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The injection of energy into the Earth's magnetosphere during geomagnetic storms and substorms has a direct impact on the ionosphere in the auroral and sub-auroral regions. This influence can be observed through phenomena such as the expansion of the auroral oval, and fluctuations in plasma density and the intensity of the field-aligned current (FAC) system. Changes in the geomagnetic environment significantly affect the main ionospheric trough (MIT) and field-aligned currents (FACs). In this study, we analysed two geomagnetic storms of different origins—October 2015 and September 2017 that occurred during solar cycle 24. Both storms were characterised by two minima of the Dst index and classified as two-step storms. In this work, we investigate the evolution of FACs density, the displacement of MIT and FACs during the development of geomagnetic storms, and we quest for the relationship between field-aligned currents and the main ionospheric trough. We noticed a connection between the positions of the main ionospheric trough minima and the Dst index, found cases especially during the main and recovery phase of the storms when FACs increase after leaving the ionospheric trough, and observed the predominance of downward currents in the area of the MIT which suggest their influence on the formation of this region of depleted plasma density. [ABSTRACT FROM AUTHOR]

The impact of interplanetary (IP) shocks on the Earth's magnetosphere can greatly disturb the geomagnetic field and electric currents in the magnetosphere-ionosphere system. At high latitudes, the current systems most affected by the shocks are the auroral electrojet currents. These currents then generate ground geomagnetically induced currents that couple with and are highly detrimental to ground artificial conductors including power transmission lines, oil/gas pipelines, railways, and submarine cables. Recent research has shown that the shock impact angle, the angle the shock normal vector performs with the Sun-Earth line, plays a major role in controlling the subsequent geomagnetic activity. More specifically, due to more symmetric magnetospheric compressions, nearly frontal shocks are usually more geoeffective than highly inclined shocks. In this study, we utilize a subset (332 events) of a shock list with more than 600 events to investigate, for the first time, shock impact angle effects on the subsequent GICs right after shock impact (compression effects) and several minutes after shock impact (substorm-like effects). We use GIC recordings from the Finnish natural gas pipeline performed near the Mäntsälä compression station in southern Finland. We find that GIC peaks ( > 5 A) occurring after shock impacts are mostly caused by nearly frontal shocks and occur in the post-noon/dusk magnetic local time sector. These GIC peaks are presumably triggered by partial ring current intensifications in the dusk sector. On the other hand, more intense GIC peaks ( > 20 A) generally occur several minutes after shock impacts and are located around the magnetic midnight terminator. These GIC peaks are most likely caused by intense energetic particle injections from the magnetotail which frequently occur during substorms. The results of this work are relevant to studies aiming at predicting GICs following solar wind driving under different levels of asymmetric solar wind forcing. [ABSTRACT FROM AUTHOR]

The cyclic properties of solar-geomagnetic activity and global surface temperature have been investigated using trend, frequency and time-frequency analyses. Results reveal that on decadal-to-centennial timescales, low-frequency cycles in the half-century (~49 to 56 years per cycle) and Gleisberg (~99 to 114 years per cycle) range run in the background of the Schwabe (~9 to 11 years per cycle) as the dominant cycle of solargeomagnetic activity. The only dominant cycle in the global surface temperature series is the half-century cycle and suggests a possible causal link between it and solar-geomagnetic activity phenomena. Evolution of the amplitudes of the cycles is such that the Schwabe and Gleisberg periods have increased in power from the beginning of the series until the mid-20th century after which they declined. The half-century cycle decreased in amplitude after 1800 to the present. For geomagnetic activity, the amplitude of Gleisberg cycle increased from the beginning of the series around 2000 while the amplitudes of Schwabe and half-century cycles declined within the same interval, except the Schwabe cycle which amplitude increased rapidly after 1980 to the present. For the global surface temperature, the amplitudes of Gleisberg and half-century cycles have continuously increased from the beginning of the series while Schwabe cycle oscillates with very low amplitudes until 1980 after which it increased slightly. Evolution of the amplitudes of cycles of solar-gemagnetic activity suggests a recovery from Maunder Minimum and decline into a grand epsode most likely to be a minimum. [ABSTRACT FROM AUTHOR]

Among the effects of space weather, the degradation of air traffic communications and satellite-based navigation systems are the most notable. For this reason, it is of uttermost importance to understand the nature and origin of ionospheric irregularities that are at the base of the observed communication outages. Here we focus on polar cap patches (PCPs) that constitute a special class of ionospheric irregularities observed at very high latitudes in the F region. To this purpose we use the so-called PCP flag, a Swarm Level 2 product, that allows for identifying PCPs. We relate the presence of PCPs to the values of the first- and second-order scaling exponents and intermittency estimated from Swarm A electron density fluctuations and to the values of the Rate Of change of electron Density Index (RODI) for two different levels of geomagnetic activity, over a time span of approximately 3.5 years starting on 16 July 2014. Our findings show that values of RODI, first- and second-order scaling exponents and intermittency corresponding to measurements taken inside PCPs differ from those corresponding to measurements taken outside PCPs. Additionally, the values of the first- and second-order scaling exponents and of intermittency indicate that PCPs are in a turbulent state. Investigation of the coincidence of loss of lock (LoL) events with PCPs displayed that approximately 57.4% of LoLs in the Northern hemisphere and 45.7% in the Southern hemisphere occur in coincidence of PCPs when disturbed geomagnetic activity is considered. During quiet geomagnetic conditions these percentages decrease to 51.4% in the Northern hemisphere and to 20.1% in the Southern hemisphere. [ABSTRACT FROM AUTHOR]

This paper is focused on study of the geomagnetic field variation response caused by a series of earthquakes with magnitudes of Mw = 7.5–7.8 in Turkey on February 6, 2023. The initial data include high-precision observations of the geomagnetic field with a one-second sampling rate recorded at magnetic observatories in Russia and neighboring countries from middle to high latitudes. The paper analyzes the morphology of the geomagnetic signal, its amplitude-frequency characteristics, pulses in the rate of change and delays of the geomagnetic field response to earthquakes with magnitudes Mw = 7–8 depending on the distance to the source. The results suggest that the geomagnetic effect is detected best in the rate of change recordings, reaching anomalous amplitudes of 10 nT/s. The signal delay ranges from 221 to 592 s depending on the magnetic field component and the distance to the epicenter, which is in the range from 765 to 2650 km for the selected observatories. [ABSTRACT FROM AUTHOR]

Waves which couple to energetic electrons are particularly important in space weather, as they drive rapid changes in the topology and intensity of Earth's outer radiation belt during geomagnetic storms. This includes Ultra Low Frequency (ULF) waves that interact with electrons via radial diffusion which can lead to electron dropouts via outward transport and rapid electron acceleration via inward transport. In radiation belt simulations, the strength of this interaction is specified by ULF wave radial diffusion coefficients. In this paper we detail the development of new models of electric and magnetic radial diffusion coefficients derived from in‐situ observations of the azimuthal electric field and compressional magnetic field. The new models use L∗ ${L}^{\ast }$ as it accounts for adiabatic changes due to the dynamic magnetic field coupled with an optimized set of four components of solar wind and geomagnetic activity, Bz ${B}_{z}$, V $V$, Pdyn ${P}_{\mathrm{d}\mathrm{y}\mathrm{n}}$, and Sym−H $\mathrm{S}\mathrm{y}\mathrm{m}-H$, as independent variables (inputs). These independent variables are known drivers of ULF waves and offer the ability to calculate diffusion coefficients at a higher cadence then existing models based on Kp. We investigate the performance of the new models by characterizing the model residuals as a function of each independent variable and by comparing to existing radial diffusion models during a quiet geomagnetic period and through a geomagnetic storm. We find that the models developed here perform well under varying levels of activity and have a larger slope or steeper gradient as a function of L∗ ${L}^{\ast }$ as compared to existing models (higher diffusion at higher L∗ ${L}^{\ast }$ values). Plain Language Summary: The outer radiation belt is a region of space comprising highly energetic electrons. During periods of extreme space weather, the number and energy of these electrons can rapidly vary. During these periods as the electron energies and numbers become enhanced, they can pose a threat to satellite and space infrastructure. While we have an excellent understanding of the physical processes which drive radiation belt electron dynamics, we still have a limited ability to model and forecast radiation belt dynamics; this is a result of the complexity of Earth's radiation belt system. One of the key processes controlling radiation belt dynamics is Ultra Low Frequency (ULF) wave radial diffusion. In this work we detail the development a new model quantifying the strength of ULF wave radial diffusion in the outer radiation belt utilizing space base observations of the electric and magnetic fields in Earth's magnetosphere. Accurately quantifying ULF wave radial diffusion is fundamental to understanding radiation belt dynamics and any improvement or refinements in radial diffusion models can help to provide a better understanding of the complex radiation belt system and importantly improve hindcasts, nowcasts, and forecasts. Key Points: A new four‐component L*‐dependent radial diffusion modelThe new model uses L* accounting for adiabatic changes under varying levels of solar and geomagnetic activityA detailed parametric study identifies an optimized set of independent variables for the new radial diffusion models [ABSTRACT FROM AUTHOR]

Two important phenomena of the solar wind–magnetosphere–ionosphere coupling are auroral particle precipitation and the formation of ions flowing upward from the ionosphere. They have opposite transport directions of energy and substance. Based on the observations of particle precipitation and ion drift from the DMSP F13 satellite in January and July 2005, the ionospheric ion upflows in dayside auroral oval (0600–1800 MLT) can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation, and the distribution for different types of ion upflows is studied. The results show that the ion upflows mainly occur in the geomagnetic latitude (MLAT) range of 70–80°.The main magnetospheric source region of ion upflows (type A and D) caused by the accelerated electron (mainly the soft electron) corresponds to Low Latitude Boundary Layer (LLBL) and Cusp, and ion upflows of type B and C (related to the process of ambipolar diffusion caused by electron acceleration) mainly occur in LLBL and Boundary Plasma Sheet (BPS), while ion upflows of type E without electron acceleration mainly occur in the central plasma sheet (CPS).The dawn–dusk asymmetry is obvious in the winter season, with the ion upflows mainly occurring on the dawn/dusk side ionosphere. However, the ion upflows in summer mainly occur at the magnetic noon, with a symmetric distribution centered at the magnetic noon. The occurrence of ion upflow in winter is significantly higher than that in summer, and it is significantly enhanced during the period of moderate geomagnetic activity. The upward region expands to the lower latitude when the geomagnetic activity is enhanced. The effect of interplanetary magnetic field (IMF) components has also been studied in this paper. When IMF Bx is negative, the upflow occurrence increases in the region of 1500–1800 MLT and 0600–0900 MLT, with the MLAT range below 70°. The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region. The occurrence of ion upflows with the MLAT range below 75° increases significantly when IMF is southward. Type A ion upflow has the highest velocity of ion upflows, followed by type E, and type D has the lowest. The average velocity of ion upflows in winter is significantly higher than that in summer. [ABSTRACT FROM AUTHOR]

From meteor radar observations typically measuring neutral winds and temperatures in the upper atmosphere, we showed that under‐dense meteor plasma trails respond to geomagnetic activity. Depending on the geomagnetic activity conditions, the parameters of the under‐dense trail echoes show substantial anomalies, and their responses are immediate. As geomagnetic activity increases, the decay time decreases up to about 10% at Kp = 8, while both the returned signal power and radial velocity error increase. In addition, the types of diffuse evolution vary with geomagnetic activity, resulting in strong geomagnetic activity that immediately affects the trail. The evolution of the trail is affected not only by the ambient mesospheric neutral atmospheric properties but also by electromagnetic effects, such as strong electric fields inside meteor trails. Furthermore, our findings suggest that the geomagnetic effect should be considered when estimating atmospheric parameters from MR during a geomagnetically active period. Plain Language Summary: Through long‐term meteor radar (MR) observation (2007–2021) at King Sejong Station in the Antarctic Peninsula, we found that the diffusion process in the meteor trail immediately accelerated under enhanced geomagnetic activity. The backscattered‐returned signal powers, which are proportional to the square of the electron line density of the meteor trail, also instantly increased. These anomalous characteristics in meteor trails appear while the background atmospheric parameters remain constant. Therefore, we propose that the observed immediate responses in the MR may be associated with the strong electric field in the ambient ionosphere D/E region induced by the increased geomagnetic activity. The strong external electric field can stimulate an electric field and current inside the meteor trail, owing to the difference in electrical conductivities between the meteor trail and ambient atmosphere. Thus, the electric field, current, and charge separation inside the meteor trail can lead to faster diffusion and enhanced electron line density in the trail. The meteor plasma trails are observed in regions that are affected by electric fields caused by geomagnetic activity; therefore, when deriving neutral atmospheric parameters from MRs, the impact of geomagnetic activity must be considered. Key Points: Under‐dense meteor echo parameters at a geomagnetic latitude of 50.2°S revealed an instantaneous response to geomagnetic activityGeomagnetic activity can directly modulate the evolution of meteor trails, such as the decay time and returned signal powerEffects of geomagnetic activity should be considered when estimating neutral atmospheric parameters from meteor radars [ABSTRACT FROM AUTHOR]

Induction vectors represent geomagnetic transfer functions used in magnetotellurics and related passive electromagnetic sounding methods in geophysics. They are obtained from the measurements of geomagnetic variation and carry information on the distribution of local and regional electric resistivity in the subsurface, which can be interpreted in terms of geology and tectonics. The underlying concept of their interpretation works properly if the so-called far-field condition is fulfilled, i.e., if certain assumptions on the geometry of utilized natural electromagnetic source fields are met. The magnetotelluric practitioner expects problems in the regions where the electromagnetic variations originate to a high extent from ionospheric currents as sources. Due to the polar (or auroral) electrojets, this skepticism towards the electromagnetic far-field methods clearly applies to the high latitudes, polar regions, and auroral zones. In the present study, the investigation focuses on the extent to which problems typical for the auroral electrojet sources occur in the geomagnetic variation data from the Argentine Islands INTERMAGNET observatory (AIA) located at the Ukrainian Antarctic Akademik Vernadsky station. Induction vectors from one month of AIA variation data measured in the normal framework of the INTERMAGNET observatory are analysed for their stability over both period and time, where a time resolution of one day allows for the detection of changes originating from the source signals instead of from subsurface resistivity distribution. The outcomes from AIA are compared to the corresponding ones of two northern hemisphere stations which belong to the International Monitor for Auroral Geomagnetic Effects (IMAGE) network, located in Finland and Poland. Results show that AIA induction vectors do not exhibit the problems expected in the high latitudes; their time stability is very similar to that of stations at a comparable but opposite geomagnetic latitude of 50 degrees, which corresponds geographically to mid-latitudes in Europe. A further outcome of this study is that some slight, occasional changes in induction vectors can be attributed to increased geomagnetic activity because they are correlated to the planetary diurnal Ap index. [ABSTRACT FROM AUTHOR]

Ionospheric long‐term variation has attracted wide attention since the upper atmosphere cooling due to increasing greenhouse gas was suggested. Observations of the lower ionosphere have indicated that cooling effect, whereas the F2 layer long‐term variation still remains controversial as multiple driving sources may cause it. It is crucial for investigating the F2 layer long‐term variation to distinguish contributions of different sources. foF2 records covering both long‐term increasing and decreasing phases of geomagnetic activity were selected for this study. foF2 long‐term component related to those increasing and decreasing phases is separable from the linear trend due to increasing greenhouse gas; it was identified and investigated. Geomagnetic activity induced long‐term component was found to be seasonally discrepant. With long‐term increasing geomagnetic activity, foF2 increases in winter while decreases in summer at middle and low latitudes; it decreases at higher latitudes while turns to increases with decreasing latitudes in equinox. In addition to the geomagnetic activity induced component, the linear component is dominated by long‐term decreasing trend, which is in line with the increasing greenhouse gas. Long‐term evolution of frequent weak geomagnetic activity was suggested to be primarily responsible for the seasonally discrepant long‐term variation of foF2 related to geomagnetic activity; it may change thermospheric composition by modulating average circulation. Moreover, geomagnetic activity has a decreasing trend as a whole. That may lead to misleading correlation between foF2 long‐term variation and geomagnetic activity if linear trend is dominant, and cause significant deviation when estimating greenhouse gas related decreasing trend using linear regression. Key Points: Geomagnetic activity related long‐term variation of foF2 was distinguished from the linear trend and found to be seasonally discrepantFrequent weak geomagnetic activity is the main driver of the seasonally discrepant long‐term variation by modulating background circulationThe linear decreasing trend of foF2 is in line with the increasing greenhouse gas but may be modulated by geomagnetic activity [ABSTRACT FROM AUTHOR]

We studied the temporal and periodic variations of the monthly solar flare index (FI) and selected geomagnetic-activity parameters (Ap, Dst, Scalar B, and aa) measured during Solar Cycles 21 – 24 (from January 1, 1975 to December 31, 2020) and report the following findings: 1) all data sets except the FI peak values gradually decreased after 1992, while the FI peak values began their gradual decrease in 1982; 2) all data sets show double or multiple peaks during the maximum phase of solar cycles; 3) the FI shows meaningful correlations with the investigated geomagnetic-activity parameters; 4) the 11-year sunspot-cycle periodicity and periodicities lower than 3.9 months were observed in all data sets without exception; 5) the FI time series exhibits a unique period of 4.8 – 5.2 months that is not present in all the other indices, while geomagnetic aa, Ap, and Dst indices show a unique 6 – 6.1 months periodicity that does not appear in the scalar B and FI; 6) crosswavelet transform (XWT) spectra between FI and other parameters generally show phase mixing in the short (2 – 8 months) period range, while all parameters used in this study were found to be inphase and highly correlated with the 11-year solar-activity period. All these results show that the FI variations are one of the main drivers of the geomagnetic activity. [ABSTRACT FROM AUTHOR]

• Solar and geomagnetic activity (SGA) were associated with lower scores on a dementia screening test. • Increased solar activity was associated with improved global cognitive scores. • Associations between SGA and different aspects of cognitive function were mixed. Studies show that changes in solar and geomagnetic activity (SGA) influence melatonin secretion and the autonomic nervous system. We evaluated associations between solar and geomagnetic activity and cognitive function in the Normative Aging Study from 1992 to 2013. We used logistic and linear generalized estimating equations and regressions to evaluate the associations between moving averages of sunspot number (SSN) and K p index (a measure of geomagnetic activity) and a binary measure for Mini-Mental State Examination (MMSE) scores (≤25 or > 25) and six other cognitive tests as continuous measures, combined into one global composite score and considered separately. A one-IQR increase in same-day SSN and K p index were associated with 17% (95% CI: 3%, 34%) and 19% (95% CI: 4%, 36%) increases in the odds of low MMSE score. We observed small increases in the global cognitive score with increasing SSN, although we observed decreases specifically in relation to the backwards digit span test. Periods of high SGA were associated with cognitive function. SGA may not equally impact all aspects of cognitive function, as evidenced by differences in associations observed for the MMSE, global cognitive score, and individual cognitive tests. Given that much of the pathology of cognitive decline in the elderly remains unexplained, studies specifically targeting decline and with longer follow-up periods are warranted. [ABSTRACT FROM AUTHOR]

We study the spatial structure of a polarization jet/Sub‐Auroral Ion Drift (PJ/SAID) based on data from the NorSat‐1 and Swarm satellites during a geomagnetic storm. Observations of plasma parameters inside the PJ/SAID are obtained with NorSat‐1 using a system of Langmuir probes with a nominal sampling rate of up to 1 kHz, which allowed measurements with such a high temporal resolution for the first time. A comparative analysis of plasma parameters and electron density spectra inside PJ according to the data from both satellites is presented. Our results show that fluctuations of plasma parameters inside the PJ increase at all scales with increasing geomagnetic activity. Small‐scale irregularities in the PJ are measured in situ down to hundreds of meters. The role of large‐scale effects in the PJ increases in comparison with the small‐scale ones during high geomagnetic activity. The PJ consists of structures ∼0.2° latitude in size within which small‐scale irregularities are present. Plain Language Summary: Polarization jet (PJ), also known as Sub‐Auroral Ion Drift (SAID), events are fast westward plasma drifts with a narrow latitudinal extent, occurring at subauroral latitudes in the Earth's ionosphere. The decrease in the density of the ionospheric plasma inside PJ/SAID significantly affects the conditions for the propagation of shortwave radio waves, which indicates the practical importance of studying this phenomenon. Despite the importance of using a variety of ground‐based observation facilities for studying and analyzing PJ/SAID properties, as well as developing analytical models and numerical modeling, in situ observations are the most valuable. Such in situ observations can be obtained only with satellites flying through a developing PJ/SAID. Large‐scale features of PJ/SAID are currently well understood, but small‐scale processes within PJ/SAID are practically not studied, and many open questions remain. In this work, we study the small‐scale structures in PJ/SAID during a geomagnetic storm of 20 April 2018, using multi‐instrumental approach involving low‐Earth orbit. Key Points: Fluctuations of plasma parameters inside the polarization jet (PJ) increase at all scales during higher geomagnetic activitySmall‐scale irregularities inside the PJ are measured in situ down to hundreds of metersThe role of large‐scale effects in the PJ increases in comparison with small‐scale ones with geomagnetic activity [ABSTRACT FROM AUTHOR]

The influence of magnetic fields and natural geomagnetic storms on biological circadian rhythms are actively studied. This study reveals an impact of local natural perturbations in the geomagnetic field that occurred at different times of the day on circadian patterns of locomotor activity of zebrafish. A decrease in zebrafish swimming speed was observed during the geomagnetic disturbances before or after the fluctuations of diurnal geomagnetic variation. However, if the geomagnetic perturbations coincided with the fluctuations of diurnal geomagnetic variation, the decrease in zebrafish swimming speed was insignificant. This result suggests that the biological effects of geomagnetic disturbances may depend on synchronization with the diurnal geomagnetic variation. It implies that the previously published correlations between geomagnetic activity and medical or biological parameters could result from a disruption in circadian biorhythms. [ABSTRACT FROM AUTHOR]

Between 17 and 19 July 2017, four potentially destructive seismic events were recorded (M6.3 Russia earthquake, recorded on July 17, 2017 at 11:05:19 UTC; M7.7 Russia earthquake, recorded on July 17, 2017 at 23: 34:13 UTC; M6.4 Peru earthquake, recorded on July 18, 2017 at 02:05:19 UTC and M6.0 Mauritius earthquake, recorded on July 19, 2017 at 12:16:23 UTC). The authors, analyzing the modulation of the "near Earth" solar activity and the terrestrial geomagnetic activity between 13 and 19 July 2017, found that the four M6+ seismic events were preceded by a solar wind proton density increase and by a series of intense geomagnetic increases. [ABSTRACT FROM AUTHOR]

Between 13 and 16 April 2016, eight potentially destructive seismic events were recorded on a global scale (M6.9 Burma earthquake, recorded on April 13, 2016 at 13:55:17 UTC; 6.0 Philippines earthquake, recorded on April 13, 2016 at 18:21:35 UTC; M6.2 Japan earthquake, recorded on April 14, 2016 at 12:26:35 UTC; M6.0 Japan earthquake, recorded on April 14, 2016 at 15:03:47 UTC; M6.4 Vanuatu earthquake, recorded on April 14, 2016 at 21:50:27 UTC; M6.1 Guatemala earthquake, recorded on April 15, 2016 at 14:11:26 UTC; M7.0 Japan earthquake, recorded on April 15, 2016 at 16:25:06 UTC; M7.8 Ecuador earthquake, recorded on April 16, 2016 at 23:58:36 UTC). The authors verified the existence of a close correlation between this seismic train and the solar activity recorded between 12 and 17 April 2016. [ABSTRACT FROM AUTHOR]

Between 7 and 20 November 2017, ten high intensity seismic events (M6+) were recorded on our planet. The authors, analyzing the characteristics of solar ion flux and terrestrial geomagnetic activity, found that the ten potentially destructive seismic events were preceded by solar wind proton density increases and by increases in terrestrial geomagnetic activity. [ABSTRACT FROM AUTHOR]

In this work, the Global Ionospheric Maps (GIMs) are used to analyze the behavior of the mid-latitude ionospheric trough (MIT) during the solar cycle 24 (2008–2019). This analysis is performed for the Northern and Southern Hemispheres at different local times: 00, 02 and 04 LT. We study the MIT position dependence on the phase of the solar cycle, seasonal, and geomagnetic activity during the post-midnight period. We find that the MIT position shows an interhemispheric asymmetry. Its equatorward movement from low to high solar activity is about 3 ° and 1 ° for Northern and Southern Hemisphere respectively for the three local times analyzed. There is also a clear seasonal variation, the shift between winter and summer is around 3 ° and 1 ° at 00 LT and 6 ° and 4 ° at 04 LT for the Northern and Southern Hemispheres, respectively. In general, the MIT position reaches the highest geomagnetic latitude in winter, without variation with local time. However, in summer it takes the lowest geomagnetic latitude, moving towards the equator from 00LT to 04LT. The MIT position moves equatorward under disturbed geomagnetic conditions, and the difference between the MIT position during quiet and perturbed days is greater in the Northern than in the Southern Hemisphere. In addition, the periodicity of the variability of the MIT position for both Hemispheres versus the solar wind speed and IMF Bz-component are analyzed using the wavelet transform, showing a clear dependence between them during the descending and minimum solar phase at 13.5 and 27-day time scales. [ABSTRACT FROM AUTHOR]

Permanent monitoring and real‐time indexing of the geomagnetic activity is of utmost importance for space weather services. In particular, providing a continuous and reliable local magnetic activity nowcast is of increasing importance as it can be used to generate alerts for various users, for instance for GNSS‐based applications or to protect electric power grids. This study presents a novel nowcast system for calculating a K‐type index of the local magnetic activity in Belgium. This includes a fully automated computer procedure for digital magnetogram data acquisition, data cleaning, calculating the index, displaying the results, and possibly issuing an alert to interested users, if the storm‐level activity is identified. Novel characteristics are the higher cadence of index calculation, an index reliability estimate based on data quality, and the high availability of the nowcast guaranteed by the operation of two identical instruments at observatories in close proximity. An evaluation of the index nowcast accuracy was carried out, and its results are also presented. Plain Language Summary: As we increasingly rely on GNSS based technologies, not only major geomagnetic storms are worth being nowcasted, but also more frequent lower intensity events. The well‐known Kp‐index is a geomagnetic activity scale based on ground‐based magnetic field variations. Aside this planetary index, a local K‐index provides a more detailed geomagnetic activity level over a limited area. This study addresses two issues related to local K‐index nowcasting: data validation and service availability. Validation of geomagnetic data is a challenging issue because it can significantly fluctuate from one second to another, unpredictably, resulting in a difficult outliers identification process. For instance, a spike due to local powergrid issue may generate an alarm if not removed. Our approach is to produce a local K‐index, KBEL, based on two independent magnetometers, located in the two magnetic observatories of Belgium. The distance between the two sites is sufficient to consider local conditions are independent, but small enough that the variations recorded by the magnetometers should be similar. The real‐time comparison of the data sets offers a reliable tool to eliminate any outliers. This publication also discloses the parameters, specific to the chosen sites, as a support to any other local K‐index nowcasting service implementations. Key Points: An improved system for real‐time monitoring of the local geomagnetic activity is presentedCombining data from two compatible magnetic observatories allows automatic data cleaningUse of two geomagnetic observatories improves availability of magnetic field nowcasting [ABSTRACT FROM AUTHOR]

The ionosphere characteristics are important for radio propagation and to monitor climate. At present, its research is confined to global scale or a single station. There are only few local area studies of ionosphere. In view of this situation, we will first verify the reliability of Global Ionosphere Map (GIM, IGS final products) in the Qinghai–Tibet Plateau, then implement low-power filtering and time series analysis to study the periodic, semiannual, and seasonal variation, the peak characteristic, and the "winter anomaly" phenomenon of the ionosphere. Finally, correlations between total electron content (TEC), solar activity indices, and geomagnetic indices are investigated, respectively, by executing quadratic polynomial fitting and establishing the relationship of TEC and F 10.7p. The experimental results show that GIM is a reliable resource to research on the temporal and spatial characteristics of the ionosphere in the Qinghai–Tibet Plateau. The minimum TEC always occurs in autumn, whereas the maximum TEC occurs in spring or winter alternatively, which depends on the ascending or descending phase of solar activity. The "winter anomaly" phenomenon that existed for few years normally appears during the ascending phase of solar activity. The correlation coefficients of TEC with three solar activity indices, sunspot number, F 10.7 , and F 10.7p are 0.79, 0.82, and 0.83, respectively, which show strong correlations between them. The correlation coefficients of TEC with three geomagnetic indices, Dst, Kp, and Ap are −0.48, 0.43, and 0.38, respectively, which show weak correlations between them. Quadratic polynomial regression of F 10.7p and TEC is implemented. The regression line reflects that the ionosphere TEC in the Qinghai–Tibet Plateau has a saturated status. [ABSTRACT FROM AUTHOR]

On March 20, 2019 at 15:23:58 UTC, an M6.3 earthquake was recorded in Vanuatu at a depth of 119 km. The analysis of solar activity and terrestrial geomagnetic activity allowed the authors to verify that the M6.3 Vanuatu earthquake was preceded by an increase in solar activity (solar wind proton density increase; Interplanetary Seismic Precursor) and in terrestrial geomagnetic activity (Seismic Geomagnetic Precursor). This type of correlation was first observed by the authors in 2011 and is currently related to all potentially destructive seismic events recorded on a global scale from January 1, 2012 to date. [ABSTRACT FROM AUTHOR]

On 3-4 March 2021, seven M6+ seismic events were recorded on our planet: 1) Greece M6.3 earthquake, recorded on March 3, 2021 at 10:16 UTC; 2) New Zealand M7.3 earthquake, recorded on March 4, 2021 at 13:27 UTC; 3) Vanuatu M6.1 earthquake, recorded on March 4, 2021 at 16:53 UTC; 4) Kermadec Islands M7.4 earthquake, recorded on March 4, 2021 at 17:41 UTC 5) New Zealand 8.1 earthquake, recorded on March 4, 2021 at 19:28 UTC; 6) Kermadec Islands M6.1 earthquake, recorded on March 4, 2021 at 20:25 UTC; 7) Kermadec Islands M6.2 earthquake, recorded on March 4, 2021 at 23:12. The peculiarity that unites these potentially destructive earthquakes was the fact that they were recorded during a solar wind proton density increase that started on March 28, 2021 at 00:00 UTC and ended on March 5, 2021 at 00:00 UTC which caused a series of geomagnetic perturbations. [ABSTRACT FROM AUTHOR]

On February 22, 2019 at 10:17:23 UTC, an M7.5 earthquake was recorded in Ecuador. The authors, by monitoring in real time solar activity and terrestrial geomagnetic activity, identified a solar wind proton density increase and an increase in terrestrial geomagnetic activity that preceded the Ecuadorian seismic event of 72 hours (respect to solar wind ionic flux) and 48 hours (respect to geomagnetic perturbation). This type of correlation was first observed by the authors in 2011. To date, all destructive seismic events that are recorded on a global scale are always preceded by a solar wind proton density increase. [ABSTRACT FROM AUTHOR]

In this article, we investigate the interconnection and phase asynchrony between the periodicities of geomagnetic activity indices Kp , Ap , aa , and Dst according to the interplanetary magnetic field (IMF) polarities, toward (T) or away (A), during the time interval 1967–2018. For this purpose, the daily data of Kp , Ap, aa , and Dst indices during the considered period have been sorted into two groups (T and A) according to the IMF polarities. The wavelet transform (WT), the cross-wavelet transform (XWT), and the wavelet coherence (WTC) have been applied on the monthly averages of T and A groups for each geomagnetic index. Moreover, the correlation analyses (linear and running correlations) between the annual averages of T and A groups of each geomagnetic index have been investigated. The results of XWT and WTC revealed the existence of a long-term periodicity in the frequency range 8–16 yr for the monthly averages of T and A groups for aa , Kp , and Ap indices existed during the entire period. In contrast, the Dst index revealed this periodicity during the period 1980–2018. In addition, during this frequency band, both T and A groups of each geomagnetic index revealed a highly positive correlation and nearly in-phase relationship behavior. Furthermore, during the frequency band 4–8 yr, the XWT displayed a prominent periodicity that occurred for the monthly averages of T and A groups of each geomagnetic index, revealing a phase change during some time intervals. Periodicity in the range 2–4 yr for the monthly averages of T and A groups of aa , Kp , Ap , and Dst occurred in the intervals; 1967–2009 for aa and Kp , 1967–2007 for Ap , and 1976–1995 for Dst. The annual periodicity is also identified for all considered indices. Both T and A groups of Dst shared a semiannual periodicity (~187 days) during different intervals in the entire period. On the other hand, a periodicity around 0.25-yr (~90 days) appeared only near the times of solar activity maxima in the case of the T and A groups of aa , Kp , and Ap indices. [ABSTRACT FROM AUTHOR]

Over the last three solar cycles, the precursor method has proven to be a very reliable technique for forecasting ensuing solar cycles. In the present work, we have used the geomagnetic activity indices: a a and A p measured during the last 4 years of the descending phase of solar activity cycles as precursors for predicting the strength of the next solar cycle 25. From the indices a a and A p , we estimate the maximum sunspot number (SSN) amplitude of the upcoming solar cycle i . e ., solar activity cycle 25 to be 119.42 ± 28.41 and 113.70 ± 23.51 , respectively. This suggests that the activity of the next solar cycle 25 is likely to be comparable to that of cycle 24. The results further suggest that this forecast of the maximum SSN will be associated with the values a a = 16.67 ± 3.11 nT and A p = 8.78 ± 2.34 nT. This indicates that the maximum solar cycle 25 is expected to be accompanied by higher geomagnetic activity levels than in cycle 24, but less than those in the previous cycles 22 and 23. Predicting the level of solar activity is of particular interest because it enhances understanding on establishing a consistent picture of the solar dynamo process and changes in the magnetic field therein; and also helps us in taking decisions having implications in our operational technological capability in space. [ABSTRACT FROM AUTHOR]

On February 7, 2021 two M6+ seismic events were recorded on our planet (M6.0 Philippines earthquake, recorded at 04:22:56 UTC; M6.3 Papua New Guinea earthquake, recorded at 05:45:52 UTC). The authors, analyzing the characteristics of solar ion flux and terrestrial geomagnetic activity, verified that the two potentially destructive seismic events were preceded by a solar wind proton density increase and by an increase in terrestrial geomagnetic activity. This type of correlation is already known to the international scientific community thanks to the studies conducted by the authors in this field of research since 2011. [ABSTRACT FROM AUTHOR]

On February 13, 2021 at 14:07:50 UTC, an M7.1 earthquake was recorded in Japan at a depth of 49.9 km. The analysis of solar activity and terrestrial geomagnetic activity allowed the authors to verify that the M7.1 Japanese earthquake was preceded by an increase in solar activity which subsequently produced an increase in terrestrial geomagnetic activity: phenomena of electromagnetic nature that the authors have related to the M6+ global seismic activity since 2011. [ABSTRACT FROM AUTHOR]

On February 3, 2021, at 05:23:44 UTC, an M6.7 earthquake was recorded off the west coast of Chile. The monitoring of solar activity and terrestrial geomagnetic activity allowed the authors to highlight that the Chilean seismic event was preceded by a solar wind proton density increase (Interplanetary Seismic Precuror) and by an increase in terrestrial geomagnetic activity (Seismic Geomagnetic Precursor), confirming also this time that all potentially destructive earthquakes that are recorded on a global scale are always preceded by an increase in solar activity. [ABSTRACT FROM AUTHOR]

In this study we use the CHAMP wind observations from 2002 to 2004 to investigate features of mid-latitude thermospheric winds at low and high geomagnetic activity levels. The winds are observed between the geomagnetic latitudes 40–50° north or south within an altitude range of 370–450 Km and averaged longitudinally. The low geomagnetic activity level wind generally leads eastward in both hemispheres for all the seasons. Maximum westward speeds going above 100 m/s are observed at all levels of geomagnetic activity. Most investigations on F-region parameters assume the equinoxes are fundamentally the same. A first time separation of Equinox season using CHAMP winds reveals equinoctial asymmetric behavior of the wind speed at the two levels considered. Interhemispheric asymmetry in neutral wind behaviour is clearly evident in the solstice seasons with local winds considered in each of the hemispheres. This is consistent with asymmetry in the amount of solar illumination received in each of the hemispheres and differences in the magnetic field strength at magnetically conjugate regions. [ABSTRACT FROM AUTHOR]

This paper presents the results of the creation of a geomagnetic data storage system that combines raw observation data from different geomagnetic observation networks along with derived indices and indicators of geomagnetic activity. Geomagnetic data, provided by observation networks, undergo a series of data quality validation procedures. The implemented instruments and procedures facilitate the creation of a uniform database from multiple sources.

In this study, the response to geomagnetic storms of the ionospheric F2 layer critical frequency (foF2) was investigated at the magnetic conjugate points. The hourly foF2 data observed at the magnetic conjugate points of middle and high latitudes for the geomagnetic stormy days around both of 1976 and foF2 data received from IRI-2016 Model for same points were used. The foF2 data observed in magnetic conjugate points and received from IRI Model were examined using the superposed epoch analysis method and the results obtained were compared. From the results of analysis, it was observed that the foF2 data observed at magnetic conjugate points and received from IRI Model simultaneously respond to geomagnetic activity changes for both the middle latitudes and the high latitudes. [ABSTRACT FROM AUTHOR]

In this paper extreme value theory (EVT) has been used to estimate the return levels for geomagnetic activity based on the aa index. The aa index is the longest, continuously recorded, geomagnetic data set (from 1868 to present). This long, 150‐year data set is an ideal candidate for extreme value analysis. However, the data are not independent and identically distributed as required for EVT since they are impacted by the approximately 11‐year solar cycle. The Hilbert‐Huang transform has been used to identify the solar cycle component in the data, and the data have been split into solar maximum and minimum times. In these two regimes the generalized extreme value distribution has been fit to the data sets. These have also been combined for an estimate of the overall return times. The results suggest that the largest event in the database (March 1989) is a 1‐in‐25‐year event. However, considering separate solar maximum and minimum times has a large impact on the return times. During solar minimum conditions the return time of the March 1989 event is 130 years. This suggests that the occurrence of extreme space weather events is conditionally dependent on where in the solar cycle we are. Key Points: A Hilbert‐Huang transform is applied to the geomagnetic aa data to identify the solar cycle dependency in the dataExtreme value theory is applied to the aa data separately in solar minimum and maximum conditionsMarch 1989 (Quebec) event is shown to overall be a 1‐in‐25‐year event, but a 1‐in‐130‐year event during solar minimum [ABSTRACT FROM AUTHOR]

The most important driver of geomagnetic activity is the north–south (Bz) component of the interplanetary magnetic field (IMF), which dominates the solar wind‐magnetosphere coupling and all solar wind coupling functions. While the east–west (By) IMF component is also included in most coupling functions, its effect is always assumed to be symmetric with respect of its sign. However, recent studies have shown that, for a fixed value of any coupling function, geomagnetic activity is stronger for By>0 than for By<0 in Northern Hemisphere winter. In Southern Hemisphere winter, the dependence on the By sign is reversed. In this paper, we use measurements of National Oceanic and Atmospheric Administration Polar‐Orbiting Operational Environmental Satellites to show that the flux of magnetospheric electrons precipitating into the atmosphere also exhibits an explicit By dependence. This By dependence is strong in the midnight and dawn sectors where it causes a related By effect in the westward electrojet and geomagnetic activity by modulating ionospheric conductivity. Key Points: Fluxes of energetic electrons precipitating into atmosphere are strongly dependent on the sign and amplitude of IMF ByThis IMF By effect on electron fluxes is strong around midnight and at dawn but weak at duskThis IMF By effect is expected to modulate ionospheric conductivity and to affect a similar effect in geomagnetic activity [ABSTRACT FROM AUTHOR]

This paper presents a multi-parameter global statistical model of extreme horizontal geomagnetic field fluctuations (dBH/dt), which are a useful input to models assessing the risk of geomagnetically induced currents in ground infrastructure. Generalised Pareto (GP) distributions were fitted to 1-min measurements of |dBH/dt| from 125 magnetometers (with an average of 28 years of data per site) and return levels (RL) predicted for return periods (RP) between 5 and 500 years. Analytical functions characterise the profiles of maximum-likelihood GP model parameters and the derived RLs as a function of corrected geomagnetic latitude, λ. A sharp peak in both the GP shape parameter and the RLs is observed at |λ| = 53° in both hemispheres, indicating a sharp equatorward limit of the auroral electrojet region. RLs also increase strongly in the dayside region poleward of the polar cusp (|λ| > 75°) for RPs > 100 years. We describe how the GP model may be further refined by modelling the probability of occurrences of |dBH/dt| exceeding the 99.97th percentile as a function of month, magnetic local time, and the direction of the field fluctuation, dBH, and demonstrate that these patterns of occurrence align closely to known patterns of auroral substorm onsets, ULF Pc5 wave activity, and (storm) sudden commencement impacts. Changes in the occurrence probability profiles with the interplanetary magnetic field (IMF) orientation reveal further details of the nature of the ionospheric currents driving extreme |dBH/dt| fluctuations, such as the changing location of the polar cusp and seasonal variations explained by the Russell-McPherron effect. [ABSTRACT FROM AUTHOR]

Recent studies based on CLUSTER, CRRES, and especially on THEMIS satellite data have revealed the statistical behavior of the global plasmapause such as eastward azimuthal plasmapause propagation and radial plasmapause motion between 21 and 07 magnetic local times (MLTs) most likely at postmidnight. The results are shown to be in a good agreement with characteristics of the plasmapause modeled using interchange instability mechanism. The present study is based on the plasmapause modeled with the mentioned physical mechanism, and it aims to link the observed global plasmapause dynamic with formation and evolution of plasmapause structures. We investigated two plasmapause datasets obtained using real Kp values and certain type of time‐dependent changes in the Kp (thereafter Kp jumps) as input in the simulations. The Kp jumps include sharp Kp increase, sharp Kp decrease, short‐time burst enhancement (increase‐decrease within 3 hr) in Kp, and their combinations in order to obtain plumes, shoulders, and notches, the structures most often observed in the nature. The cross‐correlation analyses is applied to the modeled plasmapause and to the geomagnetic Kp index at different 1‐hr MLT bins. We have shown that the cross‐correlation curves provide deeper insight in the physical processes related to the plasmapause dynamic and evolution. Their behavior is interpreted as the imprint of the plasmapause structure passages through specific MLT sector. Taking into account that the plasmapause in the single events shows very complex and different behaviors, the most important finding of the present study is the simple explanation of what causes global plasmapause motions and deformation in time. Key Points: Interchange instability simulations that employ real Kp values and a few types of Kp jumps as input provide same plasmapause characteristicsStatistical plasmapause behavior is successfully explained by considering only three plasmapause structures: plumes, shoulders, and notchesGlobal plasmapause evolution in time (azimuthal propagation and MLT sectors of radial deformation) is simplified and systematized [ABSTRACT FROM AUTHOR]

Recent studies suggest a response in the North Atlantic winter circulation which lags by a couple of years with respect to sunspot maximum. This has been explained by two different top‐down mechanisms: a solar wind driven particle effect in the polar atmosphere during the declining phase of the solar cycle, and the re‐emergence and amplification of heat anomalies in the Atlantic Ocean produced by enhanced solar ultraviolet (UV). Here we study how December to February climate is affected by two solar‐related drivers: geomagnetic activity (proxy of particle precipitation) and sunspot activity (proxy of solar UV) during 1948–2017. We use reanalysis data of sea‐level pressure (SLP) and zonal wind (U) to show that both geomagnetic activity and sunspot activity independently and simultaneously produce atmospheric circulation responses in the North Atlantic whose evolutions clearly differ from each other. Geomagnetic activity produces a strengthening of the polar vortex and a negative poleward SLP gradient between mid‐ and high latitudes, resembling a positive NAO‐type circulation pattern during December to February. Solar UV produces a positive U anomaly in the low‐latitude stratosphere during December, which moves poleward and downward during the winter resulting in a negative poleward SLP gradient between mid‐ and high latitudes during February. We find the lagged sunspot activity responses in SLP to form zonal pressure patterns (wave‐train structure) resembling the Eurasian pattern. Geomagnetic activity responses remain essentially the same when we introduce the lag with respect to sunspot activity supporting its independency as a driving mechanism. Our results suggest that solar wind related particle precipitation and (lagged) solar UV mechanism provide independent, significant circulation signals in the North Atlantic winter. [ABSTRACT FROM AUTHOR]

The irregularity of the solar activities based on sunspot numbers (SSNs) and areas (SSAs) over the solar disk has been considered. More activities phenomena occurred in one of the solar hemispheres than the other at the same time, which they are referred to as the North-South (N-S) asymmetry of solar activity. Daily averages of geomagnetic indices aa , Ap , Kp , and Dst over the period 1967–2016 have been examined according to the asymmetrical distribution of both solar hemispheric activities. The possible connection between the geomagnetic activity disturbances and the sign of non-uniformity of solar activity, i.e. the N-S asymmetry for each geomagnetic index has been confirmed. The dependence of the sign of geomagnetic disturbances on the solar activity cycle, has been examined. We have classified the considered data into two groups according to the activity of northern (N) or southern (S) solar hemisphere. The solar cycles 20 and 24 have northern hemisphere dominance. These activities shifted from northern to southern hemisphere in solar cycles 21, 22, and 23. The geomagnetic disturbances exhibited significant asymmetrical states at different periods. The most significant northern and southern peaks occurred at/near the minimum of the solar cycle or in periods of descending phase of the solar cycle. The geomagnetic activity has southern dominance during solar cycle 22 and it favoured the northern activity during solar cycle 23. The dependence of the geomagnetic activity disturbance of aa , Ap, Kp , and Dst indices over the solar activity cycle is confirmed and the sign of the asymmetry changes from one solar cycle to another. [ABSTRACT FROM AUTHOR]

Abstract We discuss the issues of primary importance to understand the nature of climate changes in the 20th century and main physical processes responsible for these changes and present a physical model for the solar activity (SA) effect on climate characteristics. A key concept of this model is the heliogeophysical disturbance effect on the Earth climate system parameters driving the long-wave radiation flux moving away from the Earth out into space in high-latitude regions. We address the solar activity effect on the changes in the temperature of the atmosphere and of the World Ocean. The aa–index of the geomagnetic activity (GA) was used as an SA proxy index. We discuss the results of analyzing the regularities and peculiarities of the tropospheric and sea surface temperature (SST) responses to both separate heliogeophysical disturbances and long-term changes in solar and geomagnetic activity. The structure of the tropospheric and SST temperature responses was shown to feature a spatial time irregularity. We revealed the regions, where long-term SST changes are determined mainly by SA variations. Highlights • Influence of solar activity on the climate. • Wind-stress effect on the response sea surface temperature to geomagnetic activity. • Solar variability manifestations in the troposphere. [ABSTRACT FROM AUTHOR]

In the present work we show that it is possible to predict the maximum sunspot number for a particular solar cycle from the maximum value of the solar dipole magnetic field of the previous cycle. Based on the measured dipole field maximum, we determine the geomagnetic activity in the upcoming solar minimum during the intervals when the Earth is not exposed to CME and HSS influences. The physical meaning of the relationship between the geomagnetic activity in the solar activity minimum and the maximum value of the solar dipole magnetic field is that the basic factor determining the geomagnetic activity during the minimum is not the heliospheric current sheet thickness but the physical parameters of the slow solar wind in this period. Then, based on the established relationship between the average geomagnetic activity at the specified minimum and the next solar maximum, we can predict the sunspot maximum of the next solar cycle. [ABSTRACT FROM AUTHOR]

Spring-Autumnal asymmetry (SA asymmetry) from years 1873–2010 in the geomagnetic activity is investigated based on the geomagnetic indices (aa, Ap and Kp). Results have shown that in general the SA asymmetry of the geomagnetic activity appears to be alternation, except for the interval during which the change of dominant solar dipole magnetic field polarity occurs. Our study implies that both the polarity of the main solar dipole field and the north-south asymmetry of the sunspot area in the two solar hemispheres control the strength of the south component ( Bs ) of the interplanetary magnetic field (IMF) near the Earth and the resulting SA asymmetry of the geomagnetic activity in the corresponding seasons. A simple sector structure model is devised to establish the relationship between the polarity of solar main dipole magnetic field, the IMF Bs component and the corresponding SA asymmetry in the geomagnetic activity. This is confirmed by examining the solar wind parameters from the spacecraft observations during the recent decades. [ABSTRACT FROM AUTHOR]

Geomagnetic activity is usually gauged by a single time‐dependent geomagnetic index. One drawback is that an individual geomagnetic index measures only one aspect of the activity in the Earth's magnetosphere. Here we construct a time‐dependent 11‐element magnetospheric state vector E for Earth that consists of measures of high‐latitude currents, polar cap current, magnetospheric convection, plasma pressure, ion and electron precipitation rates, the intensity of substorm‐injected electrons, and the elapsed time since the last substorm onset. At the same time we construct an eight‐element time‐dependent solar‐wind state vector S from the measured properties of the solar wind at Earth. In this S → E picture a time‐dependent "magnetospheric‐activity index" E(1) is created from a weighted sum of the 11 variables in the magnetospheric state vector, with the weights chosen by the vector correlation properties between the magnetospheric state vector E and the solar wind state vector S. The properties and advantages of this E(1) index are examined for the years 1991–2007. Comparing fits made on different subsets of the data demonstrates the robustness of the definition of E(1); tests using out‐of‐sample data demonstrate the accuracy of solar wind predictions of E(1). The advantages of the composite index E(1) include a more direct association with the solar wind, linearity, high predictability, and versatility with respect to (a) storm‐versus‐quiet intervals, (b) solar maximum versus solar minimum, and (c) the various types of solar wind plasma. Defining magnetospheric storms with the composite index E(1) is explored, and categorizing magnetospheric storms using the magnetospheric state vector E is considered. Key Points: An 11‐variable magnetospheric state vector E is used to create a scalar magnetospheric‐activity index E(1) driven by a solar wind scalar S(1)Fitting E(1) by S(1) is very accurate, and one fit holds for both weak and strong activities and for the different phases of the solar cycleDefining magnetospheric storms with the global magnetospheric index E(1) is explored; the vector E can be used to categorize storms [ABSTRACT FROM AUTHOR]

Variations of airglow intensity, Volume Emission Rate (VER), and VER peak height induced by the CO 2 increase, and by the F10.7 solar cycle variation and geomagnetic activity were investigated to quantitatively assess their influences on airglow. This study is an extension of a previous study by Huang (2016) covering a time period of 55 years from 1960 to 2015 and includes geomagnetic variability. Two airglow models, OHCD-90 and MACD-90, are used to simulate the induced variations of O( 1 S) greenline, O 2 (0,1) atmospheric band, and OH(8,3) airglow for this study. Overall, our results demonstrate that airglow intensity and the peak VER variations of the three airglow emissions are strongly correlated, and in phase, with the F10.7 solar cycle variation. In addition, there is a linear trend, be it increasing or decreasing, existing in the airglow intensities and VERs due to the CO 2 increase. On other hand, airglow VER peak heights are strongly correlated, and out of phase, with the Ap index variation of geomagnetic activity. The CO 2 increase acts to lower the VER peak heights of OH(8,3) airglow and O( 1 S) greenline by 0.2 km in 55 years and it has no effect on the VER peak height of O 2 (0,1) atmospheric band. [ABSTRACT FROM AUTHOR]

The interaction of the solar wind with the Earth's magnetic field produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic field (IMF). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so‐called IMF clock angle in a way, which is symmetric with respect to the sign of the By component. However, recent studies have suggested that the sign of By is an additional, independent driver of high‐latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for By > 0 (By<0). In this paper we quantify the size of this explicit By effect with respect to the solar wind coupling function, both for northern and southern high‐latitude geomagnetic activity. We show that high‐latitude geomagnetic activity is significantly (by about 40%–50%) suppressed for By < 0 in NH winter and for By > 0 in Southern Hemisphere winter. When averaged over all months, high‐latitude geomagnetic activity in NH is about 12% weaker for By < 0 than for By > 0. The By effect affects the westward electrojet strongly, but hardly at all the eastward electrojet. We also show that the suppression of the westward electrojet in NH during By < 0 maximizes when the Earth's dipole axis points toward the night sector, that is, when the auroral region is maximally in darkness. Key Points: IMF By is an explicit driver of high‐latitude geomagnetic activityHigh‐latitude geomagnetic activity is suppressed in local winter for By < 0 in Northern Hemisphere and for By > 0 in Southern HemisphereExplicit By effect maximizes when the Earth's dipole axis points toward night [ABSTRACT FROM AUTHOR]

For the 2007 to 2014 period, we use a statistical approach to evaluate the performance of Tsyganenko and Sitnov [2005] semi-empirical model (TS05) in estimating the magnetospheric transient signal observed at four Northern Hemisphere mid-latitude ground stations: Coimbra, Portugal; Panagyurishte, Bulgary; Novosibirsk, Russia and Boulder, USA. Using hourly mean data, we find that the TS05 performance is clearly better for the X (North-South) than for the Y (East-West) field components and for more geomagnetically active days as determined by local K-indices. In ∼ 50 % (X) and ∼ 30 % (Y) of the total number of geomagnetically active days, correlation values yield r ≥ 0.7 . During more quiet conditions, only ∼ 30 % (X) and ∼ 15 % (Y) of the number of analyzed days yield r ≥ 0.7 . We compute separate contributions from different magnetospheric currents to data time variability and to signal magnitude. During more active days, all tail, symmetric ring and partial ring currents contribute to the time variability of X while the partial ring and field aligned currents contribute most to the time variability of Y. The tail and symmetric ring currents are main contributors to the magnitude of X. In the best case estimations when r ≥ 0.7 , remaining differences between observations and TS05 predictions could be explained by global induction in the Earth's upper layers and crustal magnetization. The closing of field aligned currents through the Earth's center in the TS05 model seems to be mainly affecting the Y magnetospheric field predictions. [ABSTRACT FROM AUTHOR]

Twenty-seven-day variation caused by solar rotation is one of the main periodic effects of solar radiation influence on the ionosphere, and there have been many studies on this periodicity using peak electron density $$\mathrm{N_{m}F_{2}}$$ and solar radio flux index F10.7. In this paper, the global electron content (GEC) and observation of Solar EUV Monitor (SEM) represent the whole ionosphere and solar EUV flux, respectively, to investigate the 27-day variation. The 27-day period components of indices $$(\hbox {GEC}_{27}$$ , $$\hbox {SEM}_{27}$$ , $$\hbox {F10.7}_{27}$$ , $$\hbox {Ap}_{27})$$ are obtained using Chebyshev band-pass filter. The comparison of regression results indicates that the index SEM has higher coherence than F10.7 with 27-day variation of the ionosphere. The regression coefficients of $$\hbox {SEM}_{27 }$$ varied from 0.6 to 1.4 and the coefficients of $$\hbox {Ap}_{27}$$ varied from $${-}$$ 0.6 to 0.3, which suggests that EUV radiation seasonal variations are the primary driver for the 27-day variations of the ionosphere for most periods. TEC map grid points on three meridians where IGS stations are dense are selected for regression, and the results show that the contribution of solar EUV radiation is positive at all geomagnetic latitudes and larger than geomagnetic activity in most latitudes. The contribution of geomagnetic activity is negative at high geomagnetic latitude, increasing with decreasing geomagnetic latitudes, and positive at low geomagnetic latitudes. The global structure of 27-day variation of ionosphere is presented and demonstrates that there are two zonal anomaly regions along with the geomagnetic latitudes lines and two peaks in the north of Southeast Asia and the Middle Pacific where $$\hbox {TEC}_{27}$$ magnitude values are notably larger than elsewhere along zonal anomaly regions. [ABSTRACT FROM AUTHOR]

In this paper, based on observations of the European Incoherent Scatter Svalbard Radar (ESR) between 1997 and 2008, we analyzed variations of H m F 2 , the ionospheric scale height around the peak height of F 2 layer (h m F 2 ) at high latitude with geomagnetic activities, as well as variations of the H m F 2 with the local time (LT), season and solar activity under disturbed conditions (2 < Kp ≤ 5). We found that the H m F 2 shows a significant increment with enhancements of geomagnetic activities. In addition, based on a linear regression, the correlation and fitting coefficients are shown, which quantitatively describe the correlations between polar H m F 2 and geomagnetic activity index Kp. The H m F 2 shows a diurnal variation with a maximum early in the morning and a minimum around noon in disturbed days (2 < Kp ≤ 5), which is more complex in comparison with that in quiet days. However, in summer and autumn, the H m F 2 in disturbed days shows a bulge during 06:00–11:00 LT instead of the continuous decline under quiet condition. We consider that the ESR was under the cusp region during the period so that the bulge might be related to the high-energy particles precipitating into the ionosphere resulting in changes of the electron density profile. The H m F 2 has the highest seasonal magnitude in summer and the lowest seasonal magnitude in winter generally. The seasonal magnitude of the H m F 2 in autumn is lower than that in spring and larger than that in winter under low solar activity, while the H m F 2 shows the same seasonal variations in spring and autumn under moderate and high solar activities. [ABSTRACT FROM AUTHOR]

The influence of geomagnetic activity on the metrological characteristics of inclinometric informationmeasuring systems was studied. The necessity of introducing indices of geomagnetic activity with the aim of formalizing this influence and clarifying the metrological characteristics of inclinometer equipment is substantiated. A step-by-step methodology for calculating the introduced indices is proposed and described. We numerically calculate and estimate the proposed indexes on the basis of real models of geomagnetic activity over a 72-hour time period. The obtained results are analyzed. [ABSTRACT FROM AUTHOR]

In this paper, we study the solar-terrestrial relation through the wavelet analysis. We report periodicities common between multiple solar wind coupling functions and geomagnetic indices during five solar cycles and also and the strength of this correspondence. The $\mathit{Dst}$ (found to be most predictable in Newell et al., J. Geophys. Res. Space Phys. 112(A1):A01206, 2007) and $\mathit{AL}$ (least predictable in Newell et al., J. Geophys. Res. Space Phys. 112(A1):A01206, 2007) indices are used for this purpose. During the years 1966-2016 (which includes five solar cycles 20, 21, 22, 23, and 24), prominent periodicities $\leq720$ days with power above 95% confidence level were found to occur around 27, 182, 385, and 648 days in the $\mathit{Dst}$ index while those in the $\mathit{AL}$ index were found in bands around 27, 187, and 472 days. Ten solar wind coupling functions were then used to find periodicities common with the indices. All the coupling functions had significant power in bands centered around 27, 280, and 648 days while powers in fluctuations around 182, 385, and 472 days were only found in some coupling functions. All the drivers and their variants had power above the significant level in the 280-288 days band, which was absent in the $\mathit{Dst}$ and $\mathit{AL}$ indices. The normalized scale averaged spectral power around the common periods in the coupling functions and the indices indicated that the coupling functions most correlated with the $\mathit{Dst}$ index were the Newell (27 and 385 days), Wygant (182 days), and Scurry-Russell and Boynton (648 days) functions. An absence of common power between the coupling functions and the $\mathit{Dst}$ index around the annual periodicity was noted during the even solar cycles. A similar analysis for the $\mathit{AL}$ index indicated that Newell (27 days), Rectified (187 days), and Boynton (472 days) were the most correlated functions. It was also found that the correlation numbers were relatively weaker for the $\mathit{AL}$ index, specially for the 187 day periodicity. It is concluded that as the two indices respond to solar wind forcing with varying levels of strength at various prominent scales and the coupling function used, the response might be dependent on the scale (days or months or years) of interest at which the solar wind driving is to be predicted. [ABSTRACT FROM AUTHOR]

During the last years a possible link between different levels of solar and geomagnetic disturbances and human physiological parameters is suggested by several published studies. In this work the examination of the potential association between heart rate variations and specific space weather activities was performed. A total of 482 individuals treated at Hippocratio General Hospital in Athens, the Cardiology clinics of Nikaia General Hospital in Piraeus and the Heraklion University Hospital in Crete, Greece, were assessed from July 2011 to April 2013. The heart rate of the individuals was recorded by a Holter monitor on a n hourly basis, while the hourly variations of the cosmic ray intensity measured by the Neutron Monitor Station of the Athens University and of the geomagnetic index Dst provided by the Kyoto Observatory were used. The ANalysis Of VAriance (ANOVA) and the Multiple Linear Regression analysis were used for analysis of these data. A statistically significant effect of both cosmic rays and geomagnetic activity on heart rate was observed, which may indicate that changes in space weather could be linked to heart rate variations. [ABSTRACT FROM AUTHOR]