Bibliography

A Simulation Study on the Variation of Thermospheric O/N2 With Solar Activity

The ratio of number density of atomic oxygen (O) to that of molecular nitrogen (N2) in the thermosphere (O/N2) on the constant pressure surface, which has complex temporal and spatial characteristics, is widely regarded as an important parameter connecting the terrestrial thermosphere and daytime ionosphere. Previous studies demonstrated that the thermospheric O/N2 increases with increasing solar activity, and the changes in O/N2 with solar activity show significant difference between winter and summer hemispheres. However, the root causes, which are responsible for the solar activity variation of O/N2, are not fully understood. In this study, the contributions of various physical and chemical processes on the response of O/N2 to the solar radiation change were quantitatively investigated through a series of controlled simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model. The simulation results suggested that the chemical processes lead to the increase of thermospheric O/N2 over the globe with increasing solar activity. The increase of O/N2 with solar activity is dominated by the enrichment of O abundance and the loss of N2 abundance in the lower and upper thermosphere, respectively. Moreover, the simulation results suggested that the stronger hemispheric asymmetry is attributed to the stronger thermospheric circulation, which changes the vertical advection of O/N2 through both direct and indirect effects.

Li, Zhongli; Luan, Xiaoli; Lei, Jiuhou; Ren, Dexin;

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

YEAR: 2022     DOI: 10.1029/2022JA030305

circulation; O/N2; photochemistry; solar cycle; thermosphere

The Universal Time Variations of the Intensity of Afternoon Aurora in Equinoctial Seasons

The afternoon auroral emissions are investigated in the equinoxes for geomagnetically quiet conditions (Kp = 1) using auroral images from ultraviolet imager (UVI) aboard the Polar satellite. They are compared with solar illumination effects (the solar zenith angle [SZA] and the consequent ionospheric conductivity) and the dipole tilt angle, as well as the observational region 1 upward field-aligned currents (FACs) from AMPERE data. The averaged afternoon auroral emissions have pronounced universal time (UT) variations with valley (2.8 photons/cm2/s) at around 01:00–03:00 UT and peak (4.7 photons/cm2/s) at around 17:00–19:00 UT. They generally vary with the solar illumination, the dipole tilt angle and the observed region 1 upward FACs as a function of UT. The afternoon auroral intensity is anticorrelated with the SZA and positively proportional to the solar EUV-produced Pedersen conductivity, region 1 upward FACs and dipole tilt angle. Additionally, they depend weakly on solar flux under geomagnetically quiet conditions. These results suggest that in the afternoon auroral region, the peak auroral emissions are closely associated with the peak conductivity and the maximum upward FACs. Other mechanisms, such as the dipole tilt angle, may also contribute. Further comparison between the northern afternoon aurora and the FACs in the two conjugate hemispheres suggests little contributions on the auroral UT variations from the interhemispheric FACs in the equinoxes.

Wang, Lingmin; Luan, Xiaoli; Lei, Jiuhou; Lynch, Kristina; Zhang, Binzheng;

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

YEAR: 2021     DOI: 10.1029/2020JA028504

afternoon auroral emissions; auroral hot spots; dipole tilt angle; region 1 upward FACs; solar zenith angle; UT variations

Equatorial Ionization Anomaly Variations During Geomagnetic Storms

The equatorial ionization anomaly (EIA) was discovered in the 1940s. Since then, the research on ionospheric storm effects at the equatorial and low latitudes has become one of the hottest topics in the ionospheric community. During the past 2 decades, large amounts of ionospheric and thermospheric data from the ground-based and satellite-borne observations and also from the novel capability of three-dimensional numerical models stimulated the ionospheric weather studies. Recent scientific progresses on the EIA response to geomagnetic storms are briefly described here, together with some suggestions for the future research directions of the EIA storm effects.

Luan, Xiaoli;

Published by:       Published on:

YEAR: 2021     DOI: 10.1002/9781119815617.ch13

Geomagnetic storms; Equatorial ionization anomaly; equatorial ionospheric response; equatorial regions; low latitude regions; physical mechanisms

Global Effects of a Polar Solar Eclipse on the Coupled Magnetosphere-Ionosphere System

It is well-known that solar eclipses can significantly impact the ionosphere and thermosphere, but how an eclipse influences the magnetosphere-ionosphere system is still unknown. Using a coupled magnetosphere-ionosphere-thermosphere model, we examined the impact on geospace of the northern polar-region eclipse that occurred on June 10, 2021. The simulations reveal that the eclipse-induced reduction in polar ionospheric conductivity causes large changes in field-aligned current, cross-polar cap potential and auroral activity. While such effects are expected in the northern hemisphere where solar obscuration occurred, they also occurred in the southern hemisphere through electrodynamic coupling. Eclipse-induced changes in monoenergetic auroral precipitation differ significantly between the northern hemisphere and southern hemisphere while diffuse auroral precipitation is interhemispherically symmetric. This study demonstrates that the geospace response to a polar-region solar eclipse is not limited just to the eclipse region but has global implications.

Chen, Xuetao; Dang, Tong; Zhang, Binzheng; Lotko, William; Pham, Kevin; Wang, Wenbin; Lin, Dong; Sorathia, Kareem; Merkin, Viacheslav; Luan, Xiaoli; Dou, Xiankang; Luo, Bingxian; Lei, Jiuhou;

Published by: Geophysical Research Letters      Published on:

YEAR: 2021     DOI: 10.1029/2021GL096471

auroral activity; magnetosphere-ionosphere coupling; polar solar eclipse

Isolated Auroral Spots Observed by DMSP/SSUSI

This work reports auroral spots event observed by the SSUSI instruments on board the DMSP spacecraft between 22 and 23 July 2009 during the recovery phase of a moderate magnetic storm. The spots were observed between 18:00 and 02:00 magnetic local time and stayed at ~60\textdegree magnetic latitude. They lasted for ~10 hr and corotated with ~64\% of the Earth\textquoterights rotational speed. In situ observations indicate that the isolated auroral spots were produced by energetic ions at energies between 10 and 240 keV, with significantly anisotropic electron (30\textendash300 keV) precipitations. It is expected that the energetic ions originate from the ring current and can be scattered by the EMIC waves through cyclotron resonance. The energetic electrons can be precipitated by the nonresonant interaction between the electrons and EMIC waves, which is suggested by previous works.

Zhou, Su; Luan, Xiaoli; Pierrard, Viviane; Han, Desheng;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2019

YEAR: 2019     DOI: 10.1029/2019JA026853

Longitudinal variations of the occurrence probability of the ionospheric F1 layer peak at middle and high latitudes

Li, Zhenxing; Luan, Xiaoli; Ren, Dexin;

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

YEAR: 2019     DOI:

Topside ionospheric conditions during the 7—8 September 2017 geomagnetic storm

The uplooking total electron contents (TECs) from the GRACE, SWARM-A, TerraSAR-X, and MetOp-A satellites and in situ electron density (Ne) from SWARM-A were utilized to investigate the topside ionospheric conditions during the 7–8 September 2017 geomagnetic storm. The rate of TEC index (ROTI) and rate of density index (RODI), which are derivative indices of TEC and Ne, respectively, were also used to characterize the topside ionospheric irregularities. The main results of this study are as follows: (1) There were significant enhancements seen in the uplooking TEC during the first main phase of the storm. (2) The uplooking TEC did not show unusual enhancement at the morning and evening local times in the Asian-Australian sector during the recovery phase of the storm. (3) Prominent TEC hemispheric asymmetry at the middle and high latitudes was observed at both day and night sectors. (4) Long-duration recovery of topside TEC with respect to the prestorm condition was also detected in this event. (5) Nighttime ROTI enhancements were presented in a wide latitudinal range from the equator to the poles during the main phases of the storm. (6) The ionospheric electric field disturbances associated with IMF-Bz fluctuations probably played a very important role in triggering ionospheric irregularities during the relatively weak geomagnetic activity on 7 September, which implies that ionospheric irregularities do not necessarily occur under the severe geomagnetic conditions only.

Jimoh, Oluwaseyi; Lei, Jiuhou; Zhong, Jiahao; Owolabi, Charles; Luan, Xiaoli; Dou, Xiankang;

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

YEAR: 2019     DOI: 10.1029/2019JA026590

An Empirical Dayglow Model for the Lyman-Birge-Hopfield-Long Band Derived From the Polar Ultraviolet Imager Data

The Lyman-Birge-Hopfield-long band dayglow emissions near 1,700\ \r A, which were observed by the ultraviolet imager on board Polar satellite, are characterized as a cosine-like function of the solar zenith angle. These emissions are mainly excited by the solar extreme ultraviolet produced photoelectrons acting on the nitrogen molecules. The amplitude and phase factors are used to quantify the cosine-like function and subsequently develop a dayglow model. In this study, a model is developed by considering broader dayglow emission areas outside the auroral oval, as the dayglow intensities in the dayside can exceed the auroral brightness, especially in summer. Also, this model is constructed by considering the seasonal variations of the two factors. It is demonstrated that, besides the strong solar cycle and universal time dependencies, the amplitude factors of the cosine-like function show prominent seasonal variations, which are associated with the solar zenith angle changes. The amplitude factors are the largest in summer and smallest in winter. In addition, the dayglow phase factors show nearly constant values within each season, but throughout the year, they are higher in summer and equinoctial months and lower in winter. The dayglow model can benefit the investigation of global auroral patterns for all seasons.

Wang, Lingmin; Luan, Xiaoli; Lei, Jiuhou; Dou, Xiankang;

Published by: Space Weather      Published on: 07/2018

YEAR: 2018     DOI: 10.1029/2018SW001954

Was Magnetic Storm the Only Driver of the Long-Duration Enhancements of Daytime Total Electron Content in the Asian-Australian Sector Between 7 and 12 September 2017?

In this study, multiple data sets from Beidou geostationary orbit satellites total electron contents (TECs), ionosonde, meteor radar, magnetometer, and model simulations have been used to investigate the ionospheric responses in the Asian-Australian sector during the September 2017 geomagnetic storm. It was found that long-duration daytime TEC enhancements that lasted from 7 to 12 September 2017 were observed by the Beidou geostationary orbit satellite constellation. This is a unique event as the prominent TEC enhancements persisted during the storm recovery phase when geomagnetic activity became quiet. The Thermosphere-Ionosphere Electrodynamics Global Circulation Model predicted that the TEC enhancements on 7\textendash9 September were associated with the geomagnetic activity, but it showed significant electron density depletions on 10 and 11 September in contrast to the observed TEC enhancements. Our results suggested that the observed long-duration TEC enhancements from 7 to 12 September are mainly associated with the interplay of ionospheric dynamics and electrodynamics. Nevertheless, the root causes for the observed TEC enhancements seen in the storm recovery phase are unknown and require further observations and model studies.

Lei, Jiuhou; Huang, Fuqing; Chen, Xuetao; Zhong, Jiahao; Ren, Dexin; Wang, Wenbin; Yue, Xinan; Luan, Xiaoli; Jia, Mingjiao; Dou, Xiankang; Hu, Lianhuan; Ning, Baiqi; Owolabi, Charles; Chen, Jinsong; Li, Guozhu; Xue, Xianghui;

Published by: Journal of Geophysical Research: Space Physics      Published on: 04/2018

YEAR: 2018     DOI: 10.1029/2017JA025166

Solar cycle variations of thermospheric O/N ₂ longitudinal pattern from TIMED/GUVI

Thermospheric composition (O/N₂ ratio) is well known to have a great impact on the variation of daytime ionospheric electron density. This study aims to investigate the local time, seasonal, and solar cycle variations of the O/N₂ longitudinal pattern in both hemispheres during daytime in solstices. The O/N₂ data used are from TIMED/Global Ultraviolet Imager observations made over a solar cycle for geomagnetically quiet conditions. The main findings are as follows: (1) The O/N₂ longitudinal patterns are generally similar during 10:00\textendash14:00 LT and between solar minimum and maximum, although the O/N₂ values change with local time and solar cycle. (2) The winter O/N₂ subauroral enhancement is unexpectedly smaller in the longitudes where the magnetic pole is (near-pole longitudes), rather than in the longitudes far from the magnetic pole, especially during solar maximum, and consequently, the longitudinal pattern of O/N₂ depends on latitude in local winter. (3) The winter O/N₂ subauroral enhancement generally moves to more poleward latitudes during solar maximum, as compared to solar minimum. (4) At higher midlatitudes (~45\textdegree\textendash60\textdegreeN and ~40\textdegree\textendash50\textdegreeS in geographic latitudes) in solar minimum, the winter-to-summer ratio of O/N₂ in each hemisphere has an obvious minimum in near-pole longitudes. This minimum becomes more evident during solar maximum. The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model simulations indicate that in the winter hemisphere, the unexpected O/N₂ longitudinal pattern in higher midlatitudes is mainly associated with high-latitude Joule heating under the impact from ion convection and auroral precipitation.

Luan, Xiaoli; Wang, Wenbin; Burns, Alan; Dou, Xiankang;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2018

YEAR: 2017     DOI: 10.1002/jgra.v122.210.1002/2016JA023696

Solar cycle variations of thermospheric O/N2 longitudinal pattern from TIMED/GUVI

Luan, Xiaoli; Wang, Wenbin; Burns, Alan; Dou, Xiankang;

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

YEAR: 2017     DOI:

Solar activity dependence of nightside aurora in winter conditions

The dependence of the nightside (21:00\textendash03:00 MLT; magnetic local time) auroral energy flux on solar activity was quantitatively studied for winter/dark and geomagnetically quiet conditions. Using data combined from Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager and Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager observations, we separated the effects of geomagnetic activity from those of solar flux on the nightside auroral precipitation. The results showed that the nightside auroral power was reduced by ~42\% in solar maximum (F_10.7 = 200 sfu; solar flux unit 1 sfu = 10^-22 W m^-2 Hz^-1) with respect to that under solar minimum (F_10.7 = 70 sfu) for the\ Kp = 1 condition, and this change rate became less (~21\%) for the\ Kp = 3 condition. In addition, the solar cycle dependence of nightside auroral power was similar with that from both the premidnight (21:00\textendash23:00 MLT) and postmidnight (01:00\textendash03:00 MLT) sectors. These results indicated that as the ionospheric ionization increases with the enhanced auroral and geomagnetic activities, the solar activity dependences of nightside auroral power become weaker, at least under geomagnetically quiet conditions.

Zhou, Su; Luan, Xiaoli; Dou, Xiankang;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2016

YEAR: 2016     DOI: 10.1002/2015JA021865

auroral conjugate effects; auroral geomagnetic activity variation; auroral imaging scaling; auroral solar cycle variation

Universal time variations of the auroral hemispheric power and their interhemispheric asymmetry from TIMED/GUVI observations

This paper quantitatively analyzes the auroral hemispheric power (HP) and its interhemispheric asymmetry as a function of universal time (UT) for geomagnetically quiet conditions (Kp 1\textendash3) from Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) imaging observations. The HP variation with UT can be approximately characterized as two cases: One is for similar HP variations in the equinoxes in the Northern Hemisphere and for the June solstices of both hemispheres, and the other is for similar HP patterns in the equinoxes in the Southern Hemisphere and for the December solstices of both hemispheres. In the equinoxes, the HP variations are interhemispherically asymmetric due to different occurrence time of the HP peak. In the solstices, the HP is generally interhemispherically symmetric in its diurnal variations, but there is interhemispheric asymmetry in the magnitudes of the maximum HP. For geomagnetically quiet conditions (Kp = 2), in the equinoxes relative interhemispheric differences are typically between 0 and 20\%, with respect to the averaged HP from the two hemispheres, while during the solstices, the maximum relative interhemispheric asymmetry can be as large as 30\% in December, but it is only ~15\% in June. These two cases are mainly associated with variations of auroral precipitation power in the night side sector (21:00\textendash03:00 magnetic local time/MLT), which are primarily controlled by solar illumination conditions in both hemispheres and are also attributed to the difference in the geographical area of the auroral oval in the two hemispheres. Furthermore, the general interhemispheric symmetry of the HP variations in solstices suggests that auroral acceleration is not only controlled locally by solar illumination conditions, which has been well known previously, but also might be affected by processes in the precipitation source region.

Luan, Xiaoli; Wang, Wenbin; Burns, Alan; Dou, Xiankang;

Published by: Journal of Geophysical Research: Space Physics      Published on: 01/2016

YEAR: 2016     DOI: 10.1002/2016JA022730

Longitudinal variations of the nighttime E layer electron density in the auroral zone

Longitudinal variations of the nighttime E layer electron density (21:00\textendash03:00 magnetic local time) in the auroral zone are investigated, and their sources are discussed in terms of auroral precipitation and solar radiation. The electron density data used in this study are retrieved from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation observations during 2006\textendash2009 under quiet geomagnetic activity (Kp <= 3) and solar minimum conditions. The main conclusions of this study are as follows: (1) the nighttime E layer electron density had pronounced longitudinal variations in the auroral zone. These variations depended on season and had large hemispheric asymmetry for all seasons. In winter, relatively larger electron density was located in 120\textendash310\textdegree magnetic longitude (MLON) in the northern hemisphere and in 170\textendash360\textdegree MLON in the southern hemisphere, and greater maximum density occurred in the northern hemisphere than in the southern one. In summer and equinox, the longitudinal asymmetry was greater in the southern hemisphere. (2) The peaks of the E layer electron density along latitude generally occurred between 65\textdegree and 70\textdegree magnetic latitude in the auroral zone in all seasons for both hemispheres except for the sunlit sector of the southern summer. (3) The greater electron density in local winter in the auroral zone was generally associated with the more intense auroral precipitation intensity at roughly the same longitude, whereas the longitudinal patterns of the electron density were under the combined impact of both auroral precipitation and solar radiation in the local summer and equinoxes.

Luan, Xiaoli; Wang, Wenbin; Dou, Xiankang; Burns, Alan; Yue, Xinan;

Published by: Journal of Geophysical Research: Space Physics      Published on: 01/2015

YEAR: 2015     DOI: 10.1002/2014JA020610

auroral E layer; hemispheric asymmetry; longitudinal variations; Seasonal variations

Longitudinal variations of the nighttime E layer electron density in the auroral zone

Luan, Xiaoli; Wang, Wenbin; Dou, Xiankang; Burns, Alan; Yue, Xinan;

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

YEAR: 2015     DOI:

Solar Activity Dependence of Night Side Aurora in Winter/Dark Conditions

Luan, Xiaoli; Zhou, Su; Dou, Xiankang;

Published by:       Published on:

YEAR: 2015     DOI:

Simulations of the equatorial thermosphere anomaly: Geomagnetic activity modulation

The modulation of geomagnetic activity on the equatorial thermosphere anomaly (ETA) in thermospheric temperature under the high solar activity condition is investigated using the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations. The model simulations during the geomagnetically disturbed interval, when the north-south component of the interplanetary magnetic field (B_z) oscillates between southward and northward directions, are analyzed and also compared with those under the quiet time condition. Our results show that ionospheric electron densities increase greatly in the equatorial ionization anomaly (EIA) crest region and decrease around the magnetic equator during the storm time, resulting from the enhanced eastward electric fields. The impact of both the direct heat deposition at high latitudes and the modulation of the storm time enhanced EIA crests on the ETA are subsequently studied. The increased plasma densities over the EIA crest region enhance the field-aligned ion drag that accelerates the poleward meridional winds and consequently their associated adiabatic cooling effect. This process alone produces a deeper temperature trough over the magnetic equator as a result of the enhanced divergence of meridional winds. Moreover, the enhanced plasma-neutral collisional heating at higher latitudes associated with the ionospheric positive storm effect causes a weak increase of the ETA crests. On the other hand, strong changes of the neutral temperature are mainly confined to higher latitudes. Nevertheless, the changes of the ETA purely due to the increased plasma density are overwhelmed by those associated with the storm time heat deposition, which is the major cause of an overall elevated temperature in both the ETA crests and trough during the geomagnetically active period. Associated with the enhanced neutral temperature at high latitudes due to the heat deposition, the ETA crest-trough differences become larger under the minor geomagnetic activity condition than under the quiet time condition. However, when geomagnetic activity is further elevated, the ETA crests tend to be masked by high temperatures at middle and high latitudes.

Lei, Jiuhou; Wang, Wenbin; Thayer, Jeffrey; Luan, Xiaoli; Dou, Xiankang; Burns, Alan; Solomon, Stanley;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2014

YEAR: 2014     DOI: 10.1002/2014JA020152

equatorial thermosphere anomaly; geomagnetic activity; ion-neutral coupling; positive ionospheric storm

Longitudinal and Hemispheric Variations of Nighttime E-Layer Electron Density in the Auroral Zone

Luan, Xiaoli; Wang, Wenbin; Dou, Xiankang; Burns, Alan; Yue, Xinan;

Published by:       Published on:

YEAR: 2014     DOI:

Annual asymmetry in thermospheric density: Observations and simulations

[1]\ In this paper, the Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) observations during 2002\textendash2010 are utilized to study the variation of the annual asymmetry in thermospheric density at 400 km under low solar activity condition (F10.7 = 80) based on the method of empirical orthogonal functions (EOFs). The derived asymmetry index (AI) in thermospheric density from the EOF analysis shows a strong latitudinal variation at night but varies a little with latitudes in daytime. Moreover, it exhibits a terdiurnal tidal signature at low to middle latitudes. The global mean value of the AI is 0.191, indicating that a 47\% difference in thermosphere between the December and June solstices in the global average. In addition, the NCAR Thermosphere-Ionosphere Electrodynamics Global Circulation Model (TIEGCM) is used to explore the possible mechanisms responsible for the observed annual asymmetry in thermospheric density. It is found that the standard simulations give a lower AI and also a weaker day-to-night difference. The simulated AI shows a semidiurnal pattern in the equatorial and low-latitude regions in contrast with the terdiurnal tide signature seen in the observed AI. The daily mean AI obtained from the simulation is 0.125, corresponding to a 29\% December-to-June difference in thermospheric density at 400 km. Further sensitivity simulations demonstrated that the effect of the varying Sun-Earth distance between the December and June solstices is the main process responsible for the annual asymmetry in thermospheric density, while the magnetic field configuration and tides from the lower atmosphere contribute to the temporal and spatial variations of the AI. Specifically, the simulations show that the Sun-Earth distance effect explains 93\% of the difference in thermospheric density between December and June, which is mainly associated with the corresponding changes in neutral temperature. However, our calculation from the density observations reveals that the varying Sun-Earth distance effect only accounts for ~67\% of the December-to-June difference in thermosphere density, indicating that the TIEGCM might significantly underestimate the forcing originating from the lower atmosphere.

Lei, Jiuhou; Dou, Xiankang; Burns, Alan; Wang, Wenbin; Luan, Xiaoli; Zeng, Zhen; Xu, JiYao;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2013

YEAR: 2013     DOI: 10.1002/jgra.50253

Annual asymmetry; Empirical orthogonal functions; Sun-Earth distance; Upper thermosphere

Geomagnetic and auroral activity driven by corotating interaction regions during the declining phase of Solar Cycle 23

A superposed epoch analysis is performed to investigate the relative impact of the solar wind/interplanetary magnetic field (IMF) on geomagnetic activity, auroral hemispheric power, and auroral morphology during corotating interaction regions (CIRs) events between 2002 and 2007, when auroral images from Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager were available. Four categories of CIRs have been compared. These were classified by the averaged IMF Bz and the time of maximum solar wind dynamic pressure around the CIR stream interface or onset time. It is found that during CIR events: (1) The peaks of auroral power and Kp were largely associated with dominant southward Bz, whereas auroral activity also became stronger with increases of solar wind speed, density, and dynamic pressure. (2) The percentage and absolute increases of auroral hemispheric power with solar wind speed were much greater under dominantly northward Bz conditions than under dominantly southward Bz conditions. (3) The enhancement of the auroral power and Kp with increasing solar wind speed followed the same pattern, for both dominantly southward and northward Bz conditions, regardless of the behavior of solar wind density and dynamic pressure. These results suggest that, during CIR events, southward Bz played the most critical role in determining geomagnetic and auroral activity, whereas solar wind speed was the next most important contributor. The solar wind dynamic pressure was the less important factor, as compared with Bz and solar wind speed. Relatively strong auroral precipitation energy flux (\> ~3 mW/m²) occurred in a wider auroral oval region after the stream interface than before it for both dominantly northward and southward Bz conditions. These conditions enhanced the auroral hemispheric power after the stream interface. Intense auroral precipitation (\> ~4 mW/m²) generally occurred widely at night under dominantly southward Bz conditions, but the location of this precipitation in the auroral oval was different when it was associated with different solar wind density and speed conditions.

Luan, Xiaoli; Wang, Wenbin; Lei, Jiuhou; Burns, Alan; Dou, Xiankang; Xu, JiYao;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2013

YEAR: 2013     DOI: 10.1002/jgra.50195

auroral morphology; corotating interaction regions; solar wind/IMF forcing

Annual and semiannual variations of thermospheric density: EOF analysis of CHAMP and GRACE data

Lei, Jiuhou; Matsuo, Tomoko; Dou, Xiankang; Sutton, Eric; Luan, Xiaoli;

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

YEAR: 2012     DOI:

Longitudinal variations of nighttime electron auroral precipitation in both the Northern and Southern hemispheres from the TIMED global ultraviolet imager

Luan, Xiaoli; Wang, Wenbin; Burns, Alan; Solomon, Stanley; Zhang, Yongliang; Paxton, L.; Xu, JiYao;

Published by: Journal of Geophysical Research      Published on: Jan-01-2011

YEAR: 2011     DOI: 10.1029/2010JA016051

Seasonal and hemispheric variations of the total auroral precipitation energy flux from TIMED/GUVI

Luan, Xiaoli; Wang, Wenbin; Burns, Alan; Solomon, Stanley; Zhang, Yongliang; Paxton, L.;

Published by: Journal of Geophysical Research      Published on: Jan-01-2010

YEAR: 2010     DOI: 10.1029/2009JA015063

Unusual declining phase of solar cycle 23: Weak semi-annual variations of auroral hemispheric power and geomagnetic activity

Luan, Xiaoli; Wang, Wenbin; Burns, Alan; Solomon, Stanley; Zhang, Yongliang; Paxton, L.;

Published by: Geophysical Research Letters      Published on: Jan-01-2009

YEAR: 2009     DOI: 10.1029/2009GL040825

Variations of Auroral Electron Precipitation Measured by TIMED/GUVI

Luan, X; Wang, W; Burns, A; Zhang, Y; Solomon, S;

Published by:       Published on:

YEAR: 2008     DOI: