Bibliography

Auroral ionospheric E region parameters obtained from satellite-based far-ultraviolet and ground-based ionosonde observations—effects of proton precipitation

At the nadir, there are ∼57.5 pixels per averaging area for GUVI and ∼28.5 for SSUSI. Only 0.030 counts per R per averaging area for GUVI, F16 SSUSI, and F18 SSUSI, respectively.

Knight, Harold;

Published by:       Published on:

YEAR: 2021     DOI: 10.5194/angeo-39-105-2021

The comparative analysis of the sudden stratospheric warming of the Northern Hemisphere (1980-2020) characteristics

The analysis of the dynamics of the characteristics of stratospheric warmings in the Northern Hemisphere from 1980 to 2020 is carried out. In most cases, stratospheric warmings were

Valerevic, Muradanc;

Published by:       Published on:

YEAR: 2021     DOI:

Toward a Next Generation Particle Precipitation Model: Mesoscale Prediction Through Machine Learning (a Case Study and Framework for Progress)

We advance the modeling capability of electron particle precipitation from the magnetosphere to the ionosphere through a new database and use of machine learning (ML) tools to gain utility from those data. We have compiled, curated, analyzed, and made available a new and more capable database of particle precipitation data that includes 51 satellite years of Defense Meteorological Satellite Program (DMSP) observations temporally aligned with solar wind and geomagnetic activity data. The new total electron energy flux particle precipitation nowcast model, a neural network called PrecipNet, takes advantage of increased expressive power afforded by ML approaches to appropriately utilize diverse information from the solar wind and geomagnetic activity and, importantly, their time histories. With a more capable representation of the organizing parameters and the target electron energy flux observations, PrecipNet achieves a \textgreater50\% reduction in errors from a current state-of-the-art model oval variation, assessment, tracking, intensity, and online nowcasting (OVATION Prime), better captures the dynamic changes of the auroral flux, and provides evidence that it can capably reconstruct mesoscale phenomena. We create and apply a new framework for space weather model evaluation that culminates previous guidance from across the solar-terrestrial research community. The research approach and results are representative of the “new frontier” of space weather research at the intersection of traditional and data science-driven discovery and provides a foundation for future efforts.

McGranaghan, Ryan; Ziegler, Jack; Bloch, Téo; Hatch, Spencer; Camporeale, Enrico; Lynch, Kristina; Owens, Mathew; Gjerloev, Jesper; Zhang, Binzheng; Skone, Susan;

Published by: Space Weather      Published on:

YEAR: 2021     DOI: 10.1029/2020SW002684

space weather; magnetosphere-ionosphere coupling; data science; evaluation; machine learning; particle precipitation

Long Term Ionospheric VTEC Variation during Solar cycle 24 as Observed from Indian IGS GPS Station

Thermo-ionosheric O/N2 ratio obtained by GUVI for March and September equinox days, and June and December solstice days of 2014 represented as the equinox month and solstice

Kundu, S; Sasmal, S; Chakrabarti, SK;

Published by: Int. J. Sci. Res. in Physics and Applied Sciences Vol      Published on:

YEAR: 2021     DOI:

SABER Observation of Storm-Time Hemispheric Asymmetry in Nitric Oxide Radiative Emission

The nitric oxide (NO) 5.3 μm radiative emission is the dominating and most efficient cooling agent in the thermosphere above 100 km. The NO 5.3 μm radiative cooling is an important

Bag, Tikemani; Li, Zheng; Rout, Diptiranjan;

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

YEAR: 2021     DOI: 10.1029/2020JA028849

Implication of Tidal Forcing Effects on the Zonal Variation of Solstice Equatorial Plasma Bubbles

Equatorial plasma bubbles (EPBs) are plasma depletions that can occur in the nighttime ionospheric F region, causing scintillation in satellite navigation and communications signals. Past research has shown that EPB occurrence rates are higher during the equinoxes in most longitude zones. An exception is over the central Pacific and African sectors, where EPB activity has been found to maximize during solstice. Tsunoda et al. (2015) hypothesized that the solstice maxima in these two sectors could be driven by a zonal wavenumber 2 atmospheric tide in the lower thermosphere. In this study, we utilize satellite observations to examine evidence of such a wave-2 feature preconditioning the nighttime ionosphere to favor higher EPB growth rates over these two regions. We find the postsunset total electron content (TEC) observed by FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) during boreal summer from 2007 to 2012 exhibits a wave-2 zonal distribution, consistent with elevated vertical plasma gradients favorable for EPB formation. Numerical experiments are also carried out to determine whether such an ionospheric wave-2 can be produced as a result of vertical coupling from atmospheric tides with zonal wavenumber 2 in the local time frame. We find that forcing from these tidal components produced increases in the Rayleigh-Taylor growth rate over both sectors during solar maximum and minimum, as well as wave-2 modulations on vertical ion drift, ion flux convergence, and nighttime TEC. Our results are consistent with the aforementioned hypothesis over both regions with vertical coupling effects from atmospheric tides preconditioning the nighttime ionosphere to favor higher EPB growth rates.

Chang, Loren; Salinas, Cornelius; Chiu, Yi-Chung; , Jones; Rajesh, P.; Chao, Chi-Kuang; Liu, Jann-Yenq; Lin, Charles; Hsiao, Tung-Yuan;

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

YEAR: 2021     DOI: 10.1029/2020JA028295

Ionosphere; Atmospheric tides; equatorial plasma bubble; scintillation; vertical coupling; wind dynamo

On the Relationship of the O (1D) 630.0 nm Dayglow Emission to the F10. 7 cm Solar Flux and the Solar Zenith Angle

explanation, that the lower summer measurements were the result of atmospheric composition change, based on the change of [O/N2] observed during the Boston summer by the GUVI

Shepherd, Gordon; Cho, Young-Min;

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

YEAR: 2021     DOI: 10.1029/2020JA028715

Determination of Auroral Electrodynamic Parameters From AMPERE Field-Aligned Current Measurements

We calculate high latitude electrodynamic parameters using global maps of field-aligned currents from the Active Magnetosphere and Planetary Response Experiment (AMPERE). The model is based on previous studies that relate field-aligned currents to auroral Pedersen and Hall conductances measured by incoherent scatter radar. The field-aligned currents and conductances are used to solve for the electric potential at high latitudes from which electric fields are computed. The electric fields are then used with the conductances to calculate horizontal ionospheric currents. We validate the results by simulating the SuperMAG magnetic indices for 30 geomagnetically active days. The correlation coefficients between derived and actual magnetic indices were 0.68, 0.76, and 0.84 for the SMU, SML, and SME indices, respectively. We show examples of times when the simulations differ markedly from the measured indices and attribute them to either small-scale, substorm-related current structures or the effects of neutral winds. Overall, the performance of the model demonstrates that with few exceptions, auroral electrodynamic parameters can be accurately deduced from the global field-aligned current distribution provided by AMPERE.

Robinson, R.; Zanetti, Larry; Anderson, Brian; Vines, Sarah; Gjerloev, Jesper;

Published by: Space Weather      Published on:

YEAR: 2021     DOI: 10.1029/2020SW002677

space weather; auroral currents; auroral electrodynamics; conductivities; electric fields; field-aligned currents

Uses of the ENVISAT payload for Mesospheric and Thermospheric Investigations: The AALIM Project

The ENVISAT satellite, due to be launched in 2000, crosses the auroral ovals which are the location of important spectral emissions. The variety of sensors, especially the limb sounders

Muller, C; Aben, I; Van der Zande, WJ; Ubachs, W;

Published by:       Published on:

YEAR: 2021     DOI:

The impact of a stealth CME on the Martian topside ionosphere

Solar cycle 24 is one of the weakest solar cycles recorded, but surprisingly the declining phase of it had a slow coronal mass ejection (CME) that evolved without any low coronal

Thampi, Smitha; Krishnaprasad, C; Nampoothiri, Govind; Pant, Tarun;

Published by: Monthly Notices of the Royal Astronomical Society      Published on:

YEAR: 2021     DOI: 10.1093/mnras/stab494

Solar flares and geomagnetic storms of September 2017: Their impacts on the TEC over 75 E longitude sector

This study investigates the ionospheric Total Electron Content (TEC) responses over 75E longitude to the solar flares and geomagnetic storms of September 6–9, 2017. The results of

Chakraborty, Monti; Singh, AK; Rao, SS;

Published by: Advances in Space Research      Published on:

YEAR: 2021     DOI: 10.1016/j.asr.2021.04.012

Explicit IMF By-Dependence in Geomagnetic Activity: Quantifying Ionospheric Electrodynamics

Geomagnetic activity is mainly driven by the southward (Bz) component of the interplanetary magnetic field (IMF), which dominates all solar wind coupling functions. Coupling functions also depend on the absolute value of the dawn-dusk (By) component of the IMF, but not on its sign. However, recent studies have shown that for a fixed level of solar wind driving, auroral electrojets in the Northern Hemisphere (NH) are stronger for By \textgreater 0 than for By \textless 0 during NH winter. In NH summer, the dependence on the By sign is reversed. While this By sign dependence, also called the explicit By-dependence, is very strong in the winter hemisphere, it is weak in the summer hemisphere. Moreover, the explicit By-dependence is much stronger in the westward electrojet than in the eastward electrojet. In this study, we study how the explicit IMF By-dependence is coupled with large-scale field-aligned currents (FACs) by using FAC measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment and an empirical ionospheric conductance model. We model the complete ionospheric electrodynamics by solving the current continuity equation, and show that during periods of elevated solar wind driving (Bz \textless 0), the IMF By component modulates Regions 1 and 2 FACs in the dawn sector of the winter hemisphere. This leads to an explicit By-dependence in ionospheric conductance and the westward electrojet. We also show that the By-dependence of FACs and conductance is weak in the dusk sector, which explains the earlier observation of the weak By-dependence of the eastward electrojet.

Holappa, L.; Robinson, R.; Pulkkinen, A.; Asikainen, T.; Mursula, K.;

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

YEAR: 2021     DOI: 10.1029/2021JA029202

space weather; magnetosphere-ionosphere coupling; field-aligned currents; geomagnetic activity

Deriving column-integrated thermospheric temperature with the N 2 Lyman—Birge—Hopfield (2, 0) band

This paper presents a new technique to derive thermospheric temperature from space-based disk observations of far ultraviolet airglow. The technique, guided by findings from principal

Cantrall, Clayton; Matsuo, Tomoko;

Published by: Atmospheric Measurement Techniques      Published on:

YEAR: 2021     DOI: 10.5194/amt-14-6917-2021

3.1 High-latitude F-region plasma irregularities

The first radio instruments used to study the ionosphere in detail were ionosondes. Also known as a “vertical sounder,” an ionosonde provides a vertical plasma density profile of the

Perrya, Gareth; Goodwina, Lindsay;

Published by: Cross-Scale Coupling and Energy Transfer in the Magnetosphere-Ionosphere-Thermosphere System      Published on:

YEAR: 2021     DOI:

Ionospheric response to solar and magnetospheric protons during January 15—22, 2005: EAGLE whole atmosphere model results

We present an analysis of the ionosphere and thermosphere response to Solar Proton Events (SPE) and magnetospheric proton precipitation in January 2005, which was carried out

Bessarab, Fedor; Sukhodolov, Timofei; Klimenko, Maxim; Klimenko, Vladimir; Korenkov, Yu; Funke, Bernd; Zakharenkova, Irina; Wissing, Jan; Rozanov, EV;

Published by: Advances in Space Research      Published on:

YEAR: 2021     DOI: 10.1016/j.asr.2020.10.026

Geomagnetic Pulsations Driving Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) are driven by the geoelectric field induced by fluctuations of Earth s magnetic field. Drivers of intense GICs are often associated with large impulsive events such as coronal mass ejections. To a lesser extent fluctuations from regular oscillations of the geomagnetic field, or geomagnetic pulsations, have also been identified as possible drivers of GICs. In this work we show that these low-frequency pulsations are directly observed in measured GIC data from power networks. Due to the low-pass nature of GICs, Pc5 and lower-frequency pulsations drive significant GICs for an extended duration even at midlatitudes. Longer-period Ps6-type disturbances apparently not typical of midlatitudes are seen with GIC amplitudes comparable to the peak GIC at storm sudden commencement. The quasi-ac (alternating current) nature of the sustained pulsation driving affects the power system response and cannot be properly modeled using only direct current (dc) models. A further consideration is that the often used dB/dt GIC proxy is biased to the sampling rate of the geomagnetic field measurements used. The dB/dt metric does not adequately characterize GIC activity at frequencies in the low ultralow-frequency (ULF) range, and a frequency-weighted proxy akin to geoelectric field should be used instead.

Heyns, M.; Lotz, S.; Gaunt, C.;

Published by: Space Weather      Published on:

YEAR: 2021     DOI: 10.1029/2020SW002557

space weather; geomagnetic pulsations; geomagnetically induced currents

Equatorial Ionospheric Electrodynamics

The low-latitude ionosphere is one of the most dynamic regions of the Earth s upper atmosphere. The morphology of this region is controlled by radiative and coupled chemical, neutral, and plasma transport processes. Equatorial electrodynamics plays a fundamental role on the low-latitude plasma density, total electron content (TEC), and plasma structures and waves extending from the E-region to the protonosphere. Ground-based and satellite measurements over the last six decades determined the climatology of quiet- and storm-time equatorial electrodynamic processes. Extensive theoretical and numerical simulations, particularly in the last two decades, investigated the main electrodynamic driving mechanisms. These combined studies have led to major advances in the understanding of the short-term variability of equatorial electrodynamics, which is essential for the accurate forecast of low-latitude ionospheric weather, and its effects on ground- and space-based technological systems. In this work, we review the main properties of low-latitude electrodynamics, focusing on recent results of the equatorial ambient plasma drifts, which are the main drivers of low-latitude ionospheric weather. We also briefly mention some outstanding questions and suggest possible future directions for their more complete understanding.

Fejer, Bela; Maute, Astrid;

Published by:       Published on:

YEAR: 2021     DOI: 10.1002/9781119815617.ch9

total electron content; equatorial ionospheric electrodynamics; low-latitude plasma density; quiet-time equatorial plasma drifts; storm-time equatorial electric fields

Interaction Between an EMSTID and an EPB in the EIA Crest Region Over China

Few observations investigated the interaction between an electrical medium-scale traveling ionospheric disturbance (EMSTID) and an equatorial plasma bubble (EPB). This paper presents another interaction between a southwestward propagating EMSTID and an eastward drifting EPB in the equatorial ionization anomaly (EIA) crest region of China. When the EMSTID and the EPB touched each other, several depletions of the EMSTID (EPB) showed the eastward (westward) velocity disturbances of the EPB (EMSTID) depletions. Besides, phase elongations of the EPB depletions contrarotated as the EMSTID propagated southwestward. However, of important finding is that the interaction of the EMSTID and the EPB could have polarized one depletion of the postmidnight EPB that should have become a fossilized bubble. Inside that polarized EPB depletion were meter-scale irregularities that caused activated radar echoes and enhanced ranged spread F (RSF). The interaction occurred in descending ionosphere and the lower density regions got filled up with an enhanced density plasma. We propose that the EMSTID and the EPB could have electrically coupled with each other, causing an enhanced polarization electric field (PEF) that polarized that EPB depletion; the E × B gradient drift instability (Kelley, 1989) could have caused the meter-scale irregularities when that enhanced PEF was imposed on that reactivated EPB depletion surrounded by that enhanced density plasma. This study provides observational evidence that how an electrical couple of EMSTID and EPB events can activate a postmidnight EPB depletion that should become a fossilized structure.

Sun, Longchang; Xu, JiYao; Zhu, Yajun; Xiong, Chao; Yuan, Wei; Wu, Kun; Hao, Yongqiang; Chen, Gang; Yan, Chunxiao; Wang, Zhihua; Zhao, Xiukuan; Luo, Xiaomin;

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

YEAR: 2021     DOI: 10.1029/2020JA029005

airglow; EIA crest region; Interaction between MSTID and EPB; Nighttime plasma density enhancement; Polarization of postmidnight EPB; VHF radar echoes and range spread F

Estimating Precipitating Energy Flux, Average Energy, and Hall Auroral Conductance From THEMIS All-Sky-Imagers With Focus on Mesoscales

Recent attention has been given to mesoscale phenomena across geospace (∼10 s km to 500 km in the ionosphere or ∼0.5 RE to several RE in the magnetosphere), as their contributions to the system global response are important yet remain uncharacterized mostly due to limitations in data resolution and coverage as well as in computational power. As data and models improve, it becomes increasingly valuable to advance understanding of the role of mesoscale phenomena contributions—specifically, in magnetosphere-ionosphere coupling. This paper describes a new method that utilizes the 2D array of Time History of Events and Macroscale Interactions during Substorms (THEMIS) white-light all-sky-imagers (ASI), in conjunction with meridian scanning photometers, to estimate the auroral scale sizes of intense precipitating energy fluxes and the associated Hall conductances. As an example of the technique, we investigated the role of precipitated energy flux and average energy on mesoscales as contrasted to large-scales for two back-to-back substorms, finding that mesoscale aurora contributes up to ∼80\% (∼60\%) of the total energy flux immediately after onset during the early expansion phase of the first (second) substorm, and continues to contribute ∼30–55\% throughout the remainder of the substorm. The average energy estimated from the ASI mosaic field of view also peaked during the initial expansion phase. Using the measured energy flux and tables produced from the Boltzmann Three Constituent (B3C) auroral transport code (Strickland et al., 1976; 1993), we also estimated the 2D Hall conductance and compared it to Poker Flat Incoherent Scatter Radar conductance values, finding good agreement for both discrete and diffuse aurora.

Gabrielse, Christine; Nishimura, Toshi; Chen, Margaret; Hecht, James; Kaeppler, Stephen; Gillies, Megan; Reimer, Ashton; Lyons, Larry; Deng, Yue; Donovan, Eric; Evans, Scott;

Published by: Frontiers in Physics      Published on:

YEAR: 2021     DOI:

Planetary Waves and Their Impact on the Mesosphere, Thermosphere, and Ionosphere

Large-scale planetary waves (also known as Rossby waves), such as the Quasi-two day wave, 5 day wave and Kelvin wave, play crucial roles in coupling the lower and middle atmosphere to the mesosphere, thermosphere and ionosphere. Upward propagation and global structure of planetary waves in the stratosphere and mesosphere are affected by the zonal mean winds. Baroclinic or barotropic instability of the background mesospheric winds can amplify the waves en route to the upper atmosphere. Fast traveling planetary waves with deep vertical wavelengths, such as Kelvin waves, are able to reach the upper thermosphere and modulate air density and winds. More commonly, planetary waves influence the thermosphere-ionosphere system by modulating the E-region and F-region dynamo electric fields. Dissipation of planetary waves in the lower thermosphere modifies the background winds, and induces extra meridional circulation, consequently altering thermospheric constituents, such as O/N2, and ionospheric electron densities. Interactions between planetary waves and tides not only provide an additional source of traveling planetary waves in the mesosphere, but are key sources of variability in E-region dynamo electric fields and plasma drift.

Yue, Jia; Lieberman, Ruth; Chang, Loren;

Published by:       Published on:

YEAR: 2021     DOI: 10.1002/9781119815631.ch10

barotropic instability; E-region dynamo electric fields; F-region dynamo electric fields; Kelvin waves; mesosphere; planetary waves; plasma drift; thermosphere-ionosphere system

An Observational Investigation of Mid-Latitude Thermospheric Temperatures and High-Latitude E-Region Neutral Wind Structures

The Earth s atmosphere is a complicated environment. Different physical processes affect it depending on the altitude and latitude, among other factors. Three different aspects of the Earth s upper atmosphere are investigated here, using two different techniques. These investigations are: the mid-latitude midnight temperature maximum (MTM), the mesosphere and low-thermosphere Kelvin-Helmholtz instability (KHI), and the advective acceleration in the E-region. All of these studies occur in the Earth s thermosphere and expand our understanding of these phenomena that represent different ways in which energy is transferred throughout the Earth s atmosphere. Observing and characterizing these energy transfer pathways is crucial to further our knowledge of these geophysical processes. The MTM is typically understood as an equatorial phenomenon that has a characteristic temperature increase around midnight due to the constructive interference between tidal components. While this phenomenon has been studied thoroughly in latitudes \textless ±20° and modeled to reach \textasciitilde60°; previous observations of temperature and winds had not confirmed its occurrence in latitudes \textgreater 20° N. In Mesquita (2018) and Chapter 2 the following scientific question is addressed: What are the characteristics of the mid-latitude MTM? To answer it, a technique was developed to observe the phenomenon and estimate its amplitude between 32° N and 42° N. This investigation used the North American Thermosphere Ionosphere Observing Network (NATION) containing 5 Fabry-Perot interferometers (FPI). Its data set includes a total of 846 nights of observations over a period of approximately 5 years. The new approach for calculating the MTM amplitude was developed by using a series of fits to determine the tidal background. Removing this background from the temperatures and applying an inversion algorithm allowed for the construction of two-dimensional temperature and wind maps, which illustrated the effects of the MTM on the wind field. A statistical analysis of the feature proved that both MTM peaks oscillate with semi-annual and annual periods. The KHI has been observed and characterized in the mesosphere (statically unstable region). However, the few observations of this phenomena in the low thermosphere (statically stable region) were not detailed and did not show evidence of turbulence above the mesopause. The following scientific questions were still unanswered: What is the triggering mechanism of KHIs in statically stable regions and how does it evolve? These questions are addressed by Mesquita (2020) and in Chapter 3. The triangulation of vapor traces from sounding rockets showed the KHI in great detail above 100 km. Characterizing the KHI development in three dimensions revealed wavelength, eddy diameter, and vertical length scale of 9.8, 5.2, and 3.8 km, respectively, centered at 102 km altitude. Further analysis of dimensionless numbers—such as Richardson, Reynolds, and Froude numbers—illustrated that the presence of strong and sustained shears was the mechanism involved in generating KHIs in the thermosphere. Advection has been modeled to be an important acceleration in high-latitude. However, observations of this forcing mechanism have been scarce. Moreover, previous studies investigated the effects of the Hall drag on the Coriolis parameter without including the centrifugal force in the analysis. Chapter 4 addresses the following scientific question: How does geomagnetic activity affect the vertical distribution of forces (including advection) and the modified Coriolis parameter in the E-region? Triangulation of vapor traces released from sounding rockets was used to calculate the meridional advective acceleration. The observations took place during 5 different geomagnetic conditions for the JOULE II, HEX II, MIST, Auroral Jets, and Super Soaker launches. The instantaneous Lorentz acceleration, which is often considered a dominant force in high-latitude active conditions, was calculated by using the Poker Flat Incoherent Scatter Radar (PFISR) data. These calculations showed that advection can become a dominant term depending on the geomagnetic activity level. The analysis of modified Coriolis parameter Φ, which includes the centrifugal acceleration, revealed that in strong geomagnetic activity an air parcel tends to remain in the auroral oval (channel of enhanced Lorentz acceleration) for an extended period of time. This potentially provides an explanation for why winds are enhanced in the low thermosphere above 115 km during strong geomagnetic activity.

de Mesquita, Rafael;

Published by:       Published on:

YEAR: 2021     DOI:

Advective acceleration; E-region neutral wind forcing; Kelvin-Helmholtz instability; Midnight temperature maximum

Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect

We use the \textlessi\textgreateram\textlessi/\textgreater, \textlessi\textgreateran, as\textlessi/\textgreater and the \textlessi\textgreateraσ\textlessi/\textgreater geomagnetic indices to the explore a previously overlooked factor in magnetospheric electrodynamics, namely the inductive effect of diurnal motions of the Earth’s magnetic poles toward and away from the Sun caused by Earth’s rotation. Because the offset of the (eccentric dipole) geomagnetic pole from the rotational axis is roughly twice as large in the southern hemisphere compared to the northern, the effects there are predicted to be roughly twice the amplitude of those in the northern hemisphere. Hemispheric differences have previously been discussed in terms of polar ionospheric conductivities generated by solar photoionization, effects which we allow for by looking at the dipole tilt effect on the time-of-year variations of the indices. The electric field induced in a geocentric frame is shown to also be a significant factor and gives a modulation of the voltage applied by the solar wind flow in the southern hemisphere that is typically a ±30\% diurnal modulation for disturbed intervals rising to ±76\% in quiet times. For the northern hemisphere these are 15\% and 38\% modulations. Motion away from/towards the Sun reduces/enhances the directly-driven ionospheric voltages and reduces/enhances the magnetic energy stored in the tail and we estimate that approximately 10\% of the effect appears in directly driven ionospheric voltages and 90\% in changes of the rate of energy storage or release in the near-Earth tail. The hemispheric asymmetry in the geomagnetic pole offsets from the rotational axis is shown to be the dominant factor in driving Universal Time (\textlessi\textgreaterUT\textlessi/\textgreater) variations and hemispheric differences in geomagnetic activity. Combined with the effect of solar wind dynamic pressure and dipole tilt on the pressure balance in the near-Earth tail, the effect provides an excellent explanation of how the observed Russell-McPherron pattern with time-of-year \textlessi\textgreaterF\textlessi/\textgreater and \textlessi\textgreaterUT\textlessi/\textgreater in the driving power input into the magnetosphere is converted into the equinoctial \textlessi\textgreaterF\textlessi/\textgreater-\textlessi\textgreaterUT\textlessi/\textgreater pattern in average geomagnetic activity (after correction is made for dipole tilt effects on ionospheric conductivity), added to a pronounced \textlessi\textgreaterUT\textlessi/\textgreater variation with minimum at 02–10 UT. In addition, we show that the predicted and observed \textlessi\textgreaterUT\textlessi/\textgreater variations in average geomagnetic activity has implications for the occurrence of the largest events that also show the nett \textlessi\textgreaterUT\textlessi/\textgreater variation.

Lockwood, Mike; Haines, Carl; Barnard, Luke; Owens, Mathew; Scott, Chris; Chambodut, Aude; McWilliams, Kathryn;

Published by: Journal of Space Weather and Space Climate      Published on:

YEAR: 2021     DOI: 10.1051/swsc/2020077

Middle-Low Latitude Neutral Composition and Temperature Responses to the 20 and 21 November 2003 Superstorm From GUVI Dayside Limb Measurements

TIMED/Global Ultraviolet Imager (GUVI) limb measurements of far-ultraviolet airglow emission have been used to investigate middle-low latitude thermospheric composition and neutral temperature responses to the 20 and 21 November 2003 (day of year [DOY] 324 and 325) superstorm. Altitude profiles of O, N2 number densities and temperature, as well as O/N2 column density ratio (∑O/N2), on the storm days along the GUVI limb tracks are compared with those on DOY 323 (quiet time). The storm-time composition and temperature responses were global and evolved continuously as the storm progressed. Specially, N2 and temperature increased almost globally at all altitudes during the storm and their perturbation structures were similar. The magnitudes of their enhancements both increased with altitude and latitude. The storm-induced O perturbations decreased in the lower thermosphere but increased in the upper thermosphere. Transition heights of O perturbations from decrease to increase changed with latitude and time. During the storm main and recovery phases, the storm-induced ∑O/N2 decreases were mostly related to the O depletion in the low-middle thermosphere, whereas ∑O/N2 increases during the storm were primarily caused by N2 depletion. There was a remarkable hemispheric asymmetry in composition responses as they have different morphologies and lifetime, especially during the storm recovery phase.

Yu, Tingting; Wang, Wenbin; Ren, Zhipeng; Yue, Jia; Yue, Xinan; He, Maosheng;

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

YEAR: 2021     DOI: 10.1029/2020JA028427

neutral composition; altitude profile; hemispheric asymmetry in composition responses; neutral temperature; superstorm; transition heights of O responses

The Response of Middle Thermosphere (∼160 km) Composition to the November 20 and 21, 2003 Superstorm

TIMED/GUVI limb measurements and first-principles simulations from the Thermosphere Ionosphere Electrodynamics Global Circulation Model (TIEGCM) are used to investigate thermospheric atomic oxygen (O) and molecular nitrogen (N2) responses in the middle thermosphere on a constant pressure surface (∼160 km) to the November 20 and 21, 2003 superstorm. The consistency between GUVI observations and TIEGCM simulated composition changes allows us to utilize TIEGCM outputs to investigate the storm-time behaviors of O and N2 systematically. Diagnostic analysis shows that horizontal and vertical advection are the two main processes that determine the storm-induced perturbations in the middle thermosphere. Molecular diffusion has a relatively smaller magnitude than the two advection processes, acting to compensate for the changes caused by the transport partly. Contributions from chemistry and eddy diffusion are negligible. During the storm initial and main phases, composition variations at high latitudes are determined by both horizontal and vertical advection. At middle-low latitudes, horizontal advection is the main driver for the composition changes where O mass mixing ratio decreases (N2 mass mixing ratio increases); whereas horizontal and vertical advection combined to dominate the changes in the regions where increases ( decreases). Over the entire storm period, horizontal advection plays a significant role in transporting high-latitude composition perturbations globally. Our results also demonstrate that storm-time temperature changes are not the direct cause of the composition perturbations on constant pressure surfaces.

Yu, Tingting; Wang, Wenbin; Ren, Zhipeng; Cai, Xuguang; Yue, Xinan; He, Maosheng;

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

YEAR: 2021     DOI: 10.1029/2021JA029449

atomic oxygen; GUVI limb observations; middle thermosphere; molecular nitrogen; storm-time perturbations; TIEGCM

Corotation of ring current auroral spots at sub-auroral latitudes

We report observations of auroral spots s at sub-auroral latitudes. The auroral spots occurred during storm-recovery phases and corotated with the Earth at a speed either higher (super-rotation) or lower (sub-rotation) than the Earth\textquoterights rotation rate. In the dawn side, the spots have a slightly higher probability of super-rotation than that of the duskside auroral spots. The super- and sub-rotation is likely due to dynamics of the plasmasphere that is controlled by both drag (sub-rotation) and solar wind driven plasma convection.

Zhang, Yongliang; Paxton, Larry;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: Jan-02-2020

YEAR: 2020     DOI: 10.1016/j.jastp.2020.105195

Auroral spots; Corotation; Sub-auroral latitude

Improving Neutral Density Predictions Using Exospheric Temperatures Calculated on a Geodesic, Polyhedral Grid

A new model of exospheric temperatures has been developed, with the objective of predicting global values with greater spatial and temporal accuracy. From these temperatures, the neutral densities in the thermosphere can be calculated, through use of the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar Extended (NRLMSISE-00) model. The exospheric temperature model is derived from measurements of the neutral densities on several satellites. These data were sorted into triangular cells on a geodesic grid, based on location. Prediction equations are derived for each grid cell using least error fits. Several versions of the model equations have been tested, using parameters such as the date, time, solar radiation, and nitric oxide emissions, as measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. Accuracy is improved with the addition of the total Poynting flux flowing into the polar regions, from an empirical model that uses the solar wind velocity and interplanetary magnetic field. Given such inputs, the model can produce global maps of the exospheric temperature. These maps show variations in the polar regions that are strongly modulated by the time of day, due to the daily rotation of the magnetic poles. For convenience the new model is referred to with the acronym EXTEMPLAR (EXospheric TEMperatures on a PoLyhedrAl gRid). Neutral densities computed from the EXTEMPLAR-NRLMSISE-00 models combined are found to produce very good results when compared with measured values.

Weimer, D.; Mehta, P.; Tobiska, W.; Doornbos, E.; Mlynczak, M.; Drob, D.; Emmert, J.;

Published by: Space Weather      Published on: 12/2019

YEAR: 2020     DOI: 10.1029/2019SW002355

Multi-scale ionosphere responses to the May 2017 magnetic storm over the Asian sector

We investigate multi-scale ionospheric responses to the May 27, 2017, geomagnetic storm over the Asian sector by using multi-instrumental observations, including ground-based global navigation satellite systems (GNSS) network, constellation observing system for meteorology, ionosphere and climate radio occultation, the FengYun-3C (FY-3C) GNSS occultation sounder electron density profiles and in situ plasma density observations provided by both Swarm and defense meteorological satellite program missions. This geomagnetic storm was an intense storm with the minimum symmetric horizontal component reaching - 150\ nT and was caused by a coronal mass ejection released on May 23. The main observations are summarized below: (1) two ionospheric positive storm periods were observed. The first one was observed in the noon\textendashafternoon sector during the main phase of the storm on May 28, with nearly 120\% TEC enhancement. The second one was of a smaller scale and occurred on the nightside during the recovery phase of the storm on May 29. The first dayside positive storm was initiated by the interplanetary magnetic field (IMF) Bz southward turning and eastward penetration electric field, while the second nightside one was terminated by a later southward turning of the IMF Bz since the Asian sector was on the nightside and the penetration electric field changed westward. (2) A negative storm occurred from 00:00 to 12:00 UT on May 30 over the Asian sector, nearly 2\ days after the main phase, which was due to the thermospheric composition change, i.e., decrease in the O/N₂ ratio, as shown in the TIMED/GUVI measurements. (3) A band-like TEC enhancement was observed aligning in the northwest\textendashsoutheast direction and propagated slowly southwestward from 15:00 to 20:00 UT (23:00\textendash04:00 LT, near midnight) on May 28 during the recovery phase of the storm. In situ density observations from the Swarm B and DMSP F15\&16 satellites confirmed the density enhancement at 510\ km and 850\ km, respectively, and revealed that this band-like TEC enhancement structure resembles the so-called plasma blob. The similarities of the observed plasma blob characteristics in terms of spatial structure, propagation trend and temporal evolution with the nighttime traveling ionospheric disturbance (TID) are consistent with the TID-blob theory.

Liu, Lei; Zou, Shasha; Yao, Yibin; Aa, Ercha;

Published by: GPS Solutions      Published on: 12/2019

YEAR: 2020     DOI: 10.1007/s10291-019-0940-1

Blob structure; Positive and negative ionosphere responses; TID; Geomagnetic storms

Effect of moderate geomagnetic storms on equatorial plasma bubbles over eastern Africa in the year 2012: Evolution and electrodynamics

Equatorial plasma bubbles (EPBs) are common features of the equatorial and low-latitude ionosphere and are known to cause radio wave scintillation which leads to the degradation of communication and navigation systems. Although these structures have been studied for decades, a full understanding of their evolution and dynamics remains important for space weather mitigation purposes. In this study, we present cases of EPBs occurrences around April and July 2012 geomagnetic storm periods over the African equatorial sector. The EPBs were observed from the Communications/Navigation Outage Forecasting System (C/NOFS) and generally correlated well to the ionospheric irregularities observed from the Global Positioning System total electron content (GPS-TEC) measurements (rate of TEC change, ROT). This study revealed that the evolution of the EPBs during moderate storms is controlled by the strength of the daytime equatorial electrojet (EEJ) currents regardless of the strength of the equatorial ionization anomaly (EIA), the latter is observed during the July storm case in particular. These effects were more evident during the main and part of the early recovery phases of the geomagnetic storm days considered. However, the evening hours TEC gradients between regions of the magnetic equator and ionization crests also played roles in the existence of ionospheric irregularities.

Giday, Nigussie; Katamzi-Joseph, Zama; Stoneback, Russell;

Published by: Advances in Space Research      Published on: 04/2020

YEAR: 2020     DOI: 10.1016/j.asr.2020.01.013

C/NOFS; Equatorial electrojets; equatorial plasma bubbles

A method to derive global O/N2 ratios from SSUSI/DMSP based on Re-AURIC algorithm

Global thermospheric O/N₂ column density ratios are obtained using the SSUSI/DMSP far-ultraviolet (FUV) dayglow data and the Re-AURIC simulation results. The Re-AURIC is derived from the AURIC algorithm after some old modules are updated. The calculation processes of O/N₂ ratio are then established using the simulations of Re-AURIC to calibrate the ratios of the OI 135.6\ nm emission and N₂ LBHS emission from SSUSI observations. The standard deviation (1σ) and correlation coefficient are 0.045 and 0.769 compared with the O/N₂ ratios provided by the SSUSI EDR data. The statistical errors between the calculated ratios and the EDR references are generally less than 0.2 with 96.40\% at 2σ (95.44\%) and less than 0.1 with 60.51\% at about 1σ (68.26\%). Two global O/N₂ ratio maps are obtained using this method to study its variations when the magnetic storm occurs. The significant O/N₂ depletion can be seen in one O/N₂ ratio map whose Kp index is 6. Also, the depletion is not uniform at different longitudes and the scales extend from high latitude to low latitude during magnetic storm. This proposed method provides us with a simple and useful tool to obtain the global O/N₂ distribution and even the future modeling from the observations on satellites.

Ding, GuangXing; Chen, Bo; Zhang, Xiaoxin; He, Fei;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 03/2020

YEAR: 2020     DOI: 10.1016/j.jastp.2020.105196

FUV dayglow; Magnetic storm; O/N2 ratio; Re-AURIC

Multi-wavelength coordinated observations of ionospheric irregularity structures from an anomaly crest location during unusual solar minimum of the 24th cycle

The present paper reports coordinated ionospheric irregularity measurements at optical as well as GPS wavelengths. Optical measurements were obtained from Tiny Ionospheric Photometer (TIP) sensors installed onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. GPS radio signals were obtained from a dual frequency GPS receiver operational at Calcutta (22.58\textdegreeN, 88.38\textdegreeE geographic; geomagnetic dip: 32.96\textdegree; 13.00\textdegreeN, 161.63\textdegreeE geomagnetic) under the SCIntillation Network Decision Aid (SCINDA) program. Calcutta is located near the northern crest of Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The observations were conducted during the unusually low and prolonged solar minima period of 2008\textendash2010. During this period, four cases of post-sunset GPS scintillation were observed from Calcutta. Among those cases, simultaneous fluctuations in GPS Carrier-to-Noise ratios (C/N_o) and measured radiances from TIP over a common ionospheric volume were observed only on February 2, 2008 and September 25, 2008. Fluctuations observed in measured radiances (maximum 0.95 Rayleigh) from TIP due to ionospheric irregularities were found to correspond well with C/N₀ fluctuations on the GPS links observed from Calcutta, such effects being noted even during late evening hours of 21:00\textendash22:00 LT from locations around 40\textdegree magnetic dip. These measurements indicate the existence of electron density irregularities of scale sizes varying over several decades from 135.6\ nm to 300\textendash400\ m well beyond the northern crest of the EIA in the Indian longitude sector during late evening hours even in the unusually low solar activity conditions.

Paul, Ashik; Sur, Dibyendu; Haralambous, Haris;

Published by: Advances in Space Research      Published on: 03/2020

YEAR: 2020     DOI: 10.1016/j.asr.2019.11.035

GPS radio measurements; ionospheric irregularities; Northern crest of EIA; Optical measurements; solar minimum; TIP

Response of the low- to mid-latitude ionosphere to the geomagnetic storm of September 2017

We study the impact of the geomagnetic storm of 7\textendash9\ September\ 2017 on the low- to mid-latitude ionosphere. The prominent feature of this solar event is the sequential occurrence of two SYM-H minima with values of -146 and -115 nT on 8\ September at 01:08 and 13:56 UT, respectively. The study is based on the analysis of data from the Global Positioning System (GPS) stations and magnetic observatories located at different longitudinal sectors corresponding to the Pacific, Asia, Africa and the Americas during the period 4\textendash14\ September\ 2017. The GPS data are used to derive the global, regional and vertical total electron content (vTEC) in the four selected regions. It is observed that the storm-time response of the vTEC over the Asian and Pacific sectors is earlier than over the African and American sectors. Magnetic observatory data are used to illustrate the variation in the magnetic field particularly, in its horizontal component. The global thermospheric neutral density ratio; i.e., O/N₂ maps obtained from the Global UltraViolet Spectrographic Imager (GUVI) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite are used to characterize the storm-time response of the thermosphere. These maps exhibit a significant storm-time depletion of the O/N₂ density ratio in the northern middle and lower latitudes over the western Pacific and American sectors as compared to the eastern Pacific, Asian and African sectors. However, the positive storm effects in the O/N₂ ratio can be observed in the low latitudes and equatorial regions. It can be deduced that the storm-time thermospheric and ionospheric responses are correlated. Overall, the positive ionospheric storm effects appear over the dayside sectors which are associated with the ionospheric electric fields and the traveling atmospheric disturbances. It is inferred that a variety of space weather phenomena such as the coronal mass ejection, the high-speed solar wind stream and the solar radio flux are the cause of multiple day enhancements of the vTEC in the low- to mid-latitude ionosphere during the period 4\textendash14\ September\ 2017.

Imtiaz, Nadia; Younas, Waqar; Khan, Majid;

Published by: Annales Geophysicae      Published on: 03/2020

YEAR: 2020     DOI: 10.5194/angeo-38-359-2020

Temporal evolution of substorm-driven global Alfv\ en wave power above the auroral acceleration region

The onset of substorms is associated with bursty enhancements of Alfv\ en wave power throughout the magnetotail. While impossible to assess the total Alfv\ en wave power in the entire magnetotail, we have instead monitored waves that are funneled into the auroral acceleration region, in order to assess the temporal evolution of Alfv\ en wave power above the nightside auroral zone in relation to substorm phases. The substorms were grouped by three conditions: nonstorm periods, storm periods, and all (unconditioned) periods. Using superposed epoch analysis, we found that the global magnetohydrodynamic Alfv\ en wave power increased significantly at onset for all three conditions, while a power decrease to pre-onset values occurred within 2 h. Specifically, the peak inflowing power during the expansion phase was 5.7 GW for unconditioned substorms, 5.6 GW for nonstorm-time substorms, and 7.8 GW for storm-time substorms. These results correspond to power increases with respect to pre-onset values of 138\%, 366\%, and 200\%, respectively. Additional analysis in relation to the aurora was performed for nonstorm-time substorms only. During the expansion phase, about 50\% of the Alfv\ en wave power over the entire nightside auroral zone is collocated with the auroral bulge region. Furthermore, the total inflowing Alfv\ en wave power over the entire nightside auroral zone is 17\% of the conjugate auroral power, while the inflowing power over the auroral bulge region is 32\% of the conjugate aurora. However, allowing for a finite absorption efficiency inside the auroral acceleration region, the likely average Alfv\ enic contributions to the aurora are approximately 10\% and 18\%,respectively.

Keiling, Andreas; Thaller, Scott; Dombeck, John; Wygant, John;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2020

YEAR: 2020     DOI: 10.1029/2019JA027444

Alfven wave; Alfvenic electron; AURORA; auroral acceleration; magnetotail; Substorm

Aurora in the Polar Cap: A Review

This paper reviews our current understanding of auroral features that appear poleward of the main auroral oval within the polar cap, especially those that are known as Sun-aligned arcs, transpolar arcs, or theta auroras. They tend to appear predominantly during periods of quiet geomagnetic activity or northwards directed interplanetary magnetic field (IMF). We also introduce polar rain aurora which has been considered as a phenomenon on open field lines. We describe the morphology of such auroras, their development and dynamics in response to solar wind-magnetosphere coupling processes, and the models that have been developed to explain them.

Hosokawa, Keisuke; Kullen, Anita; Milan, Steve; Reidy, Jade; Zou, Ying; Frey, Harald; Maggiolo, Romain; Fear, Robert;

Published by: Space Science Reviews      Published on: 02/2020

YEAR: 2020     DOI: 10.1007/s11214-020-0637-3

Auroral Structure and Dynamics From GOLD

The Global-scale Observations of the Limb and Disk (GOLD) mission data contain significant quantitative information about the aurora on a global scale. Here we present techniques for quantifying such information, including the temporal development of the structure within the auroral oval using the GOLD images. These techniques are applied to auroral observations in the GOLD data, in particular showing an example of how the longitudinal structure within the aurora varies over the course of six consecutive days with differing levels of geomagnetic activity. A simple model of the solar-induced airglow is presented that is used to remove the sunlight contamination from the dayside auroral observations. Comparisons to ground-based auroral imaging are used for the overall auroral context and to make estimates of the proportionality between the intensities of the green line (557.7\ nm) emission in the visible and the 135.6\ nm emissions in the GOLD data. These observations are consistent with the intensity of the 135.6\ nm auroral emission being on the same order as the intensity of the 557.7\ nm auroral emission. They were both found to be around 1\ kR for a stable auroral arc on a day with low geomagnetic activity (3 November 2018) and around 10\ kR for an active auroral display on a day with higher levels of geomagnetic activity (5 November 2018). This could have important implications for making direct comparisons between space-based ultraviolet auroral imaging and ground-based visible-light auroral imaging and the total energy input estimates that are derived from them.

Michell, R.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2020

YEAR: 2020     DOI: 10.1029/2019JA027650

AURORA; GOLD; GUVI

Dynamical Properties of Peak and Time-Integrated Geomagnetic Events Inferred From Sample Entropy

We provide a comprehensive statistical analysis of the sample entropy of peak and time-integrated geomagnetic events in 2001\textendash2017, considering different measures of event strength, different geomagnetic indices, and a simplified solar wind-magnetosphere coupling function . Our investigations reveal the existence of significant correlations between the entropies of , , and , and between such entropies and event strengths, as well as good correlations between peak levels of solar wind-magnetosphere coupling and ring current ( ) and entropies, suggesting a potential predictability of significant and events on the basis of appropriate functions of . Sensibly weaker correlations are found with entropy. We further show the presence of several significant entropy correlations between geomagnetic indices, solar wind-magnetosphere coupling, and trapped or precipitated energetic electron and ion fluxes measured by geostationary and low Earth orbit satellites in the outer radiation belt during the same periods. Entropy correlations between and trapped or precipitated 30- to 80-keV ion fluxes at low and between and trapped 40-keV electron fluxes at geostationary orbit correspond well with ring current properties and substorm-induced injections, respectively. Entropy correlations between and precipitation rates of energetic ion and electron fluxes demonstrate the sensibility of index entropy to both low-energy (5\textendash30 keV) electron injections and ring current. The stronger entropy correlation between solar wind-magnetosphere coupling and than likely stems from the more stochastic behavior of electron injections and fast losses near geostationary orbit.

Mourenas, D.; Artemyev, A.; Zhang, X.-J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2020

YEAR: 2020     DOI: 10.1029/2019JA027599

Dynamical complexity; Entropy; geomagnetic indices; Geomagnetic storms; Solar wind magnetosphere coupling

Evaluation on the Quasi-Realistic Ionospheric Prediction Using an Ensemble Kalman Filter Data Assimilation Algorithm

In this work, we evaluated the quasi-realistic ionosphere forecasting capability by an ensemble Kalman filter (EnKF) ionosphere and thermosphere data assimilation algorithm. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model is used as the background model in the system. The slant total electron contents (TECs) from global International Global Navigation Satellite Systems Service ground-based receivers and from the Constellation Observing System for Meteorology, Ionosphere and Climate are assimilated into the system, and the ionosphere is then predicted in advance during the quiet interval of 23 to 27 March 2010. The predicted ionosphere vertical TEC (VTEC) and the critical frequency foF₂ are validated by the Massachusetts Institute of Technology VTEC and global ionosondes network, respectively. We found that the ionosphere forecast quality could be enhanced by optimizing the thermospheric neutral components via the EnKF method. The ionosphere electron density forecast accuracy can be improved by at least 10\% for 24 hr. Furthermore, the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) [O/N₂] observations are used to validate the predicted thermosphere [O/N₂]. The validation shows that the [O/N₂] optimized by EnKF has better agreement with the TIMED/GUVI observation. This study further demonstrates the validity of EnKF in enhancing the ionospheric forecast capability in addition to our previous observing system simulation experiments by He et al. (2019, https://doi.org/10.1029/2019JA026554).

He, Jianhui; Yue, Xinan; Le, Huijun; Ren, Zhipeng; Wan, Weixing;

Published by: Space Weather      Published on: 02/2020

YEAR: 2020     DOI: 10.1029/2019SW002410

Investigating Magnetosphere-Ionosphere-Thermosphere (M-I-T) Coupling Occurring During the 7\textendash8 November 2004 Superstorm

In this study, we investigate the shock-sheath driven 7\textendash8 November 2004 superstorm for its flux transfer events and resultant flow channel (FC) events and associated neutral (D_N) and electron (Ne) density features in order to understand better the underlying coupled magnetosphere (M) and ionosphere (I) processes and responses in the thermosphere (T). We focus on the (i) subauroral, auroral, and polar cap regions, (ii) localized D_N increases and associated Ne features and FCs developed, and (iii) energy deposition occurred. Results show the development of localized D_N increases (1) within/over FCs and associated enhanced small-scale field aligned currents suggesting Joule heating driving upwelling during forward and reverse polar convections, (2) appearing with Ne increases during storm-enhanced density (SED) events suggesting strong M-I-T coupling and with Ne depletions during plasmaspheric erosion events suggesting weak M-I-T coupling, and (3) in the thermosphere\textquoterights increasing NO and continuously low O/N₂ composition regions. During erosion events, strong storm-time subauroral polarization streams (SAPS) E fields developed. Meanwhile the well-developed plasmapause appeared with decreased total electron content (TEC) on its poleward side and with increased TEC and Ne (appearing as a shoulder feature that is the signature of SED) on its equatorward side. From these we conclude that although strong M-I-T coupling was apparent during SED events, M-I-T coupling was also strong during erosion events when the combination of strong convection E field and large storm-time SAPS E fields eroded the high-latitude region and thus decreased the high-latitude Ne and TEC.

Horvath, Ildiko; Lovell, Brian;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2020

YEAR: 2020     DOI: 10.1029/2019JA027484

flow channels; large-scale FACs; localized neutral density increases; nitric oxide (NO); Poynting flux; type-1 and type-2 aurorae

Modeled IMF B _y Effects on the Polar Ionosphere and Thermosphere Coupling

There is still an inadequate understanding of how the interplanetary magnetic field (IMF) east-west component (B_y) affects thermospheric composition, and other ionospheric and thermospheric fields in a systematic way. Utilizing the state-of-art first-principles Coupled Magnetosphere Ionosphere Thermosphere (CMIT) modeling and TIMED/Global Ultraviolet Imager (GUVI)-observed ΣO/N₂ covering an entire solar cycle (year 2002\textendash2016), as well as a neutral parcel trajectory tracing technique, we emphasize that not only the direction of B_y, but also its strength relative to the IMF north-south component (B_z) that has important effects on high latitude convection, Joule heating, electron density, neutral winds, and neutral composition patterns in the upper thermosphere. The Northern Hemisphere convection pattern becomes more twisted for positive B_y cases than negative cases: the dusk cell becomes more rounded compared with the dawn cell. Consequently, equatorward neutral winds are stronger during postmidnight hours in negative B_y cases than in positive B_y cases, creating a favorable condition for neutral composition disturbances (characterized by low ΣO/N₂) to expand to lower latitudes. This may lead to a more elongated ΣO/N₂ depletion area along the morning-premidnight direction for negative B_y conditions compared with the positive B_y conditions. Backward neutral parcel trajectories indicate that a lower ΣO/N₂ parcel in negative B_y cases comes from lower altitudes, as compared with that for positive B_y cases, leading to larger enhancements of N₂ in the former case.

Liu, Jing; Burns, Alan; Wang, Wenbin; Zhang, Yongliang;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2020

YEAR: 2020     DOI: 10.1029/2019JA026949

Modeling the Impact of Metallic Ion Layers on Equatorial Spread With SAMI3/ESF

The impact of region metal ion layers on the development of equatorial plasma bubbles is investigated using the SAMI3/ESF model. We find that metal ion layers reduce the growth rate of the generalized Rayleigh-Taylor instability (GRTI) and act to suppress the development of equatorial plasma bubbles. This is consistent with theoretical expectations and observations and is attributed to the increase in both the Pedersen and Hall conductances. Additionally, inhomogeneities in the region metal ion layer can map into the layer and alter the morphology of equatorial spread (ESF) bubble evolution. Lastly, we find that if EFS bubbles develop in the presence of a metal ion layer, then the electric fields generated by the instability can lift the metal ions into the region. This is consistent with observations of Fe in the region during equatorial spread .

Huba, J.; Krall, J.; Drob, D.;

Published by: Geophysical Research Letters      Published on: 02/2020

YEAR: 2020     DOI: 10.1029/2020GL087224

Equatorial ionosphere; Equatorial Spread F; metal ions; sporadic E

Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites

During the night, in the F-region, equatorial ionospheric irregularities manifest as plasma depletions observed by satellites, and they may cause radio signals to fluctuate. In this study, the distribution characteristics of ionospheric F-region irregularities in the low latitudes were investigated using 16 Hz electron density observations made by a faceplate which is a component of the electric field instrument (EFI) onboard Swarm satellites of the European Space Agency (ESA). The study covers the period from October\ 2014 to October\ 2018 when the 16 Hz electron density data were available. For comparison, both the absolute (dN_e) and relative (dN_e/N_e) density perturbations were used to quantify the level of ionospheric irregularities. The two methods generally reproduced the local-time (LT), seasonal and longitudinal distribution of equatorial ionospheric irregularities as shown in earlier studies, demonstrating the ability of Swarm 16 Hz electron density data. A difference between the two methods was observed based on the latitudinal distribution of ionospheric irregularities where (dN_e) showed a symmetrical distribution about the magnetic equator, while dN_e/N_e showed a magnetic-equator-centred Gaussian distribution. High values of dN_e and dN_e/N_e were observed in spatial bins with steep gradients of electron density from a longitudinal and seasonal perspective. The response of ionospheric irregularities to geomagnetic and solar activities was also investigated using Kp index and solar radio flux index (F10.7), respectively. The reliance of dN_e/N_e on solar and magnetic activity showed little distinction in the correlation between equatorial and off-equatorial latitudes, whereas dN_e showed significant differences. With regard to seasonal and longitudinal distribution, high dN_e and dN_e/N_e values were often found during quiet magnetic periods compared to magnetically disturbed periods. The dN_e increased approximately linearly from low to moderate solar activity. Using the high-resolution faceplate data, we were able to identify ionospheric irregularities on the scale of only a few hundred of metres.

Aol, Sharon; Buchert, Stephan; Jurua, Edward;

Published by: Annales Geophysicae      Published on: 02/2020

YEAR: 2020     DOI: 10.5194/angeo-38-243-2020

A case study of isolated auroral spots based on DMSP data

This study employed ultraviolet images and particle data to investigate isolated auroral spots away from the Earth\textquoterights auroral oval. Data from SSUSI (Special Sensor Ultraviolet Spectrographic Imager) and SSJ (Special Sensor J) mounted on the DMSP (Defence Meteorological Satellite Program) spacecraft were examined. The isolated auroral spots were observed by DMSP F16/SSUSI and F17/SSUSI on 29 May 2010 during the recovery phase of a moderate geomagnetic storm with a minimum SYM-H index of -70 nT. The auroral spots were observed between 18:00\textendash21:00 MLT and corotated with the Earth, but stayed almost at the same magnetic latitude (MLAT) of -60\textdegree. It is found that the isolated auroral spots were produced mainly by energetic ring current ions at energies above ~10\ keV. The enhancement in the electron flux with energy below ~200\ eV was also observed for the isolated auroral spots. The MLAT of the electron flux was nearly 2\textdegreehigher than that for the precipitating ions.

Zhou, Su; Chen, Yuqing; Zhang, Jin;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 01/2020

YEAR: 2020     DOI: 10.1016/j.jastp.2019.105176

Isolated auroral spots; Proton aurora; Subauroral electron precipitation

Comparison of Reference Heights of O/N ₂ and ∑O/N ₂ Based on GUVI Dayside Limb Measurement

We define a new thermospheric concept, the reference heights of O/N₂, referring to a series of thermospheric heights corresponding to the fixed ratios of O to N₂ number density. Here, based on Global Ultraviolet Imager (GUVI) limb measurement, we compare O/N₂ column density ratio (∑O/N₂) and the reference heights of O/N₂. We choose the transition height of O and N₂ (transition height hereafter), a special reference height at which O number density is equal to N₂ number density, to verify the connection with ∑O/N₂ during geomagnetically quiet periods. It is found that transition height and ∑O/N₂ have noticeable negative correlation with correlation coefficient of -0.887. An empirical model of transition height (O/N₂ model hereafter) is established based on nonlinear least-squares-fitting method. The considerable correlation (greater than 0.96), insignificant errors (less than 4\%) and the great influencing weight of ∑O/N₂ to reference heights indicate the validity of O/N₂ model and the existence of quantitative relation between ∑O/N₂ and transition height. Besides, it is verified that the similar quantitative relation also exists between ∑O/N₂ and reference heights of other O/N₂ values. Namely, using the O/N₂ model coefficients, we can roughly get the whole altitude profiles of O/N₂ within 6\% precision for any given ∑O/N₂.

Yu, Tingting; Ren, Zhipeng; Yu, You; Yue, Xinan; Zhou, Xu; Wan, Weixing;

Published by: Space Weather      Published on: 01/2020

YEAR: 2020     DOI: 10.1029/2019SW002391

O/N2 ratio

Diffuse and Pulsating Aurora

This chapter reviews fundamental properties and recent advances of diffuse and pulsating aurora. Diffuse and pulsating aurora often occurs on closed field lines and involves energetic electron precipitation by wave-particle interaction. After summarizing the definition, large-scale morphology, types of pulsation, and driving processes, we review observation techniques, occurrence, duration, altitude, evolution, small-scale structures, fast modulation, relation to high-energy precipitation, the role of ECH waves, reflected and secondary electrons, ionosphere dynamics, and simulation of wave-particle interaction. Finally we discuss open questions of diffuse and pulsating aurora.

Nishimura, Yukitoshi; Lessard, Marc; Katoh, Yuto; Miyoshi, Yoshizumi; Grono, Eric; Partamies, Noora; Sivadas, Nithin; Hosokawa, Keisuke; Fukizawa, Mizuki; Samara, Marilia; Michell, Robert; Kataoka, Ryuho; Sakanoi, Takeshi; Whiter, Daniel; Oyama, Shin-ichiro; Ogawa, Yasunobu; Kurita, Satoshi;

Published by: Space Science Reviews      Published on: 01/2020

YEAR: 2020     DOI: 10.1007/s11214-019-0629-3

The Far Ultraviolet Signatures of Conjugate Photoelectrons Seen by the Special Sensor Ultraviolet Spectrographic Imager

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

Impacts of Binning Methods on High-Latitude Electrodynamic Forcing: Static Versus Boundary-Oriented Binning Methods

An outstanding issue in the general circulation model simulations for Earth\textquoterights upper atmosphere is the inaccurate estimation of Joule heating, which could be associated with the inaccuracy of empirical models for high-latitude electrodynamic forcing. The binning methods used to develop those empirical models may contribute to the inaccuracy. Traditionally, data are binned through a static binning approach by using fixed geomagnetic coordinates, in which the dynamic nature of the forcing is not considered and therefore the forcing patterns may be significantly smeared. To avoid the smoothing issue, data can be binned according to some physically important boundaries in the high-latitude forcing, that is, through a boundary-oriented binning approach. In this study, we have investigated the sensitivity of high-latitude forcing patterns to the binning methods by applying both static and boundary-oriented binning approaches to the electron precipitation and electric potential data from the Defense Meteorological Satellite Program satellites. For this initial study, we have focused on the moderately strong and dominantly southward interplanetary magnetic field conditions. As compared with the static binning results, the boundary-oriented binning approach can provide a more confined and intense electron precipitation pattern. In addition, the magnitudes of the electric potential and electric field in the boundary-oriented binning results increase near the convection reversal boundary, leading to a ~11\% enhancement of the cross polar cap potential. The forcing patterns obtained from both binning approaches are used to drive the Global Ionosphere and Thermosphere Model to assess the impacts on Joule heating by using different binning patterns. It is found that the hemispheric-integrated Joule heating in the simulation driven by the boundary-oriented binning patterns is 18\% higher than that driven by the static binning patterns.

Zhu, Qingyu; Deng, Yue; Richmond, Arthur; Maute, Astrid; Chen, Yun-Ju; Hairston, Marc; Kilcommons, Liam; Knipp, Delores; Redmon, Robert; Mitchell, Elizabeth;

Published by: Journal of Geophysical Research: Space Physics      Published on: 01/2020

YEAR: 2020     DOI: 10.1029/2019JA027270

Electric field; high latitude; Joule heating; particle precipitation

The physics of space weather/solar-terrestrial physics (STP): what we know now and what the current and future challenges are

Major geomagnetic storms are caused by un-usually intense solar wind southward magnetic fields thatimpinge upon the Earth\textquoterights magnetosphere (Dungey, 1961).How can we predict the occurrence of future interplanetary events? Do we currently know enough of the underlying physics and do we have sufficient observations of solar wind phenomena that will impinge upon the Earth\textquoterights magnetosphere? We view this as the most important challenge in space weather. We discuss the case for magnetic clouds (MCs), interplanetary sheaths upstream of interplanetary coronal mass ejections (ICMEs), corotating interactionregions (CIRs) and solar wind high-speed streams (HSSs).The sheath- and CIR-related magnetic storms will be difficult to predict and will require better knowledge of the slow solar wind and modeling to solve. For interplanetaryspace weather, there are challenges for understanding the fluences and spectra of solar energetic particles (SEPs). This will require better knowledge of interplanetary shock properties as they propagate and evolve going from the Sun to1 AU (and beyond), the upstream slow solar wind and energetic \textquotedblleftseed\textquotedblright particles. Dayside aurora, triggering of night-side substorms, and formation of new radiation belts can all be caused by shock and interplanetary ram pressure impingements onto the Earth\textquoterights magnetosphere. The acceleration and loss of relativistic magnetospheric \textquotedblleftkiller\textquotedblright electronsand prompt penetrating electric fields in terms of causingpositive and negative ionospheric storms are reasonably well understood, but refinements are still needed. The forecasting of extreme events (extreme shocks, extreme solar energeticparticle events, and extreme geomagnetic storms (Carrington events or greater)) are also discussed. Energetic particle precipitation into the atmosphere and ozone destructionare briefly discussed. For many of the studies, the Parker Solar Probe, Solar Orbiter, Magnetospheric Multiscale Mission(MMS), Arase, and SWARM data will be useful.

Tsurutani, Bruce; Lakhina, Gurbax; Hajra, Rajkumar;

Published by: Nonlinear Processes in Geophysics      Published on: 01/2020

YEAR: 2020     DOI: 10.5194/npg-27-75-2020

Real-Time Thermospheric Density Estimation via Two-Line Element Data Assimilation

Inaccurate estimates of the thermospheric density are a major source of error in low Earth orbit prediction. Therefore, real-time density estimation is required to improve orbit prediction. In this work, we develop a dynamic reduced-order model for the thermospheric density that enables real-time density estimation using two-line element (TLE) data. For this, the global thermospheric density is represented by the main spatial modes of the atmosphere and a time-varying low-dimensional state and a linear model is derived for the dynamics. Three different models are developed based on density data from the TIE-GCM, NRLMSISE-00, and JB2008 thermosphere models and are valid from 100 to maximum 800 km altitude. Using the models and TLE data, the global density is estimated by simultaneously estimating the density and the orbits and ballistic coefficients of several objects using a Kalman filter. The sequential estimation provides both estimates of the density and corresponding uncertainty. Accurate density estimation using the TLEs of 17 objects is demonstrated and validated against CHAMP and GRACE accelerometer-derived densities. The estimated densities are shown to be significantly more accurate and less biased than NRLMSISE-00 and JB2008 modeled densities. The uncertainty in the density estimates is quantified and shown to be dependent on the geographical location, solar activity, and objects used for estimation. In addition, the data assimilation capability of the model is highlighted by assimilating CHAMP accelerometer-derived density data together with TLE data to obtain more accurate global density estimates. Finally, the dynamic thermosphere model is used to forecast the density.

Gondelach, David; Linares, Richard;

Published by: Space Weather      Published on: 01/2020

YEAR: 2020     DOI: 10.1029/2019SW002356

density estimation; reduced-order modeling; satellite drag; thermospheric density modeling; two-line element data

Ionospheric parameters in the European sector during the magnetic storm of August 25—26, 2018

Blagoveshchensky, DV; Sergeeva, MA;

Published by: Advances in Space Research      Published on:

YEAR: 2020     DOI:

A New method for deriving the nightside thermospheric density based on guvi dayside limb observations

Yu, Tingting; Ren, Zhipeng; Yu, You; Wan, Weixing;

Published by: Space Weather      Published on:

YEAR: 2020     DOI:

An observational review on influence of intense geomagnetic storm on positional accuracy of NavIC/IRNSS system

Desai, Mehul; Shah, Shweta;

Published by: IETE Technical Review      Published on:

YEAR: 2020     DOI: