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11 pages, 3334 KiB

Open AccessArticle

Statistical Characterization of the Magnetic Field in Space during Magnetic Storms

by Shi-Han Wang, Lei Li, Tao Chen, Shuo Ti, Chun-Lin Cai, Wen Li and Jing Luo

Atmosphere 2022, 13(10), 1578; https://doi.org/10.3390/atmos13101578 - 27 Sep 2022

Cited by 2 | Viewed by 1527

Abstract

Magnetic storms are an important type of space weather and are usually caused by large streams of charged elementary particles (ions, for example) generated during solar wind production. The occurrence of magnetic storms can pose a threat to the internal electronics of satellites, [...] Read more.

Magnetic storms are an important type of space weather and are usually caused by large streams of charged elementary particles (ions, for example) generated during solar wind production. The occurrence of magnetic storms can pose a threat to the internal electronics of satellites, communication, navigation, remote sensing, etc. Additionally, ground-based electrical facilities may be impacted. In this paper, we focus on the statistical characteristics of the space channel during the occurrence of magnetic storms. By analyzing the observed data for each component of the magnetic field during a magnetic storm and applying the relevant cognitive radio theory, we obtain the probability density function, autocorrelation function, and power spectrum of the magnitude of each component of the magnetic field. The results show that the probability density of the magnitude of each component of the magnetic field gradually deviates from the Gaussian distribution as the Magnetic storm ring current index (Dst index) increases during a magnetic storm, and the autocorrelation function exhibits nonstationary characteristics, which further leads to the time-varying characteristics of the power spectrum. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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24 pages, 11753 KiB

Open AccessArticle

Investigating the Role of Gravity Waves on Equatorial Ionospheric Irregularities Using TIMED/SABER and C/NOFS Satellite Observations

by Melessew Nigussie, Mark Moldwin and Endawoke Yizengaw

Atmosphere 2022, 13(9), 1414; https://doi.org/10.3390/atmos13091414 - 1 Sep 2022

Cited by 6 | Viewed by 2239

Abstract

In this paper, for the first time, simultaneous atmospheric temperature perturbation profiles obtained from the TIMED/SABER satellite and equatorial ion density and vertical plasma drift velocity observations with and without ESF activity obtained from the C/NOFS satellite are used to investigate the effect [...] Read more.

In this paper, for the first time, simultaneous atmospheric temperature perturbation profiles obtained from the TIMED/SABER satellite and equatorial ion density and vertical plasma drift velocity observations with and without ESF activity obtained from the C/NOFS satellite are used to investigate the effect of gravity waves (GW) on ESF. The horizontal and vertical wavelengths of ionospheric oscillations and GWs are estimated by applying wavelet analysis techniques. In addition, vertically propagating GWs that dissipate energy in the ionosphere-thermosphere system are investigated using the spectral analysis technique. We find that the vertical wavelength of GW, corresponding to dominant wavelet power, ranges from 12 to 31 km regardless of the conditions of the ionosphere; however, GWs with vertical wavelengths between about 1 to 13 km are found every day, saturated between 90 and 110 km at different longitudinal sectors. Filtering out vertical wavelengths above 13 km from temperature perturbations, ranges of zonal wavelengths of GW (i.e., from about 290 to 950 km) are found corresponding to irregular and non-irregular ionosphere. Similarly, corresponding to dominant oscillations, the zonal wavelength of ion density perturbations is found within 16 to 1520 km. Moreover, we find an excellent agreement among the median zonal wavelengths of GW for the cases of irregular and non-irregular ionosphere and ion density perturbations that are 518, 495, and 491 km, respectively. The results imply that seed perturbations due to GW with a vertical wavelength from about 1 to 13 km evolve to ion density irregularity and may be amplified due to post-sunset vertical upward drift velocity. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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21 pages, 10156 KiB

Open AccessEditor’s ChoiceArticle

Characteristics of Low-Latitude Ionosphere Activity and Deterioration of TEC Model during the 7–9 September 2017 Magnetic Storm

by Jianfeng Li, Yongqian Wang, Shiqi Yang and Fang Wang

Atmosphere 2022, 13(9), 1365; https://doi.org/10.3390/atmos13091365 - 26 Aug 2022

Cited by 2 | Viewed by 2620

Abstract

Under the influence of space weather, abnormal disturbances in the ionosphere will distort the ionosphere model seriously and affect the global navigation satellite system negatively. This study analyzes the ionospheric activity characteristics and the ionospheric model performance in low latitude during a strong [...] Read more.

Under the influence of space weather, abnormal disturbances in the ionosphere will distort the ionosphere model seriously and affect the global navigation satellite system negatively. This study analyzes the ionospheric activity characteristics and the ionospheric model performance in low latitude during a strong geomagnetic storm from 7 to 9 September 2017. The research goals are to determine the abnormal behavior of the ionosphere during the geomagnetic storm and to refine the ionosphere model in the low latitude. In the experiment, the vertical total electron content (VTEC) peak value at low latitudes caused by this geomagnetic storm was significantly higher than that on the geomagnetic quiet day, and the VTEC peak value increased by approximately 75%. In the main phase of the geomagnetic storm, the degree of VTEC variation with longitude is significantly higher than that of the geomagnetic quiet day. The VTEC variation trend in the northern hemisphere is more severe than that in the southern hemisphere. In the region where VTEC decreases with longitude, the VTEC in the northern hemisphere is higher than that in the southern hemisphere on the same longitude at low latitudes, and this phenomenon is not significantly affected by the geomagnetic disturbance of the recovery phase. During the geomagnetic storm, the daily minimum value of VTEC at different latitudes was basically the same, approximately 5 TECU, indicating that the nighttime VTEC of the ionosphere in low latitudes was weakly affected by latitude and geomagnetic storms. Geomagnetic disturbances during geomagnetic storms will lead to anomalous features of the “Fountain effect” in the ionosphere at low latitudes. In addition, this geomagnetic storm event caused the accuracy of spherical harmonics (SH), polynomial, and ICE models to decrease by 7.12%, 27.87%, and 48.56%, respectively, and caused serious distortion, which is negative VTEC values fitted by the polynomial model. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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18 pages, 4169 KiB

Open AccessArticle

The Ionospheric Responses from Satellite Observations within Middle Latitudes to the Strong Magnetic Storm on 25–26 August 2018

by Xuemin Zhang, Lei Dong and Lei Nie

Atmosphere 2022, 13(8), 1271; https://doi.org/10.3390/atmos13081271 - 11 Aug 2022

Cited by 3 | Viewed by 1974

Abstract

The multi observations from the China Seismo-Electromagnetic Satellite (CSES) were presented and analyzed during the biggest magnetic storm on 25–26 August in the quiet solar activity year of 2018, together with the Swarm satellite and GNSS TEC (Global Navigation Satellite System, Total Electron [...] Read more.

The multi observations from the China Seismo-Electromagnetic Satellite (CSES) were presented and analyzed during the biggest magnetic storm on 25–26 August in the quiet solar activity year of 2018, together with the Swarm satellite and GNSS TEC (Global Navigation Satellite System, Total Electron Content). The whole tempo-spatial evolutional process was demonstrated in electromagnetic fields and in-situ plasma parameters within the whole magnetic storm time period of three phases, the main phase with quick decrease in SYM-H, the quick recovery phase, and the slow recovery phase. Strong correlations were revealed in time and space between electric fields and electron density. During the main phase, the penetrated electric field was the major factor to induce the injection of electric fields to low latitudes even to the equator and contribute to constructing the double peaks of Ne at altitudes above 500 km of CSES in daytime. In the quick recovery phase, Ne depletion was found in low middle and low latitudes in the daytime, associated with a quick decrease in solar wind dynamic pressure, but in the nightside Ne maintained or increased. Due to the high solar wind speed following the quick recovery phase, it controlled the enhancements in an electric field below 1125 Hz at medium and low latitudes in daytime and produced similar structures in a 225 Hz electric field with the mid-latitude trough of Ne in local nighttime and maintained their equator-ward movements in this time period. Ne/TEC showed typical local time-dependence in this magnetic storm, which illustrated that although the electron density in the ionosphere was mainly caused by this solar activity event, local background environments must also not be ignored for their final evolutional modes. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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15 pages, 3000 KiB

Open AccessArticle

Middle Latitude Geomagnetic Disturbances Caused by Hall and Pedersen Current Circuits Driven by Prompt Penetration Electric Fields

by Takashi Kikuchi, Kumiko K. Hashimoto, Takashi Tanaka, Yukitoshi Nishimura and Tsutomu Nagatsuma

Atmosphere 2022, 13(4), 580; https://doi.org/10.3390/atmos13040580 - 4 Apr 2022

Cited by 2 | Viewed by 2622

Abstract

The prompt penetration electric field (PPEF) drives the DP2 currents composed of the two-cell Hall current vortices surrounding the Region-1 field-aligned currents (R1FACs), and the zonal equatorial electrojet (EEJ, Cowling current) at the dayside equator, which is connected to the R1FACs by the [...] Read more.

The prompt penetration electric field (PPEF) drives the DP2 currents composed of the two-cell Hall current vortices surrounding the Region-1 field-aligned currents (R1FACs), and the zonal equatorial electrojet (EEJ, Cowling current) at the dayside equator, which is connected to the R1FACs by the Pedersen currents at middle latitudes. The midlatitude H- and D-components of the disturbance magnetic field are caused by the DP2 currents, as well as by the magnetospheric currents, such as magnetopause currents, FACs, ring currents, and so on. If the DP2 current is the major source for the midlatitude geomagnetic disturbances, H and D are supposed to be caused by the Hall and Pedersen currents, respectively. The H-D correlation would be negative in both morning and afternoon sectors, and H/D-EEJ correlation would be negative/positive in the morning and positive/negative in the afternoon. We picked out 39 DP2 events in the morning and 34 events in the afternoon from magnetometer data at Paratunka, Russia (PTK, 45.58° N geomagnetic latitude (GML)), which are characterized by negative H–D correlation with correlation coefficient (cc) < −0.8. We show that the midlatitude H/D is highly correlated with EEJ at Yap, Micronesia (0.38° S GML) in the same local time zone, meeting the Pedersen–Cowling current circuit between midlatitude and equator in the DP2 current system. Using the global simulation, we confirmed that the ionospheric currents with north–south direction at midlatitude is the Pedersen currents developing concurrently with the Cowling current. We suggest that the negative H-D correlation provides a clue to detect the PPEF when magnetometers are available at middle latitudes. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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21 pages, 7170 KiB

Open AccessArticle

Low-Latitude Ionospheric Responses and Coupling to the February 2014 Multiphase Geomagnetic Storm from GNSS, Magnetometers, and Space Weather Data

by Andres Calabia, Chukwuma Anoruo, Munawar Shah, Christine Amory-Mazaudier, Yury Yasyukevich, Charles Owolabi and Shuanggen Jin

Atmosphere 2022, 13(4), 518; https://doi.org/10.3390/atmos13040518 - 24 Mar 2022

Cited by 12 | Viewed by 4018

Abstract

The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, particularly during the February 2014 multiphase geomagnetic storm. In this paper, the low-latitude ionosphere responses and their coupling mechanisms, during the February 2014 multiphase geomagnetic storm, are investigated from ground-based [...] Read more.

The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, particularly during the February 2014 multiphase geomagnetic storm. In this paper, the low-latitude ionosphere responses and their coupling mechanisms, during the February 2014 multiphase geomagnetic storm, are investigated from ground-based magnetometers and global navigation satellite system (GNSS), and space weather data. The residual disturbances between the total electron content (TEC) of the International GNSS Service (IGS) global ionospheric maps (GIMs) and empirical models are used to investigate the storm-time ionospheric responses. Three clear sudden storm commencements (SSCs) on 15, 20, and 23 February are detected, and one high speed solar wind (HSSW) event on 19 February is found with the absence of classical SSC features due to a prevalent magnetospheric convection. The IRI-2012 shows insufficient performance, with no distinction between the events and overestimating approximately 20 TEC units (TECU) with respect to the actual quiet-time TEC. Furthermore, the median average of the IGS GIMs TEC during February 2014 shows enhanced values in the southern hemisphere, whereas the IRI-2012 lacks this asymmetry. Three low-latitude profiles extracted from the IGS GIM data revealed up to 20 TECU enhancements in the differential TEC. From these profiles, longer-lasting TEC enhancements are observed at the dip equator profiles than in the profiles of the equatorial ionospheric anomaly (EIA) crests. Moreover, a gradual increase in the global electron content (GEC) shows approximately 1 GEC unit of differential intensification starting from the HSSW event, while the IGS GIM profiles lack this increasing gradient, probably located at higher latitudes. The prompt penetration electric field (PPEF) and equatorial electrojet (EEJ) indices estimated from magnetometer data show strong variability after all four events, except the EEJ’s Asian sector. The low-latitude ionosphere coupling is mainly driven by the variable PPEF, DDEF (disturbance dynamo electric fields), and Joule heating. The auroral electrojet causing eastward PPEF may control the EIA expansion in the Asian sector through the dynamo mechanism, which is also reflected in the solar-quiet current intensity variability. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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16 pages, 1619 KiB

Open AccessArticle

Geomagnetic Storm Effect on F₂-Region Ionosphere during 2012 at Low- and Mid-Latitude-Latitude Stations in the Southern Hemisphere

by Edwin A. Kumar and Sushil Kumar

Atmosphere 2022, 13(3), 480; https://doi.org/10.3390/atmos13030480 - 15 Mar 2022

Cited by 6 | Viewed by 2753

Abstract

The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, [...] Read more.

The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F₂-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2%) of 45.3% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2% of −63.5% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2% of −65.1% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N₂] ratio. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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19 pages, 2872 KiB

Open AccessArticle

PCA-MRM Model to Forecast TEC at Middle Latitudes

by Anna L. Morozova, Teresa Barata and Tatiana Barlyaeva

Atmosphere 2022, 13(2), 323; https://doi.org/10.3390/atmos13020323 - 15 Feb 2022

Cited by 4 | Viewed by 1574

Abstract

The total electron content (TEC) over the Iberian Peninsula was modelled using PCA-MRM models based on decomposition of the observed TEC series using the principal component analysis (PCA) and reconstruction of the daily modes’ amplitudes by a multiple linear regression model (MRM) using [...] Read more.

The total electron content (TEC) over the Iberian Peninsula was modelled using PCA-MRM models based on decomposition of the observed TEC series using the principal component analysis (PCA) and reconstruction of the daily modes’ amplitudes by a multiple linear regression model (MRM) using space weather parameters as regressors. The following space weather parameters are used: proxies for the solar UV and XR fluxes, number of the solar flares of different classes, parameters of the solar wind and of the interplanetary magnetic field, and geomagnetic indices. Time lags of 1 and 2 days between the TEC and space weather parameters are used. The performance of the PCA-MRM model is tested using data for 2015, both geomagnetically quiet and disturbed periods. The model performs well for quiet days and days with solar flares but without geomagnetic disturbances. The MAE and RMSE metrics are of the order of 3–5 TECu for daytime and ~2 TECu for night-time. During geomagnetically disturbed periods, the performance of the model deteriorates but only for daytime: MAE and RMSE are of the order of 4–6 TECu and can rise to ~13 TECu for the strongest geomagnetic storms. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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17 pages, 4961 KiB

Open AccessArticle

Automatic Detection of Sfe: A Step Forward

by Juan José Curto Subirats, Alba Fischer-Carles and Anna Solé

Atmosphere 2022, 13(2), 199; https://doi.org/10.3390/atmos13020199 - 26 Jan 2022

Cited by 2 | Viewed by 2169

Abstract

Solar flare effects (Sfe) are magnetic variations caused by solar flare events. They only show up in the illuminated hemisphere. Their detection is a difficult task because they do not have a definite pattern and, additionally, they must be separated from other magnetic [...] Read more.

Solar flare effects (Sfe) are magnetic variations caused by solar flare events. They only show up in the illuminated hemisphere. Their detection is a difficult task because they do not have a definite pattern and, additionally, they must be separated from other magnetic perturbations. However, we attempted to automatize these detections by using two different strategies. The first strategy takes advantage of one of the Sfe characteristics, as they usually have a rapid rise, followed by a smooth decay, which typically produces a crochet-like shape in the magnetograms. Thus, we created several morphological models for each magnetic component. Then, we identified a definite Sfe time interval by setting the conditions for various parameters, such as the correlations of the measured data with the models, or the model similarities among the different components. In the second stage of this strategy, we observed clusters of time intervals. Each of these clusters were attributed to a timespan of event possibility. We found the statistical optimal value of the correlation parameters by using the ROC curve method and Youden index. The second strategy was based on some of the properties of Sfe ionospheric electric currents, such as their spherical symmetry around the vortex. Here, the algorithm calculated the derivative of the data in order to avoid contamination of the daily variation

S_{q}

, and, by means of trigonometric formulas, computed the magnetic radial component relative to the Sfe current vortex (the focus). It then created an Sfe index with this data. A prior assumption of the focus position in a preceding work is no longer needed since we made a wide patrol of the space area to find it. Through a progressive thresholding process, we found its statistical optimal value (0.4 nT min⁻¹) again by using the ROC curve method and Youden index. For both of the strategies, we have made a large calculation of Sfe detection (for the period of 2000–2020), which included 33 Sfe. Finally, we combined the results of both methods—which in fact are complementary—and obtained a unified list that gave a higher hit ratio than those that were obtained separately. This unified method gave promising results towards the possibility of Sfe automatic detection. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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24 pages, 3952 KiB

Open AccessEditor’s ChoiceArticle

A Study of Solar Flare Effects on the Geomagnetic Field Components during Solar Cycles 23 and 24

by Oswald Didier Franck Grodji, Vafi Doumbia, Paul Obiakara Amaechi, Christine Amory-Mazaudier, Kouassi N’guessan, Kassamba Abdel Aziz Diaby, Tuo Zie and Kouadio Boka

Atmosphere 2022, 13(1), 69; https://doi.org/10.3390/atmos13010069 - 31 Dec 2021

Cited by 12 | Viewed by 4666

Abstract

In this paper, we investigated the impact of solar flares on the horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field during solar cycles 23 and 24 (SC23/24) using data of magnetometer measurements on the sunlit side of the Earth. [...] Read more.

In this paper, we investigated the impact of solar flares on the horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field during solar cycles 23 and 24 (SC23/24) using data of magnetometer measurements on the sunlit side of the Earth. We examined the relation between sunspot number and solar flare occurrence of various classes during both cycles. During SC23/24, we obtained correlation coefficient of 0.93/0.97, 0.96/0.96 and 0.60/0.56 for C-class, M-class and X-class flare, respectively. The three components of the geomagnetic field reached a peak a few minutes after the solar flare occurrence. Generally, the magnetic crochet of the H component was negative between the mid-latitudes and Low-latitudes in both hemispheres and positive at low latitudes. By contrast, the analysis of the latitudinal variation of the Y and Z components showed that unlike the H component, their patterns of variations were not coherent in latitude. The peak amplitude of solar flare effect (sfe) on the various geomagnetic components depended on many factors including the local time at the observing station, the solar zenith angle, the position of the station with respect to the magnetic equator, the position of solar flare on the sun and the intensity of the flare. Thus, these peaks were stronger for the stations around the magnetic equator and very low when the geomagnetic field components were close to their nighttime values. Both cycles presented similar monthly variations with the highest sfe value (ΔH_sfe = 48.82 nT for cycle 23 and ΔH_sfe = 24.68 nT for cycle 24) registered in September and lowest in June for cycle 23 (ΔH_sfe = 8.69 nT) and July for cycle 24 (ΔH_sfe = 10.69 nT). Furthermore, the sfe was generally higher in cycle 23 than in cycle 24. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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22 pages, 4493 KiB

Open AccessArticle

A Global Empirical Model of the Ion Temperature in the Ionosphere for the International Reference Ionosphere

by Vladimír Truhlík, Dieter Bilitza, Dmytro Kotov, Maryna Shulha and Ludmila Třísková

Atmosphere 2021, 12(8), 1081; https://doi.org/10.3390/atmos12081081 - 23 Aug 2021

Cited by 8 | Viewed by 3767

Abstract

This study presents a suggestion for improvement of the ion temperature (Ti) model in the International Reference Ionosphere (IRI). We have re-examined ion temperature data (primarily available from NASA’s Space Physics Data Facility (SPDF)from older satellites and combined them with newly available data [...] Read more.

This study presents a suggestion for improvement of the ion temperature (Ti) model in the International Reference Ionosphere (IRI). We have re-examined ion temperature data (primarily available from NASA’s Space Physics Data Facility (SPDF)from older satellites and combined them with newly available data from the Defense Meteorological Satellite Program (DMSP), the Communication Navigation Outage Forecasting System (C/NOFS), and from the recently launched Ionospheric Connection Explorer (ICON). We have compiled these data into a unified database comprising in total Ti data from 18 satellites. By comparisons with long term records of ion temperature from the three incoherent scatter radars (ISRs) (Jicamarca, Arecibo, and Millstone Hill), it was found that an intercalibration is needed to achieve consistency with the ISR data and among individual satellite data sets. This database with thus corrected data has been used for the development of a new global empirical model of Ti with inclusion of solar activity variation. This solar activity dependence is represented by an additive correction term to the Ti global pattern. Due to the limited data coverage at altitudes above 1000 km, the altitude range described by the model ranges from 350 km to 850 km covering only the region where generally Ti is higher than the neutral temperature (Tn) and lower than the electron temperature (Te). This approach is consistent with the current description of Ti in the IRI model. However, instead of one anchor point at 430 km altitude as in the current IRI, our approach includes anchor points at 350, 430, 600, and 850 km. At altitudes above 850 km Ti is merged using a gradient derived from the model at 600 and 850 km, with the electron temperature described by the IRI-2016/TBT-2012 option. Comparisons with the ISR data (Jicamarca, Arecibo, Millstone Hill, and Kharkiv) for high and low solar activity and equinox show that the proposed Ti model captures local time variation of Ti at different altitudes and latitudes better than the current IRI-2016 Ti model. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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Review

Jump to: Research, Other

34 pages, 10252 KiB

Open AccessReview

The Sun and Space Weather

by Nat Gopalswamy

Atmosphere 2022, 13(11), 1781; https://doi.org/10.3390/atmos13111781 - 28 Oct 2022

Cited by 20 | Viewed by 3642

Abstract

The explosion of space weather research since the early 1990s has been partly fueled by the unprecedented, uniform, and extended observations of solar disturbances from space- and ground-based instruments. Coronal mass ejections (CMEs) from closed magnetic field regions and high-speed streams (HSS) from [...] Read more.

The explosion of space weather research since the early 1990s has been partly fueled by the unprecedented, uniform, and extended observations of solar disturbances from space- and ground-based instruments. Coronal mass ejections (CMEs) from closed magnetic field regions and high-speed streams (HSS) from open-field regions on the Sun account for most of the disturbances relevant to space weather. The main consequences of CMEs and HSS are their ability to cause geomagnetic storms and accelerate particles. Particles accelerated by CME-driven shocks can pose danger to humans and their technological structures in space. Geomagnetic storms produced by CMEs and HSS-related stream interaction regions also result in particle energization inside the magnetosphere that can have severe impact on satellites operating in the magnetosphere. Solar flares are another aspect of solar magnetic energy release, mostly characterized by the sudden enhancement in electromagnetic emission at various wavelengths—from radio waves to gamma-rays. Flares are responsible for the sudden ionospheric disturbances and prompt perturbation of Earth’s magnetic field known as magnetic crochet. Nonthermal electrons accelerated during flares can emit intense microwave radiation that can drown spacecraft and radar signals. This review article summarizes major milestones in understanding the connection between solar variability and space weather. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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23 pages, 2549 KiB

Open AccessReview

Equatorial Plasma Bubbles: A Review

by Archana Bhattacharyya

Atmosphere 2022, 13(10), 1637; https://doi.org/10.3390/atmos13101637 - 8 Oct 2022

Cited by 22 | Viewed by 6041

Abstract

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in [...] Read more.

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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15 pages, 2747 KiB

Open AccessEditor’s ChoiceReview

Thermospheric Neutral Wind Measurements and Investigations across the African Region—A Review

by Daniel Okoh, Aziza Bounhir, John Bosco Habarulema, Babatunde Rabiu, Zama Katamzi-Joseph, Taiwo Ojo, Qian Wu and Jonathan J. Makela

Atmosphere 2022, 13(6), 863; https://doi.org/10.3390/atmos13060863 - 25 May 2022

Cited by 5 | Viewed by 2580

Abstract

This paper briefly reviews studies of thermospheric neutral wind dynamics over the African region. The literature includes a review of the observations of neutral winds over five African locations using the Fabry–Perot Interferometer (FPI), and the comparison between the FPI observations and predictions [...] Read more.

This paper briefly reviews studies of thermospheric neutral wind dynamics over the African region. The literature includes a review of the observations of neutral winds over five African locations using the Fabry–Perot Interferometer (FPI), and the comparison between the FPI observations and predictions of the horizontal wind model (HWM-14). So far, there are reports of FPI thermospheric wind measurements in South Africa and Morocco representing the mid-latitude regions in the southern and northern hemispheres, respectively. Within the low latitudes, FPI instruments are installed in the Ivory Coast, Ethiopia, and Nigeria. For the literature reviewed, the years covered in the FPI data are 2018–2019 (South Africa), 2016–2017 (Nigeria), 2015–2016 (Ethiopia), 2013–2016 (Morocco), and 1994–1995 (Ivory Coast). Overall, the HWM-14 reproduces the climatological behavior of the meridional and zonal winds, with varying levels of fidelity for the different regions. The HWM-14 is more accurate in the stations located in the northern hemisphere of the African region; a result attributed to the presence of data during the development of this empirical model. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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8 pages, 821 KiB

Open AccessReview

Long-Term Changes in Ionospheric Climate in Terms of foF2

by Jan Laštovička

Atmosphere 2022, 13(1), 110; https://doi.org/10.3390/atmos13010110 - 10 Jan 2022

Cited by 19 | Viewed by 2798

Abstract

There is not only space weather; there is also space climate. Space climate includes the ionospheric climate, which is affected by long-term trends in the ionosphere. One of the most important ionospheric parameters is the critical frequency of the ionospheric F2 layer, foF2, [...] Read more.

There is not only space weather; there is also space climate. Space climate includes the ionospheric climate, which is affected by long-term trends in the ionosphere. One of the most important ionospheric parameters is the critical frequency of the ionospheric F2 layer, foF2, which corresponds to the maximum ionospheric electron density, NmF2. Observational data series of foF2 have been collected at some stations for as long as over 60 years and continents are relatively well covered by a network of ionosondes, instruments that measure, among others, foF2. Trends in foF2 are relatively weak. The main global driver of long-term trends in foF2 is the increasing concentration of greenhouse gases, namely CO₂, in the atmosphere. The impact of the other important trend driver, the secular change in the Earth’s main magnetic field, is very regional, being positive in some regions, negative in others, and neither in the rest. There are various sources of uncertainty in foF2 trends. One is the inhomogeneity of long foF2 data series. The main driver of year-to-year changes in foF2 is the quasi-eleven-year solar cycle. The removal of its effect is another source of uncertainty. Different methods might provide somewhat different strengths among trends in foF2. All this is briefly reviewed in the paper. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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27 pages, 5637 KiB

Open AccessEditor’s ChoiceReview

Review of Long-Term Trends in the Equatorial Ionosphere Due the Geomagnetic Field Secular Variations and Its Relevance to Space Weather

by Ana G. Elias, Blas F. de Haro Barbas, Bruno S. Zossi, Franco D. Medina, Mariano Fagre and Jose V. Venchiarutti

Atmosphere 2022, 13(1), 40; https://doi.org/10.3390/atmos13010040 - 28 Dec 2021

Cited by 11 | Viewed by 3237

Abstract

The Earth’s ionosphere presents long-term trends that have been of interest since a pioneering study in 1989 suggesting that greenhouse gases increasing due to anthropogenic activity will produce not only a troposphere global warming, but a cooling in the upper atmosphere as well. [...] Read more.

The Earth’s ionosphere presents long-term trends that have been of interest since a pioneering study in 1989 suggesting that greenhouse gases increasing due to anthropogenic activity will produce not only a troposphere global warming, but a cooling in the upper atmosphere as well. Since then, long-term changes in the upper atmosphere, and particularly in the ionosphere, have become a significant topic in global change studies with many results already published. There are also other ionospheric long-term change forcings of natural origin, such as the Earth’s magnetic field secular variation with very special characteristics at equatorial and low latitudes. The ionosphere, as a part of the space weather environment, plays a crucial role to the point that it could certainly be said that space weather cannot be understood without reference to it. In this work, theoretical and experimental results on equatorial and low-latitude ionospheric trends linked to the geomagnetic field secular variation are reviewed and analyzed. Controversies and gaps in existing knowledge are identified together with important areas for future study. These trends, although weak when compared to other ionospheric variations, are steady and may become significant in the future and important even now for long-term space weather forecasts. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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13 pages, 4047 KiB

Open AccessEditor’s ChoiceViewpoint

Magnetic Signatures of Large-Scale Electric Currents in the Earth’s Environment at Middle and Low Latitudes

by Christine Amory-Mazaudier

Atmosphere 2022, 13(10), 1699; https://doi.org/10.3390/atmos13101699 - 17 Oct 2022

Viewed by 2177

Abstract

The purpose of space weather is the systemic study of the Sun–Earth system, in order to determine the impact of solar events on the electromagnetic environment of the Earth. This article proposes a new transdisciplinary approach of the Sun–Earth system based on the [...] Read more.

The purpose of space weather is the systemic study of the Sun–Earth system, in order to determine the impact of solar events on the electromagnetic environment of the Earth. This article proposes a new transdisciplinary approach of the Sun–Earth system based on the universal physical process of the dynamo. The dynamo process is based on two important parameters of the different plasmas of the Sun–Earth system, the motion and the magnetic field. There are four permanent dynamos in the Sun–Earth system: the solar dynamo, the Earth dynamo, the solar wind-magnetosphere dynamo, and the ionospheric dynamo. These four permanent dynamos are part of different scientific disciplines. This transdisciplinary approach links all of these dynamos in order to understand the variations in the Earth’s magnetic field. During a magnetic disturbed period, other dynamos exist. We focused on the ionospheric disturbed dynamo generated by Joule energy dissipated in the high latitude ionosphere during magnetic storms. Joule heating disrupts the circulation of thermospheric winds and in turn generates disturbances in the Earth’s magnetic field. This systemic approach makes it possible to understand magnetic disturbances previously not well understood. Full article

(This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling)

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