Bibliography
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Found 34 entries in the Bibliography.
Showing entries from 1 through 34
| 2022 |
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The latitudinal and temporal variation of atomic oxygen (O) is opposite between the empirical model, NRLMSISE-00 (MSIS) and the whole atmosphere model, whole atmosphere community climate model with thermosphere and ionosphere extension (WACCM-X) at 97–100 km. Atomic Oxygen from WACCM-X has maxima at solstices and summer mid-high latitudes, similar to [O] from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). We use the densities and dynamics from WACCM-X to drive the Global Ionosphere Thermosphere Model (GITM) at its lower boundary and compare it with the MSIS driven GITM. We focus on the differences in the modeling of the thermospheric and ionospheric semiannual oscillation (T-I SAO). Our results reveal that driving GITM with WACCM-X causes the T-I SAO to maximize around solstices, opposite to when MSIS is used. This is because the global mixing in GITM during solstices is not strong enough to decrease the solstitial [O] densities below the equinoctial values between mesosphere and lower thermosphere (MLT) and upper thermosphere. Larger summer [O] in the MLT leads to the accumulation of [O] at lower latitudes in the thermosphere due to weaker meridional transport, which further increases the amplitude of the oppositely phased SAO. WACCM-X itself has the right phase of SAO in the upper thermosphere but wrong at lower altitudes. The exact mechanisms that can correct the phase of T-I SAO in GITM while using SABER-like [O] in the MLT are currently unknown and warrant further investigation. We suggest mechanisms that can reduce the solstitial maxima in the lower thermosphere, for example, stronger interhemispheric meridional winds, stronger residual circulation, seasonal variations in eddy diffusion, and momentum from breaking gravity waves. Malhotra, Garima; Ridley, Aaron; , Jones; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2022 DOI: 10.1029/2021JA029320 global ionosphere thermosphere modeling; semiannual oscillation; thermospheric and ionospheric SAO; thermospheric spoon mechanism; vertical coupling of thermosphere with lower atmosphere; whole atmosphere community climate model with thermosphere and ionosphere extension (WACCM-X) |
| 2021 |
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FTA: A Feature Tracking Empirical Model of Auroral Precipitation The Feature Tracking of Aurora (FTA) model was constructed using 1.5 years of Polar Ultraviolet Imager data and is based on tracking a cumulative energy grid in 96 magnetic local time (MLT) sectors. The equatorward boundary, poleward boundary, and 19 cumulative energy bins are tracked with the energy flux and the latitudinal position. With AE increasing, the equatorward boundary moves to lower latitudes everywhere, while the poleward boundary moves poleward in the 2300–0300 MLT region and equatorward in other MLT sectors. This results in the aurora getting wider on the nightside and becoming narrower on the dayside. The peak intensity of the aurora in each MLT sector is almost linearly related to AE, with the global peak moving from pre-midnight to post-midnight as geomagnetic activity increases. Ratios between the Lyman-Birge-Hopfield-long and -short models allow the average energy to be calculated. Predictions from the FTA and two other auroral models were compared to the measurements by the Defense Meteorological Satellite Program Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) on March 17, 2013. Among the three models, the FTA model specified the most confined patterns with the highest energy flux, agreeing with the spatial and temporal evolution of SSUSI measurements better and predicted auroral power (AP) better during higher activity levels (SSUSI AP \textgreater 20 GW). The Fuller-Rowell and Evans (1987) and FTA models specified very similar average energy compared with SSUSI measurements, doing slightly better by ∼1 keV than the OVATION Prime model. Wu, Chen; Ridley, Aaron; DeJong, Anna; Paxton, Larry; Published by: Space Weather Published on: YEAR: 2021 DOI: 10.1029/2020SW002629 Auroral Precipitation Model; cumulative energy bins; data-model comparisons; M-I coupling; statistical analyses |
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Mlynczak, Martin; Yee, Jeng-Hwa; Paxton, Larry; Ridley, Aaron; Published by: Published on: |
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Carter, Jennifer; Samsonov, AA; Milan, Stephen; Branduardi-Raymont, Graziella; Ridley, Aaron; Paxton, Larry; Anderson, Brian; Waters, Colin; Edwards, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: |
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Carter, Jennifer; Samsonov, Andrey; Milan, Stephen; Branduardi-Raymont, Graziella; Ridley, Aaron; Paxton, Larry; Anderson, Brian; Waters, Colin; Edwards, Thomas; Published by: Earth and Space Science Open Archive ESSOAr Published on: |
| 2020 |
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Malhotra, Garima; Ridley, Aaron; Marsh, Daniel; Wu, Chen; Paxton, Larry; Mlynczak, Martin; Published by: Journal of Geophysical Research: Space Physics Published on: |
| 2019 |
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The datasets that are used in these study for comparisons are GPS, GUVI, COSMIC and GRACE observations. Malhotra, Garima; Ridley, Aaron; Marsh, Daniel; Wu, Chen; Paxton, Larry; Published by: Published on: |
| 2018 |
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Malhotra, Garima; Ridley, Aaron; Marsh, Daniel; Wu, Chen; Paxton, Larry; Published by: Published on: |
| 2017 |
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The effect of ring current electron scattering rates on magnetosphere-ionosphere coupling This simulation study investigated the electrodynamic impact of varying descriptions of the diffuse aurora on the magnetosphere-ionosphere (M-I) system. Pitch angle diffusion caused by waves in the inner magnetosphere is the primary source term for the diffuse aurora, especially during storm time. The magnetic local time (MLT) and storm-dependent electrodynamic impacts of the diffuse aurora were analyzed using a comparison between a new self-consistent version of the Hot Electron Ion Drift Integrator with varying electron scattering rates and real geomagnetic storm events. The results were compared with Dst and hemispheric power indices, as well as auroral electron flux and cross-track plasma velocity observations. It was found that changing the maximum lifetime of electrons in the ring current by 2\textendash6\ h can alter electric fields in the nightside ionosphere by up to 26\%. The lifetime also strongly influenced the location of the aurora, but the model generally produced aurora equatorward of observations. Perlongo, N.; Ridley, A.; Liemohn, M.; Katus, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023679 |
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Malhotra, Garima; Ridley, Aaron; Marsh, Daniel; Wu, Chen; Paxton, Larry; Published by: Published on: |
| 2016 |
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Using a three-dimensional nonhydrostatic general circulation model, we investigate the response of the thermosphere–ionosphere system to the 5–6 August 2011 major geomagnetic Yi\ugit, Erdal; Frey, Harald; Moldwin, Mark; Immel, Thomas; Ridley, Aaron; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: YEAR: 2016 DOI: 10.1016/j.jastp.2015.10.002 |
| 2015 |
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Exploring Geospace: Novel Instruments and New Opportunities II Posters Paxton, Larry; Ridley, Aaron; Rowland, Douglas; Vierinen, Juha; Published by: Published on: |
| 2014 |
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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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Strong ionospheric field-aligned currents for radial interplanetary magnetic fields The present work has investigated the configuration of field-aligned currents (FACs) during a long period of radial interplanetary magnetic field (IMF) on 19 May 2002 by using high-resolution and precise vector magnetic field measurements of CHAMP satellite. During the interest period IMF By and Bz are weakly positive and Bx keeps pointing to the Earth for almost 10 h. The geomagnetic indices Dst is about -40 nT and AE about 100 nT on average. The cross polar cap potential calculated from Assimilative Mapping of Ionospheric Electrodynamics and derived from DMSP observations have average values of 10\textendash20 kV. Obvious hemispheric differences are shown in the configurations of FACs on the dayside and nightside. At the south pole FACs diminish in intensity to magnitudes of about 0.1 μA/m2, the plasma convection maintains two-cell flow pattern, and the thermospheric density is quite low. However, there are obvious activities in the northern cusp region. One pair of FACs with a downward leg toward the pole and upward leg on the equatorward side emerge in the northern cusp region, exhibiting opposite polarity to FACs typical for duskward IMF orientation. An obvious sunward plasma flow channel persists during the whole period. These ionospheric features might be manifestations of an efficient magnetic reconnection process occurring in the northern magnetospheric flanks at high latitude. The enhanced ionospheric current systems might deposit large amount of Joule heating into the thermosphere. The air densities in the cusp region get enhanced and subsequently propagate equatorward on the dayside. Although geomagnetic indices during the radial IMF indicate low-level activity, the present study demonstrates that there are prevailing energy inputs from the magnetosphere to both the ionosphere and thermosphere in the northern polar cusp region. Wang, Hui; Lühr, Hermann; Shue, Jih-Hong; Frey, Harald.; Kervalishvili, Guram; Huang, Tao; Cao, Xue; Pi, Gilbert; Ridley, Aaron; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2014 YEAR: 2014 DOI: 10.1002/2014JA019951 air upwelling; field-aligned currents; radial interplanetary magnetic field |
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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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Understanding Hemispheric Asymmetry and Space Weather I Posters Paxton, Larry; Newell, Patrick; Stromme, Anja; Ridley, Aaron; Published by: Published on: |
| 2012 |
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Huang, Yanshi; Deng, Yue; Lei, Jiuhou; Ridley, Aaron; Lopez, Ramon; Allen, Robert; Butler, Brandon; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: Jan-02-2012 YEAR: 2012 DOI: 10.1016/j.jastp.2011.05.013 |
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Analyzing the hemispheric asymmetry in the thermospheric density response to geomagnetic storms The thermospheric densities derived by CHAMP/STAR accelerometer within the time period from 01 May 2001 to 31 December 2007 are utilized to investigate the hemispheric asymmetry in response to strong storm driving conditions. The geomagnetic storms of 03\textendash07 April 2004 are first studied since the storms occurred close to the vernal equinox, allowing the seasonal asymmetry to be eliminated to the greatest extent. The averaged density enhancements in the southern polar region were much larger than that in the northern polar region. The comparisons of density versus Dst and Apindex indicate a strong linear dependence with the slopes of the fitted lines in the southern hemisphere being 50\% greater than that in the northern hemisphere. This effect can possibly be attributed to the non-symmetric geomagnetic field. 102 storm events are used to conduct a statistical analysis. For each storm, a linear fit is made between the averaged mass density and theDst and Ap indices independently in each hemisphere. The seasonal variation of the intercepts and the slopes of the fitted lines are further explored. The baseline is strongly dependent on season, with the hemisphere receiving the larger amount of sunlight having larger density. The slopes showed considerable hemispheric differences around the vernal equinox yet no statistical differences around other seasons. It is speculated that competing mechanisms cancel each other during the solstices, while during the equinoxes, the lower magnetic field in the southern hemisphere may allow stronger ion flows, thereby causing more Joule heating. It is uncertain why the vernal equinox would be favored in this explanation though. Ercha, A.; Ridley, Aaron; Zhang, Donghe; Xiao, Zuo; Published by: Journal of Geophysical Research Published on: 08/2012 YEAR: 2012 DOI: 10.1029/2011JA017259 Geomagnetic storms; hemispheric asymmetry; thermospheric density |
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Importance of capturing heliospheric variability for studies of thermospheric vertical winds Using the Global Ionosphere Thermosphere Model with observed real-time heliospheric input data, the magnitude and variability of thermospheric neutral vertical winds are investigated. In order to determine the role of variability in the Interplanetary Magnetic Field (IMF) and solar wind density on the neutral wind variability, the heliospheric input data are smoothed. The effects of smoothing the IMF and solar wind and density on the vertical winds are simulated for the cases of no smoothing, 5-minute, and 12-minute smoothing. Various vertical wind acceleration terms, such as the nonhydrostatic acceleration, are quantified. Polar stereographic projections of the variabilities of vertical wind and ion flows are compared to highlight existing correlations. Overall, the smoother, that is, the less variable the IMF and solar wind parameters are, the weaker are the magnitude and the variability of the thermospheric vertical winds. Weaker IMF variability leads to smaller variability in ion flows, which in turn negatively impacts the variability and the magnitude of Joule heating. Small-scale temporal variation of the vertical wind acceleration, and thus the variability of the vertical wind, is dominated by the nonhydrostatic term that is controlled primarily by the temporal variation of the Joule heating, which in turn is related to ion flow variations that are shaped by the IMF in the high-latitude thermosphere. Wavelet analysis of the vertical wind data shows that gravity waves of \~5 and \~10-minute periods are more prominent when the model is run with high-resolution real-time IMF and solar wind data. Better capturing of the temporal variation of the IMF and solar wind parameters is crucial for modeling the variability and magnitude of thermospheric vertical winds. Erdal, Yi\u; Ridley, Aaron; Moldwin, Mark; Published by: Journal of Geophysical Research Published on: 07/2012 YEAR: 2012 DOI: 10.1029/2012JA017596 gravity waves; interplanetary magnetic field; Joule heating; magnetosphere-ionosphere-thermosphere coupling; nonhydrostatic general circulation model; vertical wind variability |
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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: |
| 2011 |
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Energy input into the upper atmosphere associated with high-speed solar wind streams in 2005 Deng, Yue; Huang, Yanshi; Lei, Jiuhou; Ridley, Aaron; Lopez, Ramon; Thayer, Jeffrey; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2010JA016201 |
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The Community-based Whole Magnetosphere Model The main goals of the Community-based Whole Magnetosphere Model CWMM project were to 1. Add more models to the Space Weather Modeling Framework SWMF, including a Published by: Published on: |
| 2010 |
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Talaat, Elsayed; Fuller-Rowell, Tim; Qian, Liying; Richards, Phil; Ridley, Aaron; Burns, Alan; Bernstein, Dennis; Chamberlin, Phillip; Fedrizzi, Mariangel; Hsieh, Syau-Yun; , others; Published by: 38th COSPAR Scientific Assembly Published on: |
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Ridley, AJ; Forbes, JM; Cutler, J; Nicholas, AC; Thayer, JP; Fuller-Rowell, TJ; Matsuo, T; Bristow, WA; Conde, MG; Drob, DP; , others; Published by: Published on: |
| 2008 |
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Global model comparison with Millstone Hill during September 2005 A direct comparison between simulation results from the Global Ionosphere Thermosphere Model (GITM) and measurements from the Millstone Hill incoherent scatter radar (ISR) during the month of September 2005 is presented. Electron density, electron temperature, and ion temperature results are compared at two altitudes where ISR data is the most abundant. The model results are produced, first using GITM running in one dimension, which allows comparison at the Millstone Hill location throughout the entire month. The model results have errors ranging from 20\% to 50\% over the course of the month. In addition, the F2 peak electron density (NmF2) and height of the peak (HmF2) are compared for the month. On average the model indicates higher peak electron densities as well as a higher HmF2. During the time period from 9 September through 13 September, the trends in the data are different than the trends in the model results. These differences are due to active solar and geomagnetic conditions during this time period. Three-dimensional (3-D) GITM results are presented during these active conditions, and it is found that the 3-D model results replicate the trends in the data more closely. GITM is able to capture the positive storm phase that occurred late on 10 September but has the most difficulty capturing the density depletion on 11 and 12 September that is seen in the data. This is probably a result of the use of statistical high-latitude and solar drivers that are not as accurate during storm time. Pawlowski, David; Ridley, Aaron; Kim, Insung; Bernstein, Dennis; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2008 DOI: https://doi.org/10.1029/2007JA012390 |
| 2007 |
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Paxton, LJ; Zhang, Y; Ridley, A; Christensen, A; DeMajistre, R; Schaefer, R; Morrison, D; Published by: Published on: |
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Neutral Wind Dynamics Measured Near the Poker Flat ISR Facility Hedden, RB; Meriwether, JW; Ridley, AJ; Published by: Published on: |
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Kozyra, JU; Cattell, CA; Clilverd, M; Evans, DS; Kavanagh, A; Liemohn, MW; Mende, SB; Paxton, LJ; Ridley, A; Soraas, F; Published by: Published on: |
| 2006 |
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Kozyra, JU; Barnes, R; Fox, NJ; Fox, PA; Kuznetsova, MM; Morrison, D; Pallamraju, D; , Papitashvili; Ridley, A; Talaat, ER; , others; Published by: Published on: |
| 2005 |
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Liemohn, Michael; Ridley, Aaron; Brandt, Pontus; Gallagher, Dennis; Kozyra, Janet; Ober, Daniel; Mitchell, Donald; Roelof, Edmond; DeMajistre, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: |
| 2004 |
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Liemohn, MW; Ridley, AJ; Kozyra, JU; Gallagher, DL; Henderson, MG; Denton, MH; Jahn, J; Roelof, EC; DeMajistre, R; Mitchell, DG; , others; Published by: Published on: |
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The Global Ionosphere Thermosphere Model results of the April 2002 storm Ridley, AJ; oth, G; Deng, Y; Kozyra, J; Immel, T; Paxton, L; Published by: Published on: |
| 2002 |
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, Sharber; Winningham, JD; Frahm, RA; Crowley, G; Ridley, AJ; Link, R; Published by: Advances in Space Research Published on: |
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Malhotra, Garima; Ridley, Aaron; Marsh, Daniel; Wu, Chen; Paxton, Larry; Published by: Published on: |
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