by the Global Ultraviolet Imager (GUVI) onboard the NASA TIMED spacecraft, in terms of physical parameters such as exobase density and, crucially, vertical diffusive flux. In this work, we present results from a systematic investigation of H Lyα emission measured by TIMED/GUVI along the Earth\textquoterights dayside limb from 2002-2007, which we use to derive the vertical H flux and associated density distribution from 250 km out to 1 earth radius. Our analysis reveals that the vertical flux of thermospheric H is nearly constant ver a large range of solar activity and typically exceeds the calculated thermal evaporative flux, suggesting that terrestrial H escape is indeed limited by its vertical diffusion. The excess supply of H atoms to the exobase associated with large observed vertical fluxes requires that non-thermal escape mechanisms be operative for steady-state continuity balance. We find that such non-thermal processes are a particularly significant component of total H escape during low solar activity, when thermal evaporation is weakest. Joshi, P.P.; Phal, Y.D.; Waldrop, L.S.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA027057 |
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Equatorial and low latitude ionospheric response of the 8th September 2017 severe G4-class geomagnetic storm is investigated using the total electron content (TEC) data from a longitudinal chain of global positioning system (GPS) receivers over Asian, African and American sectors. During the main phase, a positive storm effect is observed over Asian sector, a complete negative storm effect over African sector and both are observed over American sector. A sharp increase in peak TEC is observed over the complete longitudinal chain during the recovery phase. The results show the decisive contribution of prompt penetration electric fields (PPEFs) and disturbance dynamo electric fields (DDEFs), storm time disturbed meridional (equatorward) wind as well as the neutral compositional changes over equatorial and low latitudes in the observed ionospheric storm effects. Paul, Bapan; Patari, Arup; De, Barin; Guha, Anirban; Published by: Journal of Physics: Conference Series Published on: 10/2019 YEAR: 2019 DOI: 10.1088/1742-6596/1330/1/012005 |
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Lawal, Hammed; Lester, Mark; Cowley, Stanley; Milan, S.E.; Yeoman, T.K.; Provan, Gabby; Imber, Suzie; Rabiu, A.Babatunde; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1016/j.jastp.2018.01.008 |
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Far ultraviolet observations of Earth\textquoterights dayglow from the National Aeronautics and Space Administration (NASA) Global-scale Observations of the Limb and Disk (GOLD) mission presents an unparalleled opportunity for upper atmosphere radiance data assimilation. Assimilation of the Lyman-Birge-Hopfield (LBH) band emissions can be formulated in a similar fashion to lower atmosphere radiance data assimilation approaches. To provide a proof-of-concept for such an approach, this paper presents assimilation experiments of simulated LBH emission data using an ensemble filter measurement update step implemented with National Oceanic and Atmospheric Administration (NOAA)\textquoterights Whole Atmosphere Model (WAM) and National Center for Atmospheric Research (NCAR)\textquoterights Global Airglow (GLOW) model. Primary findings from observing system simulation experiments (OSSEs), wherein \textquotedbllefttruth\textquotedblright atmospheric conditions simulated by NCAR\textquoterights Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) are used to generate synthetic GOLD data, are as follows: (1) Assimilation of GOLD LBH disk emission data can reduce the bias in model temperature specification (ensemble mean) by 60\% under both geomagnetically quiet conditions and disturbed conditions. (2) The reduction in model uncertainty (ensemble spread) as a result of assimilation is about 20\% in the lower thermosphere and 30\% in the upper thermosphere for both conditions. These OSSEs demonstrate the potential for far ultraviolet radiance data assimilation to dramatically reduce the model biases in thermospheric temperature specification and to extend the utility of GOLD observations by helping to resolve the altitude-dependent global-scale response of the thermosphere to geomagnetic storms. Cantrall, Clayton; Matsuo, Tomoko; Solomon, Stanley; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026910 |
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Time-Dependent Response of the Terrestrial Exosphere to a Geomagnetic Storm Recent observations of significant enhancements in exospheric hydrogen (H) emission in response to geomagnetic storms have been difficult to interpret in terms of the evolution of the underlying global, 3-D exospheric structure. In this letter, we report the first measurement of the timescales and spatial gradients associated with the exospheric response to a geomagnetic storm, which we derive from a novel, time-dependent tomographic analysis of H emission data. We find that global H density at 3 RE begins to rise promptly, by \~15\%, after storm onset and that this perturbation appears to propagate outward with an effective speed of \~60\ m/s, a response that may be associated with enhanced thermospheric temperature and vertical neutral wind. This effective upwelling has significant implications for atmospheric escape as well as for charge exchange reaction rates, which drive important space weather effects such as plasmaspheric refilling and ring current decay. Cucho-Padin, Gonzalo; Waldrop, Lara; Published by: Geophysical Research Letters Published on: 09/2019 YEAR: 2019 DOI: 10.1029/2019GL084327 |
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Variations of ionospheric parameters Total Electron Content (TEC) by GNSS, critical frequency (foF2) by vertical sounding and electron density (Ne) by low-altitude satellite were studied at high, mid and low latitudes of the European sector during the magnetic storm of August 25\textendash26, 2018. During the main phase of the storm the ionospheric F2-layer was under the positive disturbance at mid and low latitudes. Then the transition from the positive to negative ΔfoF2 values occurred at all latitudes. The recovery phase was characterized by negative ionospheric disturbance at all latitudes. This is due to the decrease of thermospheric O/N2 ratio during the recovery phase of the storm. The intense Es layers screened the reflections from the F2-layer on August 26th at high and at low latitudes but at different times. Some blackouts occurred due to the high absorption level at high latitudes. In general, foF2 and TEC data were highly correlated. The major Ne changes were at the low latitudes. In general, Ne data confirmed the ionospheric dynamics revealed with foF2 and TEC. Blagoveshchensky, D.V.; Sergeeva, M.A.; Published by: Advances in Space Research Published on: 08/2019 YEAR: 2019 DOI: 10.1016/j.asr.2019.07.044 |
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The National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON) mission will study the close relationship between the ionosphere, the atmospheric weather, and space weather using in situ and remote sensing instruments proving plasma density, temperature, ion drift velocity, and thermospheric wind velocity over the equatorial region. In particular, the far ultraviolet (FUV) instrument will image the terrestrial limb in two wavelength channels. During nighttime, only the channel characterizing the bright 135.6-nm emission of atomic oxygen will be used. The purpose of this study is to simulate FUV nightglow measurements under quiet as well as disturbed ionospheric conditions. Classical medium-scale traveling ionospheric disturbances (MSTIDs), which are understood as the ionospheric signature of atmospheric gravity waves, are one of the main sources of ionospheric variability. Here, we simulate their potential appearance in the FUV instrument data. The simulation model produces FUV images used as input to identify and characterize MSTIDs. MSTID propagation parameters can be retrieved under specific geometrical configurations between the FUV lines of sight and propagation direction of the MSTID, which differs depending on the limb or sublimb observing geometry. The largest MSTID signature is expected during equinoxes under solar maximum periods, for MSTID periods of less than 30\ min. The weak brightness of the 135.6-nm multiplet under solar minimum conditions is the main limitation to the MSTID detection on the nightside. Future MSTID detection algorithms would have to cope with very low signal-to-noise ratio, in particular during solstices and under solar minimum conditions. Wautelet, G.; Hubert, B.; erard, J.-C.; Immel, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2019 YEAR: 2019 DOI: 10.1029/2019JA026930 |
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The geomagnetic storm-driven ionospheric changes and the involved processes are interesting and challenging topics in understanding and predicting the ionosphere. In this study we investigate the response of the ionosphere to geomagnetic disturbances during the 30-day incoherent scatter radar measurements conducted at Millstone Hill (42.6\textdegreeN, 71.5\textdegreeW) from 4 October to 4 November 2002. During geomagnetically disturbed periods, while the peak electron density of the F2 layer (NmF2) and total electron content deviate remarkably from the quiet time ones in a similar way, the incoherent scatter radar measurements reveal that the changes in electron density are frequently different between low and high altitudes. The electron density is significantly depleted at low altitudes; however, at topside it either changes slightly or sometime is enhanced. The enhanced vertical scale height around 600 km under geomagnetically active conditions implies that the topside electron density profiles become much steeper. The increase in the peak height of F2 layer (hmF2) indicates the upward motions under the action of the storm-driven dynamic processes. Further, sometimes strong differences are shown in total electron content between Millstone Hill and longitude 100\textdegreeW. The competing contributions from dynamic processes and disturbance composition to the storm-time ionospheric changes over Millstone Hill are indicated in the different responses in electron density at the bottomside and topside of the ionosphere. Liu, Libo; Le, Huijun; Chen, Yiding; Zhang, Ruilong; Wan, Weixing; Zhang, Shun-Rong; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026806 |
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n this study, we focus on the recovery phase of a geomagnetic storm that happened on 6\textendash11 September 2017. The ground-based total electron content data, as well as the F region in situ electron density, measured by the Swarm satellites show an interesting feature, revealing at low and equatorial latitudes on the dayside ionosphere prominent positive and negative responses at the Asian and American longitudinal sectors, respectively. The global distribution of thermospheric O/N2 ratio measured by global ultraviolet imager on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite cannot well explain such longitudinally opposite response of the ionosphere. Comparison between the equatorial electrojet variations from stations at Huancayo in Peru and Davao in the Philippines suggests that the longitudinally opposite ionospheric response should be closely associated with the interplay of E region electrodynamics. By further applying nonmigrating tidal analysis to the ground-based total electron content data, we find that the diurnal tidal components, D0 and DW2, as well as the semidiurnal component SW1, are clearly enhanced over prestorm days and persist into the early recovery phase, indicating the possibility of lower atmospheric forcing contributing to the longitudinally opposite response of the ionosphere on 9\textendash11 September 2017. Xiong, Chao; Lühr, Hermann; Yamazaki, Yosuke; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026917 |
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Response of ionosphere over Korea and adjacent areas to 17 March 2015 geomagnetic storm Published by: Advances in Space Research Published on: 07/2019 YEAR: 2019 DOI: 10.1016/j.asr.2019.03.038 |
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Assimilation of Multiple Data Types to a Regional Ionosphere Model With a 3D-Var Algorithm (IDA4D) For the purpose of building a regional (bound 20\textendash60\textdegreeN in latitude and 110\textendash160\textdegreeE in longitude) ionospheric nowcast model, we investigated the performance of IDA4D (Ionospheric Data Assimilation Four-Dimension) technique considering International Reference Ionosphere model as the background. The data utilized in assimilation were slant total electron content (STEC) from 27 ground GPS (Global Positioning System) receiver stations and NmF2 (ionospheric F2 peak density) from five ionosondes and COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) Data Analysis Archive Center. The period analyzed covered both geomagnetic quiet and disturbed days (15\textendash18 March 2015). Assimilations were run under the following data combinations (cases): (1) GPS-STEC\textquoterights only; (2) GPS-STEC\textquoterights and NmF2\textquoterights from five ionosondes; (3) only NmF2\textquoterights from five ionosondes; and (4) GPS-STEC\textquoterights and NmF2\textquoterights from both five ionosondes and COSMIC. Results showed that under case 1 the root-mean-square error (RMSE) in STEC reduced by 44\% over the background International Reference Ionosphere values and on averaged over all ionosonde stations in the analysis RMSE values of foF2 (F2 layer critical frequency) reduced by 21\%. Furthermore, foF2 RMSE values under Case 2 were 36\% smaller than those under Case 1. Under Case 4, IDA4D performance improved even further in areas not covered by GPS and ionosonde measurements. Therefore, IDA4D is a potential candidate for regional ionosphere modeling that exhibits improved performance with assimilation of different data types. Mengist, Chalachew; Ssessanga, Nicholas; Jeong, Se-Heon; Kim, Jeong-Heon; Kim, Yong; Kwak, Young-Sil; Published by: Space Weather Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019SW002159 |
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This paper reports a preliminary result for estimating thermospheric temperature around 155 km from the N2 Lyman-Birge-Hopfield bands observed by TIMED/Global Ultraviolet Imager (GUVI). Atmospheric Ultraviolet Radiance Integrated Code model (Strickland et al., 1999, https://doi.org/10.1016/S0022-4073(98)00098-3) calculations indicate that the intensity ratio in the N2 Lyman-Birge-Hopfield (0,0) and (1,0) bands at 144.5- to 145.5- and 141.0- to 142.0-nm quasi-linearly depend on N2 rotational temperature. The observed ratios and the Atmospheric Ultraviolet Radiance Integrated Code results are used together to specify the thermospheric temperature around 155 km under sunlit conditions. The estimated temperature agrees fairly well with the neutral temperature at 155 km from WACCM-X model. The estimated temperature is also higher over the auroral oval and O/N2 depleted regions. Furthermore, meridional wave-like structures were clearly seen in the derived temperature and were likely caused by traveling atmospheric disturbances. Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2018JA026379 |
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Imaging of the Daytime Ionospheric Equatorial Arcs With Extreme and Far Ultraviolet Airglow We present the first global images of the daytime ionosphere equatorial arcs as manifested in the 83.4-nm airglow. These images were collected by the Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph that commenced operations on the International Space Station in early 2017. We compare these to simultaneous images of the ionospheric radiative recombination airglow at 135.6 nm measured between 250- and 350-km tangent altitudes, where the emission is generated primarily by radiative recombination of ionospheric plasma. We find that these signatures of the dense crests of the Equatorial Ionization Anomaly, their symmetry, and daily variability at 1300\textendash1600 LT over 1\textendash6 April 2017 do not show any strong periodicity during this time. These results are also important to the joint interpretation of these two correlated extreme and far ultraviolet emission features measured under solar minimum conditions and the evaluation of absorption and radiative transfer effects that affect these emissions differently. Stephan, A.; Finn, S.; Cook, T.; Geddes, G.; Chakrabarti, S.; Budzien, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019JA026624 |
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Published by: Advances in Space Research Published on: 06/2019 YEAR: 2019 DOI: 10.1016/j.asr.2019.02.009 |
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Signatures of Sudden Storm Commencement on the equatorial thermospheric dayglow It has been observed that the OI 630.0\ nm dayglow emission over a dip equatorial station, Trivandrum (8.5\textdegree\ N, 77\textdegree\ E, dip 0.5\textdegree\ N), India registered an abrupt increase of\ ~\ 2000\ R during the compression phase of the magnetosphere as dictated by a sudden increase in solar wind ram pressure. Furthermore, an unusual depletion of these emissions has been observed during the eastward interplanetary electric field (IEF), concomitant with southward excursion of IMF Bz. The ionosonde and magnetometer observations confirmed the effects of prompt penetration electric field (PPEF). Associated with the eastward PPEF, formation of F3 layers were also noticed. These unique results, which emphasize the effect of Sudden Storm Commencement/IEF on these equatorial daytime airglow emissions are discussed in context of changes in the equatorial zonal electric field and F region height variations associated with polar/auroral activities due to the magnetosphere-ionosphere coupling. Sumod, Sukumarn; Pant, Tarun; Ajesh, Asokan; Published by: Journal of Space Weather and Space Climate Published on: 06/2019 YEAR: 2019 DOI: 10.1051/swsc/2019026 |
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Wide-field auroral imager onboard the Fengyun satellite The newly launched Fengyun-3D (FY-3D) satellite carried a wide-field auroral imager (WAI) that was developed by Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CIOMP), which will provide a large field of view (FOV), high spatial resolution, and broadband ultraviolet images of the aurora and the ionosphere by imaging the N2 LBH bands of emissions. The WAI consists of two identical cameras, each with an FOV of 68\textdegree in the along-track direction and 10\textdegree in the cross-track direction. The two cameras are tilted relative to each other to cover a fan-shaped field of size 130\textdegree \texttimes 10\textdegree. Each camera consists of an unobstructed four-mirror anastigmatic optical system, a BaF2 filter, and a photon-counting imaging detector. The spatial resolution of WAI is ~10 km at the nadir point at a reference height of 110 km above the Earth\textquoterights surface. The sensitivity is \>0.01 counts s-1 Rayleigh-1 pixel-1 (140\textendash180 nm) for both cameras, which is sufficient for mapping the boundaries and the fine structures of the auroral oval during storms/substorms. Based on the tests and calibrations that were conducted prior to launch, the data processing algorithm includes photon signal decoding, geometric distortion correction, photometric correction, flat-field correction, line-of-sight projection and correction, and normalization between the two cameras. Preliminarily processed images are compared with DMSP SSUSI images. The agreement between the images that were captured by two instruments demonstrates that the WAI and the data processing algorithm operate normally and can provide high-quality scientific data for future studies on auroral dynamics. Zhang, Xiao-Xin; Chen, Bo; He, Fei; Song, Ke-Fei; He, Ling-Ping; Liu, Shi-Jie; Guo, Quan-Feng; Li, Jia-Wei; Wang, Xiao-Dong; Zhang, Hong-Ji; Wang, Hai-Feng; Han, Zhen-Wei; Sun, Liang; Zhang, Pei-Jie; Dai, Shuang; Ding, Guang-Xing; Chen, Li-Heng; Wang, Zhong-Su; Shi, Guang-Wei; Zhang, Xin; Yu, Chao; Yang, Zhong-Dong; Zhang, Peng; Wang, Jin-Song; Published by: Light: Science \& Applications Published on: 05/2019 YEAR: 2019 DOI: 10.1038/s41377-019-0157-7 |
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Annual and Semiannual Oscillations of Thermospheric Composition in TIMED/GUVI Limb Measurements The Global UltraViolet Imager (GUVI) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite provides a data set of vertical thermospheric composition (O, N2, and O2 densities) and temperature profiles from 2002\textendash2007. Even though GUVI sampling is limited by orbital constraint, we demonstrated that the GUVI data set can be used to derive the altitude profiles of the amplitudes and phases of annual oscillation (AO) and semiannual oscillation (SAO), thereby providing important constraints on models seeking to explain these features. We performed a seasonal and interannual analysis of GUVI limb O, O2, and N2 densities and volume number density ratio O/N2 at constant pressure levels. These daytime observations of O and O/N2 in the lower thermosphere show a strong AO at midlatitudes and a clear SAO at lower latitudes. The global mean GUVI O/N2 number density ratio shows the AO, with slightly larger values in January than in July and a SAO with O/N2 greater during equinoxes than at the solstices. O and N2 densities on fixed pressure levels in the upper thermosphere are anticorrelated with solar extreme ultraviolet flux. On the other hand, O/N2 is smaller during solar minimum and larger during solar maximum. The thermospheric AO and SAO in composition have a constant phase with altitude throughout the thermosphere. Yue, Jia; Jian, Yongxiao; Wang, Wenbin; Meier, R.R.; Burns, Alan; Qian, Liying; Jones, M.; Wu, Dong; Mlynczak, Martin; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019JA026544 |
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Seasonal and source variations of migrating and nonmigrating tides are studied using Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics-Sounding of the Atmosphere using Broadband Emission Radiometry temperature data at 10\textdegreeN (5\textendash15\textdegreeN) for the year 2009. The migrating DW1 shows equinoctial maximum and summer minimum at low latitudes. It shows equinoctial asymmetry with larger amplitudes during spring equinox than fall equinox. The migrating semidiurnal tidal amplitude (SW2) shows larger amplitudes (~20 K) during March\textendashOctober at 30\textendash60\textdegreeS. Its seasonal variation resembles stratospheric (10\ hPa) ozone variations at southern midlatitudes. During the sudden stratospheric warming of 2009, the SW1 shows larger amplitudes over the equator and it is generated due to nonlinear interaction between SW2 and planetary wave of zonal wave number 1. The eastward nonmigrating DE4 and DE3 tides enhance in summer. The DE3 and DE4 appear to be generated due to latent heat release in the troposphere, as their amplitudes in the National Center for Environmental Prediction (NCEP)\textquoterights Precipitable water vapor (proxy for latent heat release) enhance at similar times as in mesosphere. The DW2 and DW0 tides are likely to be generated due to nonlinear interaction between DW1 and planetary wave of zonal wave number 1. The SW3 enhancement during the early winter (November-December) may be due to nonlinear interaction between DW1 and the large-amplitude DW2. The nonlinear interactions of DW1 with planetary wave and nonmigrating tides explain the summer minimum and equinoctial asymmetry of DW1. Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026190 |
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The Global Ultraviolet Imager (GUVI) aboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet airglow emissions in the thermosphere. The retrieved altitude profiles of thermospheric neutral density from GUVI daytime limb scans are significant for ionosphere-thermosphere study. Here, we use the profiles of the main neutral density to derive the total mass density during the period 2002\textendash2007 under geomagnetic quiet conditions (ap\ \<\ =12). We attempt to compare the obtained total mass density with the Challenging Minisatellite Payload (CHAMP) observations, making use of an empirical model (GUVI model hereafter). This GUVI model is aimed to solve the difficulty of the direct comparison of GUVI and CHAMP observations due to their different local times at a given location in a given day. The GUVI model is in good agreement with CHAMP observations with the small standard deviations of their ratios (less than 10\%) except at low solar flux levels. The correlation coefficients are greater than 0.9, and the relative standard errors are less than 20\%. Comparison between the GUVI model and CHAMP observations during solar minimum shows a large bias (~30\%). The large bias at low solar flux levels might be due to the limitation of F10.7 as an extreme ultraviolet radiation flux proxy and the fitting method. Our results demonstrate the validity and accuracy of our model based on GUVI data against the density data from the CHAMP satellite. Yu, Tingting; Ren, Zhipeng; Yue, Xinan; Yu, You; Wan, Weixing; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JA026229 |
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Evaluation of Space Traffic Effects in SBUV Polar Mesospheric Cloud Data Water-rich rocket exhaust plumes, in particular those emitted by the National Aeronautics and Space Administration Space Shuttle, have been suggested to make a significant contribution to long-term trends in polar mesospheric cloud (PMC) ice water content. We investigate this claim using the combined Solar Backscatter Ultraviolet (SBUV) PMC data record from eight separate instruments, which includes 60 Shuttle launches during PMC seasons between 1985 and 2011. No statistically significant postlaunch signal in PMC total ice is observed based on superposed epoch analysis of the SBUV record. Only a few launches show individual peaks in total ice anomaly above the seasonal background that exceed an empirical threshold, and the maximum cumulative signature from these infrequent cases is typically less than 5\% of the season total in ice mass. Other non-Shuttle launches show circumstantial evidence of possible PMC effects, although supporting evidence for plume transport is not available. We conclude that space traffic effects have been a negligible component of long-term PMC behavior. DeLand, Matthew; Thomas, Gary; Published by: Journal of Geophysical Research: Atmospheres Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JD029756 |
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Inferring thermospheric composition from ionogram profiles: A calibration with the TIMED spacecraft Measurements of thermospheric composition via ground-based instrumentation are challenging to make and so details about this important region of the upper atmosphere are currently sparse. We present a technique thatdeducesquantitative estimates of thermospheric composition from ionospheric data, for which there is a global network of stations. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed bythe \textquoteleftG\textquoteright factor, a function of ion production rate and loss rates via ion-atom interchange reactionsand dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimatesof the G factor obtained from ionograms recorded at Kwajalein (9oN, 167.2oE) for 25 times during which theTIMED spacecraftrecordedapproximately co-located measurements of the neutral thermosphere.We find alinear relationship between √G and the molecular: atomic composition ratio,with agradient of 2.23 \textpm0.17 and an offset of 1.66 \textpm 0.19. This relationship reveals the potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere. Such information can be used to investigate spatial and temporal variations in thermospheric compositionwhich in turn has applications such as understanding the response of thermospheric composition to climate change and the efficacy of the upper atmosphere on satellite drag. Scott, Christopher; Jones, Shannon; Barnard, Luke; Published by: Annales Geophysicae Discussions Published on: 03/2019 YEAR: 2019 DOI: 10.5194/angeo-2019-4710.5194/angeo-2019-47-RC110.5194/angeo-2019-47-RC2 |
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The aim of the present study is to investigate the response of ionospheric total electron content (TEC), Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) scintillations during 17 March 2015 St. Patrick\textquoterights Day geomagnetic storm over Visakhapatnam, which is popularly known as Waltair (WALT) in the literature. GPS TEC observations obtained from five IGS stations (SGOC, IISC, HYDE, LCK4 and LHAZ) and WALT during the storm have been compared. The TEC derived from GPS, GLONASS constellations and CODE global ionosphere TEC map (GIM) over WALT has also been compared. Positive storm effect during the main phase of the storm and negative storm effect during the recovery phase of the storm were observed over the said stations. The variation of northern equatorial ionisation anomaly TEC (CODE GIM TEC maps) in response to the St. Patrick\textquoterights Day storm over four Indian longitudes (75oE, 80oE, 85oE and 90oE) has also been presented. Strong amplitude and phase scintillations were observed in the L-band signals of GPS and GLONASS constellations over WALT. Twelve satellite (Pseudo Random Noise) PRNs of GPS L1 and nine PRNs of each GLONASS L1 and L2-band signals were affected by strong amplitude and phase scintillation. The peak amplitude scintillation index (S4) obtained from the effected PRNs of GPS L1 signal and GLONASS L1-band signals over WALT range from 0.36 to 0.74 and 0.36 to 0.76, respectively. Strong fluctuations in rate of TEC index are noted over the said stations. This enhanced scintillation activity is mainly due to the main phase of the storm falls in the evening sector over the Indian region. Srinivasu, K; Prasad, D; Niranjan, K; Seemala, Gopi; Venkatesh, K; Published by: Journal of Earth System Science Published on: 03/2019 YEAR: 2019 DOI: 10.1007/s12040-019-1097-6 |
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The positional accuracy of Navigation with the Indian Constellation (NavIC)/Indian Regional Navigation Satellite System (IRNSS) in the low latitudes of the Indian region during the intense geomagnetic storm of 8 September 2017 being reported first time. The existence of an intense geomagnetic storm is verified with several geomagnetic indices and interplanetary field parameters. The Total Electron Content (TEC) maps from the International GNSS Service (IGS) data and the thermosphere O/N2 ratio maps from the Global Ultra Violet Imager (GUVI) are also used in the study. The one week of data (3\textendash9 September 2017) are collected based on equatorial region (Trivandrum) and Equatorial Ionization Anomaly (EIA) region (e.g. Surat, Bombay, Hyderabad and Gandhinagar), from India, using the Accord NavIC/IRNSS dual-frequency (L5 and S-band) receivers. For the intense storm day, a comparative study is being carried out for TEC, ionospheric delay and positional accuracy for L5 band. The observations perceive the positive impact in the equatorial region while the negative impact for EIA region, with reference to quiet days of the observed week. The average \~70\% and further \~25\% NavIC/IRNSS system positional accuracy is improved by applying ionospheric correction and augmenting NavIC/IRNSS with GPS system respectively. This study is very much important in satellite-based navigation application for Precise Point Positioning (PPP). Published by: IETE Technical Review Published on: 03/2019 YEAR: 2019 DOI: 10.1080/02564602.2019.1599739 |
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Observations of conjugated ring current auroras at subauroral latitudes We report three ring current aurora events that are conjugated in the two hemispheres observed by satellite and ground imagers on May 16, 2005, August 26, 2018 and September 5, 2005. The ring current auroras appeared as auroral spots or arcs in the day, dusk or night side. These events confirm that the particle sources are in the equatorial ring current ions and pitch angle diffusion of the ions lead to the ion precipitation in the both hemisphere on the same field lines, thus the auroras are conjugated. Zhang, Yongliang; Paxton, Larry; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1016/j.jastp.2019.01.005 |
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Plasma Blobs Associated With Medium-Scale Traveling Ionospheric Disturbances Plasma blobs represent plasma density enhancements with respect to ambient plasma. The formation of blobs in low and middle latitudes is understood in association with either equatorial plasma bubbles or medium-scale traveling ionospheric disturbances (MSTIDs). This study reports four blob events identified from the Swarm satellite observations in 2014. Those blobs show the conjugate property and the alignment in the northwest-southeast direction in the Northern Hemisphere and southwest-northeast direction in the Southern Hemisphere. These are the typical characteristics of nighttime MSTIDs. The observation of MSTIDs in the total electron content maps and the absence of bubbles in the equatorial region at the times of the blob detection further support the association of those blobs with MSTIDs. Kil, Hyosub; Paxton, Larry; Jee, Geonhwa; Nikoukar, Romina; Published by: Geophysical Research Letters Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2019GL082026 |
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Plasma transport process in the equatorial/low-latitude ionosphere The behaviour of the equatorial/low-latitude ionosphere and the transport processes during magnetic disturbed and quiet periods of a high solar activity year, 2014, in the American sector are investigated. Parameters used include vertical drift (Vz), transport term (W), NmF2, hmF2 and scale-height (H). The F2 plasma variations followed the diurnal local solar pattern, being higher at daytime. The sunset maximum and sunrise minimum peaks of hmF2 were directly opposite to the scale height (H) pattern. The plasma distribution was basically controlled by combined actions of the electrodynamic convection/thermospheric composition, which is geomagnetic activity dependent. The annual, semi-annual and winter-anomalies of the F2 parameters were higher at the dip equator in comparison with the low-latitude. The Vz pre-reversal peak magnitude coincided with hmF2 peak and the effects are more pronounced during geomagnetic disturbed conditions. The transport term pattern was similar to that of the scale height and it is suggested as a proxy parameter for quantifying low-latitude plasma irregularities and distribution of thermospheric composition. Adebesin, Babatunde; Adekoya, Bolarinwa; David, Timothy; Published by: Advances in Space Research Published on: 03/2019 YEAR: 2019 DOI: 10.1016/j.asr.2018.11.013 |
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It has been known for decades that the nightside aurora in the Northern Hemisphere (NH) tends to be brighter when the interplanetary magnetic field (IMF) measured at Earth has a dawnward (negative y) component compared to a duskward (positive y) component. This asymmetric response to the polarity of IMF By has been explained by an interhemispheric current flowing out of the NH due to a nonuniform \textquotedblleftpenetration\textquotedblright of IMF By onto the magnetotail. If such a hypothesis is correct, it should predict a brighter aurora in the nightside Southern Hemisphere (SH) for positive IMF By than negative IMF By. Here we investigate this hypothesis using Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics/Global Ultraviolet Imager data. The present study not only reproduces the result previously found in NH but also shows an opposite change to its Northern Hemispheric counterpart in SH in response to the different IMF By polarity. When comparing north to south, for negative IMF By, the premidnight auroral energy flux is greater in NH than that in SH. The result becomes opposite for positive IMF By. This result is consistent with the hypothesis of the existence of an interhemispheric field-aligned current. Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA025953 |
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The ion density measured by the Ionospheric Plasma and Electrodynamics Instrument (IPEI) on board the ROCSAT -1 over the 75\textdegreeE and 95\textdegreeE meridian at 600km altitude has been utilized to examine the latitudinal and longitudinal distribution within the Indian sector, in particular, the north-south and east-west asymmetries of the equatorial ionization anomaly (EIA). A longitudinal gradient in ion density at 600 km higher towards 95\textdegreeE develops during the noontime and afternoon hours when the EIA is at its peak. The density gradient persists till evening hours when pre-reversal enhancements occur. The vertical E \texttimes B plasma drift velocity measured simultaneously by ROCSAT -1 for the same space-time configuration has also been studied. In addition to diurnal, seasonal and solar activity variations in E \texttimes B drift velocity, the longitudinal gradient is also observed. The EIA at the altitude of 600 km peaks at different latitudes and are mostly asymmetric about the magnetic equator. From midnight till 0800 LT, the ion density across the equator is nearly uniform in the equinoxes. But in the solstices, the density exhibits a north-south gradient. In the June solstice, density is higher in the northern hemisphere and decreases gradually towards south. The gradient in density reverses in December solstice. Normally, the EIA peaks within 1200 LT and 1600 LT while around 2000 LT, pre-reversal enhancement of ionization occurs affecting the EIA evening structure. The strength of the EIA also exhibits seasonal, year-to-year and hemispheric variations. The longitudinal asymmetry of drift velocity along 75\textdegreeE and 95\textdegreeE longitude sectors is the contributing factor behind the observed longitudinal asymmetry in ion density. Significant positive correlation between the strength of the EIA and E \texttimes B drift is observed in both longitudes. Kakoty, Rimpy; Bora, Saradi; Bhuyan, Pradip; Published by: Advances in Space Research Published on: 02/2019 YEAR: 2019 DOI: 10.1016/j.asr.2018.10.013 |
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Impact of nitric oxide, solar EUV and particle precipitation on thermospheric density decrease Zhang, Yongliang; Paxton, Larry; Lu, Gang; Yee, Sam; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1016/j.jastp.2018.11.016 |
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Longitudinal variations of the ionospheric trough position For the first time a comprehensive pattern of the longitudinal effect of the ionospheric trough position was obtained. We present new results with longitudinal variations of the winter trough position as a function of geomagnetic latitude for both hemispheres and conditions of high and low solar activity and all local time hours. We used a large observational data set obtained onboard the Kosmos-900, Interkosmos-19 and CHAMP satellites for quiet geomagnetic conditions. We found that a magnitude of the trough position longitudinal effect averaged for a fixed local time is greater in the daytime (6\textendash8\textdegree) than in the nighttime (3\textendash5\textdegree). The longitudinal effect magnitude reaches its maximum (16\textdegree) in the morning (at 08 LT) in the Southern hemisphere at high solar activity. But on certain days at any solar activity the longitudinal effect magnitude can reach 9\textendash10\textdegree even at night. The shape of the longitudinal effect was found to differ significantly in two hemispheres. In the Northern hemisphere the trough is usually closest to the pole in the eastern (American) longitudinal sector, and in the Southern hemisphere the trough is closest in the western (Eurasian) longitudinal sector. The magnitude and shape of the longitudinal effect is also different during low and high solar activity. The Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) simulations demonstrate that during low solar activity, the longitudinal variations of the daytime trough position is mainly determined by longitudinal variations of the ionization function, formed due to the longitudinal variations in the solar zenith angle and the atomic oxygen density distribution. The longitudinal variations of the nighttime trough position is formed by the longitudinal variations in ionization of precipitating auroral particles, neutral atmosphere composition, and electric field. Karpachev, A.T.; Klimenko, M.V.; Klimenko, V.V.; Published by: Advances in Space Research Published on: 01/2019 YEAR: 2019 DOI: 10.1016/j.asr.2018.09.038 |
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As part of its International Capabilities Assessment effort, the Community Coordinated Modeling Center initiated several working teams, one of which is focused on the validation of models and methods for determining auroral electrodynamic parameters, including particle precipitation, conductivities, electric fields, neutral density and winds, currents, Joule heating, auroral boundaries, and ion outflow. Auroral electrodynamic properties are needed as input to space weather models, to test and validate the accuracy of physical models, and to provide needed information for space weather customers and researchers. The working team developed a process for validating auroral electrodynamic quantities that begins with the selection of a set of events, followed by construction of ground truth databases using all available data and assimilative data analysis techniques. Using optimized, predefined metrics, the ground truth data for selected events can be used to assess model performance and improvement over time. The availability of global observations and sophisticated data assimilation techniques provides the means to create accurate ground truth databases routinely and accurately. Robinson, Robert; Zhang, Yongliang; Garcia-Sage, Katherine; Fang, Xiaohua; Verkhoglyadova, Olga; Ngwira, Chigomezyo; Bingham, Suzy; Kosar, Burcu; Zheng, Yihua; Kaeppler, Stephen; Liemohn, Michael; Weygand, James; Crowley, Geoffrey; Merkin, Viacheslav; McGranaghan, Ryan; Mannucci, Anthony; Published by: Space Weather Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018SW002127 |
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Addressing O2R with the SSUSI Operational Space Sensor: Lessons Learned Schaefer, Robert; Paxton, Larry; Romeo, Giuseppe; Kil, Hyosub; Wolven, Brian; Zhang, Yongliang; Published by: Published on: |
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Nishimura, Toshi; Paxton, Larry; Lyons, Larry; Erickson, Philip; Published by: Published on: |
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DMSP/SSUSI and TIMED/GUVI: Contributions to GOLD and ICON, Now and by Setting Context Published by: Published on: |
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Using Artificial Neural Network Training for Space Weather Products Zhang, Yongliang; Paxton, Larry; Published by: Published on: |
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Zhang, Yongguang; Joiner, Joanna; Guan, Kaiyu; Yang, Xi; Published by: Published on: |
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Bambach-Ortiz, Nicolas; Kustas, William; McElrone, Andrew; Alsina, Maria; Published by: Published on: |
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Paul, Bapan; Patari, Arup; De, Barin; Guha, Anirban; Published by: Published on: |
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Seasonal Variations of O/N 2 Volume Density Ratio Retrieved from GUVI Dayside Limb Measurement Yu, Tingting; Ren, Zhipeng; Le, Huijun; Wan, Weixing; Published by: Published on: |