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Found 644 entries in the Bibliography.

Showing entries from 1 through 50

2022

Comments on “A new method to subtract dayglow for auroral observation of SSUSI in LBH ranges based on the improved AURIC” by Wang et al. (2021)

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

AURORA; dayglow; far ultraviolet emission

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

FUV observations of variations in thermospheric composition and topside ionospheric density during the November 2004 magnetic superstorm

We revisited the November 2004 superstorm by analyzing TIMED/GUVI data. The 135.6 nm limb radiances at 520-km 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 O/N2 depletion reached the magnetic equator, there was no observable enhancement in the equatorial arcs regardless the IEF conditions, indicating O/N2 condition significantly modulated the variations in storm-time equatorial arcs. GUVI observations also showed that a westward IEF and/or disturbance dynamo electric field could also suppress the dayside equatorial arcs.

Zhang, Yongliang; Paxton, LarryJ.; Huang, Chaosong; Wang, Wenbin;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: feb

YEAR: 2022 DOI: 10.1016/j.jastp.2022.105832

geomagnetic storm; penetration electric field; Thermosperic composition; topside ionosphere

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

Transpolar Arcs: Seasonal Dependence Identified by an Automated Detection Algorithm

Transpolar arcs (TPAs) are auroral features that occur polewards of the main auroral oval suggesting that the magnetosphere has acquired a complicated magnetic topology. They are primarily a northward interplanetary magnetic field (IMF) auroral phenomenon, and their formation and evolution have no single explanation that is unanimously agreed upon. An automated detection algorithm has been developed to detect the occurrence of TPAs in UV images captured from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument onboard the Defense Meteorological Satellite Program (DMSP) spacecraft, in order to further study their occurrence. Via this detection algorithm TPAs are identified as a peak in the average radiance intensity poleward of 12.5° colatitude, in two or more of the wavelengths/bands sensed by SSUSI. Using the detection algorithm for the years 2010 to 2016, over 5000 images containing TPAs are identified. The occurrence of these TPAs shows a seasonal dependence, with more arcs being visible in the winter hemisphere. The orbital plane of DMSP has been investigated as a possible explanation of the dependences in the results of the detection algorithm. For the spacecraft of interest this leads to a preferential observation of the northern hemisphere with the detection algorithm missing TPAs in the southern hemisphere around 01–06 UT. No seasonal bias has been found for these spacecraft. We discuss the ramifications of these findings in terms of proposed TPA generation mechanisms and suggest reasons for the seasonal dependence including it being a reflection of probability of seeing TPAs due to visibility.

Bower, G.; Milan, S.; Paxton, L.; Imber, S.;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2022 DOI: 10.1029/2021JA029743

auroras; magnetosphere; transpolar arc

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:

YEAR: 2022 DOI:

Comments on “A new method to subtract dayglow for auroral observation of SSUSI in LBH ranges based on the improved AURIC” by Wang et al.(2021)

Zhang, Yongliang; Paxton, Larry; Schaefer, Robert;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on:

YEAR: 2022 DOI:

Occurrence statistics of horse collar aurora

Bower, Gemma; Milan, Stephen; Paxton, Larry; Anderson, Brian;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2022 DOI:

Empirical modelling of SSUSI derived auroral ionization rates

Bender, Stefan; Espy, Patrick; Paxton, Larry;

Published by: Published on:

YEAR: 2022 DOI:

The origin of midlatitude plasma depletions detected during the 12 February 2000 and 29 October 2003 geomagnetic storms

Kil, Hyosub; Chang, Hyeyeon; Lee, Woo; Paxton, Larry; Sun, Andrew; Lee, Jiyun;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2022 DOI:

Two different properties of ionospheric perturbations detected in the vicinity of the Korean Peninsula after the Hunga-Tonga volcanic eruption on 15 January 2022

Hong, Junseok; Kil, Hyosub; Lee, Woo; Kwak, Young-Sil; Choi, Byung-Kyu; Paxton, Larry;

Published by: Published on:

YEAR: 2022 DOI:

Novel Observations of the Aurora (NOA) from New Platforms

Paxton, LJ; Hibbitts, CA; Swartz, WH;

Published by: Published on:

YEAR: 2022 DOI:

Increased Sensitivity FUV Spectrographic Imager

Schaefer, RK; Paxton, LJ; Zhang, Y; Kil, H; Liou, K;

Published by: Published on:

YEAR: 2022 DOI:

Statistics of transpolar arcs identified by an automated detection algorithm

Bower, Gemma; Milan, Steve; Paxton, Larry; Imber, Suzie;

Published by: Published on:

YEAR: 2022 DOI:

Height-integrated polar cap conductances during an average substorm

Carter, Jennifer; Milan, Steven; Lester, Mark; Forsyth, Colin; Paxton, Larry; Gjerloev, Jesper; Anderson, Brian;

Published by: Published on:

YEAR: 2022 DOI:

Lobe Reconnection and Cusp-Aligned Auroral Arcs

Abstract Following the St. Patrick s Day (17 March) geomagnetic storm of 2013, the interplanetary magnetic field had near-zero clock angle for almost two days. Throughout this period multiple cusp-aligned auroral arcs formed in the polar regions; we present observations of, and provide a new explanation for, this poorly understood phenomenon. The arcs were observed by auroral imagers onboard satellites of the Defense Meteorological Satellite Program. Ionospheric flow measurements and observations of energetic particles from the same satellites show that the arcs were produced by inverted-V precipitation associated with upward field-aligned currents (FACs) at shears in the convection pattern. The large-scale convection pattern revealed by the Super Dual Auroral Radar Network and the corresponding FAC pattern observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment suggest that dual-lobe reconnection was ongoing to produce significant closure of the magnetosphere. However, we propose that once the magnetosphere became nearly closed complicated lobe reconnection geometries arose that produced interleaving of regions of open and closed magnetic flux and spatial and temporal structure in the convection pattern that evolved on timescales shorter than the orbital period of the DMSP spacecraft. This new model naturally explains many features of cusp-aligned arcs, including why they focus in from the nightside toward the cusp region.

Milan, S.; Bower, G.; Carter, J.; Paxton, L.; Anderson, B.; Hairston, M.;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2022 DOI: https://doi.org/10.1029/2021JA030089

Hemispheric Asymmetry in the Auroral Ionosphere-Thermosphere System

Liou, K; Zhang, Y-L; Paxton, LJ; Kil, H; Schaefer, R;

Published by: Published on:

YEAR: 2022 DOI:

Large-Scale Traveling Atmospheric and Ionospheric Disturbances Observed in GUVI With Multi-Instrument Validations

This study presents multi-instrument observations of persistent large-scale traveling ionosphere/atmospheric disturbances (LSTIDs/LSTADs) observed during moderately increased auroral electrojet activity and a sudden stratospheric warming in the polar winter hemisphere. The Global Ultraviolet Imager (GUVI), Gravity field and steady-state Ocean Circulation Explorer, Scanning Doppler Imaging Fabry–Perot Interferometers, and the Poker Flat Incoherent Scatter Radar are used to demonstrate the presence of LSTIDs/LSTADs between 19 UT and 5 UT on 18–19 January 2013 over the Alaska region down to lower midlatitudes. This study showcases the first use of GUVI for the study of LSTADs. These novel GUVI observations demonstrate the potential for the GUVI far ultraviolet emissions to be used for global-scale studies of waves and atmospheric disturbances in the thermosphere, a region lacking in long-term global measurements. These observations typify changes in the radiance from around 140 to 180 km, opening a new window into the behavior of the thermosphere.

Bossert, Katrina; Paxton, Larry; Matsuo, Tomoko; Goncharenko, Larisa; Kumari, Komal; Conde, Mark;

Published by: Geophysical Research Letters Published on:

YEAR: 2022 DOI: 10.1029/2022GL099901

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:

YEAR: 2022 DOI:

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

Solar cycle, seasonal, and dawn-to-dusk variations of the hydrogen in the upper thermosphere

Atomic hydrogen is one of the least-understood atmospheric constituents whose distribution is important for the studies of aeronomy and magnetospheric physics. Using 6 years of space-based daytime Lyman-α observations from 2002 to 2007, we quantify the solar cycle, seasonal, and dawn-to-dusk variations of the H density in the upper thermosphere. Our results show evident dawn-dusk asymmetry of the exobase H density that decreases nearly linearly from dawn to dusk. The observed asymmetry in terms of the dawn-dusk density ratio decreases with declining solar activity and is larger in summer than in other seasons. Such variations are not predicted by the NRLMSISE-00 model and the NRLMSIS 2.0 model. Those models predict the opposite solar cycle trend and little seasonal variation of the degree of asymmetry.

Wan, Changan; Qin, Jianqi; Paxton, Larry;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2022 DOI: 10.1029/2022JA030504

2021

Periodic Variations in Solar Wind and Responses of the Magnetosphere and Thermosphere in March 2017

TIMED/GUVI observed thermospheric column ∑O/N2 depletion in both hemispheres between March 1 and 21, 2017 which was caused by large periodic variations in interplanetary magnetic field (IMF) and a high solar wind speed, likely in a solar wind. The dominant periods seen in the solar wind and magnetosphere coupling function (CF) were around 1.9, 3.0, 4.7, 7.6, 14.0 and 22.0 h on March 1 and 2. The major AE variations were around 3.0, 4.7, 7.6, 10.7, 14.0 and 22.0 h. Auroral hemispheric power (HP) also showed periodic variations similar to that of AE, except for the absence of the 3.0 h variation due to a low sampling rate in HP data. SymH data didn t show the periodic variations seen in AE but a weak 12-h periodic variation which was seen in the solar wind dynamic pressure. A weak AE and HP variation at 10.7-h period was not observed in CF or any individual solar wind parameters or IMF components. These results suggest that (a) the oscillating IMF pumped energy and mass periodically into the magnetosphere and the polar ionosphere, creating a long lasting (20-days) storm and O/N2 depletion, (b) the high latitude AE and HP responded to the solar wind and IMF variations directly, (c) SymH did not show any direct periodic responses, likely due to the fact that the ring current response resulted from the cumulative effect of solar wind and IMF drivers, (d) the 10.7-h variations in AE and HP were likely due to magnetospheric internal processes.

Zhang, Yongliang; Paxton, Larry; Wang, Wenbin; Huang, Chaosong;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2021 DOI: 10.1029/2021JA029387

AE index; geomagnetic storm; hemispheric power; periodic variation; solar wind and magnetosphere coupling; thermospheric composition

Storm-Time Neutral Composition Changes in the Upper Atmosphere

During geomagnetic storms, energy inputs, such as particle precipitation and Joule heating from the magnetosphere and solar wind, create significant disturbances in the upper atmosphere in the form of changes in the thermospheric density and temperature and, more important, composition, such as O/N 2 column density ratio, nitric oxide (NO) density, and atomic nitrogen (N) density. The composition changes control the ionosphere and have a feedback effect on thermospheric temperature and density due to a cooling effect of enhanced NO 5.3 μm radiation. We review the methods of deriving the composition information from far ultraviolet (FUV) observations as well as the signatures of the major features in the storm-time composition variations such as O/N 2 depletion and enhancement, NO and N enhancement, corotation of the O/N 2 depletion, seasonal and hemispheric asymmetry, traveling atmospheric disturbance (TAD) and its connection to traveling ionosphere disturbance (TID), and temperature increase in O/N 2 depleted regions and their interaction with TADs. A FUV spectrograph imager is a cost-effective instrument suitable for low Earth orbit missions and can monitor the response of the near-Earth space environment including the thermosphere, ionosphere, and aurora (magnetosphere) to solar wind forcing as well as forcing from low atmosphere.

Zhang, Yongliang; Paxton, Larry;

Published by: Published on:

YEAR: 2021 DOI: 10.1002/9781119815631.ch7

far ultraviolet observations; storm-time neutral composition changes; thermospheric nitric oxide variations; traveling atmospheric disturbance; traveling ionosphere disturbance; upper atmosphere

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

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

Global distribution of nighttime MSTIDs and its association with E region irregularities seen by CHAMP satellite

Lee, Woo; Kil, Hyosub; Paxton, Larry;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2021 DOI:

Space Physics and Aeronomy, Upper Atmosphere Dynamics and Energetics

Paxton, Larry;

Published by: Published on:

YEAR: 2021 DOI:

Twenty Years of Space-Based Observations of the Ionosphere-Thermosphere-Mesosphere System and a View to the Future

Mlynczak, Martin; Yee, Jeng-Hwa; Paxton, Larry; Ridley, Aaron;

Published by: Published on:

YEAR: 2021 DOI:

Field-Aligned Current During an Interval of BY-Dominated Interplanetary-Field; Modeled-to-Observed Comparisons

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:

YEAR: 2021 DOI:

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:

YEAR: 2021 DOI:

Non-storm time thermospheric O/N 2 depletion and NO enhancement

Zhang, Yongliang; Paxton, Larry; Wang, Wenbin; Huang, Chaosong;

Published by: Published on:

YEAR: 2021 DOI:

Investigating Geocoronal Absorption for Wavelength Calibration of Sounding Rockets

Donders, Nicolas; Winebarger, Amy; Kankelborg, Charles; Vigil, Genevieve; Paxton, Larry; Zank, Gary;

Published by: Published on:

YEAR: 2021 DOI:

Progresses and Challenges to specifying the IT system during weak storms

Deng, Yue; Heelis, Roderick; Paxton, Larry; Lyons, Larry; Nishimura, Toshi; Zhang, Shunrong; Bristow, Bill; Maute, Astrid; Sheng, Cheng; Zhu, Qingyu; , others;

Published by: Published on:

YEAR: 2021 DOI:

Space Physics and Aeronomy: Space Physics and Aeronomy, Solar Physics and Solar Wind

Raouafi, Nour; Vourlidas, Angelos; Zhang, Yongliang; Paxton, Larry;

Published by: Published on:

YEAR: 2021 DOI:

Signatures of conjugate photoelectrons in the ionosphere and thermosphere

Kil, Hyosub; Paxton, Larry; Schaefer, Robert; Huba, Joseph;

Published by: Published on:

YEAR: 2021 DOI:

Thermospheric ionization from auroral particle precipitation observed by the SSUSI satellite instruments

Solar, auroral, and radiation belt electrons enter the atmosphere at polar regions leading to ionization and affecting its chemistry. Climate models usually parametrize this ionization and the related changes in chemistry based on satellite particle measurements. Precise measurements of the particle and energy influx into the upper atmosphere are difficult because they vary substantially in location and time. Widely used particle data are derived from the POES and GOES satellite measurements which provide electron and proton spectra. We present the electron energy and flux measurements from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instruments on board the Defense Meteorological Satellite Program (DMSP) satellites. This formation of now three operating satellites observes the auroral zone in the UV from which electron energies and fluxes are inferred in the range from 2 keV to 20 keV. We use these observed electron energies and fluxes to calculate ionization rates and electron densities in the upper mesosphere and lower thermosphere (≈ 80–200 km). We present our validation study of the SSUSI-derived electron densities to those measured by the ground-based EISCAT radar stations. We find that with the current standard parametrizations, the SSUSI-derived auroral electron densities (90–150 km) agree well with EISCAT measurements, with differences between +/- 20% for F18, and +/- 50 % for F17. The largest differences are at the lower end of the altitude range because there the electron densities decline very rapidly.

Bender, Stefan; Espy, Patrick; Paxton, Larry;

Published by: Earth and Space Science Open Archive ESSOAr Published on:

YEAR: 2021 DOI: 10.1002/essoar.10506056.1

Validation of SSUSI-derived auroral electron densities: comparisons to EISCAT data

Bender, Stefan; Espy, Patrick; Paxton, Larry;

Published by: Published on:

YEAR: 2021 DOI:

Large-Scale Dune Aurora Event Investigation Combining Citizen Scientists Photographs and Spacecraft Observations

Recently, citizen scientist photographs led to the discovery of a new auroral form called “the dune aurora” which exhibits parallel stripes of brighter emission in the green diffuse aurora at about 100 km altitude. This discovery raised several questions, such as (i) whether the dunes are associated with particle precipitation, (ii) whether their structure arises from spatial inhomogeneities in the precipitating fluxes or in the underlying neutral atmosphere, and (iii) whether they are the auroral manifestation of an atmospheric wave called a mesospheric bore. This study investigates a large-scale dune aurora event on 20 January 2016 above Northern Europe. The dunes were observed from Finland to Scotland, spanning over 1,500 km for at least 4 h. Spacecraft observations indicate that the dunes are associated with particle precipitation and reveal the presence of a temperature inversion layer below the mesopause during the event, creating suitable conditions for mesospheric bore formation. The analysis of a time lapse of pictures by a citizen scientist from Scotland leads to the estimate that, during this event, the dunes propagate toward the west-southwest direction at about 200 m s−1, presumably indicating strong horizontal winds near the mesopause. These results show that citizen science and dune aurora studies can fill observational gaps and be powerful tools to investigate the least-known region of near-Earth space at altitudes near 100 km.

Grandin, Maxime; Palmroth, Minna; Whipps, Graeme; Kalliokoski, Milla; Ferrier, Mark; Paxton, Larry; Mlynczak, Martin; Hilska, Jukka; Holmseth, Knut; Vinorum, Kjetil; , others;