Bibliography
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Found 69 entries in the Bibliography.
Showing entries from 1 through 50
| 2022 |
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A paper A new method to subtract dayglow for auroral observation of SSUSI in LBH ranges based on the improved AURIC reports a new method to estimate the dayglow intensities in DMSP/SSUSI LBH bands using an improved AURIC model. It is claimed that the new method offers a better alternative than the SSUSI operational algorithm which uses a data based table. The paper showed a few examples and compared them with SSSUI operational results. The comparison indicated that the new method didn t offer any improvement and provided net auroral images with strong residual dayglow. On the other hand, the auroral oval can be easily recognized in the SSUSI data using the operational algorithm, despite some weak residual background which is expected due to count errors in the data. There are likely a few reasons why the method led to poor results: (1) dayglow contribution in SSUSI data covers solar zenith angles (SZA) beyond 90° and the AURIC model is limited to SZA ≤90°, (2) In addition to SZA, SSUSI radiances also depend on look angle (along and cross track pixels). Such a look-angle effect was apparently not reported in the paper. (3) The localized peaks in the plots (radiance versus SZA) were likely due to changes in solar EUV flux, SZA as well as noises caused Southern Atlantic Anomaly, MeV particles at sub-auroral latitude and glint in the Ap dependent data bins. The examples in the paper indicate that the new algorithm is not appropriate to estimate net SSUSI dayglow intensity. Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: mar YEAR: 2022 DOI: 10.1016/j.jastp.2022.105833 |
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Thermospheric density enhancement and limb O 130.4 nm radiance increase during geomagnetic storms We explore a connection between thermospheric density enhancement and increase in thermospheric O 130.4 nm radiance. We observe TIMED/GUVI enhancements in the limb 130.4 nm radiances at ∼400 and ∼520 km on the dayside during four intense geomagnetic storms in 2003 and 2004. The enhancements were well correlated with Dst and CHAMP total neutral density at 400 km which represents O density as O is the dominant species at those altitudes. At the 400 and 520 km altitudes, O 130.4 nm emissions are mostly created by two comparable sources: solar resonance scatter and photoelectron impact excitation. The coincident disk 130.4 nm radiances, mostly due to emissions below 200 km (peaked around 130–140 km), were not clearly correlated with the limb radiances. Because the limb 130.4 nm radiances depend on O density, solar EUV and 130.4 nm fluxes, variations in the limb 130.4 nm radiance respond mostly to changes in O density when the solar EUV and 130.4 nm fluxes are stable. This explains the good correlation (correlation coefficients up to 0.98) between the limb 130.4 nm radiance and CHAMP neutral density. Once a quantitative relationship is established between GUVI limb 130.4 nm radiance and neutral density under both quiet and disturbed conditions and at different altitude levels through empirical or radiative transfer modeling, the limb 130.4 nm radiances can be used to retrieve O density profiles in the upper thermosphere. Zhang, Yongliang; Paxton, Larry; Schaefer, R.; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: mar YEAR: 2022 DOI: 10.1016/j.jastp.2022.105830 FUV emission; Geomagentic storms; neutral density; thermosphere |
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Simultaneous Detection of Signatures of Conjugate Photoelectrons in the Ionosphere and Thermosphere We investigate the impact of conjugate photoelectrons (CPEs) on the topside (∼600 km altitude) ionosphere at low and midlatitudes using measurements of the ion temperature, density, and composition from the first Republic of China satellite during a period of the high to moderate solar activity (March 1999 to June 2004). Elevated ion temperatures and densities are observed in the dark Northern American-Atlantic sector during the December solstice and in the Australian sector during the June solstice. The oxygen ion fraction and density are also elevated at these locations. These observations indicate that photoelectrons from the conjugate hemisphere heat the local ionospheric plasma. The morphology of the ion temperature in the winter hemisphere is well represented by the solar zenith angle in the sunlit conjugate hemisphere. The CPE hypothesis for the observed ionospheric heating is confirmed by coincident nighttime enhancements of the far ultraviolet airglow measured by the Global Ultraviolet Imager onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. Kil, Hyosub; Paxton, Larry; Schaefer, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2022 DOI: 10.1029/2021JA030121 airglow; conjugate photoelectron; ion density; ion temperature |
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Thermospheric density enhancement and limb O 130.4 nm radiance increase during geomagnetic storms Zhang, Yongliang; Paxton, Larry; Schaefer, R; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: |
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Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: |
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Increased Sensitivity FUV Spectrographic Imager Schaefer, RK; Paxton, LJ; Zhang, Y; Kil, H; Liou, K; Published by: Published on: |
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Hemispheric Asymmetry in the Auroral Ionosphere-Thermosphere System Liou, K; Zhang, Y-L; Paxton, LJ; Kil, H; Schaefer, R; Published by: Published on: |
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Revisiting the November 2004 Superstorm: Lessons from the TIMED/GUVI Limb Observation We revisited the November 2004 superstorm by analyzing data from TIMED/GUVI, a FUV spectrograph imager. The GUVI 135.6 nm limb radiances at 520-km tangent altitude are mainly due to the O+ and electron radiative recombination and represent the daytime ionosphere density at the altitude. The 135.6 nm radiances clearly showed a signature of ionospheric equatorial arcs and their variations during the November 2004 magnetic superstorm. When an intense eastward Interplanetary Electric Field (IEF) occurred, the dayside equatorial arcs were enhanced and their latitude separation increased. The enhanced equatorial arcs were hemispherically symmetric or asymmetric in the region with non-depleted O/N2 or hemispherically asymmetric O/N2 depletion, respectively. When the O/N2 depletion reached the magnetic equator, there was no observable enhancement in the equatorial arcs regardless of the IEF conditions, indicating O/N2 conditions significantly modulated the variations in storm-time equatorial arcs. Zhang, Yongliang; Wang, Wenbin; Paxton, Larry; Schaefer, Robert; Huang, Chaosong; Published by: 44th COSPAR Scientific Assembly. Held 16-24 July Published on: |
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Thermospheric conditions associated with the loss of 40 Starlink satellites We analyzed far ultraviolet data from Defense Meteorological Satellite Program (DMSP)/Special Sensor Ultraviolet Spectrographic Imager (SSUSI) and Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI) and found significant changes in the thermospheric density and composition during the 3–5 February 2022 storm when 40 Starlink satellites started to re-enter the atmosphere associated with increased neutral drag at an altitude around 210 km. The standard NRLMSISE-00 model predicts only ∼5\% increase in neutral density at 210 km. TIMED/GUVI observations showed a clear increase in the thermospheric N2/O column density ratio and an increase in the nitric oxide (NO) column density, indicating high thermospheric density, and temperature Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Swartz, William; Published by: Space Weather Published on: YEAR: 2022 DOI: 10.1029/2022SW003168 |
| 2021 |
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Exploring the Upper Atmosphere In this chapter, we describe how we can understand the state of the upper atmosphere (the ionosphere, thermosphere, and aurora) using optical observations and how one produces a global view of the Earth s upper atmosphere from optical remote sensing, especially using far ultraviolet (FUV) wavelengths, to advance our understanding of the near Earth space environment. We examine the choice of optical signatures, the basic science behind the signatures, and the techniques for observations. Examples of the technique as applied to key geophysical processes are described and discussed for tracing the physical processes that alter the state variables (in particular, density, composition, and temperature) in the upper atmosphere. Applications of optical remote sensing will be discussed in terms of the challenges inherent in establishing a predictive capability of the global upper atmosphere system, including the high-latitude regions (such as the Arctic) where the structures of the thermosphere and ionosphere are complicated by strong coupling among the polar ionosphere, magnetosphere, and solar wind. Paxton, Larry; Zhang, Yongliang; Kil, Hyosub; Schaefer, Robert; Published by: Published on: YEAR: 2021 DOI: 10.1002/9781119815631.ch23 Earth space environment; far ultraviolet wavelengths; high-latitude regions; optical remote sensing; solar wind; upper atmosphere |
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Far Ultraviolet Hyperspectral Imager: NASA's TIMED/GUVI and DMSP SSUSI Paxton, Larry; Zhang, Yongliang; Schaefer, Robert; Kil, Hyosub; Wolven, Brian; Romeo, Giuseppe; Yonker, Justin; Published by: Published on: |
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Signatures of conjugate photoelectrons in the ionosphere and thermosphere Kil, Hyosub; Paxton, Larry; Schaefer, Robert; Huba, Joseph; Published by: Published on: |
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Exploring the Upper Atmosphere: Using Optical Remote Sensing Paxton, Larry; Zhang, Yongliang; Kil, Hyosub; Schaefer, Robert; Published by: Upper Atmosphere Dynamics and Energetics Published on: |
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Ionospheric and thermospheric contributions in TIMED/GUVI O 135.6 nm radiances Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: |
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Schaefer, Robert; Paxton, Larry; Zhang, Yongliang; Kil, Hyosub; Romeo, Giuseppe; Wolven, Brian; Yonker, Justin; Published by: Published on: |
| 2020 |
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This study investigates the origin of anomalous far ultraviolet emissions observed at night at the subauroral region by the Special Sensor Ultraviolet Spectrographic Imager on board the Defense Meteorological Satellite System-F16 satellite. The global distribution of the anomalous emission is derived using the measurements of the oxygen atom 130.4-nm emission in 2017. Our results show the extension of the anomalous emission from high latitudes to middle latitudes in the Northern American-Atlantic sector during the December solstice and in the Southern Australia-New Zealand sector during the June solstice. These observations indicate that the anomalous emission occurs in the winter hemisphere and is pronounced at locations close to the magnetic poles. The good agreement between the morphology of the anomalous emission and the predicted distribution of conjugate photoelectrons leads to the conclusion that the anomalous emissions are the signatures of conjugate photoelectrons. Kil, Hyosub; Schaefer, Robert; Paxton, Larry; Jee, Geonhwa; Published by: Geophysical Research Letters Published on: 01/2020 YEAR: 2020 DOI: 10.1029/2019GL086383 conjugate photoelectron; far ultraviolet emission; thermosphere; remote sensing data |
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Kil, Hyosub; Schaefer, Robert; Paxton, Larry; Jee, Geonhwa; Published by: Geophysical Research Letters Published on: |
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Estimation of solar EUV flux from TIMED/GUVI data Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: |
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A comparison of thermospheric FUV radiance and composition from TIMED, GOLD and ICON Zhang, Y; Paxton, LJ; Schaefer, RK; Eastes, R; McClintock, WE; Immel, TJ; Published by: Published on: |
| 2019 |
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This paper reports a preliminary result for estimating thermospheric temperature around 155 km from the N2 Lyman-Birge-Hopfield bands observed by TIMED/Global Ultraviolet Imager (GUVI). Atmospheric Ultraviolet Radiance Integrated Code model (Strickland et al., 1999, https://doi.org/10.1016/S0022-4073(98)00098-3) calculations indicate that the intensity ratio in the N2 Lyman-Birge-Hopfield (0,0) and (1,0) bands at 144.5- to 145.5- and 141.0- to 142.0-nm quasi-linearly depend on N2 rotational temperature. The observed ratios and the Atmospheric Ultraviolet Radiance Integrated Code results are used together to specify the thermospheric temperature around 155 km under sunlit conditions. The estimated temperature agrees fairly well with the neutral temperature at 155 km from WACCM-X model. The estimated temperature is also higher over the auroral oval and O/N2 depleted regions. Furthermore, meridional wave-like structures were clearly seen in the derived temperature and were likely caused by traveling atmospheric disturbances. Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2018JA026379 |
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Addressing O2R with the SSUSI Operational Space Sensor: Lessons Learned Schaefer, Robert; Paxton, Larry; Romeo, Giuseppe; Kil, Hyosub; Wolven, Brian; Zhang, Yongliang; Published by: Published on: |
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Storm-time variations in the thermsopheric density, composition and temperature. Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Published on: |
| 2018 |
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Storm-time variations of atomic nitrogen 149.3 nm emission Net radiances of atomic nitrogen emission line (N-149.3 nm) from the thermosphere are extracted from the FUV spectra observed by TIMED/GUVI on dayside at sunlit latitudes. During geomagnetic storms, the N-149.3 nm intensity is clearly enhanced in the locations where O/N2 depletion and nitric oxide (NO) enhancement are observed. The N-149.3 nm intensity is linearly and tightly correlated with N2 LBHS (140\textendash150 nm) radiance with a fixed LBHS/149.3 nm ratio of \~4.5, suggesting that dissociation of N2 is the dominant source of the N-149.3 nm emission. In the regions without storm disturbances, the N-149.3 nm intensities are closely correlated with solar EUV flux. Zhang, Y.; Paxton, L.J.; Morrison, D.; Schaefer, B.; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1016/j.jastp.2018.01.023 |
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SSUSI and SSUSI-Lite: Providing space situational awareness and support for over 25 years Paxton, Larry; Schaefer, Robert; Zhang, Yongliang; Kil, Hyosub; Hicks, John; Published by: Johns Hopkins APL Technical Digest Published on: |
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Nightime Ionosphere Climatology as observed by TIMED/GUVI Schaefer, Robert; Edenbaum, Harris; Published by: Published on: |
| 2017 |
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We present the Volume Emission Rate Tomography (VERT) technique for inverting satellite-based, multisensor limb and nadir measurements of atmospheric ultraviolet emission to create whole-orbit reconstructions of atmospheric volume emission rate. The VERT approach is more general than previous ionospheric tomography methods because it can reconstruct the volume emission rate field irrespective of the particular excitation mechanisms (e.g., radiative recombination, photoelectron impact excitation, and energetic particle precipitation in auroras); physical models are then applied to interpret the airglow. The technique was developed and tested using data from the Special Sensor Ultraviolet Limb Imager and Special Sensor Ultraviolet Spectrographic Imager instruments aboard the Defense Meteorological Satellite Program F-18 spacecraft and planned for use with upcoming remote sensing missions. The technique incorporates several features to optimize the tomographic solutions, such as the use of a nonnegative algorithm (Richardson-Lucy, RL) that explicitly accounts for the Poisson statistics inherent in optical measurements, capability to include extinction effects due to resonant scattering and absorption of the photons from the lines of sight, a pseudodiffusion-based regularization scheme implemented between iterations of the RL code to produce smoother solutions, and the capability to estimate error bars on the solutions. Tests using simulated atmospheric emissions verify that the technique performs well in a variety of situations, including daytime, nighttime, and even in the challenging terminator regions. Lastly, we consider ionospheric nightglow and validate reconstructions of the nighttime electron density against Advanced Research Project Agency (ARPA) Long-range Tracking and Identification Radar (ALTAIR) incoherent scatter radar data. Hei, Matthew; Budzien, Scott; Dymond, Kenneth; Nicholas, Andrew; Paxton, Larry; Schaefer, Robert; Groves, Keith; Published by: Radio Science Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2015RS005887 |
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Far ultraviolet instrument technology The far ultraviolet (FUV) spectral range (from about 115 nm to 180 nm) is one of the most useful spectral regions for characterizing the upper atmosphere (thermosphere and ionosphere). The principal advantages are that there are FUV signatures of the major constituents of the upper atmosphere as well as the signatures of the high-latitude energy inputs. Because of the absorption by thermospheric O2, the FUV signatures are seen against a \textquotedblleftblack\textquotedblright background, i.e., one that is not affected by ground albedo or clouds and, as a consequence, can make useful observations of the aurora during the day or when the Moon is above the horizon. In this paper we discuss the uses of FUV remote sensing, summarize the various techniques, and discuss the technological challenges. Our focus is on a particular type of FUV instrument, the scanning imaging spectrograph or SIS: an instrument exemplified by the Defense Meteorological Satellite Program Special Sensor Ultraviolet Imager and Thermosphere Ionosphere Mesosphere Energetics and Dynamics Global Ultraviolet Imager. The SIS combines spatial imaging of the disk with limb profiles as well as spectral information at each point in the scan. Paxton, Larry; Schaefer, Robert; Zhang, Yongliang; Kil, Hyosub; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/jgra.v122.210.1002/2016JA023578 |
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A New More Accurate Calibration for TIMED/GUVI Schaefer, RK; Aiello, J; Wolven, BC; Paxton, LJ; Romeo, G; Zhang, Y; Published by: Published on: |
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TIMED/GUVI Observations of Aurora, Ionosphere, Thermosphere and Solar EUV Variations Zhang, Yongliang; Paxton, Larry; Schaefer, Robert; Published by: Published on: |
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Monitoring Geospace Variations Through Remote Sensing III Posters Zhang, Yongliang; Paxton, Larry; Sibeck, David; Schaefer, Robert; Published by: Published on: |
| 2016 |
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Schaefer, Robert; Paxton, Larry; Zhang, Yongliang; Published by: Published on: |
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Validating Local Responses in OVATION Prime-2013 and OVATION-SM with DMSP SSUSI Mitchell, Elizabeth; Schaefer, Robert; Paxton, Larry; Published by: Published on: |
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Structure and Variability in the Ionosphere using DMSP/SSUSI and TIMED/GUVI Data Bruntz, Robert; Paxton, Larry; Kil, Hyosub; Schaefer, Robert; Zhang, Yongliang; Miller, Ethan; Published by: Published on: |
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Selby, Christina; Paxton, LJ; Schaefer, RK; Ogorzalek, B; Romeo, G; Wolven, B; Hsieh, SY; Published by: Published on: |
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NASA Timed Guvi and Dmsp Ssusi Observations of the St. Patricks Day Storm of Paxton, Larry; Zhang, Yongliang; Kil, Hyosub; Mitchell, Elizabeth; Schaefer, Robert; Published by: 41st COSPAR Scientific Assembly Published on: |
| 2015 |
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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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UV Observations of Hemispheric Asymmetry Schaefer, Robert; Paxton, Larry; Wolven, Brian; Zhang, Yongliang; Romeo, Giuseppe; Published by: Published on: |
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GUVI and SSUSI Observations of the St. Patrick's Day Storms Paxton, Larry; Schaefer, Robert; Zhang, Yongliang; Bust, Gary; Kil, Hyosub; Published by: Published on: |
| 2014 |
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Paxton, LJ; Schaefer, RK; Zhang, Y; Bust, GS; Kil, H; Published by: Published on: |
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Gjerloev, Jesper; Schaefer, Robert; Paxton, Larry; Zhang, Yongliang; Published by: Published on: |
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Ionospheric Data Assimilation from a Data Provider's Perspective Schaefer, Robert; Paxton, Larry; Bust, G; Zhang, Yongliang; Romeo, Giuseppe; Comberiate, Joseph; Gelinas, Lynette; Published by: Published on: |
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EMIC Wave Induced Radiation Belt Losses and Proton Aurora Erlandson, Robert; Paxton, Larry; Zhang, Yongliang; Schaefer, Robert; Published by: Published on: |
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Specification of Auroral Ionospheric Conductances Using SSUSI and GUVI UV Imagery Paxton, Larry; Zhang, Yongliang; Schaefer, Robert; Weiss, Michele; Miller, Ethan; Published by: Published on: |
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Operational Space Weather Needs-Perspectives from SEASONS 2014 Comberiate, Joseph; Kelly, MA; Paxton, Larry; Schaefer, Robert; Bust, Gary; Sotirelis, Thomas; Fox, Nicola; Published by: Published on: |
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Establishing the connection between crowd-sourced data and decision makers Paxton, Larry; Swartz, W; Strong, Shadrian; Nix, MG; Schaefer, Robert; Weiss, Michele; Published by: Published on: |
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Schaefer, Robert; Paxton, Larry; Romeo, Giuseppe; Wolven, Brian; Zhang, Yongliang; Comberiate, Joseph; Published by: Published on: |
| 2013 |
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Multi-Instrument Observations at High Latitudes Miller, E; Paxton, L; Schaefer, RK; Weiss, M; Wolven, BC; Zhang, Y; Published by: Published on: |
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Observing the mid-and low-latitude ionosphere-global UV remote sensing Paxton, LJ; Kil, H; Miller, ES; Comberiate, J; Schaefer, RK; Zhang, Y; Team, GUVI; , others; Published by: Published on: |
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Schaefer, RK; Wolven, BC; Paxton, L; Romeo, G; Selby, C; Hsieh, SW; Published by: Published on: |
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UV Remote Sensing Data Products-Turning Data Into Knowledge Weiss, M; Paxton, L; Schaefer, RK; Comberiate, J; Hsieh, SW; Romeo, G; Wolven, BC; Zhang, Y; Published by: Published on: |
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