Bibliography

The investigation on daytime conjugate hemispheric asymmetry along 100°E longitude using observations and model simulations: New insights

The hemispherical asymmetry of the low latitude region along 100°E ± 5°E is scrutinized for the year 2015 at magnetically conjugate points on seasonal and intra-seasonal time scales. Two conjugate Ionosonde station pairs are selected- one pair in the inner valley (from SEALION) and the other in the outer edges of the EIA region. The anomaly in the stations is estimated using the difference of low latitude NmF2 from the dip equatorial NmF2 in the same meridian. A monthly average scheme is used instead of a seasonal mean, as the month-to-month variations are found to provide intricate details. The anomaly at the conjugate stations is highly asymmetric even during the equinoctial months of March and October, whereas it is nearly symmetric during April. During June/July, the morning time hemispheric asymmetry (larger on the winter side) temporarily reduces in the midday period and then reverses sign (larger in summer) in the afternoon. The NmF2 observations suggest a close relation of hemispheric symmetry to the position of the subsolar point with respect to the dip equator and a shift/expansion of the trough region of the EIA towards the summer hemisphere. The inter-hemispheric comparison of the hmF2 suggests a strong modulating influence of meridional winds at both the inner and outer stations which depend strongly on the relative position of the subsolar point with respect to the field line geometry. Theoretical (SAMI3/SAMI2) and empirical model (IRI) simulations show a meridional movement of the EIA region with the subsolar point. The winter to summer hemisphere movement of the EIA trough and crest region is also reproduced in the GIM-TEC along 100°E for 2015. This shifting or tailoring of the trough and the crest region is attributed primarily to the meridional wind field, which varies with the shifting position of subsolar point relative to the field line geometry. The seasonal and intra-seasonal difference in the NmF2 hemispheric asymmetry is attributed to the misalignment of the two centers of power viz., the thermospheric/neutral processes and the electromagnetic forces, due to the geographic-geomagnetic offset in this longitude.

Kalita, B.; Bhuyan, P.; Nath, S.; Choudhury, M.; Chakrabarty, D.; Wang, K.; Hozumi, K.; Supnithi, P.; Komolmis, T.; . Y. Yatini, C; Le Huy, M.;

Published by: Advances in Space Research      Published on: may

YEAR: 2022     DOI: 10.1016/j.asr.2022.02.058

NmF2; asymmetry; Conjugate; EIA; model; Hemisphere; hmF2; Subsolar

Climatology of global, hemispheric and regional electron content variations during the solar cycles 23 and 24

We present the results of study on the variations of ionospheric total electron content (TEC) by using global, hemispheric, and regional electron contents computed from the global ionospheric maps (GIMs) for the period from 1999 to 2020. For a low and moderate solar activity, the global and regional electron contents vary linearly with solar 10.7 cm radio flux and EUV flux. While a saturation effect in the electron content verses EUV and F10.7 is found during the high solar activity periods at all regions, the maximum effect is observed at low-latitudes followed by high and mid-latitudes region. The extent of saturation effect is more pronounced for F10.7 as compared to EUV. A wavelet transform is applied to global and hemispheric electron contents to examine the relative strength of different variations. The semi-annual variations dominate in the northern hemisphere, whereas annual variations dominate in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern counterpart at all latitudes. This asymmetry in the amplitude of annual variation is maximum at low-latitudes, followed by mid and high-latitudes, respectively. The semi-annual variations are in-phase in both hemisphere and follow the solar cycle. The northern hemisphere depicts relatively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes.

Younas, Waqar; Amory-Mazaudier, C.; Khan, Majid; Amaechi, Paul;

Published by: Advances in Space Research      Published on: jul

YEAR: 2022     DOI: 10.1016/j.asr.2022.07.029

annual variation; global electron content; Ionosphere; semi-annual variation; total electron content

Middle and low latitudes hemispheric asymmetries in ∑O/N2 and TEC during intense magnetic storms of solar cycle 24

We have investigated the global hemispheric differences in thermospheric ∑O/N2 and its impact on the ionospheric total electron content (TEC) at mid- and low-latitudes. Four intense storms of solar cycle 24 (SC-24) have been considered, three of them occurred in Spring equinox and one in Summer solstice season. It is found that the mid-latitudes region has exhibited a large decrease in ∑O/N2 during all the phases of the storms under consideration, which corresponds well to the observed negative storm effects. This decrease is directly related with the storm intensity. The maximum reduction in the ∑O/N2 is observed for the St. Patrick day storm of 2015 (which was the most intense geomagnetic storm of SC-24), whereas the respective minimum decrease is found for the storm of April 2012. Strong hemispheric asymmetries, in ∑O/N2 variation, have been observed at the mid-latitudes sector, and can be associated with the asymmetric energy input as indicated by polar cap (PC) indices. The high speed solar winds streams (HSSWs) during the recovery phases of March 2013 and 2015 storms have caused a significant reduction in ∑O/N2 at mid-latitudes, which could not be reproduced by the coupled thermosphere-ionosphere-plasmasphere electrodynamics (CTIPe) model. On the other hand the low-latitudes region depicts an enhancement in ∑O/N2 during all the storms except for the early recovery phases. The positive storm effect at low-latitudes agrees well with this ∑O/N2 increase, thus indicating that the composition change is one of the major drivers of TEC enhancement at low-latitudes. The CTIPe model showed discrepancies in reproducing the satellite data for all the considered storms, especially during the recovery phases. Furthermore, the model is failed to replicate the hemispheric asymmetries at low and mid-latitudes during the main and early recovery phases.

Younas, Waqar; Khan, Majid; Amory-Mazaudier, C.; Amaechi, Paul; Fleury, R.;

Published by: Advances in Space Research      Published on: jan

YEAR: 2022     DOI: 10.1016/j.asr.2021.10.027

CTIPe model; Disturbed ∑O/N; GUVI/TIMED data; Hemispheric asymmetries; REC

Signatures of Equatorial Plasma Bubbles and Ionospheric Scintillations from Magnetometer and GNSS Observations in the Indian Longitudes during the Space Weather Events of Early September 2017

Scintillation due to ionospheric plasma irregularities remains a challenging task for the space science community as it can severely threaten the dynamic systems relying on space-based navigation services. In the present paper, we probe the ionospheric current and plasma irregularity characteristics from a latitudinal arrangement of magnetometers and Global Navigation Satellite System (GNSS) stations from the equator to the far low latitude location over the Indian longitudes, during the severe space weather events of 6–10 September 2017 that are associated with the strongest and consecutive solar flares in the 24th solar cycle. The night-time influence of partial ring current signatures in ASYH and the daytime influence of the disturbances in the ionospheric E region electric currents (Diono) are highlighted during the event. The total electron content (TEC) from the latitudinal GNSS observables indicate a perturbed equatorial ionization anomaly (EIA) condition on 7 September, due to a sequence of M-class solar flares and associated prompt penetration electric fields (PPEFs), whereas the suppressed EIA on 8 September with an inverted equatorial electrojet (EEJ) suggests the driving disturbance dynamo electric current (Ddyn) corresponding to disturbance dynamo electric fields (DDEFs) penetration in the E region and additional contributions from the plausible storm-time compositional changes (O/N2) in the F-region. The concurrent analysis of the Diono and EEJ strengths help in identifying the pre-reversal effect (PRE) condition to seed the development of equatorial plasma bubbles (EPBs) during the local evening sector on the storm day. The severity of ionospheric irregularities at different latitudes is revealed from the occurrence rate of the rate of change of TEC index (ROTI) variations. Further, the investigations of the hourly maximum absolute error (MAE) and root mean square error (RMSE) of ROTI from the reference quiet days’ levels and the timestamps of ROTI peak magnitudes substantiate the severity, latitudinal time lag in the peak of irregularity, and poleward expansion of EPBs and associated scintillations. The key findings from this study strengthen the understanding of evolution and the drifting characteristics of plasma irregularities over the Indian low latitudes.

Vankadara, Ram; Panda, Sampad; Amory-Mazaudier, Christine; Fleury, Rolland; Devanaboyina, Venkata; Pant, Tarun; Jamjareegulgarn, Punyawi; Haq, Mohd; Okoh, Daniel; Seemala, Gopi;

Published by: Remote Sensing      Published on: jan

YEAR: 2022     DOI: 10.3390/rs14030652

space weather; equatorial plasma bubbles; ionospheric irregularity; global navigation satellite system; magnetometer; poleward drift; rate of change of TEC index; scintillations; storm-time electric currents

Effect of Weak Magnetic Storms on the Propagation of HF Radio Waves

Vertical and oblique sounding data for northeastern Russia have been used to analyze the conditions for the propagation of radio waves during weak geomagnetic storms observed in fall seasons of 2018–2020 at minimal solar activity. Even during weak storms, the maximum observed frequencies have been found to decrease by 25–35\% in daytime and by 40–50\% at night. Variations in the parameters of the distribution of high frequency radio waves during disturbances depend on the spatio-temporal dynamics of large scale structures of the high-latitude ionosphere, which, in turn, depends on the processes of magnetosphere–ionosphere interaction. Here, the depth and duration of the negative disturbance are larger if the geomagnetic storm occurs on a disturbed background.

Kurkin, V.; Polekh, N.; Zolotukhina, N.;

Published by: Geomagnetism and Aeronomy      Published on: feb

YEAR: 2022     DOI: 10.1134/S0016793222020116

Performance Analysis of Ionospheric TECmodelsoverthe Africanregion during the geomagnetic storm of March 2015

This paper investigates the diurnal variations of modelled and observed Vertical Total Electron Content (VTEC) over the African region (40oN to+ 40oS, 25oW to 65oE) obtained from

Devanaboyina, Venkata; , others;

Published by:       Published on:

YEAR: 2022     DOI: 10.21203/rs.3.rs-1695991/v1

The 15 January 2022 Hunga Tonga Eruption History as Inferred From Ionospheric Observations

On 15 January 2022, the Hunga Tonga-Hunga Ha’apai submarine volcano erupted violently and triggered a giant atmospheric shock wave and tsunami. The exact mechanism of this extraordinary eruptive event, its size and magnitude are not well understood yet. In this work, we analyze data from the nearest ground-based receivers of Global Navigation Satellite System to explore the ionospheric total electron content (TEC) response to this event. We show that the ionospheric response consists of a giant TEC increase followed by a strong long-lasting depletion. We observe that the explosive event of 15 January 2022 began at 04:05:54UT and consisted of at least five explosions. Based on the ionospheric TEC data, we estimate the energy released during the main major explosion to be between 9 and 37 Megatons in trinitrotoluene equivalent. This is the first detailed analysis of the eruption sequence scenario and the timeline from ionospheric TEC observations.

Astafyeva, E.; Maletckii, B.; Mikesell, T.; Munaibari, E.; Ravanelli, M.; Coisson, P.; Manta, F.; Rolland, L.;

Published by: Geophysical Research Letters      Published on:

YEAR: 2022     DOI: 10.1029/2022GL098827

co-volcanic ionospheric disturbances; eruption timeline; GNSS; Hunga Tonga eruption; Ionosphere; ionospheric geodesy

Interhemispheric Asymmetries in Ionospheric Electron Density Responses During Geomagnetic Storms: A Study Using Space-Based and Ground-Based GNSS and AMPERE Observations

We utilize Total Electron Content (TEC) measurements and electron density (Ne) retrieval profiles from Global Navigation Satellite System (GNSS) receivers onboard multiple Low Earth Orbit (LEO) satellites to characterize large-scale ionosphere-thermosphere system responses during geomagnetic storms. We also analyze TEC measurements from GNSS receivers in a worldwide ground-based network. Measurements from four storms during June and July 2012 (boreal summer months), December 2015 (austral summer month), and March 2015 (equinoctial month) are analyzed to study global ionospheric responses and the interhemispheric asymmetry of these responses. We find that the space-based and ground-based TECs and their responses are consistent in all four geomagnetic storms. The global 3D view from GNSS-Radio Occultation (RO) Ne observations captures enhancements and the uplifting of Ne structures at high latitudes during the initial and main phases. Subsequently, Ne depletion occurs at high latitudes and starts progressing into midlatitude and low latitude as the storm reaches its recovery phase. A clear time lag is evident in the storm-induced Ne perturbations at high latitudes between the summer and winter hemispheres. The interhemispheric asymmetry in TEC and Ne appears to be consistent with the magnitudes of the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) high latitude integrated field-aligned currents (FACs), which are 3–4 MA higher in the summer hemisphere than in the winter hemisphere during these storms. The ionospheric TEC and Ne responses combined with the AMPERE-observed FACs indicate that summer preconditioning in the ionosphere-thermosphere system plays a key role in the interhemispheric asymmetric storm responses.

Swarnalingam, N.; Wu, D.; Gopalswamy, N.;

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

YEAR: 2022     DOI: 10.1029/2021JA030247

Ionospheric Disturbances and Irregularities during the 25--26 August 2018 Geomagnetic Storm

We use ground-based (GNSS, SuperDARN, and ionosondes) and space-borne (Swarm, CSES, and DMSP) instruments to study ionospheric disturbances due to the 25–26 August 2018 geomagnetic storm. The strongest large-scale storm-time enhancements were detected over the Asian and Pacific regions during the main and early recovery phases of the storm. In the American sector, there occurred the most complex effects caused by the action of multiple drivers. At the beginning of the storm, a large positive disturbance occurred over North America at low and high latitudes, driven by the storm-time reinforcement of the equatorial ionization anomaly (at low latitudes) and by particle precipitation (at high latitudes). During local nighttime hours, we observed numerous medium-scale positive and negative ionospheric disturbances at middle and high latitudes that were attributed to a storm-enhanced density (SED)-plume, mid-latitude ionospheric trough, and particle precipitation in the auroral zone. In South America, total electron content (TEC) maps clearly showed the presence of the equatorial plasma bubbles, that, however, were not seen in data of Rate-of-TEC-change index (ROTI). Global ROTI maps revealed intensive small-scale irregularities at high latitudes in both hemispheres within the auroral region. In general, the ROTI disturbance “imaged” quite well the auroral oval boundaries. The most intensive ionospheric fluctuations were observed at low and mid-latitudes over the Pacific Ocean. The storm also affected the positioning accuracy by GPS receivers: during the main phase of the storm, the precise point positioning error exceeded 0.5 m, which is more than five times greater as compared to quiet days.

Astafyeva, E.; Yasyukevich, Y.; Maletckii, B.; Oinats, A.; Vesnin, A.; Yasyukevich, A.; Syrovatskii, S.; Guendouz, N.;

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

YEAR: 2022     DOI: 10.1029/2021JA029843

Geomagnetic storms; Ionosphere; ROTI; ionospheric disturbances; ionospheric irregularities; multi-instrumental approach

Aspects related to variability of radiative cooling by NO in lower thermosphere, TEC and O/N2 correlation, and diffusion of NO into mesosphere during the Halloween storms

Nitric Oxide is a very important trace species which plays a significant role acting as a natural thermostat in Earth’s thermosphere during strong geomagnetic activity. In this paper, we present various aspects related to the variation in the NO Infrared radiative flux (IRF) exiting the thermosphere by utilizing the TIMED/SABER (Thermosphere Ionosphere Mesosphere Energetics and Dynamics/ Sounding of the Atmosphere using Broadband Emission Radiometry) observational data during the Halloween storm which occurred in late October 2003. The Halloween storm comprised of three intense-geomagnetic storms. The variability of NO infrared flux during these storm events and its connection to the strength of the geomagnetic storms were found to be different in contrast to similar super storms.

Ranjan, Alok; Krishna, MV; Kumar, Akash; Sarkhel, Sumanta; Bharti, Gaurav; Bender, Stefan; Sinnhuber, Miriam;

Published by: Advances in Space Research      Published on:

YEAR: 2022     DOI: 10.1016/j.asr.2022.07.035

Climatology of O/N2 Variations at Low-and Mid-Latitudes during Solar Cycles 23 and 24

We present a study concerning the thermospheric O/N2 variations for the period 2002 to 2020, using the measurements of global ultraviolet imager (GUVI) onboard TIMED satellite. In this regard, monthly averaged O/N2 was computed—using the five quietest days of the month—at low- and mid-latitudes. To find the longitudinal dependence of thermospheric variations, the analysis is further extended to different longitudinal sectors, namely Asia, Africa, and America. We found that the latitudinal and longitudinal O/N2 variations follow the solar activity. These variations, during a high solar activity in northern winter, are found to be always much greater than southern winter and northern summer. The latitudinal and longitudinal variations of O/N2 at low- and mid-latitudes in December solstice are observed to be higher than June solstice counterparts in the northern hemisphere. We also computed the amplitudes of annual and semiannual variations using the bandpass filters. The former variations of O/N2 for low-latitudes do not follow the solar activity in the southern hemisphere. Moreover, these variations are stronger for mid-latitudes as compared with low-latitude regions. Similarly, the annual variations in Asian and African sectors of southern hemisphere do not follow the solar cycle (SC) trends.

Khan, Jahanzeb; Younas, Waqar; Khan, Majid; Amory-Mazaudier, Christine;

Published by: Atmosphere      Published on:

YEAR: 2022     DOI: 10.3390/atmos13101645

Ionospheric Response to the 23-31 August 2018 Geomagnetic Storm in the Europe-African Longitude Sector Using Multi-Instrument Observations

This study presents ionospheric responses of the mid and low-latitude region in the Europe-African longitude sector (along 30 +/- 10 deg E) to the intense geomagnetic storm of 23–31 August 2018 (SYM-Hmin = −207 nT) using the Global Ionospheric Map (GIM) and Global Positioning System (GPS) receivers data, the satellite data (SWARM, Defense Meteorological Satellite Program (DMSP), Global Ultraviolet Imager on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (GUVI/TIMED)), and Prompt Penetration Equatorial Electric Field model (PPEFM). The percentage deviation in total electron content (TEC) denoted by TEC () was used to observe the ionospheric storm effects.

Dugassa, Teshome; Mezgebe, Nigussie; Habarulema, John; Habyarimana, Valence; Oljira, Asebe;

Published by: Advances in Space Research      Published on:

YEAR: 2022     DOI: 10.1016/j.asr.2022.10.063

Middle and low latitudes hemispheric asymmetries in∑ O/N2 and TEC during intense magnetic storms of Solar Cycle 24

We have investigated the global hemispheric differences in thermospheric ∑O/N2 and its impact on the ionospheric total electron content (TEC) at mid- and low-latitudes. Four intense storms of solar cycle 24 (SC-24) have been considered, three of them occurred in Spring equinox and one in Summer solstice season.

Younas, Waqar; Khan, Majid; Amory-Mazaudier, C; Amaechi, Paul; Fleury, R;

Published by: Advances in Space Research      Published on:

YEAR: 2022     DOI: 10.1016/j.asr.2021.10.027

Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments

Scintillations of transionospheric satellite signals during geomagnetic storms can severely threaten navigation accuracy and the integrity of space assets. We analyze vertical Total

Shahzad, Rasim; Shah, Munawar; Abbas, Ayesha; Hafeez, Amna; Calabia, Andres; Melgarejo-Morales, Angela; Naqvi, Najam;

Published by: Annales Geophysicae Discussions      Published on:

YEAR: 2022     DOI: 10.5194/angeo-2022-18

Climatological study of the ion temperature in the ionosphere as recorded by Millstone Hill incoherent scatter radar and comparison with the IRI model

Ion temperature data recorded by Millstone Hill incoherent scatter radar (42.61° N, 288.51° E) over four full solar cycles (from 1970 to 2018) are analyzed to depict its climatological behavior in the range of altitudes between 100 and 550 km. The ion temperature dependencies on altitude, local time, month of the year, and solar activity level are studied through a climatological analysis based on binning and boxplot representation of statistical values. Binned observations of ion temperature are compared with International Reference Ionosphere (IRI) modeled values (IRI-2016 version). This comparison reveals several shortcomings in the IRI modeling of the ion temperature at ionosphere altitudes, in particular for the altitudinal, diurnal, seasonal, and solar activity description. The main finding of this study is that the overall IRI overestimation of the ion temperature can be probably ascribed to the long-term ionosphere cooling. Moreover, the study suggests that the IRI ion temperature model needs to implement the seasonal and solar activity dependence, and introduce a more refined diurnal description to allow multiple diurnal maxima seen in observations. The IRI ion temperature anchor point at 430 km is investigated in more detail to show how also a better description of the altitude dependence is desirable for modeling purposes. Some hints and clues are finally given to improve the IRI ion temperature model.

Pignalberi, Alessio; Aksonova, Kateryna; Zhang, Shun-Rong; Truhlik, Vladimir; Gurram, Padma; Pavlou, Charalambos;

Published by: Advances in Space Research      Published on: sep

YEAR: 2021     DOI: 10.1016/j.asr.2020.10.025

Climatological analysis; International Reference Ionosphere model; ion temperature; Millstone Hill incoherent scatter radar

Responses of the Indian Equatorial Ionization Anomaly to two CME-induced geomagnetic storms during the peak phase of solar cycle 24

This work analyzes the geo-effectiveness of Coronal Mass Ejection- (CME-) induced storms by investigating the responses of ionospheric Vertical Total Electron Content (VTEC) and the Equatorial Ionization Anomaly (EIA) over the Indian sector to two storms. One of the storms occurred on February 19, 2014 (SYM-H: −120 nT), while the other occurred on June 23, 2015 (SYM-H: −204 nT). Both storms were driven by full halo CMEs. Global TEC maps were used to characterize VTEC variations during the storms. June 23, 2015 storm was characterized with stronger solar progenitors, right from its origin, although the VTEC response to the storm was not influenced by their strong progenitors. The CMEs that caused the selected storms are large (Halo CMEs). We inferred that irrespective of the strength of solar origin of a storm, the response of ionization distribution over equatorial and low-latitude regions to it depends on the season of storm occurrence, local time of the storm onset, and PPEF orientation. From the VTEC variations for the three Indian stations namely, Trivandrum (geographic latitude: 8.52°N, geographic longitude: 76.94°E, magnetic latitude: 0.37°N), Hyderabad (17.39°N, 78.49°E, 10.15°N) and Delhi (28.70°N, 77.10°E, 22.70°N), we observed that EIA disturbances were more prominent over Hyderabad than over Delhi. The February 19, 2014 storm was characterized by a localized EIA crest at latitude a little above Hyderabad, while in June 23, 2015 storm localized EIA crest was observed directly on Hyderabad. IRI-2016 model generally underestimated VTEC at the three Indian equatorial and low-latitude locations. Solar cycle 24 was characterized with low heliospheric pressure due to its weak polar field strength. The lower pressure allowed CMEs to expand greatly as they transit through space. As they expand, the strengths of the magnetic field inside them decrease, and such lower-strength magnetic fields cause geomagnetic storms that are less geoeffective, even when their solar/interplanetary progenitors are strong and healthy. This associated weak polar field strength of solar cycle 24 caused weak fountain effect with the attendant inability to exhibit storm-time super-fountain effect in the dayside of the equatorial/low-latitude regions.

Simi, K.; Akala, A.; Krishna, Siva; Amaechi, Paul; Ogwala, Aghogho; Ratnam, Venkata; Oyedokun, O.;

Published by: Advances in Space Research      Published on: oct

YEAR: 2021     DOI: 10.1016/j.asr.2021.06.013

Coronal mass ejection; Disturbance dynamo electric field; geomagnetic storm; prompt penetration electric field; total electron content

Responses of the Indian Equatorial Ionization Anomaly to two CME-induced geomagnetic storms during the peak phase of solar cycle 24

This work analyzes the geo-effectiveness of Coronal Mass Ejection- (CME-) induced storms by investigating the responses of ionospheric Vertical Total Electron Content (VTEC) and the Equatorial Ionization Anomaly (EIA) over the Indian sector to two storms. One of the storms occurred on February 19, 2014 (SYM-H: −120 nT), while the other occurred on June 23, 2015 (SYM-H: −204 nT). Both storms were driven by full halo CMEs. Global TEC maps were used to characterize VTEC variations during the storms. June 23, 2015 storm was characterized with stronger solar progenitors, right from its origin, although the VTEC response to the storm was not influenced by their strong progenitors. The CMEs that caused the selected storms are large (Halo CMEs). We inferred that irrespective of the strength of solar origin of a storm, the response of ionization distribution over equatorial and low-latitude regions to it depends on the season of storm occurrence, local time of the storm onset, and PPEF orientation. From the VTEC variations for the three Indian stations namely, Trivandrum (geographic latitude: 8.52°N, geographic longitude: 76.94°E, magnetic latitude: 0.37°N), Hyderabad (17.39°N, 78.49°E, 10.15°N) and Delhi (28.70°N, 77.10°E, 22.70°N), we observed that EIA disturbances were more prominent over Hyderabad than over Delhi. The February 19, 2014 storm was characterized by a localized EIA crest at latitude a little above Hyderabad, while in June 23, 2015 storm localized EIA crest was observed directly on Hyderabad. IRI-2016 model generally underestimated VTEC at the three Indian equatorial and low-latitude locations. Solar cycle 24 was characterized with low heliospheric pressure due to its weak polar field strength. The lower pressure allowed CMEs to expand greatly as they transit through space. As they expand, the strengths of the magnetic field inside them decrease, and such lower-strength magnetic fields cause geomagnetic storms that are less geoeffective, even when their solar/interplanetary progenitors are strong and healthy. This associated weak polar field strength of solar cycle 24 caused weak fountain effect with the attendant inability to exhibit storm-time super-fountain effect in the dayside of the equatorial/low-latitude regions.

Simi, K.; Akala, A.; Krishna, Siva; Amaechi, Paul; Ogwala, Aghogho; Ratnam, Venkata; Oyedokun, O.;

Published by: Advances in Space Research      Published on: oct

YEAR: 2021     DOI: 10.1016/j.asr.2021.06.013

Coronal mass ejection; Disturbance dynamo electric field; geomagnetic storm; prompt penetration electric field; total electron content

Inferring thermospheric composition from ionogram profiles: a calibration with the TIMED spacecraft

\textlessp\textgreater\textlessstrong class="journal-contentHeaderColor"\textgreaterAbstract.\textless/strong\textgreater We present a method for augmenting spacecraft measurements of thermospheric composition with quantitative estimates of daytime thermospheric composition below 200 \textlessspan class="inline-formula"\textgreaterkm\textless/span\textgreater, inferred from ionospheric data, for which there is a global network of ground-based stations. Measurements of thermospheric composition via ground-based instrumentation are challenging to make, and so details about this important region of the upper atmosphere are currently sparse. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the “\textlessspan class="inline-formula"\textgreater\textitG\textless/span\textgreater” factor, a function of ion production rate and loss rates via ion–atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the \textlessspan class="inline-formula"\textgreater\textitG\textless/span\textgreater factor obtained from ionograms recorded at Kwajalein (9\textlessspan class="inline-formula"\textgreater$^\textrm∘$\textless/span\textgreater N, 167.2\textlessspan class="inline-formula"\textgreater$^\textrm∘$\textless/span\textgreater E) for 25 times during which the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between \textlessspan class="inline-formula"\textgreater\textlessmath xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"\textgreater\textlessmsqrt\textgreater\textlessmi\textgreaterG\textless/mi\textgreater\textless/msqrt\textgreater\textless/math\textgreater\textlessspan\textgreater\textlesssvg:svg xmlns:svg="http://www.w3.org/2000/svg" width="21pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="fe020e378fd223a5491b91deb815e309"\textgreater\textlesssvg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="angeo-39-309-2021-ie00001.svg" width="21pt" height="12pt" src="angeo-39-309-2021-ie00001.png"/\textgreater\textless/svg:svg\textgreater\textless/span\textgreater\textless/span\textgreater and the molecular-to-atomic composition ratio, with a gradient of \textlessspan class="inline-formula"\textgreater2.55±0.40\textless/span\textgreater. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be \textlessspan class="inline-formula"\textgreater4.75±0.4\textless/span\textgreater. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of \textlessspan class="inline-formula"\textgreater4.20±0.8\textless/span\textgreater. This relationship has potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere via a relatively simple model. This has applications in understanding long-term change and the efficacy of the upper atmosphere on satellite drag.\textless/p\textgreater

Scott, Christopher; Jones, Shannon; Barnard, Luke;

Published by: Annales Geophysicae      Published on: mar

YEAR: 2021     DOI: 10.5194/angeo-39-309-2021

Echo occurrence in the southern polar ionosphere for the SuperDARN Dome C East and Dome C North radars

In this paper, echo occurrence rates for the Dome C East (DCE) and the new Dome C North (DCN) radars are studied. We report the ionospheric and ground scatter echo occurrence rates for selected periods around equinoxes and solstices in the final part of the solar cycle XXIV. The occurrence maps built in Altitude Adjusted Corrected Geomagnetic latitude and Magnetic Local Time coordinates show peculiar patterns highly variable with season. The comparisons of the radar observations with the International Reference Ionosphere model electron density and with ray tracing simulations allow us to explain the major features of observed patterns in terms of electron density variations. The study shows the great potential of the DCE and DCN radar combination to the Super Dual Auroral Radar Network (SuperDARN) convection mapping in terms of monitoring key regions of the high-latitude ionosphere critical for understanding of the magnetospheric dynamics.

Marcucci, Maria; Coco, Igino; Massetti, Stefano; Pignalberi, Alessio; Forsythe, Victoriya; Pezzopane, Michael; Koustov, Alexander; Longo, Simona; Biondi, David; Simeoli, Enrico; Consolini, Giuseppe; Laurenza, Monica; Marchaudon, Aurélie; Satta, Andrea; Cirioni, Alessandro; De Simone, Angelo; Olivieri, Angelo; Baù, Alessandro; Salvati, Alberto;

Published by: Polar Science      Published on: jun

YEAR: 2021     DOI: 10.1016/j.polar.2021.100684

Echo occurrence; IRI model; Polar cap radars; Ray-tracing

B2 Thickness Parameter Response to Equinoctial Geomagnetic Storms

The thickness parameters that most empirical models use are generally defined by empirical relations related to ionogram characteristics. This is the case with the NeQuick model that uses an inflection point below the F2 layer peak to define a thickness parameter of the F2 bottomside of the electron density profile, which is named B2. This study is focused on the effects of geomagnetic storms on the thickness parameter B2. We selected three equinoctial storms, namely 17 March 2013, 2 October 2013 and 17 March 2015. To investigate the behavior of the B2 parameter before, during and after those events, we have analyzed variations of GNSS derived vertical TEC (VTEC) and maximum electron density (NmF2) obtained from manually scaled ionograms over 20 stations at middle and low latitudes of Asian, Euro-African and American longitude sectors. The results show two main kinds of responses after the onset of the geomagnetic events: a peak of B2 parameter prior to the increase in VTEC and NmF2 (in \textasciitilde60\% of the cases) and a fluctuation in B2 associated with a decrease in VTEC and NmF2 (\textasciitilde25\% of the cases). The behavior observed has been related to the dominant factor acting after the CME shocks associated with positive and negative storm effects. Investigation into the time delay of the different measurements according to location showed that B2 reacts before NmF2 and VTEC after the onset of the storms in all the cases. The sensitivity shown by B2 during the studied storms might indicate that experimentally derived thickness parameter B2 could be incorporated into the empirical models such as NeQuick in order to adapt them to storm situations that represent extreme cases of ionospheric weather-like conditions.

Migoya-Orué, Yenca; Alazo-Cuartas, Katy; Kashcheyev, Anton; Amory-Mazaudier, Christine; Radicella, Sandro; Nava, Bruno; Fleury, Rolland; Ezquer, Rodolfo;

Published by: Sensors      Published on: jan

YEAR: 2021     DOI: 10.3390/s21217369

Geomagnetic storms; total electron content; ionospheric empirical models; NeQuick model; thickness parameter

Features of topside ionospheric background over China and its adjacent areas obtained by the ZH-1 satellite

\textlessp\textgreaterTopside ionospheric background distribution and its seasonal variations over China and its adjacent areas, e.g. 0°-54°N and 70°-140°E, are studied using the in situ electron density (Ne) measurements obtained by the LAP payload on board the ZH-1 (CSES) satellite. Results are as followings:(1) Regularities consistent with results from previous studies are shown on the latitudinal extension, longitudinal distribution, and seasonal variations of the EIA (Equatorial Ionization Anomaly) phenomenon in the study area. (2) In the mid-latitude regions, there is a relative low-value zone for the daytime Ne, which shows relative high-value data during nighttime. Nighttime Ne enhancement is shown in all the mid-latitudes for all the seasons when comparing the nighttime and daytime Ne together. The equatorward extension of this phenomenon is in contrast to the poleward extension of the EIA phenomenon; when this phenomenon extends, the EIA shrinks, and vice versa. (3) For the daytime Ne, semiannual anomaly demonstrates a regular pattern, in which the two peaks start in spring and autumn equinoxes at the Equator, then evolve toward the summer solstice with increasing latitude, and finally combine into one summer time peak in mid-latitudes; seasonal anomaly only appears within latitude 4° of the Equator. While for the nighttime Ne, semiannual anomaly appears between latitude 22° and 50°, and seasonal anomaly appears below latitude 22°. (4) The monthly average background of the ionosphere generally shows that the nighttime Ne varies more dramatically than the daytime Ne. For the daytime Ne, observations in both equinoxes and summer solstice vary more violently than that in winter solstice, and observations in EIA regions vary more violently than that in mid-latitude regions. And for the nighttime Ne, observation variations are roughly similar in all seasons and latitudes. (5) Features of the ionospheric background, which fluctuates with time and space in the study area, are relatively complicated, therefore it is necessary to pay attention to the ionosphere background and its fluctuations when conducting studies on ionosphere related scientific problems. Based on the above results and comparisons with other simultaneous observations, we believe that the relative variations of the in situ Ne measurements from the ZH-1 satellite are in consistent with that from other datasets. Besides the well-known ionosphere features, some features which were not found in previous studies are found from the ionosphere background in the study area. The in situ Ne measurements from the ZH-1 satellite are a good data source for systematic studies on ionosphere-related scientific problems due to the similar local times and locations of the observations.\textless/p\textgreater

XiuYing, Wang; DeHe, Yang; ZiHan, Zhou; Jing, C.; Na, Zhou; XuHui, Shen;

Published by: Chinese Journal of Geophysics      Published on: feb

YEAR: 2021     DOI: 10.6038/cjg2021O0152

Latitudinal Dependence of the Ionospheric Slab Thickness for Estimation of Ionospheric Response to Geomagnetic Storms

The changes in the ionosphere during geomagnetic disturbances is one of the prominent Space Weather effects on the near-Earth environment. The character of these changes can differ significantly at different regions on the Earth. We studied ionospheric response to five geomagnetic storms of March 2012, using data of Total Electron Content (TEC) and F2-layer critical frequency (foF2) along the meridian of 70° W in the Northern Hemisphere. There are few ionosondes along this longitudinal sector: in Thule, Sondrestrom, Millstone Hill and Puerto Rico. The lacking foF2 values between the ionosondes were determined by using the experimental latitudinal dependences of the equivalent ionospheric slab thickness and TEC values. During geomagnetic storms, the following features were characteristic: (a) two-hours (or longer in one case) delay of the ionospheric response to disturbances, (b) the more prominent mid-latitude trough and (c) the sharper border of the EIA northern crest. During four storms of 7–17 March, the general tendency was the transition from negative disturbances at high latitudes to intense positive disturbances at low latitudes. During the fifth storm, the negative ionospheric disturbance controlled by O/N2 change was masked by the overall prolonged electron density increase during 21–31 March. The multiple correlation analysis revealed the latitudinal dependence of dominant Space Weather parameters’ impacts on foF2.

Sergeeva, Maria; Maltseva, Olga; Caraballo, Ramon; Gonzalez-Esparza, Juan; Corona-Romero, Pedro;

Published by: Atmosphere      Published on: feb

YEAR: 2021     DOI: 10.3390/atmos12020164

foF2; geomagnetic storm; Ionospheric disturbance; ionospheric equivalent slab thickness; statistical analysis; TEC

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

First Look at a Geomagnetic Storm With Santa Maria Digisonde Data: F Region Responses and Comparisons Over the American Sector

Santa Maria Digisonde data are used for the first time to investigate the F region behavior during a geomagnetic storm. The August 25, 2018 storm is considered complex due to the incidence of two Interplanetary Coronal Mass Ejections and a High-Speed Solar Wind Stream (HSS). The F 2 layer critical frequency (f o F 2) and its peak height (h m F 2) collected over Santa Maria, near the center of the South American Magnetic Anomaly (SAMA), are compared with data collected from Digisondes installed in the Northern (NH) and Southern (SH) Hemispheres in the American sector. The deviation of f o F 2 (Df o F 2) and h m F 2 (Dh m F 2) are used to quantify the ionospheric storm effects. Different F region responses were observed during the main phase (August 25–26), which is attributed to the traveling ionospheric disturbances and disturbed eastward electric field during nighttime. The F region responses became highly asymmetric between the NH and SH at the early recovery phase (RP, August 26) due to a combination of physical mechanisms. The observed asymmetries are interpreted as caused by modifications in the thermospheric composition and a rapid electrodynamic mechanism. The persistent enhanced thermospheric [O]/[N2] ratio observed from August 27 to 29 combined with the increased solar wind speed induced by the HSS and IMF B z fluctuations seem to be effective in causing the positive ionospheric storm effects and the shift of the Equatorial Ionization Anomaly crest to higher than typical latitudes. Consequently, the most dramatic positive ionospheric storm during the RP occurred over Santa Maria (∼120\%).

Moro, J.; Xu, J.; Denardini, C.; Resende, L.; Neto, P.; Da Silva, L.; Silva, R.; Chen, S.; Picanço, G.; Carmo, C.; Liu, Z.; Yan, C.; Wang, C.; Schuch, N.;

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

YEAR: 2021     DOI: 10.1029/2020JA028663

Digisonde; Equatorial ionization anomaly; F-region; Ionospheric storm; SAMA; space weather

Storm time effects on latitudinal distribution of ionospheric TEC in the American and Asian-Australian sectors: August 25--26, 2018 geomagnetic storm

On the dayside of August 25–26, 2018 (main phase, MP of the storm), we unveiled the storm time effects on the latitudinal distribution of ionospheric total electron content (TEC). We used 17 and 19 Global Positioning System receivers in American and Asian-Australian sectors, respectively. Also, we employed a pair of magnetometers in each sector to unveil storm time effects on vertical E × B upward directed inferred drift velocity in the F region ionosphere. Also used is NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite airglow instrument to investigate storm time changes in neutral composition, O/N2 ratio. In this investigation, we corrected the latitudinal offset found in the works of Younas et al. (2020, https://doi.org/10.1029/2020JA027981). Interestingly, we observed that a double-humped increase (DHI) seen at a middle latitude station (MGUE, ∼22°S) after the MP on the dayside in American sector (Younas et al., 2020, https://doi.org/10.1029/2020JA027981) did straddle ∼23.58°N and ∼22°S. On August 25, 2018, storm commencement was evident in Sym-H (∼−8 nT) around 18:00 UT. It later became intensified (∼−174 nT) on August 26 around 08:00 UT. During storm s MP (after the MP), fountain effect operation was significantly enhanced (inhibited) in Asian-Australian (American) sector. Middle latitude TEC during MP got reduced in American sector (13:00 LT–15:40 LT) compared to those seen in Asian-Australian sector (13:00 LT–15:40 LT). The northern equatorial peak (∼25 TECU) seen at IHYO (14:00 LT) after MP in the American sector is higher when compared with that (∼21 TECU) seen at PPPC (11:40 LT) during MP in Asian-Australian sector.

Bolaji, O.; Fashae, J.; Adebiyi, S.; Owolabi, Charles; Adebesin, B.; Kaka, R.; Ibanga, Jewel; Abass, M.; Akinola, O.; Adekoya, B.; Younas, W.;

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

YEAR: 2021     DOI: 10.1029/2020JA029068

double-humped increase (DHI); equatorial ionization anomaly (EIA); prompt penetrating electric field (PPEF); storm time equatorward wind

Inversion of Ionospheric O/N-2 by Using FY-3D Ionospheric Photometer Data

Da-xin, Wang; Li-ping, Fu; Fang, Jiang; Nan, Jia; Tian-fang, Wang; Shuang-tuan, Dou;

Published by: SPECTROSCOPY AND SPECTRAL ANALYSIS      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

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

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

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

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:

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

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

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

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

Influence of geomagnetic storms on the mid latitude D and F2 regions

Naidu, Pyla; Madhavilatha, Tirumalaraju; Devi, Malladi;

Published by: Annals of Geophysics      Published on:

YEAR: 2020     DOI:

I. Ionospheric Response to the Second Strongest Geomagnetic Storm of the Solar Cycle 24: First Results from the Arabian Peninsula

Dayanandan, Baiju; Paul, Bapan; Galav, Praveen;

Published by:       Published on:

YEAR: 2020     DOI:

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

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

Published by:       Published on:

YEAR: 2020     DOI:

Ionospheric and magnetic signatures of a space weather event on 25—29 August 2018: CME and HSSWs

Younas, W; Amory-Mazaudier, Christine; Khan, Majid; Fleury, R;

Published by: Journal of geophysical research: space physics      Published on:

YEAR: 2020     DOI:

Correction to: Ionospheric response to the 25-26 August 2018 intense geomagnetic storm

Vaishnav, Rajesh; Jacobi, Christoph;

Published by:       Published on:

YEAR: 2020     DOI:

Dataset for Multi-scale observations of two polar cap arcs occuring on different magnetic field topologies

Reidy, Jade; Fear, Robert; Whiter, Daniel; Lanchester, Betty; Kavanagh, AJ; Price, David; Chadney, Joshua; Zhang, Yongliang; Paxton, Larry; , others;

Published by:       Published on:

YEAR: 2020     DOI:

Multiscale observation of two polar cap arcs occurring on different magnetic field topologies

Reidy, JA; Fear, RC; Whiter, DK; Lanchester, BS; Kavanagh, AJ; Price, David; Chadney, Joshua; Zhang, Y; Paxton, LJ;

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

YEAR: 2020     DOI:

Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC)

Brückner, Marlen; Lonardi, Michael; Ehrlich, Andr\; Wendisch, Manfred; Jäkel, Evelyn; Schäfer, Michael; Quaas, Johannes; Kalesse, Heike;

Published by:       Published on:

YEAR: 2020     DOI:

SIHLA, a mission of opportunity to L1 to map H Lyman alpha emissions from the heliopause, the interplanetary medium, the Earth's geocorona and comets

Paxton, Larry; Provornikova, Elena; Roelof, Edmond; emerais, Eric; Izmodenov, Vladislav; Katushkina, Olga; Mierkiewicz, Edwin; Baliukin, Igor; Gruntman, Mike; Taguchi, Makoto; , others;

Published by:       Published on:

YEAR: 2020     DOI:

Ionospheric response to the 25-26 August 2018 intense geomagnetic storm

Vaishnav, Rajesh; Jacobi, Christoph;

Published by:       Published on:

YEAR: 2020     DOI:

The atmosphere below 200 km over Norilsk at solar minimum and maximum

Yakovleva, OE; Kushnarenko, GP; Kuznetsova, GM;

Published by: Solar-Terrestrial Physics      Published on:

YEAR: 2020     DOI:

Ionospheric and magnetic signatures of a space weather event on 25—29 August 2018: CME and HSSWs

We present a study concerning a space weather event on 25–29 August 2018, accounting for its ionospheric and magnetic signatures at low latitudes and midlatitudes. The effects of a

Younas, W; Amory-Mazaudier, Christine; Khan, Majid; Fleury, R;

Published by: Journal of geophysical research: space physics      Published on:

YEAR: 2020     DOI: 10.1029/2020JA027981

Geomagnetic storm-induced plasma density enhancements in the southern polar ionospheric region: A comparative study using St. Patrick s Day storms of 2013 and 2015

order to examine if the variations in the TEC were caused by thermospheric composition changes in the southern high-latitude regions, we present O/N 2 maps obtained from the GUVI

Shreedevi, PR; Choudhary, RK; Thampi, Smitha; Yadav, Sneha; Pant, TK; Yu, Yiqun; McGranaghan, Ryan; Thomas, Evan; Bhardwaj, Anil; Sinha, AK;

Published by: Space Weather      Published on:

YEAR: 2020     DOI: 10.1029/2019SW002383

Consequences of a solar wind stream interaction region on the low latitude ionosphere: event of 7 October 2015

In this article, we present a study of the perturbations occurring in the Earth’s environment on 7 October 2015. We use a multi-instrument approach, including space and ground

Molina, Maria; Dasso, S; Mansilla, G; Namour, Jorge; Cabrera, Miguel; Zuccheretti, Enrico;

Published by: Solar Physics      Published on:

YEAR: 2020     DOI: 10.1007/s11207-020-01728-7