Bibliography
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Found 494 entries in the Bibliography.
Showing entries from 201 through 250
| 2015 |
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The August 2011 URSI World Day campaign: Initial results During a 10-day URSI World Day observational campaign beginning on August 1, 2011, an isolated, major geomagnetic storm occurred. On August 5,\ Kp\ reached values of 8-and\ Dst\ dropped to -113\ nT. The occurrence of this isolated storm in the middle of a 10-day URSI World Day campaign provides and unprecedented opportunity to observe the coupling of solar wind energy into the magnetosphere and to evaluate the varied effects that occur in the coupled magnetosphere\textendashionosphere\textendashthermosphere system. Dramatic changes in the ionosphere are seen at every one of the active radar stations, extending from Greenland down to equatorial Peru in the American sector and at middle latitudes in Ukraine. Data from TIMED and THEMIS are shown to support initial interpretations of the observations, where we focus on processes in the middle latitude afternoon sector during main phase, and the formation of a dense equatorial ionosphere during storm recovery. The combined measurements strongly suggest that the changes in ionospheric conditions observed after the main storm phase can be attributed in large part to changes in the stormtime thermosphere. This is through the generation of disturbance dynamo winds and also global neutral composition changes that either reduce or enhance plasma densities in a manner that depends mainly upon latitude. Unlike larger storms with possibly more sustained forcing, this storm exhibits minimal effects of persistent meridional stormtime wind drag, and little penetration of solar wind electric potentials to low latitudes. It is, therefore, an outstanding example of an impulsive event that exhibits longer-term effects through modification of the background atmosphere. Immel, Thomas; Liu, Guiping; England, Scott; Goncharenko, Larisa; Erickson, Philip; Lyashenko, Mykhaylo; Milla, Marco; Chau, Jorge; Frey, Harald; Mende, Stephen; Zhou, Qihou; Stromme, Anja; Paxton, Larry; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1016/j.jastp.2015.09.005 |
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Towards estimation of atmospheric tidal effects on the ionosphere via data assimilation The impact of atmospheric tides on the night time ionosphere is now being a subject of the extensive research within the scientific community. The plausible effect has been observed using the multiple space-borne instruments (e.g. COSMIC/FORMOSAT-3 constellation, TIMED GUVI and NASA IMAGE). Along with the observations, several modelling attempts has been undertaken to prove or refute the interrelation between the atmospheric tides and the wave-four longitudinal night time ionosphere structure. The scope of the current article is to assess the data assimilation ionosphere model capabilities in representing the longitudinal effect in the night time ionosphere induced by the DE3 atmospheric tide. Along with this, the core physics-based model capabilities in estimating the same effect are presented and discussed. For the current research, two periods were taken into consideration: the autumn equinox of the years 2006 and 2012. In the current article the data assimilation and physics-based models calculation results are presented and discussed along with the models\textquoteright error estimation and analysis. Solomentsev, Dmitry; Cherniak, Yakov; Titov, Anton; Khattatov, Boris; Khattatov, Vyacheslav; Published by: Advances in Space Research Published on: 11/2015 YEAR: 2015 DOI: 10.1016/j.asr.2015.07.014 Atmosphere tides; data assimilation; Ionosphere longitudinal structure |
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We report first results on the study of the high-latitude ionospheric irregularities observed in worldwide GPS data during the St. Patrick\textquoterights Day geomagnetic storm (17 March 2015). Multisite GPS observations from more than 2500 ground-based GPS stations were used to analyze the dynamics of the ionospheric irregularities in the Northern and Southern Hemispheres. The most intense ionospheric irregularities lasted for more than 24 h starting at 07 UT of 17 March. This period correlates well with an increase of the auroral Hemispheric Power index. We find hemispheric asymmetries in the intensity and spatial structure of the ionospheric irregularities. Over North America, the ionospheric irregularities zone expanded equatorward below ~45\textdegreeN geographic latitude. Additionally, the strong midlatitude and high-latitude GPS phase irregularities in the auroral oval were found to be related to the formation of storm enhanced density and deepening of the main ionospheric trough through upper atmosphere ionization by energetic particle precipitation. Significant increases in the intensity of the irregularities within the polar cap region of both hemispheres were associated with the formation and evolution of the storm enhanced density/tongue of ionization structures and polar patches. Cherniak, Iurii; Zakharenkova, Irina; Redmon, Robert; Published by: Space Weather Published on: 09/2015 YEAR: 2015 DOI: 10.1002/swe.v13.910.1002/2015SW001237 auroral precipitation; geomagnetic storm; Ionosphere; irregularities; rate of TEC |
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In this paper, we report our findings on the correlation between the neutral temperature (around the mesopause) and thermospheric column density O/N2\ ratio, along with their response to geomagnetic storms above midlatitude of North America. A temperature/wind Doppler Na lidar, operating at Fort Collins, CO (41\textdegreeN, 105\textdegreeW), and later at Logan, UT (42\textdegreeN and 112\textdegreeW), observed significant temperature increases (temperature anomaly) above 95 km (as much as 55 K at 105 km altitude) during four coronal mass ejection-induced geomagnetic storms (April 2002, November 2004, May 2005, and October 2012). Coincident Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Spectrographic Imager observations indicate significant depletion in the thermospheric O/N2\ ratio at the lidar locations. These observations suggest that the local mesopause warming seen by the lidar is due to transport of the high-latitude joule and particle heated neutrals at the\ E\ and\ F\ layers to the midlatitude region. Yuan, T.; Zhang, Y.; Cai, X.; She, C.-Y.; Paxton, L.; Published by: Geophysical Research Letters Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015GL064860 |
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We studied the contribution of the global plasmaspheric and ionospheric electron content (PEC and IEC) into total electron content (TEC). The experimental PEC was estimated by comparison of GPS TECobservations and FORMOSAT-3/COSMIC radio occultation IEC measurements. Results are retrieved for the winter solstice (January and December 2009) conditions. Global maps of COSMIC-derived IEC, PECand GPS TEC were compared with Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) results. In addition, we used GSM TIP model results in order to estimate the contribution of plasmaspheric electron content into TEC value at the different altitudinal regions. The advantages and problems of the outer ionospheric/plasmaspheric parameters (O+/H+ transition height,TEC and electron density at height above F2 layer peak) representation by the IRI (International Reference Ionosphere) model are discussed. Klimenko, M.V.; Klimenko, V.V.; Zakharenkova, I.E.; Cherniak, Iu.V.; Published by: Advances in Space Research Published on: 06/2014 YEAR: 2015 DOI: 10.1016/j.asr.2014.06.027 FORMOSAT-3/COSMIC; GPS; Numerical modeling; Plasmasphere; total electron content |
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Characteristics and mechanisms of the annual asymmetry of thermospheric mass density In this paper, globally-averaged, thermospheric total mass density, derived from the orbits of \~5000 objects at 250, 400, and 550 km that were tracked from 1967 to 2006, has been used to quantitatively study the annual asymmetry of thermospheric mass density and its mechanism(s). The results show that thermospheric mass density had a significant annual asymmetry, which changed from year to year. The annual asymmetry at the three altitudes varied synchronously and its absolute value increased with altitudes. The results suggest that there is an annual asymmetry in solar EUV radiation that is caused by the difference in the Sun-Earth distance between the two solstices and the random variation of solar activity within a year. This change in radiation results in an annual change in the thermospheric temperature and thus the scale height of the neutral gas, and is the main cause of the annual asymmetry of thermospheric mass density. The annual asymmetry of mass density increases with altitude because of the accumulating effect of the changes in neutral temperature and scale height in the vertical direction. Ma, RuiPing; Xu, JiYao; Wang, Wenbin; Chen, GuangMing; Yuan, Wei; Lei, Jiuhou; Burns, Alan; Jiang, Guoying; Published by: Science China Earth Sciences Published on: 04/2015 YEAR: 2015 DOI: 10.1007/s11430-014-5020-3 annual asymmetry of thermospheric mass density; solar EUV radiation; Sun-Earth distance |
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This paper presents an epoch analysis of global ionosphere responses to recurrent geomagnetic activity during 79 corotating interaction region (CIR) events from 2004 to 2009. The data used were GPS total electron content (TEC) data from the Madrigal Database at the Massachusetts Institute of Technology Haystack Observatory and the electron density (Ne) data obtained from CHAllenging Minisatellite Payload (CHAMP) observations. The results show that global ionosphere responses to CIR events have some common features. In high and middle latitudes, the total electron content (TEC) showed a significant positive response (increased electron densities) in the first epoch day. A negative TEC response occurred at high latitudes of the American sector following the positive response. The CHAMP Ne showed a daytime positive response in all latitudes and a nighttime negative response in the subauroral region. These negative TEC and Ne responses were found to be related to thermospheric composition (O/N2) changes during the storms. At all latitudes, the maximum of the TEC positive effect always occurred at 2\textendash6 h after the CIR starting during local daytime and 10\textendash18 h later for the CIR onset during local nighttime. Case studies indicate that the TEC and Ne positive response had a strong dependence on the southward component (Bz) of the interplanetary magnetic field and solar wind speed. This suggests that penetration electric fields that were associated with changes in solar winds might play a significant role in the positive ionospheric response to storms. During the recovery time of the CIR-produced geomagnetic activity, the TEC positive disturbance at low latitudes sometimes could last for 2\textendash4 days, whereas at middle to high latitudes the disturbance lasted only for 1 day in most cases. A comparison of the ionospheric responses between the American, European and Asian sectors shows that the ionosphere response in the North American sector was stronger than that in the other two regions. The response of foF2 to the CIR events in middle to high latitudes showed a negative response for 2\textendash3 days after the first epoch day. This is different from the response of TEC, which was mostly positive during the same period of time. Chen, Yanhong; Wang, Wenbin; Burns, Alan; Liu, Siqing; Gong, Jiancun; Yue, Xinan; Jiang, Guoying; Coster, Anthea; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020657 CIR events; epoch study; Ionospheric response; recurrent geomagnetic activity |
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We report, for the first time, an auroral undulation event on 1 May 2013 observed by an all-sky imager (ASI) at Athabasca (L = 4.6), Canada, for which in situ field and particle measurements in the conjugate magnetosphere were available from a Van Allen Probes spacecraft. The ASI observed a train of auroral undulation structures emerging spontaneously in the pre-midnight subauroral ionosphere, during the growth phase of a substorm. The undulations had an azimuthal wavelength of ~180 km and propagated westward at a speed of 3\textendash4 km s-1. The successive passage over an observing point yielded quasi-periodic oscillations in diffuse auroral emissions with a period of ~40 s. The azimuthal wave number m of the auroral luminosity oscillations was found to be m ~ -103. During the event the spacecraft \textendash being on tailward stretched field lines ~0.5 RE outside the plasmapause that mapped into the ionosphere conjugate to the auroral undulations \textendash encountered intense poloidal ULF oscillations in the magnetic and electric fields. We identify the field oscillations to be the second harmonic mode along the magnetic field line through comparisons of the observed wave properties with theoretical predictions. The field oscillations were accompanied by oscillations in proton and electron fluxes. Most interestingly, both field and particle oscillations at the spacecraft had one-to-one association with the auroral luminosity oscillations around its footprint. Our findings strongly suggest that this auroral undulation event is closely linked to the generation of second harmonic poloidal waves Motoba, T.; Takahashi, K.; Ukhorskiy, A.; Gkioulidou, M.; Mitchell, D.; Lanzerotti, L.; Korotova, G.; Donovan, E.; Wygant, J.; Kletzing, C.; Kurth, W.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020863 |
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The long-duration positive storm effects in the equatorial ionosphere over Jicamarca The long-duration positive storm (LPS) in the equatorial regions is relatively poorly understood. In this report, we conducted a statistical analysis of the LPS effects in the equatorial ionosphere over Jicamarca (12.0\textdegreeS, 283.2\textdegreeE) in 1998\textendash2010. There are 250 geomagnetic storms (minimum Dst \< -50 nT) in 1998\textendash2010, but the ionosonde observations at Jicamarca are available only for 204 storms. A total of 46 LPSs are identified in terms of the criterion that the storm time relative deviation of peak density of F2 layer (NmF2) exceeds 25\% for more than 6 h. A salient feature is that the occurrence of LPSs tends to decay approximately exponentially on the following days after the main phase of geomagnetic storms. The ratios of the number of equatorial LPSs to that of geomagnetic storms have no obvious dependence on season and solar activity. During the daytime LPSs, the disturbed zonal electric field is mostly westward, as indicated from the geomagnetic field changes in the equatorial American region. For the nighttime LPSs, the significant uplifting of F2 layer caused by an eastward electric field is the most important feature. Therefore, the disturbed electric field should play an essential role in forming the equatorial LPSs. Kuai, Jiawei; Liu, Libo; Liu, Jing; Zhao, Biqiang; Chen, Yiding; Le, Huijun; Wan, Weixing; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020552 |
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A new technique for remote sensing of O 2 density from 140 to 180 km Observations of molecular oxygen are difficult to make in the Earth\textquoterights atmosphere between 140 and 200 km altitude. Perhaps the most accurate measurements to date have been obtained from satellite instruments that measure solar occultations of the limb. These do provide height-resolved O2 density measurements, but the nature of this technique is such that the temporal/spatial distribution of the measurements is uneven. Here a new space-based technique is described that utilizes two bright dayglow emissions, the (0,0) transition of the O2 atmospheric band and the O I (630 nm), to derive the height-resolved O2 density from 140 to 180 km. Data from the Remote Atmospheric and Ionospheric Detection System, which was placed on the International Space Station in late 2009, are used to illustrate this technique. The O2 density results for periods in May 2010 that were geomagnetically quiet and disturbed are compared to model predictions. Hecht, James; Christensen, Andrew; Yee, Jeng-Hwa; Crowley, Geoff; Bishop, Rebeeca; Budzien, Scott; Stephan, Andrew; Evans, Scott; Published by: Geophysical Research Letters Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014GL062355 |
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The climatological characteristics of UHF-band scintillations over the low-latitude region of China were investigated by analyzing the observations recorded at three stations of our Zhang, Hongbo; Liu, Yumei; Wu, Jian; Xu, T; Sheng, D; Published by: Published on: YEAR: 2015 DOI: 10.5194/angeo-33-93-2015 |
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During the ascending phase of solar cycle 24, a series of interplanetary coronal mass ejections (ICMEs) in the period 7–17 March 2012 caused geomagnetic storms that strongly Prikryl, P; Ghoddousi-Fard, R; Spogli, L; Mitchell, CN; Li, G; Ning, B; Cilliers, PJ; , Sreeja; Aquino, M; Terkildsen, M; , others; Published by: Published on: YEAR: 2015 DOI: 10.5194/angeo-33-637-2015 |
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The Earth’s ionosphere is a magnetoionic medium imbedded in a background neutral atmosphere, exhibiting very interesting refractive properties, including anisotropy, dispersion, and Belehaki, Anna; Tsagouri, Ioanna; Kutiev, Ivan; Marinov, Pencho; Zolesi, Bruno; Pietrella, Marco; Themelis, Kostas; Elias, Panagiotis; Tziotziou, Kostas; Published by: Published on: YEAR: 2015 DOI: "10.1051/swsc/2015026" |
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SSULI/SSUSI UV tomographic images of large-scale plasma structuring Hei, Matthew; Budzien, Scott; Dymond, Kenneth; Paxton, Larry; Schaefer, Robert; Groves, Keith; Published by: Published on: |
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Towards a National Space Weather Predictive Capability Fox, Nicola; Ryschkewitsch, Michael; Merkin, Viacheslav; Stephens, Grant; Gjerloev, Jesper; Barnes, Robin; Anderson, Brian; Paxton, Larry; Ukhorskiy, Aleksandr; Kelly, Michael; , others; Published by: Published on: |
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A new technique for remote sensing of O2 density from 140 to 180 km Hecht, James; Christensen, Andrew; Yee, Jeng-Hwa; Crowley, Geoff; Bishop, Rebeeca; Budzien, Scott; Stephan, Andrew; Evans, Scott; Published by: Geophysical Research Letters Published on: |
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Auroral precipitation models and space weather Newell, Patrick; Liou, Kan; Zhang, Yongliang; Sotirelis, Thomas; Mitchell, EJ; Mitchell, Elizabeth; Published by: Auroral dynamics and space weather Published on: |
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Auroral precipitation models and space weather Newell, Patrick; Liou, Kan; Zhang, Yongliang; Sotirelis, Thomas; Mitchell, EJ; Mitchell, Elizabeth; Published by: Auroral dynamics and space weather Published on: |
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Thermal cell structures in the high-latitude thermosphere induced by ion drag Published by: Journal of Geophysical Research: Space Physics Published on: |
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The Scintillation Prediction Observations Research Task SA43C-04 Spann, James; Swenson, Charles; Dur\~ao, Otavio; Loures, Luis; Heelis, Rod; Bishop, Rebecca; Le, Guan; Krause, Linda; Nardin, Clezio; Fonseca, Eloi; , others; Published by: Published on: |
| 2014 |
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A study of GPS ionospheric scintillations observed at Shenzhen Ionospheric scintillation variations are studied using GPS measurements at the low latitude station of Shenzhen (22.59\textdegreeN,\ 113.97\textdegreeE), situated under the northern crest of the equatorial anomaly region, from the Chinese Meridian Project. The results are presented for data collected during the current phase of rising solar activity (low to high solar activity) from December 2010 to April 2014. The results show that GPS scintillation events were largely a nighttime phenomenon during the whole observation period. Scintillation events mainly occurred along the inner edge of the northern crest of the equatorial anomaly in China. The occurrence of scintillations in different sectors of the sky was also investigated, and the results revealed that it is more likely for the scintillations to be observed in the west sector of the sky above Shenzhen. During the present period of study, a total number of 512 total electron content (TEC) depletions and 460 lock loss events were observed. In addition, both of these events are likely to increase during periods of high solar activity, especially because the strong scintillations are often simultaneously accompanied by TEC depletions and lock losses by GPS receivers. Huang, Linfeng; Wang, Jinsong; Jiang, Yong; Chen, Zhou; Zhao, Kai; Published by: Advances in Space Research Published on: 12/2014 YEAR: 2014 DOI: 10.1016/j.asr.2014.08.023 |
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Height-integrated Pedersen conductivity in both E and F regions from COSMIC observations Altitudinal distribution of Joule heating is very important to the thermosphere and ionosphere, which is roughly proportional to the Pedersen conductance at high latitudes. Based on the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites observations from 2008 to 2011, the height-integrated Pedersen conductivities in both E (100\textendash150\ km) and F (150\textendash600\ km) regions and their ratio γPγP (∑PE/∑PF∑PE/∑PF) have been calculated. The result shows that the maximum ratio in the northern summer hemisphere is ~5.5, which is smaller than that from the Thermosphere\textendashIonosphere\textendashElectrodynamics General Circulation Model (TIE-GCM v1.94) simulation (~9). This indicates that the energy inputs into the F region may be underestimated in the model. The seasonal variations of the ratio have been investigated for both hemispheres, and an interhemispheric asymmetry has been identified. The variational trend of the ratio is similar in both hemispheres, which reaches minimum at local summer and maximum at local winter. However, the difference of the ratio from local summer to local winter in the southern hemisphere is larger than that in the northern hemisphere. Sheng, Cheng; Deng, Yue; Yue, Xinan; Huang, Yanshi; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1016/j.jastp.2013.12.013 COSMIC; Interhemispheric asymmetry; Joule heating; Pedersen conductivity |
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Large magnitude increases in ionospheric total electron content (TEC) that occur over 1\textendash3\ h on the dayside are a significant manifestation of the main phases of superstorms. For the largest superstorms of solar cycle 23 (based on the Dst index), ground networks of GPS receivers measured peak total electron content increases greater than a factor of 2 relative to quiet time TEC averaged over the broad latitude band \textpm40\textdegree for local times 1200\textendash1600\ LT. Near 30\textdegree latitude, the Halloween storms of October 29\textendash30, 2003 appeared to produce storm-time TEC exceeding quiet time values by a factor of 5 within 2\textendash3\ h of storm onset, at 1300\ LT. The physical cause of these large positive phase ionospheric storms is usually attributed to prompt penetration electric fields (PPEFs) initiated by Region 1 current closure through the ionosphere ( Nopper and Carovillano, 1978 mechanism). An unresolved question is what determines variation of the TEC response for different superstorms. It has been suggested that the cross polar cap potential and Region 1 currents are significant factors in determining PPEF in the equatorial ionosphere, which are related to the solar wind reconnection electric field estimated by Kan\textendashLee and others. In this paper, we show evidence that suggests By may be a significant factor controlling the TEC response during the main phase of superstorms. We analyzed the interplanetary conditions during the period that TEC was increasing for eight superstorms. We find that increasing daytime TEC during superstorms only occurs for large reconnection electric fields when By magnitude is less than Bz. The data suggest that Bz is a far more important factor in the TEC response than the reconnection electric field. We also find that TEC decreases following its peak storm-time value for two superstorms, even though Bz remains large and By magnitudes are less than Bz. Such decreases during the geomagnetic disturbance may indicate the role of magnetospheric shielding currents, or of changes in the thermosphere that have developed over the prolonged period of large solar wind electric field. Further analysis is warranted covering a wider range of storm intensities on the role of By in affecting the daytime TEC response for a range of storm intensities. Mannucci, A.J.; Crowley, G.; Tsurutani, B.T.; Verkhoglyadova, O.P.; Komjathy, A.; Stephens, P.; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1016/j.jastp.2014.01.001 |
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The neutral winds in the mesosphere and lower thermosphere (MLT) region are measured by a newly installed meteor trail detection system (or meteor radar) at Chung-Li, Taiwan, for the period 10\textendash25 November 2012, which includes the Leonid meteor shower period. In this study, we use the 3 m field-aligned plasma irregularities in the sporadic E (Es) region in combination with the International Geomagnetic Reference Field model to calibrate the system phase biases such that the true positions of the meteor trails can be correctly determined with interferometry technique. The horizontal wind velocities estimated from the radial velocities of the meteor trails and their locations by using a least squares method show that the diurnal tide dominates the variation of the MLT neutral wind with time over Chung-Li, which is in good agreement with the horizontal wind model (HWM07) prediction. However, harmonic analysis reveals that the amplitudes of the mean wind, diurnal, and semidiurnal tides of the radar-measured winds in height range 82\textendash100 km are systematically larger than those of the model-predicted winds by up to a factor of 3. A comparison shows that the overall pattern of the height-local time distribution of the composite radar-measured meteor wind is, in general, consistent with that of the TIMED Doppler Interferometer-observed wind, which is dominated by a diurnal oscillation with downward phase progression at a rate of about 1.3 km/h. The occurrences of the Es layers retrieved from fluctuations of the amplitude and excess phase of the GPS signal received by the FORMOSAT-3/COSMIC satellites during the GPS radio occultation (RO) process are compared with the shear zones of the radar-measured meteor wind and HWM07 wind. The result shows that almost all of the RO-retrieved Es layers occur within the wind shear zones that favor the Es layer formation based on the wind shear theory, suggesting that the primary physical process responsible for the Es layer events retrieved from the scintillations of the GPS RO signal is very likely the plasma convergence effect of the neutral wind shear. Su, C.; Chen, H.; Chu, Y.; Chung, M.; Kuong, R.; Lin, T.; Tzeng, K.; Wang, C; Wu, K.; Yang, K.; Published by: Radio Science Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2013RS005273 |
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The responses of ionospheric topside diffusive fluxes to two geomagnetic storms in October 2002 O+ field-aligned ambipolar diffusive velocities Vd and fluxes Фd in the topside ionosphere have been calculated from the observed profiles of electron density, ion, and electron temperatures during a 30 day incoherent scatter radar experiment conducted at Millstone Hill (288.5\textdegreeE, 42.6\textdegreeN) from 4 October to 4 November 2002. Two geomagnetic storms took place during this period. During the negative phases (depleted electron densities) of these two storms, the magnitudes of the daytime upward Vd and Фd were less than their averaged quiet time values. Whereas at nighttime, the downward Vd and Фd were sometimes larger than the averaged quiet time values. The variations in diffusive velocity and flux during the storm main and recovery phases were caused by changes in the ionospheric scale height or the shapes of ionospheric density profiles. The negative storm effect further reduced daytime diffusive flux. During these two storms, positive ionosphere phases (enhanced electron densities) were also observed. The diffusive velocity was much smaller during the period of positive storm effect, which led to a smaller diffusive flux than the quiet time one, although electron density was higher. It appears that storm time variations in diffusive velocity were more the results of storm time changes in the plasma vertical profile, rather than the cause of these plasma density changes. Chen, Guang-Ming; Xu, JiYao; Wang, Wenbin; Lei, Jiuhou; Zhang, Shun-Rong; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014JA020013 diffusion; geomagnetic storm; scale height; topside ionosphere |
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The CERTO radio beacon on the C/NOFS satellite sends VHF/UHF radio signals at 150 and 400 MHz to provide measurements of integrated electron density or Total Electron Content (TEC) by an east-west chain of ground receivers in Peru. Computerized Ionospheric Tomography (CIT) is used to convert the TEC data into two-dimensional images of electron densities with maximum 5 \texttimes 5 km resolution in Longitude-Altitude space. These images are updated every 95 min as the C/NOFS satellite passes over the receiver network in its low-latitude orbit with an inclination of 12\textdegree. The 2-D, high-resolution images of the ionosphere are used to predict the impact of equatorial plasma structures on HF propagation of radar and radio signals. Electron density measurements from the NRL radio tomography chain across Peru are used for simulations of the performance by HF one-way links. HF rays from transmitter to receiver are traced through the electron density images produced by radio beacon tomography. Eight separate paths are found between a transmitter and ground receiver separated by 2000 km. A total of 36 backscatter echoes are found with unique group delay, Doppler frequency shift, phase delay, and echo amplitude. This multipath effect explains the range and Doppler spreading of observations for HF monostatic radar propagation through F layer irregularities. This type of analysis is useful for prediction and interpretation of range and Doppler observations from HF systems including over-the-horizon and SuperDARN radars, HF Geolocation Arrays, and HF communications networks. Bernhardt, Paul; Hei, Matthew; Siefring, Carl; Wilkens, Matthew; Published by: Radio Science Published on: 07/2014 YEAR: 2014 DOI: 10.1002/2014RS005409 |
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Solar filament impact on 21 January 2005: Geospace consequences On 21 January 2005, a moderate magnetic storm produced a number of anomalous features, some seen more typically during superstorms. The aim of this study is to establish the differences in the space environment from what we expect (and normally observe) for a storm of this intensity, which make it behave in some ways like a superstorm. The storm was driven by one of the fastest interplanetary coronal mass ejections in solar cycle 23, containing a piece of the dense erupting solar filament material. The momentum of the massive solar filament caused it to push its way through the flux rope as the interplanetary coronal mass ejection decelerated moving toward 1 AU creating the appearance of an eroded flux rope (see companion paper by Manchester et al. (2014)) and, in this case, limiting the intensity of the resulting geomagnetic storm. On impact, the solar filament further disrupted the partial ring current shielding in existence at the time, creating a brief superfountain in the equatorial ionosphere\textemdashan unusual occurrence for a moderate storm. Within 1 h after impact, a cold dense plasma sheet (CDPS) formed out of the filament material. As the interplanetary magnetic field (IMF) rotated from obliquely to more purely northward, the magnetotail transformed from an open to a closed configuration and the CDPS evolved from warmer to cooler temperatures. Plasma sheet densities reached tens per cubic centimeter along the flanks\textemdashhigh enough to inflate the magnetotail in the simulation under northward IMF conditions despite the cool temperatures. Observational evidence for this stretching was provided by a corresponding expansion and intensification of both the auroral oval and ring current precipitation zones linked to magnetotail stretching by field line curvature scattering. Strong Joule heating in the cusps, a by-product of the CDPS formation process, contributed to an equatorward neutral wind surge that reached low latitudes within 1\textendash2 h and intensified the equatorial ionization anomaly. Understanding the geospace consequences of extremes in density and pressure is important because some of the largest and most damaging space weather events ever observed contained similar intervals of dense solar material. Kozyra, J.; Liemohn, M.; Cattell, C.; De Zeeuw, D.; Escoubet, C.; Evans, D.; Fang, X.; Fok, M.-C.; Frey, H.; Gonzalez, W.; Hairston, M.; Heelis, R.; Lu, G.; Manchester, W.; Mende, S.; Paxton, L.; Rastaetter, L.; Ridley, A.; Sandanger, M.; Soraas, F.; Sotirelis, T.; Thomsen, M.; Tsurutani, B.; Verkhoglyadova, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2014 YEAR: 2014 DOI: 10.1002/2013JA019748 cold dense plasma sheet; Equatorial anomaly; magnetotail; precipitation; prompt penetration electric field; solar filament |
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Solar filament impact on 21 January 2005: Geospace consequences On 21 January 2005, a moderate magnetic storm produced a number of anomalous features, some seen more typically during superstorms. The aim of this study is to establish the differences in the space environment from what we expect (and normally observe) for a storm of this intensity, which make it behave in some ways like a superstorm. The storm was driven by one of the fastest interplanetary coronal mass ejections in solar cycle 23, containing a piece of the dense erupting solar filament material. The momentum of the massive solar filament caused it to push its way through the flux rope as the interplanetary coronal mass ejection decelerated moving toward 1 AU creating the appearance of an eroded flux rope (see companion paper by Manchester et al. (2014)) and, in this case, limiting the intensity of the resulting geomagnetic storm. On impact, the solar filament further disrupted the partial ring current shielding in existence at the time, creating a brief superfountain in the equatorial ionosphere\textemdashan unusual occurrence for a moderate storm. Within 1 h after impact, a cold dense plasma sheet (CDPS) formed out of the filament material. As the interplanetary magnetic field (IMF) rotated from obliquely to more purely northward, the magnetotail transformed from an open to a closed configuration and the CDPS evolved from warmer to cooler temperatures. Plasma sheet densities reached tens per cubic centimeter along the flanks\textemdashhigh enough to inflate the magnetotail in the simulation under northward IMF conditions despite the cool temperatures. Observational evidence for this stretching was provided by a corresponding expansion and intensification of both the auroral oval and ring current precipitation zones linked to magnetotail stretching by field line curvature scattering. Strong Joule heating in the cusps, a by-product of the CDPS formation process, contributed to an equatorward neutral wind surge that reached low latitudes within 1\textendash2 h and intensified the equatorial ionization anomaly. Understanding the geospace consequences of extremes in density and pressure is important because some of the largest and most damaging space weather events ever observed contained similar intervals of dense solar material. Kozyra, J.; Liemohn, M.; Cattell, C.; De Zeeuw, D.; Escoubet, C.; Evans, D.; Fang, X.; Fok, M.-C.; Frey, H.; Gonzalez, W.; Hairston, M.; Heelis, R.; Lu, G.; Manchester, W.; Mende, S.; Paxton, L.; Rastaetter, L.; Ridley, A.; Sandanger, M.; Soraas, F.; Sotirelis, T.; Thomsen, M.; Tsurutani, B.; Verkhoglyadova, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2014 YEAR: 2014 DOI: 10.1002/2013JA019748 cold dense plasma sheet; Equatorial anomaly; magnetotail; precipitation; prompt penetration electric field; solar filament |
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OVATION Prime-2013: Extension of auroral precipitation model to higher disturbance levels OVATION Prime (OP) is an auroral precipitation model parameterized by solar wind driving. Distinguishing features of the model include an optimized solar wind-magnetosphere coupling function (dΦMP/dt) which predicts auroral power significantly better than\ Kp\ or other traditional parameters, the separation of aurora into categories (diffuse aurora, monoenergetic, broadband, and ion), the inclusion of seasonal variations, and separate parameter fits for each magnetic latitude (MLAT) \texttimes magnetic local time (MLT) bin, thus permitting each type of aurora and each location to have differing responses to season and solar wind input\textemdashas indeed they do. We here introduce OVATION Prime-2013, an upgrade to the 2010 version currently widely available. The most notable advantage of OP-2013 is that it uses UV images from the GUVI instrument on the satellite TIMED for high disturbance levels (dΦMP/dt \> 1.2 MWb/s which roughly corresponds toKp = 5+ or 6-). The range of validity is approximately 0 \< dΦMP/dt <= 3.0 MWb/s (Kp\ about 8+). Other upgrades include a reduced susceptibility to salt-and-pepper noise, and smoother interpolation across the postmidnight data gap. The model is tested against an independent data set of hemispheric auroral power from Polar UVI. Over the common range of validity of OP-2010 and OP-2013, the two models predict auroral power essentially identically, primarily because hemispheric power calculations were done in a way to minimize the impact of OP-2010s noise. To quantitatively demonstrate the improvement at high disturbance levels would require multiple very large substorms, which are rare, and insufficiently present in the limited data set of Polar UVI hemispheric power values. Nonetheless, although OP-2010 breaks down in a variety of ways above\ Kp = 5+ or 6-, OP-2013 continues to show the auroral oval advancing equatorward, at least to 55\textdegree MLAT or a bit less, and OP-2013 does not develop spurious large noise patches. We will also discuss the advantages and disadvantages of other precipitation models more generally, as no one model fits best all possible uses. Newell, P.; Liou, K.; Zhang, Y.; Sotirelis, T.; Paxton, L.; Mitchell, E.; Published by: Space Weather Published on: 06/2014 YEAR: 2014 DOI: 10.1002/swe.v12.610.1002/2014SW001056 |
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A specific imaging spectrometer based on a concentric off-axis dual reflector system is proposed, free of astigmatism and coma. The described imaging spectrometer consists of four spherical mirrors and a plane grating. The analytic theory of aberrations and the optical path-length concept are used to derive the astigmatism elimination and coma removal. It is shown that the astigmatism in these imaging spectrometers is eliminated by characterizing three angles, and the coma is corrected when unequal mirror radii are configured in collimating and condensing optics. The developed aberration principle is verified by comparing the performance of the astigmatism-eliminated spectrometer with the spectrometer which has neither astigmatism nor coma. Chen, Ting; Tang, Yi; Zhang, Li; Chang, Yue; Zheng, Cheng; Published by: Applied Optics Published on: 01/2014 YEAR: 2014 DOI: 10.1364/AO.53.000565 |
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A specific imaging spectrometer based on a concentric off-axis dual reflector system is proposed, free of astigmatism and coma. The described imaging spectrometer consists of four spherical mirrors and a plane grating. The analytic theory of aberrations and the optical path-length concept are used to derive the astigmatism elimination and coma removal. It is shown that the astigmatism in these imaging spectrometers is eliminated by characterizing three angles, and the coma is corrected when unequal mirror radii are configured in collimating and condensing optics. The developed aberration principle is verified by comparing the performance of the astigmatism-eliminated spectrometer with the spectrometer which has neither astigmatism nor coma. Chen, Ting; Tang, Yi; Zhang, Li; Chang, Yue; Zheng, Cheng; Published by: Applied Optics Published on: 01/2014 YEAR: 2014 DOI: 10.1364/AO.53.000565 |
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Spherical cap harmonic analysis of the Arctic ionospheric TEC for one solar cycle Precise knowledge of the Arctic ionosphere total electron content (TEC) and its variations has scientific relevance due to the unique characteristics of the polar ionosphere. Understanding the Arctic TEC is also important for precise positioning and navigation in the Arctic. This study utilized the spherical cap harmonic analysis (SCHA) method to map the Arctic TEC for the most recent solar cycle from 2000 to 2013 and analyzed the distributions and variations of the Arctic TEC at different temporal and spatial scales. Even with different ionosphere conditions during the solar cycle, the results showed that the existing International Global Navigation Satellite Systems Service stations are sufficient for mapping the Arctic TEC. The SCHA method provides adequate accuracy and resolution to analyze the spatiotemporal distributions and variations of the Arctic TEC under different ionosphere conditions and to track ionization patches in this polar region (e.g., the ionization event of 26 September 2011). The results derived from the SCHA model were compared to direct observations using the Super Dual Auroral Radar Network radar. The SCHA method is able to predict the TEC in the long and short terms. This paper presented a long-term prediction with a relative uncertainty of 75\% for a latency of one solar cycle and a short-term prediction with errors of \textpm2.2 total electron content units (TECUs, 1 TECU = 1016 el m-2), \textpm3.8 TECU, and \textpm4.8 TECU for a latency of 1, 2, and 3 days, respectively. The SCHA is an effective method for mapping, predicting, and analyzing the Arctic TEC. Liu, Jingbin; Chen, Ruizhi; An, Jiachun; Wang, Zemin; Hyyppa, Juha; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2014 YEAR: 2014 DOI: 10.1002/2013JA019501 Arctic navigation; ionosphere mapping and prediction; polar ionosphere; regional ionosphere model; spherical cap harmonic analysis |
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Auroral hemispheric power during geomagnetic storms driven by different interplanetary disturbances Although it has been a long time since the beginning of research on the auroral hemispheric power (HP), less has been done on the differences of HP among storms driven by different Chen, Xi; FU, Sui-Yan; Zheng, Ling; YANG, Li-Ping; CUI, Yan-Bo; Published by: Chinese Journal of Geophysics Published on: YEAR: 2014 DOI: 10.6038/cjg20141130 |
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Auroral hemispheric power during geomagnetic storms driven by different interplanetary disturbances Although it has been a long time since the beginning of research on the auroral hemispheric power (HP), less has been done on the differences of HP among storms driven by different Chen, Xi; FU, Sui-Yan; Zheng, Ling; YANG, Li-Ping; CUI, Yan-Bo; Published by: Chinese Journal of Geophysics Published on: YEAR: 2014 DOI: 10.6038/cjg20141130 |
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Auroral all-sky camera calibration A two-step procedure to calibrate the spectral sensitivity to visible light of auroral all-sky cameras is outlined. Center pixel response is obtained by the use of a Lambertian surface and a Sigernes, Fred; Holmen, SE; Biles, D; Bj\orklund, H; Chen, X; Dyrland, M; Lorentzen, DA; Baddeley, L; Trondsen, T; Brändström, U; , others; Published by: Geoscientific Instrumentation, Methods and Data Systems Published on: YEAR: 2014 DOI: 10.5194/gi-3-241-2014 |
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Ionospheric response to geomagnetic storm on July 14-17, 2012 in East Asia Romanova, Elena; Zherebtsov, Gelii; Wang, Guojun; Zolotukhina, Nina; Polekh, Nelya; Wang, Xiao; Shi, Jiankui; Published by: 40th COSPAR Scientific Assembly Published on: |
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Developing a Multi-Element Geospace Investigation to Understand the Impact of Hemispheric Assymetry Paxton, Larry; Newell, Patrick; Stromme, Anja; Ridley, Aaron; Kozyra, Janet; Mitchell, Elizabeth; Published by: Published on: |
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Comparative studies of theoretical models in the equatorial ionosphere Fang, Tzu-Wei; Anderson, David; Fuller-Rowell, Tim; Akmaev, Rashid; Codrescu, Mihail; Millward, George; Sojka, Jan; Scherliess, Ludger; Eccles, Vince; Retterer, John; , others; Published by: Modeling the ionosphere—thermosphere system Published on: |
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Space Weather Tools of the Trade-A Changing Mix Kunches, Joseph; Crowley, Geoff; Pilinski, Marcin; Winkler, Clive; Fish, Chad; Hunton, Don; Reynolds, Adam; Azeem, I; Published by: Published on: |
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Recent Results of the Remote Sensing of the O/N2 Ratio in the 100 to 200 Km Altitude Region Published by: Published on: |
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The Role of Thermospheric Composition in Ionospheric Forecasting Chartier, A; Morgan, F; Bust, GS; Mitchell, CN; Published by: Published on: |
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Modelling ionospheric effects for L band GNSS receivers at high latitudes The main objective of this study was to figure out a relationship between space weather environment phenomena (linked to solar and geomagnetic activity) and ionospheric events that impact L-band operating satellite systems (scintillations, electron content gradients), especially satellite navigation services, in the Nordic European area. A simple empirical model to forecast index of rate of change of the total electron content (ROTI) at high latitude has been developed associated with Kp geomagnetic prediction and the use of solar electron energy flux. Boscher, D.; Carvalho, F.; Fabbro, V.; Lemorton, J.; Fleury, R.; Published by: Published on: YEAR: 2014 DOI: 10.1109/EuCAP.2014.6902380 high latitude; Ionosphere; radiowave propagation; scintillation; solar and geomagnetic activity |
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Solomentsev, Dmitry; Cherniak, Yakov; Vyacheslav, Khattatov; Titov, Anton; Khattatov, Boris; Published by: 40th COSPAR Scientific Assembly Published on: |
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Solomentsev, Dmitry; Cherniak, Yakov; Vyacheslav, Khattatov; Titov, Anton; Khattatov, Boris; Published by: 40th COSPAR Scientific Assembly Published on: |
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Newell, Patrick; Liou, Kan; Zhang, Yongliang; Sotirelis, Thomas; Paxton, Larry; Mitchell, Elizabeth; Published by: Published on: |
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Accomplishing Transformative Research in a Challenging Fiscal Environment Mitchell, Elizabeth; Paxton, Larry; Bust, G; Published by: Published on: |
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Ionospheric symmetry caused by geomagnetic declination over North America We describe variations in total electron content (TEC) in the North American sector exhibiting pronounced longitudinal progression and symmetry with respect to zero magnetic declination. Patterns were uncovered by applying an empirical orthogonal function (EOF) decomposition procedure to a 12 year ground-based American longitude sector GPS TEC data set. The first EOF mode describes overall average TEC, while the strong influence of geomagnetic declination on the midlatitude ionosphere is found in the second EOF mode (or the second most significant component). We find a high degree of correlation between spatial variations in the second EOF mode and vertical drifts driven by thermospheric zonal winds, along with well-organized temporal variation. Results strongly suggest a causative mechanism involving varying declination with longitude along with varying zonal wind climatology with local time, season, and solar cycle. This study highlights the efficiency and key role played by the geomagnetic field effect in influencing mesoscale ionospheric structures over a broad midlatitude range. Zhang, Shun-Rong; Chen, Ziwei; Coster, Anthea; Erickson, Philip; Foster, John; Published by: Geophysical Research Letters Published on: 10/2014 YEAR: 2013 DOI: 10.1002/grl.v40.2010.1002/2013GL057933 geomagnetic field; midlatitude ionosphere; thermospheric winds; total electron content |
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Is Space Weather Different Over Africa, and If So, Why? An AGU Chapman Conference Report With the increasing reliance on technology, the impact of space weather on engineered systems will certainly increase unless suitable protective measures are taken. Understanding the physics behind space weather impacts and improving the forecasting are the major objectives of the space science community. It is well recognized that many space weather impacts, especially on communications systems, arise from structures in the ionosphere. The equatorial ionosphere, in particular, is one of the most complex and is host to numerous instabilities and interactions, with many unresolved questions regarding its dynamics and variability. Radio waves, either transmitted through the ionosphere, for satellite communication and navigation, or reflected off the ionosphere for HF and radar applications, are all impacted by ionospheric variability and structure. Ionospheric irregularities or plasma \textquotedblleftbubbles\textquotedblright occurring at low latitudes are one such source of interference. These irregularities cause scintillations on satellite radio transmissions, resulting in information loss in communications, as well as degradation in positioning and navigation used in aviation and maritime industries. Yizengaw, Endawoke; Doherty, Patricia; Fuller-Rowell, Tim; Published by: Space Weather Published on: 07/2013 YEAR: 2013 DOI: 10.1002/swe.20063 atmosphere ionosphere interactions; ionospheric irregularities; space weather |
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The total electron content (TEC) measurements from a network of GPS receivers were analyzed to investigate the storm time spatial response of ionosphere over the Indian longitude sector. The GPS receivers from the GPS Aided Geo Augmented Navigation (GAGAN) network which are uniquely located around the \~77\textdegreeE longitude are used in the present study so as to get the complete latitudinal coverage from the magnetic equator to low mid-latitude region. We have selected the most intense storms but of moderate intensity (-100\ nT\ \<\ Dst\ \<\ -50\ nT) which occurred during the unusually extremely low solar activity conditions in 2007\textendash2009. Though the storms are of moderate intensity, their effects on equatorial to low mid-latitude ionosphere are found to be very severe as TEC deviations are more than 100\% during all the storms studied. Interesting results in terms of spatial distribution of positive/negative effects during the main/early recovery phase of storms are noticed. The maximum effect was observed at crest region during two storms whereas another two storms had maximum effect near the low mid-latitude region. The associated mechanisms like equatorial electrodynamics and neutral dynamics are segregated and explained using the TIMED/GUVI and EEJ data during these storms. The TEC maps are generated to investigate the storm time development/inhibition of equatorial ionization anomaly (EIA). Sunda, Surendra; Vyas, B.M.; Khekale, P.V.; Published by: Advances in Space Research Published on: 07/2013 YEAR: 2013 DOI: 10.1016/j.asr.2013.03.006 Electrodynamics; Equatorial and low-latitude; geomagnetic storm; Total electron content (TEC) |
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This paper is the first study to employ a three-dimensional physics-based ionosphere model, SAMI3, coupled with the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) and Global Scale Wave Model to simulate the mesospheric and lower thermospheric tidal effects on the development of midlatitude summer nighttime anomaly (MSNA). Using this coupled model, the diurnal variation of MSNA electron densities at 300 km altitude is simulated on both June solstice (day of year (DOY) 167) and December solstice (DOY 350) in 2007. Results show successful reproduction of the southern hemisphere MSNA structure including the eastward drift feature of the southern MSNA, which is not reproduced by the default SAMI3 runs using the neutral winds provided by the empirical Horizontal Wind Model 93 neutral wind model. A linear least squares algorithm for extracting tidal components is utilized to examine the major tidal component affecting the variation of southern MSNA. Results show that the standing diurnal oscillation component dominates the vertical neutral wind manifesting as a diurnal eastward wave-1 drift of the southern MSNA in the local time frame. We also find that the stationary planetary wave-1 component of vertical neutral wind can cause diurnal variation of the summer nighttime electron density enhancement around the midlatitude ionosphere. Chen, C.; Lin, C.; Chang, L.; Huba, J.; Lin, J.; Saito, A.; Liu, J; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2013 YEAR: 2013 DOI: 10.1002/jgra.50340 |