Bibliography

Spatial-Temporal Behaviors of Large-Scale Ionospheric Perturbations During Severe Geomagnetic Storms on September 7–8 2017 Using the GNSS, SWARM and TIE-GCM Techniques

Geomagnetic storms on 7–8 September 2017 triggered severe ionospheric disturbances that had a serious effect on satellite navigation and radio communication. Multiple observations derived from Global Navigation Satellite System receivers, Earth s Magnetic Field and Environment Explorers (SWARM) and the Thermosphere-Ionosphere -Electrodynamics General Circulation Model s simulations are utilized to investigate the spatial-temporal ionospheric behaviors under storm conditions. The results indicate that the electron density in the Asia-Australia, Europe-Africa and America sectors suddenly changed with the Bz southward excursion, and the ionosphere over low-middle latitudes under the sunlit hemisphere is easily affected by the disturbed magnetic field. The SWARM observations verified the remarkable double-peak structure of plasma enhancements over the equator and middle latitudes. The physical mechanism of low-middle plasma disturbances can be explained by a combination effect of equatorial electrojets, vertical E × B drifts, meridional wind and thermospheric O/N2 change. Besides, the severe storms triggered strong Polar plasma disturbances on both dayside and nightside hemispheres, and the Polar disturbances had a latitudinal excursion associated with the offset of geomagnetic field. Remarkable plasma enhancements at the altitudes of 100–160 km were also observed in the auroral zone and middle latitudes (\textgreater47.5°N/S). The topside polar ionospheric plasma enhancements were dominated by the O+ ions. Furthermore, the TIE-GCM s simulations indicate that the enhanced vertical E × B drifts, cross polar cap potential and Joule heating play an important role in generating the topside plasma perturbations.

Li, Wang; Zhao, Dongsheng; He, Changyong; Hancock, Craig; Shen, Yi; Zhang, Kefei;

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

YEAR: 2022     DOI: 10.1029/2021JA029830

hemispheric asymmetry; ionospheric disturbances; Magnetic storms; thermospheric composition changes; TIE-GCM

Comparison of ionospheric anomalies over African equatorial/low-latitude region with IRI-2016 model predictions during the maximum phase of solar cycle 24

The capability of IRI-2016 in reproducing the hemispheric asymmetry, the winter and semiannual anomalies has been assessed over the equatorial ionization anomaly (EIA) during quiet periods of years 2013–2014. The EIA reconstructed using Total Electron Content (TEC) derived from Global Navigation Satellite System was compared with that computed using IRI-2016 along longitude 25° − 40oE. These were analyzed along with hemispheric changes in the neutral wind derived from the horizontal wind model and the TIMED GUVI columnar O/N2 data. IRI-2016 clearly captured the hemispheric asymmetry of the anomaly during all seasons albeit with some discrepancies in the magnitude and location of the crests. The winter anomaly in TEC which corresponded with greater O/N2 in the winter hemisphere was also predicted by IRI-2016 during December solstice. The model also captured the semiannual anomaly with stronger crests in the northern hemisphere. Furthermore, it reproduced the variation trend of the asymmetry index (A) in December solstice and equinox during noon. However, in June solstice the model failed to capture the winter anomaly and misrepresented the variation of A. This was linked with its inability to accurately predict the pattern of the neutral wind, the maximum height of the F2 layer and the changes in O/N2 in both hemispheres. The difference between the variations of EUV and F10.7 fluxes was also a potential source of errors in IRI-2016. The results highlight the significance of the inclusion of wind data in IRI-2016 in order to enhance its performance over East Africa.

Amaechi, Paul; Oyeyemi, Elijah; Akala, Andrew; Kaab, Mohamed; Younas, Waqar; Benkhaldoun, Zouhair; Khan, Majid; Mazaudier, Christine-Amory;

Published by: Advances in Space Research      Published on: aug

YEAR: 2021     DOI: 10.1016/j.asr.2021.03.040

Equatorial ionization anomaly; hemispheric asymmetry; IRI-2016; Semiannual anomaly; Winter anomaly

Ionospheric response to the 2015 St. Patrick's Day storm: A global multi-instrumental overview

We present the first multi-instrumental results on the ionospheric response to the geomagnetic storm of 17\textendash18 March 2015 (the St. Patrick\textquoterights Day storm) that was up to now the strongest in the 24th solar cycle (minimum SYM-H value of -233 nT). The storm caused complex effects around the globe. The most dramatic positive ionospheric storm occurred at low latitudes in the morning (~100\textendash150\% enhancement) and postsunset (~80\textendash100\% enhancement) sectors. These significant vertical total electron content increases were observed in different local time sectors and at different universal time, but around the same area of the Eastern Pacific region, which indicates a regional impact of storm drivers. Our analysis revealed that this particular region was most concerned by the increase in the thermospheric O/N₂\ ratio. At midlatitudes, we observe inverse hemispheric asymmetries that occurred, despite the equinoctial period, in different longitudinal regions. In the European-African sector, positive storm signatures were observed in the Northern Hemisphere (NH), whereas in the American sector, a large positive storm occurred in the Southern Hemisphere, while the NH experienced a negative storm. The observed asymmetries can be partly explained by the thermospheric composition changes and partly by the hemispherically different nondipolar portions of the geomagnetic field as well as by the IMF By component variations. At high latitudes, negative ionospheric storm effects were recorded in all longitudinal regions, especially the NH of the Asian sector was concerned. The negative storm phase developed globally on 18 March at the beginning of the recovery phase.

Astafyeva, Elvira; Zakharenkova, Irina; Förster, Matthias;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2015

YEAR: 2015     DOI: 10.1002/2015JA021629

geomagnetic storm; hemispheric asymmetry; Ionosphere; negative storm; positive storm; Swarm mission

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

Solar cycle dependence of the seasonal variation of auroral hemispheric power

Although much has been done on the hemispheric asymmetry (or seasonal variations) of auroral hemispheric power (HP), the dependence of HP hemispheric asymmetry on solar cycle has not yet been studied. We have analyzed data during 1979\textendash2010 and investigated the dependence of HP hemispheric asymmetry/seasonal variation for the whole solar cycle. Here we show that (1) the hemispheric asymmetry of HP is positively correlated to the value of solar F10.7 with some time delay; (2) it is closely related to the coupling function between the solar wind and magnetosphere; and (3) the winter hemisphere receives more auroral power than the summer hemisphere for K _p\~0 to 6. The statistic results can be partly understood in the framework of the ionospheric conductivity feedback model. The similarity and differences between our results and previous results are discussed in the paper.

Zheng, Ling; Fu, SuiYan; Zong, QuiGang; Parks, George; Wang, Chi; Chen, Xi;

Published by: Chinese Science Bulletin      Published on: 02/2013

YEAR: 2013     DOI: 10.1007/s11434-012-5378-6

auroral power; coupling function; hemispheric asymmetry; precipitation; solar cycle

Analyzing the hemispheric asymmetry in the thermospheric density response to geomagnetic storms

The thermospheric densities derived by CHAMP/STAR accelerometer within the time period from 01 May 2001 to 31 December 2007 are utilized to investigate the hemispheric asymmetry in response to strong storm driving conditions. The geomagnetic storms of 03\textendash07 April 2004 are first studied since the storms occurred close to the vernal equinox, allowing the seasonal asymmetry to be eliminated to the greatest extent. The averaged density enhancements in the southern polar region were much larger than that in the northern polar region. The comparisons of density versus Dst and Apindex indicate a strong linear dependence with the slopes of the fitted lines in the southern hemisphere being 50\% greater than that in the northern hemisphere. This effect can possibly be attributed to the non-symmetric geomagnetic field. 102 storm events are used to conduct a statistical analysis. For each storm, a linear fit is made between the averaged mass density and theDst and Ap indices independently in each hemisphere. The seasonal variation of the intercepts and the slopes of the fitted lines are further explored. The baseline is strongly dependent on season, with the hemisphere receiving the larger amount of sunlight having larger density. The slopes showed considerable hemispheric differences around the vernal equinox yet no statistical differences around other seasons. It is speculated that competing mechanisms cancel each other during the solstices, while during the equinoxes, the lower magnetic field in the southern hemisphere may allow stronger ion flows, thereby causing more Joule heating. It is uncertain why the vernal equinox would be favored in this explanation though.

Ercha, A.; Ridley, Aaron; Zhang, Donghe; Xiao, Zuo;

Published by: Journal of Geophysical Research      Published on: 08/2012

YEAR: 2012     DOI: 10.1029/2011JA017259

Geomagnetic storms; hemispheric asymmetry; thermospheric density