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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]

A novel tool utilizing machine learning techniques was designed to forecast ap index values for the next three consecutive days (24 values). The tool employs time series data from the 3 h ap index of solar cycles 23 and 24 to train the Long Short-Term Memory (LSTM) model, predicting ap index values for the next 72 h at three-hour intervals. During periods of quiet geomagnetic activity, the LSTM model's performance is sufficient to yield favorable outcomes. Nevertheless, during geomagnetically disturbed conditions, such as geomagnetic storms of different levels, the model needs to be adapted in order to provide accurate ap index results. In particular, when coronal mass ejections occur, the ap Prediction tool is modulated by inserting predominant features of coronal mass ejections such as the date of the event, the estimated time of arrival and the linear speed. In the present work, this tool is described thoroughly; moreover, results for G2 and G3 geomagnetic storms are presented. [ABSTRACT FROM AUTHOR]

On 4 November 2021, during the rising phase of solar cycle 25, an intense geomagnetic storm (Kp = 8−) occurred. The effects of this storm on the outer magnetospheric region up to the ionospheric heights have already been examined in previous investigations. This work is focused on the analysis of the solar wind conditions before and during the geomagnetic storm, the high-latitude electrodynamics conditions, estimated through empirical models, and the response of the atmosphere in both hemispheres, based on parameters from the ECMWF ERA5 atmospheric reanalysis dataset. Our investigations are also supported by counter-test analysis and Monte Carlo tests. We find, for both hemispheres, a significant correspondence, within 1–2 days, between high-latitude electrodynamics variations and changes in the temperature, specific humidity, and meridional and zonal winds, in both the troposphere and stratosphere. The results indicate that, in the complex solar wind–atmosphere relationship, a significant role might be played by the intensification of the polar cap potential. We also study the reciprocal relation between the ionospheric Joule heating, calculated from a model, and two adiabatic invariants used in the analysis of solar wind turbulence. [ABSTRACT FROM AUTHOR]

Based on two meteor radars in mid‐latitudes of China, the mid‐latitude lower thermospheric neutral wind responses to the 2015 St. Patrick's Day great storm are investigated. The AE and PCN indices presented the similar quasi‐5‐hour oscillations during the storm. Interestingly, the analogous and close‐correlated storm‐time quasi‐5‐hour oscillations were also observed in both the meridional wind differences at 90–102 km derived from meteor radars. The meridional wind disturbances in the lower thermosphere also showed the extension toward the lower latitudes. It has been found that the enhanced equatorward wind disturbances at 250 km estimated by the Horizontal Wind Model‐14 and Fabry‐Perot Interferometer (FPI) emerged accordingly with the increases of AE and PCN with a time delay. And the enhancements of equatorward (poleward) wind disturbances at 250 km were accompanied by the increments of equatorward (poleward) wind disturbances at 94 km with a time lag of a few hours. It is thus suggested that the multiple intensified Joule heating events with quasi‐5‐hour time intervals were triggered by the successive substorm expansions during the storm. Then the Joule heating events led to the vertical wind and temperature disturbances in the mid‐latitude lower thermosphere via disturbing the thermospheric meridional circulation, which consequently induced the quasi‐5‐hour meridional wind disturbances therein. Plain Language Summary: The neutral temperature and global circulation in the middle and upper atmosphere can be strongly disturbed by the solar and geomagnetic activity. However, the effects of geomagnetic activity on the neutral winds in the mesosphere and lower thermosphere region at middle latitudes have not been fully understood. Using the neutral wind measurements from two meteor radars located at latitudes of 53.5°N and 40.3°N around 120°E meridian in China, we found that the meridional winds at different latitudes showed the prominent and similar disturbance patterns during the 2015 St. Patrick's Day geomagnetic storm. There exhibited the obvious quasi‐5‐hour oscillations in the meridional wind differences at 90–102 km derived from meteor radars. And such wind oscillations appeared to be analogous and close‐correlated to the quasi‐5‐hour oscillations in the AE and PCN indices. The possible contributors and physical processes responsible for such wind disturbances in the mid‐latitude lower thermosphere are discussed. This study is helpful to understand the influences of geomagnetic activity on the neutral winds in the mid‐latitude lower thermosphere region as well as the possible dynamic processes therein. Key Points: Storm‐time quasi‐5‐hour oscillations emerged in both the AE/PCN indices and the meridional winds in the mid‐latitude lower thermosphereThe increments of equatorward/poleward winds at 94 km exhibited the close correspondence and correlation to those at 250 km with a time lagThe successive Joule heating events led to the periodic meridional wind disturbances via disturbing thermospheric meridional circulation [ABSTRACT FROM AUTHOR]

The updated database of Forbush effects and interplanetary disturbances (https://tools.izmiran.ru/feid) is used for an extensive analysis of various characteristics of events caused by the influence of interacting solar wind disturbances on the near-Earth space. In particular, the cases of different combinations of the pair interaction of high-speed streams from coronal holes and coronal mass ejections over the long period from 1995 to 2022 are considered. Variations in the flux of galactic cosmic rays (with a rigidity of 10 GV) and changes in the parameters of the interplanetary medium and geomagnetic activity are described. It is shown that the degree of mutual influence depends on the time between the detection of neighboring events; with the most pronounced changes in various parameters for events whose interaction occurred before reaching Earth's orbit. It is also established that in interacting solar wind disturbances not only the extremes of the parameters of cosmic rays, interplanetary medium, and geomagnetic activity but also their time profiles are subject to changes. [ABSTRACT FROM AUTHOR]

Space weather forecasts are of utmost importance in safeguarding navigation, communication, and electric power system operations, satellites from orbital drag, and the astronauts in the International Space Station from hazardous space radiation during extreme space weather conditions. The finest space weather prediction requires a clear understanding of solar wind‐magnetosphere coupling. The in‐situ measurements of the solar wind properties give unique information about the Sun and its activity on smaller to longer timescales. The present work investigates the influence of solar activity on the coupling of solar wind and Earth's magnetosphere during 23–24 solar cycles. The geomagnetic storms with Symmetric H‐component (SYMH) ≤ −85 nT during the 23–24 solar cycles are considered. We present the results of statistical analysis and relationships between the various solar wind parameters such as the total strength of interplanetary magnetic field (B) and its three‐axis components (Bx, By, and Bz), solar wind proton density (Nsw), solar wind speed (Vsw), SYMH indices, the amplitude, duration, and profile of the geomagnetic storms. The integrated electric field and integrated SYMH index during storms show the highest correlation of 0.92, implying that integrated SYMH is a better proxy of the injected solar wind energy in the magnetosphere in the form of the ring current. Moreover, we do see the difference in the solar wind‐magnetosphere coupling efficiency during the phases of 23–24 solar cycles which is intriguing. Key Points: First observation: The Integrated Ey of solar wind and Integrated Symmetric H‐component show a strikingly high correlationSolar Wind (SW)‐Magnetosphere (M) coupling shows higher average efficiency during the 24th solar cycle compared to the 23rdLow solar activity (or solar minimum) shows elevated efficiency of SW‐M coupling [ABSTRACT FROM AUTHOR]

The dynamics of the intensity of cosmic rays is known to be different on the ascending and descending branches of the 11-year solar cycle, i.e., hysteresis phenomena are observed. Recently, it has been obtained that at shorter intervals on the scale of magnetic storms there are also signs of hysteresis in dependences of cosmic ray cutoff rigidities R (geomagnetic thresholds) on heliosphere and geosphere parameters. R is the rigidity below which a particle flux is cut off due to geomagnetic shielding. In this paper, we have analyzed the dependence of the geomagnetic storm index Dst and the variation of the ΔR thresholds on interplanetary magnetic field (IMF) and solar wind (SW) parameters during the two-step magnetic storm on September 7–8, 2017. We have found hysteresis phenomena in the following paired series: (1) dependences of Dst on SW and IMF parameters, and (2) dependences of ΔR on SW and IMF parameters. We have established that the dependence curves in the storm descending phase (main phase) and ascending phase (recovery phase) do not coincide — hysteresis loops are formed. A specific feature of the storm under study is the second lowering of Dst in the recovery phase. The hysteresis pattern reflects this specific storm dynamics, forming two hysteresis loops in response to the two Dst drops.

Using annual average values, the relationships are examined of the geomagnetic indices SYM-H, ASY-H, and Dst with solar wind parameters in 1981–2015. The data used was divided into two samples according to the sign of the north-south component Bn of the interplanetary magnetic field (IMF). Variations in the annual average values of each of the Dst, SYM-H, and ASY-H indices for southward and northward IMF have been found to be similar and their linear correlation coefficients r to be high: 0.871, 0.863, and 0.943 respectively. The similarity between variations of the indices with different signs of Bn is probably due to their connection with the number of sunspots. It has been established that Dst, SYM-H, and ASY-H depend on the solar wind parameter β: their absolute values decrease with increasing β, regardless of Bn sign. The decrease in the indices with increasing β is likely to be caused by the transition of the magnetosphere to a quiet state due to the increasing predominance of thermal pressure over magnetic one in the solar wind and a decrease in the level of solar wind turbulence. SYM-H and ASY-H have been found to reveal the closest relationships with β, whereas SYM-H more strongly depends on β for southward IMF (r=0.744) than for northward IMF (r=0.677). On the contrary, for ASY-H r=–0.741 at northward IMF and r=–0.719 at southward IMF. Similar to SYM-H, Dst (to a lesser extent) significantly correlates with β at southward IMF (r=0.629) and weaker at northward IMF (r=0.456).

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 magnetosphere‐ionosphere‐thermosphere system is externally driven by the energy input from the solar wind. A part of the solar wind energy deposited in the magnetosphere during geomagnetically active periods dissipates into the thermosphere. Previous studies have reported temperature perturbations in the lower thermosphere during geomagnetic storms. The present study aims to assess the climatological spatial pattern of the lower thermospheric response to geomagnetic activity at high latitudes based on 21 years of temperature measurements by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite and their comparison with the recently developed half‐hourly geomagnetic activity index Hp30. The temperature response to geomagnetic activity, evaluated at different seasons and altitudes, is better organized in magnetic coordinates than in geographic coordinates. At 110 km, the temperature increases with Hp30 at all magnetic local times, but with a prominent dusk‐dawn asymmetry in the magnitude. That is, the temperature variation per unit Hp30 is larger in the dusk sector than in the dawn sector. At 106 km, the response in the dawn sector is further reduced or even negative. These results provide observational evidence to support earlier theoretical predictions; according to which, both storm‐induced vertical wind and Joule heating contribute to the temperature increase in the dusk sector, while in the dawn sector, the vertical wind acts to cool the air and thus counteracts Joule heating. Key Points: High‐latitude lower thermospheric temperature response to geomagnetic activity depends on magnetic local time and magnetic latitudeAbove 100 km, strong and weak (or even negative) responses occur in the dusk and dawn sectors, respectivelyThe results agree with earlier theoretical predictions, highlighting the importance of storm‐induced vertical wind and Joule heating [ABSTRACT FROM AUTHOR]

The effects of solar activity and the accompanying space weather events on human pathological conditions, physiological parameters and other psycho-physiological disturbances have been analyzed in numerous recent investigations. Moreover, many of these studies have particularly focused on the different physical reactions humans have, according to their sex, during variations in the physical environment. In the framework of the above, this work analyses heart rate data obtained from volunteers (687 men and 534 women) from three different regions (Athens, Piraeus and Heraklion) of Greece in relation to the geophysical activity and variations of environmental factors. Dst index and Ap index data, along with cosmic ray intensity data derived from the Athens Neutron Monitor Station (A.Ne.Mo.S.), were used. The study expands from April 2011 to January 2018, covering solar cycle 24. The ANalysis Of Variance (ANOVA) and the superimposed epochs methods were used in order to examine heart rate variations depending on sex. Results revealed that women tend to be more sensitive to physical environmental changes. Statistically significant results are related to the geomagnetic activity but were not obtained for cosmic ray variations. [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]

The results of the analysis of time series for 5 years of observations of geophysical (ecological) rhythms, atmospheric pressure, and geomagnetic activity, were considered and their effect on human blood pressure and heart rate for time periods of fluctuations more than daily was assessed. It was found that during periods of about 15 days, when atmospheric pressure changed smoothly and slightly, a calmer heart rate and fluctuations in blood pressure were observed. Such "calm" periods of time were observed mainly in the summer months from July to August, usually only once per season. A comparison of the graphs of fluctuations in systolic pressure and the geomagnetic activity index showed a correlation between them three times higher than the correlation between systolic pressure and atmospheric pressure. This means that a geomagnetic field with an activity index of more than 2 had a greater effect on increasing systolic pressure in humans. The analysis also showed that the periods of peaks in the atmospheric pressure spectra were in good agreement with the periods of heart rate rhythms. The result indicates that these rhythms in humans might be affected by synoptic processes passing through the region in the atmosphere such as cyclones and anticyclones; ultimately, the well-being of elderly and sick people might depend on them. This study, as well as taking the variability of geophysical parameters published by hydrometeorological services into account, makes it possible to predict the state of human health. [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.

Aim. To study the seasonal dynamics of cardiovascular events (CVE) in the Russian Federation (RF) using medical and statistical data for the period 2016-2019, and also to establish an association of CVE risk with meteorological conditions.Material and methods. We used data on hospitalizations for 2016-2019 for hemorrhagic stroke (HS), ischemic stroke (IS), myocardial infarction (MI), and acute coronary syndrome (ACS).Results. Data analysis showed that the maximum number of HSs occurred in winter and spring, and the minimum in summer. The maximum number of ISs was recorded in spring and summer, while the minimum in winter and autumn. ACS occurred more often in winter and spring, MI — more often in spring. ACS was accompanied by MI in 44% of cases. In winter, the probability of HS increased with decreasing latitude.In summer, the risk of HS and IS was greater at lower air temperatures. In summer, the probability of IS and MI was associated with lower values of atmospheric pressure and partial density of oxygen (ρO2). In winter, the risk of IS increased at highr atmospheric pressure values. No convincing evidence was obtained of the influence of geomagnetic activity on the seasonal dynamics of the CVEs either throughout the Russian Federation or in the circumpolar regions.Conclusion. As a result, meteorological conditions influence the seasonal risk of CVEs. A decrease in ρO2 in summer significantly increases the CVE risk associated with ischemia, which should be taken into account when preventing CVEs.

Background: 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. Methods: We used logistic and linear generalized estimating equations and regressions to evaluate the associations between moving averages of sunspot number (SSN) and Kp 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. Results: A one-IQR increase in same-day SSN and Kp 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. Conclusions: 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.

A novel tool utilizing machine learning techniques was designed to forecast ap index values for the next three consecutive days (24 values). The tool employs time series data from the 3 h ap index of solar cycles 23 and 24 to train the Long Short-Term Memory (LSTM) model, predicting ap index values for the next 72 h at three-hour intervals. During periods of quiet geomagnetic activity, the LSTM model’s performance is sufficient to yield favorable outcomes. Nevertheless, during geomagnetically disturbed conditions, such as geomagnetic storms of different levels, the model needs to be adapted in order to provide accurate ap index results. In particular, when coronal mass ejections occur, the ap Prediction tool is modulated by inserting predominant features of coronal mass ejections such as the date of the event, the estimated time of arrival and the linear speed. In the present work, this tool is described thoroughly; moreover, results for G2 and G3 geomagnetic storms are presented.

On 4 November 2021, during the rising phase of solar cycle 25, an intense geomagnetic storm (Kp = 8−) occurred. The effects of this storm on the outer magnetospheric region up to the ionospheric heights have already been examined in previous investigations. This work is focused on the analysis of the solar wind conditions before and during the geomagnetic storm, the high-latitude electrodynamics conditions, estimated through empirical models, and the response of the atmosphere in both hemispheres, based on parameters from the ECMWF ERA5 atmospheric reanalysis dataset. Our investigations are also supported by counter-test analysis and Monte Carlo tests. We find, for both hemispheres, a significant correspondence, within 1–2 days, between high-latitude electrodynamics variations and changes in the temperature, specific humidity, and meridional and zonal winds, in both the troposphere and stratosphere. The results indicate that, in the complex solar wind–atmosphere relationship, a significant role might be played by the intensification of the polar cap potential. We also study the reciprocal relation between the ionospheric Joule heating, calculated from a model, and two adiabatic invariants used in the analysis of solar wind turbulence.

This study investigates the interannual cross‐seasonal association between the winter energetic particle precipitation, which is related to the geomagnetic activity (GA), and the southern annular mode (SAM) in the following summer by employing the ERA5 reanalysis dataset. The results reveal a marked negative correlation between these variables on an interannual timescale. Therefore, we analyse the GA signatures in the southern atmosphere and find that the evolution of SAM to the negative phase driven by GA may be caused by the following two mechanisms: First, for high GA levels, the middle and lower stratospheric polar vortex becomes weaker from October to November, with considerable changes in the stratospheric thermal structure and more anomalous planetary wave upwelling, accompanied by weakening of the circumpolar westerly. Over time, the anomalous signal from the upper layer can be transmitted downward and is conducive to inducing and strengthening the negative SAM in the following summer, which may serve as the stratospheric pathway for the geomagnetic impact on the SAM and Southern Hemisphere (SH) climate. Second, another possible way is that the preceding GA also appreciably regulates negative anomalies in the Ferrel circulation in SH, implying poleward anomalies in the direction of the pressure gradient, which promotes the development and enhancement of the negative phase of the SAM. In addition, easterly quasi‐biennial oscillation conditioning plays a positive role in the response of the southern atmosphere to geomagnetic forcing, thereby strengthening the connection between them. [ABSTRACT FROM AUTHOR]

The correlation coefficients between the electron fluence, the solar wind speed and the geomagnetic activity Ap-index with different delay times are calculated. Calculations are based on measurements of magnetospheric electron fluxes with energy >2 MeV in geostationary orbits for 35 years (1987–2021).We use >2 MeV relativistic electron flux measurements from the different Energetic Particle Sensors (EPS) on the geosynchronous spacecrafts GOES. The correlation coefficients between electron fluences on neighboring days are calculated as well. There is significant inertia in the behavior of the fluence of high-energy magnetospheric electrons. It is found that the fluence of high-energy magnetospheric electrons is weakly related to the level of geomagnetic activity on the same day, but correlates with the geomagnetic activity Ap-index observed 2–3 days earlier. The fluence of high-energy magnetospheric electrons is quite closely related to the speed of the solar wind, especially with the speed measured 2 days earlier. In general, in cycles 22–24 of solar activity, higher correlation coefficients of the electron fluence with the solar wind speed and the Ap-index are observed in the phases of decline and minimum of solar activity. A three-parameter model has also been obtained based on the prehistory of the fluence behavior, data on the Ap-index of geomagnetic activity, and measurements of the solar wind speed. The created model allows to make the prediction of high-energy magnetospheric electrons fluence for the next day.The model shows good agreement with the experimental data with a high correlation coefficient (0.82) for the entire period 1987–2021. [ABSTRACT FROM AUTHOR]

The new approaches to the modelling of the Sun-solar wind-magnetosphere-radiation belts chain and their implementation at MSU's Space weather center (Space Monitoring Data Center, SMDC) are presented. The main idea is to use data from medium-term (3–5 days) forecasts of the speed of quasi-stationary solar wind streams based on data obtained from solar images in the UV wavelength range to improve the quality of forecasts of the magnetospheric factors of the space environment. An operational model for predicting the daily fluence of relativistic electrons (>2 MeV) in the Earth's outer radiation belt has been developed, with the extended set of input parameters that include the forecast of the solar wind velocity. To validate the model, the period from October 11, 2016 to February 18, 2017 was considered, during which the Sun made several revolutions and it was possible to observe the evolution of coronal holes and the development of solar sporadic phenomena. The arrival of high-speed solar wind streams from coronal holes to the Earth's magnetosphere, as well as, as impact of coronal mass ejections, provoked geomagnetic disturbances of various intensity, and caused significant variations of the electron fluxes of the Earth's outer radiation belt. SMDC website implements solar wind model based on the data of solar observations by the AIA instrument of the SDO space observatory at wavelengths of 19.3 and 21.1 nm that forecasts the daily fluence of relativistic electrons (E > 2 MeV) in geostationary orbit. It is shown that the use of the results of medium-term forecasting of the solar wind speed as an input parameter in the daily electron fluence forecast model can significantly improve its quality with a forecast horizon of up to 4 days. [ABSTRACT FROM AUTHOR]

We have studied the relationship of geomagnetic activity indices (Ap, Dst) on time intervals, equal to solar cycles (∼11 years), with solar activity indicators and heliospheric parameters. It is shown that the plots of the Ap and Dst indices versus solar activity indicators, as well as versus heliospheric parameters, i.e. solar wind and IMF parameters in the ascending and descending phases of solar activity cycles 21–24 do not coincide, which is indicative of the hysteresis phenomenon. The Ap and Dst indices form hysteresis loops with all parameters we analyze during cycles 21–24. The shape and area of the hysteresis loops, as well as the direction of rotation, clockwise or counterclockwise, depend significantly on indicators of solar activity, heliospheric parameters and change from cycle to cycle. We have found a tendency for the extension and area of the hysteresis loops to decrease from cycle 21 to cycle 24. Analysis of the variability in the shape and size of the hysteresis loops formed by the Ap and Dst indices with solar indicators and heliospheric parameters gives reason to believe that the obtained loops reflect the long-term evolution of the solar wind energy flux, which determines global geomagnetic activity and the magnetospheric ring current intensity in the ascending and descending phases of solar activity cycles 21‒24.

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.

The effects of solar activity and the accompanying space weather events on human pathological conditions, physiological parameters and other psycho-physiological disturbances have been analyzed in numerous recent investigations. Moreover, many of these studies have particularly focused on the different physical reactions humans have, according to their sex, during variations in the physical environment. In the framework of the above, this work analyses heart rate data obtained from volunteers (687 men and 534 women) from three different regions (Athens, Piraeus and Heraklion) of Greece in relation to the geophysical activity and variations of environmental factors. Dst index and Ap index data, along with cosmic ray intensity data derived from the Athens Neutron Monitor Station (A.Ne.Mo.S.), were used. The study expands from April 2011 to January 2018, covering solar cycle 24. The ANalysis Of Variance (ANOVA) and the superimposed epochs methods were used in order to examine heart rate variations depending on sex. Results revealed that women tend to be more sensitive to physical environmental changes. Statistically significant results are related to the geomagnetic activity but were not obtained for cosmic ray variations.

As an important part of the inner magnetosphere, the Earth's plasmasphere plays a vital role in linking the occurrence and development of space weather processes. The Earth's plasmasphere is a torus-shaped cold (< 10 eV) and dense (10~104 cm−3) plasma region of ionospheric origin co-rotating with the planet. The plasmasphere contains several populations of particles such as electrons, H+, He+, and O+ ions. The outer boundary of the plasmasphere is defined by a sharp gradient of density called the plasmapause, in which the density decreases by 1~ 2 orders of magnitude within 0.5 RE (the Earth radius). Additionally, large scale plasmaspheric features have been observed, including shoulders, plumes, notches, bulges, and refiling. The Earth's plasmasphere is dynamic, and the abundance of particles in it changes substantially with interplanetary and geomagnetic activity. The large-scale structure evolution of the plasmasphere during geomagnetic storms controls the generation and propagation of waves in the plasmasphere, thus affecting the wave-particles interaction, resulting in a change in the spatial distribution of electrons and ions in the plasmasphere, and then affecting other magnetospheric and ionospheric processes. During periods of geomagnetic storms, the plasmaspheric material eroded is transported sunward and observed near the dayside magnetopause regularly. This local plasmaspheric density enhancement greatly impacts global large-scale convection. Therefore, the plasmaspheric density is undoubtedly an important parameter in space weather. The structural dynamic change of the Earth's plasmasphere is an indicator of the disturbance state of the space weather environment. Its structural form and dynamic process are controlled by the geomagnetic activity, and the short-term changes in the geomagnetic field originate from the sun-terrestrial disturbance caused by solar activity. The high-speed plasma ejected from the solar corona impacts the Earth and induces large-scale convective motion in the magnetosphere. Part of the energy enters the magnetosphere, causing disturbances in its inner regions, including the plasmasphere. Further research on the Earth’s plasmasphere is of great significance to reveal the mass transport and energy transfer in the solar wind-magnetosphere-ionosphere coupling process, and space weather forecast. Here, we introduce the research progress in the response of the plasmasphere to geomagnetic activities, the waves in the plasmasphere, variation of the electron content in the topside ionosphere and plasmasphere, and plasmasphere models. Finally, we also list some important issues for future studies.

The geomagnetic cutoff rigidity of cosmic rays (CRs) is the main factor regulating the arrival of CR particles at a given point on Earth's surface or inside the magnetosphere. To study the relationship between cutoffs and near-Earth space parameters, we have selected the strongest magnetic storm that occurred on March 8–11, 2012 during the CAWSES-II interval, recommended by SCOSTEP for detailed studies of solar-terrestrial relations. We have found the geomagnetic cutoffs by two methods: 1) by trajectory calculations in the magnetic field of the perturbed magnetosphere according to the Ts01 model and 2) by the spectrographic global survey method according to the data from the world network of neutron monitors. The largest drop in the cutoffs (−1.1 GV) obtained by the latter method was observed during the recovery phase of the storm. Apparently, this is due to the influence of the supersubstorms that occurred at that time. The analysis has shown that the closest connection of variations in the cutoffs can be traced with the geomagnetic activity index Dst, which indicates the determining contribution of the ring current to the transport of CRs. In addition, we have found a significant connection with the electromagnetic field parameters (with the Bz component of the interplanetary magnetic field and the azimuthal component of the electric field Ey). The dynamic solar wind parameters practically do not control variations in CR geomagnetic cutoff rigidities.

Solar wind dynamic pressure pulse is one of the sources of ultra‐low frequency (ULF) waves. Based on 1‐second resolution magnetic field observations from SuperMAG from 2012 to 2019, we conducted a statistical study on temporal and spatial variations of global ULF power after the arrival of positive dynamic pressure pulses. The magnetosphere responds quickly to the dynamic pressure pulse within 1 min. At low L‐shells, it takes 4–6 min for the ULF waves to reach a power maximum, then ULF waves decay on a timescale of about 10 min. The spatial distribution of ULF wave power is closely related to the direction of the interplanetary magnetic field (IMF) when the dynamic pressure pulse arrives. The southward IMF leads to the reconnection on the dayside and more intense substorm activities on the nightside, accompanied by stronger ULF wave power globally. The power enhancement in the Pc2 band exhibits a notable fluctuation concentrated primarily in the range of L = 7 to 9, compared with the quiet period. In contrast, the amplification of Pc3 wave power occurs predominantly at higher L‐shells. However, the fluctuation of Pc5 power exhibits an opposite pattern, indicating disparate excitation and propagation mechanisms. In addition, seasonal effects affect the ULF power in different bands, which can be explained by the Russell‐McPherron (R‐M) effect. Our statistical results on long‐term, global‐scale geomagnetic observations illustrate that pressure pulses are important sources of ULF waves, and the spatial distribution of wave power varies greatly under different solar wind conditions. Key Points: SuperMAG ultra‐low frequency (ULF) parameters are used to study the spatial and temporal responses of ULF waves to pressure impulsesThe ULF power has great differences in the distribution as a function of magnetic local time and L‐shellSeasonal effects have significant influences on the magnetic field power in different bands [ABSTRACT FROM AUTHOR]

The coupling of the interplanetary magnetic field (IMF) with the Earth's magnetic field can result in spectacular auroral displays, including substorms. An important feature of substorms is the westward electrojet that is routinely monitored by the AL index, based on ground magnetometer measurements. Recent research shows that, during periods of significant dipole tilt, the value of the AL index is strongly modulated by the dawn‐dusk (or y) component of the IMF (By): the AL index is stronger for By > 0 than By < 0 during negative dipole tilt (Northern Hemisphere winter). Kubyshkina et al. (2023, https://doi.org/10.1029/2022ja031275) argued that this By dependence of the AL index is not really caused by IMF By but by the component along the Sun‐Earth line (x axis)—namely IMF Bx, which is strongly anticorrelated with By. Here we provide strong evidence that the By dependence of the AL index is indeed much stronger than the suggested Bx dependence. In fact, the analysis of Kubyshkina et al. (2023, https://doi.org/10.1029/2022ja031275) provided similar evidence. We also note that the physical mechanism proposed by Kubyshkina et al. (2023, https://doi.org/10.1029/2022ja031275) to explain the suggested Bx dependence is contradicted by observations. However, we cannot completely rule out its existence. Plain Language Summary: The most important driver controlling magnetospheric activity, such as displays of aurora and disturbances in the terrestrial magnetic field is the north‐south directed z component of the magnetic field in solar wind. Recent research has shown that during winter and summer solstices the magnetospheric activity is significantly modulated also by the dawn‐dusk y component, which is statistically correlated with the Sun‐Earth directed x component, due to the well‐known geometry of the magnetic field in solar wind. It is therefore challenging to separate the effects of y and x components. Here we show that magnetospheric activity is strongly modulated by the y component, but not by the x component, contrary to Kubyshkina et al. (2023, https://doi.org/10.1029/2022ja031275), who argued that the opposite is true. Key Points: The interplanetary magnetic field (IMF) Bx component does not significantly modulate the AL index as proposed by Kubyshkina et al. (2023, https://doi.org/10.1029/2022ja031275)The AL index is strongly modulated by IMF By during periods of large dipole tilt [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]

Abstract The presence of grand minima, characterized by significantly reduced solar and stellar activity, brings a challenge to the understanding of solar and stellar dynamo. The Maunder Minimum (1645–1715 AD) is a representative grand solar minimum. The cyclic variation of solar activity, especially the cycle length during this period, is critical to understand the solar dynamo but remains unknown. By analyzing the variations in solar activity‐related equatorial auroras recorded in Korean historical books in the vicinity of a low‐intensity paleo‐West Pacific geomagnetic anomaly, we find clear evidence of an 8‐year solar cycle rather than the normal 11‐year cycle during the Maunder Minimum. This result provides a key constraint on solar dynamo models and the generation mechanism of grand solar minima.

Introduction: The auroral E-region is an important interface where forces from the magnetosphere and the lower atmosphere converge and have a significant effect on the vertical structure of the neutral winds. The resulting vertical neutral wind structure has been reported to be associated with altitude-dependent and nonlinear effects from different forces. We conduct a statistical examination of the reactions of wintertime neutral winds to four various degrees of geomagnetic activity, with a focus on the impacts of ion drag.Methods: We derive neutral winds using the PFISR measurements covering 2010–2019 and will give a statistical view of the auroral E-region neutral wind with a focus on the winter nighttime during different disturbed conditions. We investigate the effects of the geomagnetic activity on the neutral winds and the tidal components by dividing the dataset into 4 subsets. Tidal decomposition is conducted by least square fitting of the seasonal median winds to obtain the mean, diurnal amplitude, diurnal phase, semidiurnal amplitude, and semidiurnal phase.Results and discussion: We find that 1) when geomagnetic activity increases, dawn-dusk asymmetry exists in both zonal and meridional winds in the upper E-region with stronger zonal wind in the dusk sector than in the dawn sector and much stronger meridional wind in the dawn sector than in the dusk sector. 2) Tidal decomposition results reveal that geomagnetic activity has more significant effects on the meridional diurnal amplitude than zonal diurnal amplitude while the zonal and meridional semidiurnal amplitudes show similar changes when the geomagnetic activity increases. In addition, the maximum semidiurnal amplitude, particularly in the zonal direction, appears at a higher altitude with larger values as geomagnetic activity increases, indicating an ascending transition altitude for the semidiurnal oscillations. The ascending trend of maximum semidiurnal amplitude appearing at higher altitudes during more disturbed conditions has not been reported before. 3) Zonal wind over 110 km demonstrates increasing ion drag effects in the evening sector and the effects of coupled ion drag and other factors after midnight.

For community use, a new composite whole-Earth index E(1) and its matching composite solar wind driving function S(1) are derived. A system science methodology is used based on a time-dependent magnetospheric state vector and a solar wind state vector, with canonical correlation analysis (CCA) used to reduce the two state vectors to the two time-dependent scalars E(1)(t) and S(1)(t). The whole-Earth index E(1) is based on a diversity of measures via six diverse geomagnetic indices that will be readily available in the future: SML, SMU, Ap60, SYMH, ASYM, and PCC. The CCA-derived composite index has several advantages: 1) the new “canonical” geomagnetic index E(1) will provide a more powerful description of magnetospheric activity, a description of the collective behavior of the magnetosphere–ionosphere system. 2) The new index E(1) is much more accurately predictable from upstream solar wind measurements on Earth. 3) Indications are that the new canonical geomagnetic index E(1) will be accurately predictable even when as-yet-unseen extreme solar wind conditions occur. The composite solar wind driver S(1) can also be used as a universal driver function for individual geomagnetic indices or for magnetospheric particle populations. To familiarize the use of the new index E(1), its behavior is examined in different phases of the solar cycle, in different types of solar wind plasma, during high-speed stream-driven storms, during CME sheath-driven storms, and during superstorms. It is suggested that the definition of storms are the times when E(1) >1.

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]

The ionosphere is an important part in the solar-terrestrial space, with complex spatiotemporal variation characteristics under the influence of many factors. It is necessary to analyze its long-term temporal and spatial characteristics. Based on the ionospheric VTEC grid data from 2000 to 2019 provided by the Centre for Orbit Determination in Europe(CODE),the spatiotemporal characteristics of the ionosphere in Sichuan and surrounding is studied. The main feathers are outlined as follows:(1)The daily correlation,monthly correlation and annual correlation between VTEC and F10. 7 from 2000 to 2019 are 0. 879,0. 923 and 0. 998,respectively. (2)VTEC is weakly correlated with the daily mean value of Dst and Kp index,and moderately correlated with the monthly and annual mean values from 2000 to 2019,while the monthly correlation with the geomagnetic index is not stable in each year. (3)The maximum daily value of VTEC appearing around 14:00LT,and the peak value of VTEC in most summer years is slightly delayed. The winter anomalies appearing in the high solar activity years,usually at 21:00LT, except for the winter anomaly years. The VTEC value of the area show significant semi-annual variations,almost seasonal maximum during the vernal equinox. VTEC has an annual period of 365. 1 days,semiannual period of 182. 6 days and a quasi-period of 27 days. (4)VTEC is decreased with the increase of latitude. In the low solar activity year,the zonal VTEC value gradient changed significantly from 02:00 to 14:00 UTC. With the increase of solar activity, the gradient of VTEC vuillbe extend for 2-4 hours, and there is no obvious change in the same longitude direction. This study provides certain reference for the establishment and improvement of ionospheric prediction model and ionospheric delay correction model in Sichuan and surrounding areas. [ABSTRACT FROM AUTHOR]

The coupling function monitors solar wind driving of geomagnetic activity. Magnetic indices, including the polar cap (PC) index, the auroral lower (AL) index, and the midlatitude positive bay index (MPB), provide measures of the magnetospheric response. Sharp changes in these are associated with the onset of a substorm and a maximum in coupling. Many reinterpret this association as evidence that northward turnings of the interplanetary magnetic field (IMF) trigger onset. We investigate this hypothesis using a list of over 100,000 negative bay onsets. When data are available, we calculate coupling and its time derivatives. From these, we construct ensembles of data segments centered on the onsets.'For all lists, a pulse occurs 20 min before onset and appears to trigger onset. By correlating the average derivative with every event in the ensemble, we conclude that a pulse of either sign precedes 40% of all onsets. More than half of the triggered onsets display a positive pulse, and slightly fewer show a negative pulse. Substorms following a positive pulse are stronger than those after a negative pulse. The pulse is usually hidden by noise, but ensemble averaging and correlation analysis can detect the pulse in the coupling data. Plain Language Summary: The solar wind drives auroral and magnetic activity. Solar wind coupling becomes stronger when the IMF is oriented opposite to Earth's. Auroral arcs move equatorward around the magnetic poles. The arcs near midnight are activated within about 1 hour and expand poleward. At the same time, strong currents flow out of the tail along field lines closing in the ionosphere beneath the expanding aurora. Because of its shape, this system is called the substorm current wedge. The current wedge causes changes in the magnetic field in the polar cap, in the auroral zone, and at mid‐latitudes. The auroral lower (AL) index measures the strength of the auroral zone changes. A sudden negative deviation in this index is a proxy for the onset of the current wedge and auroral expansion. In this report, we investigate the possibility that a rapid change in coupling triggers the onset of the current wedge. The rapid change happens in a 20‐min interval before expansion onset, and the pulse can be positive or negative. Large changes are easily visible in the raw data, but most changes are too small to be seen without data processing. Key Points: We use several substorm onset lists to investigate the behavior of the solar wind coupling function relative to the negative bay onsetOn average, the time derivative of coupling shows a pulse in coupling in a 20‐min interval before the onsetPulses can be of either sign, with positive pulses causing more numerous and larger substorms than is the case for negative pulses [ABSTRACT FROM AUTHOR]

The influence of solar and geomagnetic activities on electrical propulsion system of ultra-low orbit gravity satellite was evaluated for the current 25th solar cycle. The orbit simulation was carried out and the data of GOCE mission was analyzed. The variation of atmospheric drag was analyzed. The influence of solar activity on propellant consumption and the influence of geomagnetic storm on drag-free operation were obtained. The results show that the orbit altitude of the satellite in the low solar activity years can be reduced by about 20 km compared with that in the high solar activity years, which is conducive to improving the gravity signal intensity. Strong geomagnetic storms usually increase the drag by 30% to 90% at ultra-low orbit, so thrust margin is required for geomagnetic storms. Designer should ensure high specific impulse in thrust range of 10% to 70% of the maximum thrust. The life consideration of this range is important.

The dependences of the geomagnetic indices SYM-H and ASY-H on interplanetary parameters for the period from 1981 to 2015 according to their daily averages are studied. The study is carried out in two ways: the first — the entire data array is analyzed, the second — the data are divided into 9 activity groups in accordance with the average daily values of the planetary geomagnetic index Ap. A correlation analysis of the indices with the solar wind speed, magnitude, and the north-south component of the interplanetary magnetic field (IMF) has been performed. The search for a relationship between the ASY-H and SYM-H indices and interplanetary parameters turned out to be more successful when considering the entire data array than in the case of splitting the data into groups of magnetic activity. Regression equations relating ASY-H and SYM-H to interplanetary parameters are determined. It has been found that when describing the relationship between the ASY-H and SYM-H indices and the IMF north-south component, it is necessary to take into account the contribution of the IMF modulus.

Background and Objective: Stroke has a high prevalence and is associated with a high premature mortality rate. Thus, it is important to identify the effective factors in increasing the incidence of stroke. The aim of this study was to investigate the role of seasonal changes and environmental factors in the occurrence of stroke. Methods: This descriptive-analytical study was done on 3,639 patients including 3,102 (85.3%) with ischemic stroke, 472 (12.9%) with intracerebral hemorrhage and 65 (1.9%) with subarachnoid hemorrhage patients. After measuring environmental factors such as air temperature, air pressure, humidity and geomagnetic field, admission data of stroke patients between 2015-2019 were extracted from the Sayyad Shirazi Hospital information system. Results: The mean occurrence of intracerebral hemorrhage was highest in winter, especially in January and March, and lowest in summer, especially in July and August. Intracerebral hemorrhage had a positive significant correlation with air pressure (P=0.001, r=0.452) and a negative correlation with ambient temperature (P

Abstract Predicting geomagnetic conditions based on in-situ solar wind observations allows us to evade disasters caused by large electromagnetic disturbances originating from the Sun to save lives and protect economic activity. In this study, we aimed to examine the relationship between the K p index, representing global magnetospheric activity level, and solar wind conditions using an interpretable neural network known as potential learning (PL). Data analyses based on neural networks are often difficult to interpret; however, PL learns by focusing on the “potentiality of input neurons” and can identify which inputs are significantly utilized by the network. Using the full advantage of PL, we extracted the influential solar wind parameters that disturb the magnetosphere under southward Interplanetary magnetic field (IMF) conditions. The input parameters of PL were the three components of the IMF (Bx, By, Bz), solar wind flow speed (Vx), and proton number density (Np) in geocentric solar magnetospheric (GSM) coordinates obtained from the OMNI solar wind database between 1998 and 2019. Furthermore, we classified these input parameters into two groups (targets), depending on the K p level: K p = 6–9 (positive target) and K p = 0 to 1 + (negative target). Negative target samples were randomly selected to ensure that numbers of positive and negative targets were equal. The PL results revealed that solar wind flow speed is an influential parameter for increasing K p under southward IMF conditions, which was in good agreement with previous reports on the statistical relationship between the K p index and solar wind velocity, and the K p formulation based on the IMF and solar wind plasma parameters. Based on this new neural network, we aim to construct a more correct and parameter-dependent space weather forecasting model. Graphical Abstract

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]

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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]

Studying the relationship of total electron content (TEC) to solar or geomagnetic activities at different solar activity stages can provide a reference for ionospheric modeling and prediction. On the basis of solar activity indices, geomagnetic activity parameters, and ionospheric TEC data at different solar activity stages, this study analyzes the overall variation relationships of solar and geomagnetic activities with ionospheric TEC, the characteristics of the quasi-27-day periodic oscillations of the three variables at different stages, and the delayed TEC response of solar activity by conducting correlation analysis, Butterworth band-pass filtering, Fourier transform, and time lag analysis. The following results are obtained. (1) TEC exhibits a significant linear relationship with solar activity at different solar activity stages. The correlation coefficients |R| are arranged as follows: |R| EUV > |R| F10.7 > |R| sunspot number. No significant linear relationship exists between TEC and geomagnetic activity parameters (|R| < 0.35). (2) TEC, solar activity indices, and geomagnetic activity parameters have a period of 10.5 years. The maximum amplitudes of the Fourier spectrum for TEC and solar activity indices are nearly 27 days and those of geomagnetic activity parameters are nearly 27 and 13.5 days. (3) The deviations of the quasi-27-day significant periodic oscillation of TEC and solar activity indices are consistent. (4) No evident relationship exists between the quasi-27-day periodic oscillation of TEC and geomagnetic activity parameters. (5) The delay time of TEC for the 10.7 cm solar radio flux and extreme ultraviolet is always consistent, whereas that for sunspot number varies at each stage. [ABSTRACT FROM AUTHOR]

Interplanetary shocks are disturbances commonly observed in the solar wind. IP shock impacts can cause a myriad of space weather effects in the Earth’s magnetopause, inner magnetosphere, ionosphere, thermosphere, and ground magnetic field. The shock impact angle, measured as the angle the shock normal vector performs with the Sun-Earth line, has been shown to be a very important parameter that controls shock geoeffectivess. An extensive review provided by Oliveira and Samsonov (2018) summarized all the work known at the time with respect to shock impact angles and geomagnetic activity; however, this topic has had some progress since Oliveira and Samsonov (2018) and the main goal of this mini review is to summarize all achievements to date in the topic to the knowledge of the author. Finally, this mini review also brings a few suggestions and ideas for future research in the area of IP shock impact angle geoeffectiveness.

Abstract 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.

We study the dependencies of Earth’s magnetosphere on Universal Time, UT. These are introduced because Earth’s magnetic axis is not aligned with the rotational axis and complicated because it is eccentric, which makes the offset of the magnetic and rotation poles considerably greater in the Southern hemisphere and the longitudinal separation of the magnetic poles less than 180°: hence consequent UT variations in the two hemispheres are not in equal in amplitude nor in exact antiphase and do not cancel, as they would for a geocentric dipole. We use long series of a variety of geomagnetic data to demonstrate the inductive effect of motions of the polar caps in a “geocentric-solar” frame, which is phase-locked to the Russell-McPherron (R-M) effect on solar-wind magnetosphere coupling. This makes the response of the magnetosphere-ionosphere system different for the two polarities of the Y-component of the Interplanetary Magnetic Field in the GSEQ reference frame, explaining the difference in response to the March and September equinox peaks in solar wind forcing. The sunward/antisunward pole-motion effect is detected directly in satellite transpolar voltage data and is shown to have a greater effect on the geomagnetic data than the full dipole tilt effect which generates the equinoctial pattern, the potential origins of which are discussed in terms of the dipole tilt effect on ionospheric conductivities and the stability of the near-Earth tail. Persistent UT variations in Region-1 and Region-2 field-aligned currents and in partial ring current indices are presented: their explanation is an important challenge for numerical modelling of the magnetosphere-ionosphere-thermosphere system which we need to quantify the relative contributions of the various mechanisms and to give understanding of the effect of arrival time on the response of the system to large, geoeffective disturbances in interplanetary space.Plain language summary: The effect on terrestrial space weather of Earth’s magnetic axis not being aligned with the rotational axis is investigated. It is complex because not only do these two axes not align in direction (the “dipole tilt”), the magnetic axis does not pass through the centre of the Earth, which sets a requirement for an “eccentric” model of the field and not the commonly-used “geocentric” one. For many years, it has been known that the dipole tilt gives a peak in geomagnetic activity at the equinoxes (the semi-annual variation) through the “Russell-McPherron” (R-M) effect. However, although the variation with Universal Time is consistent with the R-M effect for the September equinox, it is not for the March equinox. We here solve this long-standing puzzle by investigating the effects of the motions of the two poles in a frame fixed with respect to both the Earth and the Sun for an eccentric dipole model. But solving one puzzle generates many others. We present observations of the Universal Time variations that these mechanisms combine to generate, which set an important challenge to the numerical modelling of the near-Earth space environment.