Bibliography
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Found 137 entries in the Bibliography.
Showing entries from 1 through 50
| 2019 |
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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 |
| 2018 |
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Extreme ionospheric storms and their effects on GPS systems Given the central importance of Global Positioning System (GPS) to modern society, it is important to consider the effects of extreme ionospheric storms on GPS signals. We Published by: Published on: YEAR: 2018 DOI: 10.1016/B978-0-12-812700-1.00023-6 |
| 2016 |
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RENU 2 UV Measurements of Atomic Oxygen in the Cusp Region Fritz, Bruce; Lessard, Marc; Paxton, Larry; Cook, Timothy; Lynch, Kristina; Clemmons, James; Hecht, James; Hysell, David; Crowley, Geoff; Published by: Published on: |
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Analysis of TIMED/GUVI Dayglow Utraviolet Oxygen Images Christensen, Andrew; Crowley, Geoff; Meier, Robert; Published by: Published on: |
| 2015 |
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A data assimilation algorithm is used to delineate the time-dependent three-dimensional ionospheric response to the 2009 sudden stratospheric warming (SSW) event. We use the Ionospheric Data Assimilation Four-Dimensional (IDA4D) algorithm to study the global ionospheric response to the 2009 SSW. This is the first study to utilize global ionospheric measurements in a data assimilation framework to unambiguously characterize atmosphere-ionosphere coupling via tidal modifications during the 2009 SSW event. Model results reveal that the dominant mode of ionospheric variability during the 2009 SSW is driven by the enhancements in westward propagating semidiurnal tide with zonal wave number 1. The IDA4D results completely characterize the tidal perturbation during the 2009 SSW for the first time and show the global 3-D structure of the tide in total electron content (TEC) and electron density. The largest ionospheric responses were seen at low latitudes, where ionospheric plasma is extremely sensitive to the zonal electric field and susceptible to modifications by tidal winds in the lower thermosphere. The ionospheric response to the warming was characterized by an increase in TEC in the morning/early afternoon sector and a decrease during the late afternoon/evening period. The effects of coupling between the stratosphere and ionosphere were strongest between 220 km and 380 km. The IDA4D results also show a reversal of asymmetry in the equatorial ionization anomaly crests occurring several days after the peak of the 2009 SSW event. We suggest that this could be a result of the equatorial fountain effect being further modified by the summer-to-winter meridional neutral winds. Azeem, I.; Crowley, G.; Honniball, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA020993 Atmospheric tides; data assimilation; ionosphere/atmosphere interactions; sudden stratospheric warming |
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Seasonal variability in global eddy diffusion and the effect on neutral density We describe a method for making single-satellite estimates of the seasonal variability in global-average eddy diffusion coefficients. Eddy diffusion values as a function of time were estimated from residuals of neutral density measurements made by the Challenging Minisatellite Payload (CHAMP) and simulations made using the thermosphere-ionosphere-mesosphere electrodynamics global circulation model (TIME-GCM). The eddy diffusion coefficient results are quantitatively consistent with previous estimates based on satellite drag observations and are qualitatively consistent with other measurement methods such as sodium lidar observations and eddy diffusivity models. Eddy diffusion coefficient values estimated between January 2004 and January 2008 were then used to generate new TIME-GCM results. Based on these results, the root-mean-square sum for the TIME-GCM model is reduced by an average of 5\% when compared to density data from a variety of satellites, indicating that the fidelity of global density modeling can be improved by using data from a single satellite like CHAMP. This approach also demonstrates that eddy diffusion could be estimated in near real-time from satellite observations and used to drive a global circulation model like TIME-GCM. Although the use of global values improves modeled neutral densities, there are limitations to this method, which are discussed, including that the latitude dependence of the seasonal neutral-density signal is not completely captured by a global variation of eddy diffusion coefficients. This demonstrates the need for a latitude-dependent specification of eddy diffusion which is also consistent with diffusion observations made by other techniques. Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021084 annual; eddy diffusion; neutral density; satellite drag; seasonal variability; semiannual |
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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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Remote sensing of Earth's limb by TIMED/GUVI: Retrieval of thermospheric composition and temperature The Global Ultraviolet Imager (GUVI) onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet emissions from O and N2 in the thermosphere. Transformation of far ultraviolet radiances measured on the Earth limb into O, N2, and O2 number densities and temperature quantifies these responses and demonstrates the value of simultaneous altitude and geographic information. Composition and temperature variations are available from 2002 to 2007. This paper documents the extraction of these data products from the limb emission rates. We present the characteristics of the GUVI limb observations, retrievals of thermospheric neutral composition and temperature from the forward model, and the dramatic changes of the thermosphere with the solar cycle and geomagnetic activity. We examine the solar extreme ultraviolet (EUV) irradiance magnitude and trends through comparison with simultaneous Solar Extreme EUV (SEE) measurements on TIMED and find the EUV irradiance inferred from GUVI averaged (2002\textendash2007) 30\% lower magnitude than SEE version 11 and varied less with solar activity. The smaller GUVI variability is not consistent with the view that lower solar EUV radiation during the past solar minimum is the cause of historically low thermospheric mass densities. Thermospheric O and N2 densities are lower than the NRLMSISE-00 model, but O2 is consistent. We list some lessons learned from the GUVI program along with several unresolved issues. Meier, R.; Picone, J.; Drob, D.; Bishop, J.; Emmert, J.; Lean, J.; Stephan, A.; Strickland, D.; Christensen, A.; Paxton, L.; Morrison, D.; Kil, H.; Wolven, B.; Woods, Thomas; Crowley, G.; Gibson, S.; Published by: Earth and Space Science Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014EA000035 airglow and aurora; remote sensing; thermosphere: composition and chemistry; thermosphere: energy deposition |
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Characteristics of extreme geoelectric fields and their possible causes: Localized peak enhancements Ngwira, Chigomezyo; Pulkkinen, Antti; Bernabeu, Emanuel; Eichner, Jan; Viljanen, Ari; Crowley, Geoff; Published by: Geophysical Research Letters Published on: |
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First light from a kilometer-baseline Scintillation Auroral GPS Array Datta-Barua, S; Su, Y; Deshpande, K; Miladinovich, D; Bust, GS; Hampton, D; Crowley, G; Published by: Geophysical Research Letters 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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Community-wide model validation study for systematic assessment of ionosphere models Shim, Ja; Kuznetsova, Maria; Rastaetter, Lutz; Bilitza, Dieter; Bingham, Suzy; Bust, Gary; Calfas, Roy; Codrescu, Mihail; Coster, Anthea; Crowley, Geoff; , others; Published by: Published on: |
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Azeem, Irfan; Yue, Jia; Hoffmann, Lars; Miller, Steven; Straka, William; Crowley, Geoff; Published by: Geophysical research letters Published on: |
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First Measurements of Ionospheric TEC and GPS Scintillations from an Unmanned Marine Vehicle Azeem, Irfan; Crowley, Geoff; Reynolds, Adam; Published by: 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: |
| 2014 |
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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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Seasonal Variability in Global Eddy Diffusion and the Effect on Thermospheric Neutral Density Pilinski, Marcin; Crowley, Geoff; Published by: Published on: |
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Hunton, Don; Pilinski, Marcin; Crowley, Geoff; Azeem, I; Fuller-Rowell, Timothy; Matsuo, Tomoko; Fedrizzi, Mariangel; Solomon, Stanley; Qian, Liying; Thayer, Jeffrey; , others; Published by: Published on: |
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Topside Ionospheric Sounder for CubeSats Swenson, C; Pratt, J; Fish, CS; Winkler, C; Pilinski, M; Azeem, I; Crowley, G; Jeppesen, M; Martineau, R; Published by: 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: |
| 2013 |
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First storm-time plasma velocity estimates from high-resolution ionospheric data assimilation Datta-Barua, Seebany; Bust, Gary; Crowley, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: |
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Clauer, Robert; Kim, Hyomin; Deshpande, Kshitija; Xu, Zhonghua; Fish, Chad; Musko, Steve; Crowley, Geoff; Humphreys, Todd; Bhatti, Jahshan; Bust, Grary; Published by: Published on: |
| 2012 |
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Characteristics of traveling ionospheric disturbances observed by the TIDDBIT sounder Crowley, Geoff; Rodrigues, FS; Published by: Radio Science Published on: |
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Emery, B; Roble, Raymond; Ridley, Cicely; Richmond, Arthur; Knipp, Delores; Crowley, Geoff; Evans, David; Rich, Frederick; Maeda, Sawako; Published by: NCAR Tech. Note NCAR/TN-491+ STR Published on: |
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Tutorial: The Neutral Atmosphere and the Satellite Drag Environment Crowley, Geoff; Pilinski, Marcin; Azeem, Irfan; Published by: Advances in the Astronautical Sciences Published on: |
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Heterogeneous Measurements for Advances in Space Science and Space Weather Forecasting Examples of heterogenous data might include GPS radio occultation limb data and ultraviolet nadir photometry; GUVI/SSUSI cross-track O/N2 maps coupled with SSULI in-track Budzien, Scott; Chua, Damien; Coker, Clayton; Dandenault, Patrick; Dymond, Kenneth; Nicholas, Andrew; Stephan, Andrew; Doe, Richard; Crowley, Geoff; Published by: To emphasize that space weather forecasting with new, full-physics models requires heterogeneous datasets with complementary characteristics—not merely a higher volume of any single data type Published on: |
| 2011 |
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Sahai, Y.; Fagundes, P.; de Jesus, R.; de Abreu, A.; Crowley, G.; Kikuchi, T.; Huang, C.-S.; Pillat, V.; Guarnieri, F.; Abalde, J.; Bittencourt, J.; Published by: Annales Geophysicae Published on: Jan-01-2011 YEAR: 2011 DOI: 10.5194/angeo-29-919-2011 |
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A study of space shuttle plumes in the lower thermosphere Meier, R.; Stevens, Michael; Plane, John; Emmert, J.; Crowley, G.; Azeem, I.; Paxton, L.; Christensen, A.; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2011JA016987 |
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Sahai, Y; De Abreu, AJ; Fagundes, PR; De Jesus, R; Crowley, G; Klimenko, MV; Klimenko, VV; Brunini, C; Gende, M; Pillat, VG; , others; Published by: Asian Journal of Physics Published on: |
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The Storm Time Energy and Dynamics Explorers Swenson, C; Fish, CS; Crowley, G; Earle, GD; Anderson, BJ; Dyrud, LP; Carlson, HC; Erickson, PJ; Fejer, BG; Mertens, CJ; , others; Published by: Published on: |
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Christensen, AB; Yee, J; Budzien, SA; Bishop, RL; Hecht, JH; Stephan, AW; Crowley, G; Published by: Published on: |
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Teodosiev, Dimitar; Yordanova, Emiliya; Nenovski, Petko; Nikolova, Tatyana; Danov, Dimitar; Crowley, Geoff; Baddeley, Lissa; Buchert, Stefan; Published by: Comptes rendus de l’Acad\ emie bulgare des Sciences Published on: |
| 2010 |
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Can molecular diffusion explain Space Shuttle plume spreading? Meier, R.; Plane, John; Stevens, Michael; Paxton, L.; Christensen, A.; Crowley, G.; Published by: Geophysical Research Letters Published on: Jan-04-2010 YEAR: 2010 DOI: 10.1029/2010GL042868 |
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Comparison of the Hill\textendashSiscoe polar cap potential theory with the Weimer and AMIE models Kelley, Michael; Crowley, Geoffrey; Weimer, Daniel; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: Jan-03-2010 YEAR: 2010 DOI: 10.1016/j.jastp.2009.02.011 |
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Effects of the Shuttle Plumes on the Chemistry and Energetics of the Lower Thermosphere Azeem, SI; Crowley, G; Stevens, MH; Meier, RR; Published by: Published on: |
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Dynamical Properties of Shuttle Plumes in the Lower Thermosphere Meier, RR; Stevens, MH; Plane, JM; Emmert, JT; Crowley, G; Paxton, LJ; Christensen, AB; Azeem, SI; Published by: Published on: |
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Periodic spacing between consecutive equatorial plasma bubbles Makela, Jonathan; Vadas, SL; Muryanto, R; Duly, T; Crowley, G; Published by: Geophysical Research Letters Published on: |
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On the causes of plasmaspheric rotation variability: IMAGE EUV observations Galvan, David; Moldwin, Mark; Sandel, Bill; Crowley, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: |
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A comprehensive rocket and radar study of midlatitude spread F Earle, GD; Bhaneja, P; Roddy, PA; Swenson, CM; Barjatya, Aroh; Bishop, RL; Bullett, TW; Crowley, G; Redmon, R; Groves, K; , others; Published by: Journal of Geophysical Research: Space Physics Published on: |
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Sahai, Yogeshwar; de Jesus, Rodolfo; Fagundes, Paulo; de Abreu, Alessandro; Crowley, Geoff; Pillat, Valdir; Guede, Jose; Bittencourt, Jose; Published by: 38th COSPAR Scientific Assembly Published on: |
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Evolved Tiny Ionospheric Photometer (ETIP): A sensor for ionospheric specification Budzien, Scott; Chua, Damien; Coker, Clayton; Dandenault, Patrick; Dymond, Kenneth; Nicholas, Andrew; Doe, Richard; Crowley, Geoff; Published by: To address the requirements for space weather sensors, and includes adequate flexibility for accommodation on a range of future flight opportunities, including microsatellite constellations Published on: |
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Comparison of the Hill–Siscoe polar cap potential theory with the Weimer and AMIE models The magnetic storm on November 2004 was characterized by a high solar wind pressure and thus offers a unique opportunity to test the Hill–Siscoe formula (H–S) for the polar cap potential (PCP). To estimate the polar cap potential, we use the Weimer Statistical Convection Model (WCM), and the Assimilative Mapping of Ionospheric Electrodynamics Model (AMIE), based on ingestion of a number of data sets. H–S is in excellent agreement with WCM, and with AMIE during times when DMSP is used in the latter. The implication is that the AMIE conductivity model yields conductivities that are too high by a factor of 2–3. Both H–S and WCM display saturation effects, although WCM is more severe. The two methods track well until an IEF of about 20mV/m occurs, where H–S continues to increase while WCM levels off. Even at high electric field values, the pressure increases the denominator of the H–S formula by 60\%, keeping the potential lower than its saturation value. There are several H–S points above 250kV, even up to 400kV, that are not found in WCM and occur right after a rapid transition from Bz north to south. For Bz north, we find evidence for a saturation effect on the PCP at large IEF, little effect as a function of solar wind velocity, and an increase of the PCP with increasing pressure. This seems to rule out viscous interaction but may involve geometric changes in the high-altitude polar cusp that affect recombination there for Bz north. Kelley, Michael; Crowley, Geoffrey; Weimer, Daniel; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: YEAR: 2010 DOI: https://doi.org/10.1016/j.jastp.2009.02.011 Magnetic storm; Polar cap potential; Hill–Siscoe formula; solar wind |
| 2009 |
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On the origin of pre-reversal enhancement of the zonal equatorial electric field Kelley, MC; Ilma, RR; Crowley, G; Published by: Published on: |
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Large-scale instabilities of the lower thermosphere during an active period Published by: Journal of Geophysical Research: Space Physics Published on: |
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Physics-Based Modeling of Space Weather in the Ionosphere and Thermosphere Published by: Published on: |
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Sahai, Y; Fagundes, PR; De Jesus, R; De Abreu, AJ; Crowley, G; Pillat, VG; Guarnieri, FL; , Abalde; Bittencourt, JA; Published by: Published on: |
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Global Ultra-Violet Ionosphere-Thermosphere Observatory (GUVITO) Curtis, N; Crowley, G; Christensen, AB; Paxton, LJ; Robichaud, J; Barry, MA; Bust, GS; Published by: Published on: |
| 2008 |
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Periodic modulations in thermospheric composition by solar wind high speed streams Crowley, G.; Reynolds, A.; Thayer, J.; Lei, J.; Paxton, L.; Christensen, A.; Zhang, Y.; Meier, R.; Strickland, D.; Published by: Geophysical Research Letters Published on: Jan-01-2008 YEAR: 2008 DOI: 10.1029/2008GL035745 |
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Disturbed O/N 2 ratios and their transport to middle and low latitudes Published by: Washington DC American Geophysical Union Geophysical Monograph Series Published on: |
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Mapping the time-varying distribution of high-altitude plasma during storms Published by: Washington DC American Geophysical Union Geophysical Monograph Series Published on: |