High Geomagnetic Activity Research Articles

Interhemispheric Asymmetries in Magnetosphere and Ionosphere Magnetic Field Residuals Between Swarm Observations and Earth Magnetic Field Models

AbstractWe present a statistical study of magnetic field vector residual between Swarm observations and two Earth magnetic field models: the 13th generation International Geomagnetic Reference Field (IGRF) model and the CHAOS‐7 model. Statistics of these residuals are important for estimating potential errors for satellite operations when using Earth magnetic models as a reference, as well as for magnetosphere‐ionosphere‐thermosphere studies examining energy input into the system. Magnetic field residuals are calculated as vector differences between observations and model estimation at Swarm satellite positions from 2014 to 2020. Magnetic field residuals for both models increase as geomagnetic activity level increases, and the largest magnitude of vector difference can be around 1800 nT with relatively small angle differences. The CHAOS‐7 model shows lower magnetic field residuals compared to IGRF‐13. North‐south hemispheric asymmetries are seen in magnetic field residuals for high Kp values larger than 6 with the southern hemisphere (SH) having more frequent occurrence of magnetic field residuals larger than 300 nT, especially during SH summer. Most large residual values appear in the high‐latitude region with SH seeing additional large residuals around the South Atlantic Anomaly region. Midnight and noon sectors show the strongest interhemispheric asymmetries. The northern hemisphere shows more frequent occurrence of large residuals above 75° magnetic latitude throughout all local times compared to the SH. Identifying asymmetries in large magnetic residuals under high geomagnetic activity levels is helpful for studying the difference in response to ionospheric disturbances in the two hemispheres.

Regional application of C1 finite element interpolation method in modeling of ionosphere total electron content over Europe

• A novel approach for regional ionosphere grid model with high spatial-temporal resolution is suggested. • The results of the new model is analyzed at different disturb geomagnetic and solar conditions. • A comparative analysis between the results of new model, GIM, NeQuick and GPS-TEC is made. In this paper, a novel approach based on C 1 finite element (FE) interpolation is used to construct a regional ionospheric grid model (RIGM) with high spatio-temporal resolution over Europe. The spatial resolution of the new model is 0.5 0 for a longitude and latitude and a temporal resolution is 15 min. Observations of 38 GPS stations at different days and seasons with different geomagnetic and solar activity conditions are used to evaluate the new method. All stations are used to discretize the whole domain of the problem into separate triangular patches using a Delaunay triangulation algorithm. In this case, GPS stations would be the vertices of the triangular patches. Also, the position of stations in sun-fixed coordinate system with coordinates of latitude and longitude are chosen in order to consider the temporal variations of vertical total electron content (VTEC). To model the behavior of VTEC in each triangular patch, a particular shape function is defined which is fitted to VTEC values at three vertices of each triangle while it satisfies C 1 continuity of VTEC at the common edges of the adjacent triangles. The results of the new model are compared with the VTEC of GPS at 4 control stations as well as global ionosphere map (GIM) and NeQuick models. Statistical parameters, including correlation coefficient, root mean square error (RMSE), standard deviation and dVTEC = |VTEC GPS - VTEC model | have been used to evaluate the error of the models. In low geomagnetic activity (KP < 4), the average RMSE at 4 control stations for FE, GIM and NeQuick models are 0.89, 1.05 and 6.42 TECU, respectively, while in the high geomagnetic activity (KP > 4), they are 1.24, 1.68 and 7.62 TECU, respectively. For further analysis, the accuracy of three models in precise point positioning (PPP) has been also evaluated. In PPP method, there is an improvement of about 1–16 mm compared to GIM and NeQuick models at coordinate components of control stations in high geomagnetic activity. The results of the analysis performed in this paper show that the FE model has a very high capability and accuracy in regional VTEC modeling in high and low geomagnetic conditions. The regional accuracy of this model is higher than GIM and NeQuick models and therefore can be considered as a new model for the ionosphere.

Assessment of the Earth’s Cold Plasmatrough Modeling by Using Van Allen Probes/EMFISIS and Arase/PWE Electron Density Data

AbstractThe Space Weather Integrated Forecasting Framework (SWIFF) Plasmasphere Model (SPM) is a 3D kinetic model of the plasmasphere coupled to the ionosphere. This combined system has been routinely used to evaluate principally the plasmapause formation and evolution, and the plasmasphere’s dynamics. The model contains analytical equations for the plasmasphere and plasmatrough regions that have been empirically determined using observations of satellite and ground‐based data. In the present work, a revision of the plasmatrough equations is proposed using electron density data from the Van Allen Probes mission and paying particular attention to the spatiotemporal variation as well as to geomagnetic activity influence. Comparisons are performed with other parametrizations and with electron density data from the Arase mission. This assessment demonstrates that the plasmatrough electron density was slightly underestimated with respect to the new observations, in particular for high L values (L &gt; 3) and high geomagnetic activity. In addition, the overall performance of the new parametrization follows a satisfactory general trend despite a large variability of density data observed in the plasmatrough. The plasmatrough is separated from the refilling zone in the model by considering vestigial and outer edge plasmapause positions.

Decadal Geomagnetic Secular Variations From Greigite Bearing Dead Sea Sediments

AbstractArcheomagnetic data from the Levant revealed periods within the Holocene with fast and extreme changes in the geomagnetic field. Yet, the availability of the archeomagnetic data is sporadic and the correlation with the available sedimentary records from the region is rather poor. To further explore decadal variations in the directions of the field, we investigate three outcrops of the late Holocene Dead Sea that are exposed along the western retreating shores of the modern lake. The sediments were deposited under spatially varying limnological‐environmental conditions, influencing their magnetic properties. The southern section, located near Ein‐Gedi Spa (EG section) is dominated by detrital titanomagnetite whereas the northern sections, Nahal Og (Og section) and Ein‐Feshkha (EF section), are dominated by authigenic greigite. The chronology of the sections was established by radiocarbon dating of short lived organic debris. The magnetic data were obtained in a 2 cm resolution. The EF section, spanning the time interval from ca. 2,500 cal yr BP to ca. 1,000 cal yr BP, is dominated by greigite and thus providing the most robust geomagnetic record with precise paleomagnetic directions. Greigite forms very early in the sediment and the effects of smoothing and the inclination shallowing are negligible. The new data reveal a maximal deviation of 20° from the geocentric axial dipole field between 2,400 to 2,200 cal yr BP accompanied with a fast swing in inclination from 60° to 35° over about a century. This suggests high geomagnetic field activity associated with the Levantine Iron Age geomagnetic anomaly.

ROTI maps of Greenland using kriging

Abstract GNSS satellite signals are affected by the media when traversing Earth’s atmosphere, and the performance of GNSS based positioning and navigation is correlated with these effects. In the ionosphere, the signals are affected by the number of electrons along the signal path which can be quantified by the total electron content. The focus of this article is scintillation effects caused by electrons in the Arctic ionosphere, and the rate of the total electron content index, the ROTI, is used as a measure of the scintillation. Data from permanent GNSS reference stations in Greenland is used to generate maps of the ROTI in Greenland, and the novelty of the work in this paper is the application of the ordinary kriging method as the basis for ROTI maps in the Arctic. Further, the choice of satellite constellations as well as the elevation mask used in the data analyses are analyzed and discussed. Also, the performance of using ordinary kriging for ROTI maps during times with both a low and a very high geomagnetic activity are discussed. The results show that ordinary kriging performs well during high geomagnetic activity, while during low activity the natural neighbor interpolation method is a better choice for the Arctic.

On the correction of temperatures derived from meteor wind radars due to geomagnetic activity

Abstract Radars used to observe meteor trails in the mesosphere deliver information on winds and temperature. Use of these radars is becoming a standard method for determining mesospheric dynamics and temperatures worldwide due to relatively low costs and ease of deployment. However, recent studies have revealed that temperatures may be overestimated in conditions such as high geomagnetic activity. The effect is thought to be most prevalent at high latitude, although this is not yet proven. Here, we demonstrate how temperatures might be corrected for geomagnetic effects; the demonstration is for a particular geographic location (Svalbard, 78°N, 16°E) because it is local geomagnetic disturbances that affects local temperature measurements, therefore requiring co-located instruments. We see that summer temperatures require a correction (reduction) of a few Kelvin, but winter estimates are more accurate.

Biotic and Abiotic Factors of Sperm nDNA Fragmentation in Farm Animals

Infertility and subfertility are among the global challenges of our time. Fertility in livestock farming is not only biologically important, it is also economically important. The aim of this study was to study the effect of these factors on sperm chromatin nucleus and to assess the impact of the fragmentation index degree on bull reproductive performance. The influence of abiotic factors such as ambient temperature, the level of geomagnetic activity and the biotic factor-infectious diseases of male reproductive organs - was studied. At high ambient temperatures (28-30°C), the proportion of sperm with damaged DNA increased by 70% compared to temperatures below 15°C. A Multivariate Analysis Of Variance (MANOVA) confirmed the influence of the geomagnetic activity factor on the degree of nuclear DNA fragmentation in bull sperm cells (level p<0.05). During the summer period, on days with increased geomagnetic activity, the Nuclear DNA fragmentation index in the samples studied was 20.5%. In some of the samples studied, this index exceeded 38% and the coefficient of variation for this index reached 44%. The proportion of sperm cells with abnormal movement also increased during geomagnetic activity. The content of such sperm cells reached 9.1% in bull semen ejaculates obtained during the winter period. More than 12% of sperm had non-progressive movement in summer semen obtained with a K-index ≥5.0, which was 83.8% higher than with a K-index ≤1.0. High geomagnetic activity and temperature and infection of the reproductive organs lead to pathological changes in spermatozoa, an increase in the proportion of spermatozoa with damaged nuclear DNA and a decrease in fertility.

Экзогенные факторы фрагментации ядерной ДНК сперматозоидов быков‑производителей

Herd reproduction is the most important indicator of the economic efficiency of the industry. Assisted reproductive technology, especially artificial insemination, is widely used in dairy farming. When using this method, tens of thousands of cows and heifers are inseminated with the seed of a single bull, therefore, the used biomaterial must meet high requirements, since the use of low-quality sperm products can lead to multi-million losses. The reproductive performance of breeding bulls depends on numerous biotic and abiotic factors. breeding bulls depends on numerous biotic and abiotic factors. The purpose of the study the influence of meteorological factors on the biological usefulness of sperm from bulls of different breeds. A multidimensional dispersion analysis of the effect of temperature and geomagnetic activity on the quality of spermatozoa was performed. The results of multidimensional dispersion analysis show that the combination of temperature factors with geomagnetic activity has a statistically significant effect on the content of spermatozoa with abnormal movement in the fresh seed and on the activity of spermatozoa (p&lt;0,05). Geomagnetic activity (K-index ≥5,0) leads to an increase in the proportion of spermatozoa with pathological morphology. This trend was observed regardless of the season of the year. During the summer period, on days with increased geomagnetic activity, the content of spermatozoa with pathology increased by 66% compared to the period when there is no magnetic disturbance. Under the influence of geomagnetic activity, the proportion of spermatozoa with abnormal movement increased – such spermatozoa in the ejaculate contained an average of 10,2%, depending on the season and temperature, this indicator varied from 6 to 21,5%. High geomagnetic activity and temperature lead to an increase in the proportion of spermatozoa with a violation of the structure of nDNA.

Estimating the maximum of the smoothed highest 3-hourly &amp;lt;i&amp;gt;a&amp;lt;/i&amp;gt;&amp;lt;i&amp;gt;a&amp;lt;/i&amp;gt; index in 3 d by the preceding minimum for the solar cycle

Abstract. Predicting the maximum intensity of geomagnetic activity for an upcoming solar cycle is important in space weather service and for planning future space missions. This study analyzed the highest and lowest 3-hourly aa index (aaH∕aaL) in a 3 d interval, smoothed by 363 d to analyze their variation with the 11-year solar cycle. It is found that the maximum of aaH (aaHmax) is well correlated with the preceding minimum of either aaH (aaHmin, r=0.85) or aaL (aaLmin, r=0.89) for the solar cycle. Based on these relationships, the intensity of aaHmax for solar cycle 25 is estimated to be aaHmax(25)=83.7±6.9 (nT), about 29 % stronger than that of solar cycle 24. This value is equivalent to the ap index of apmax(25)=47.4±4.4 (nT) if employing the high correlation between ap and aa (r=0.93). The maximum of aaL (aaLmax) is also well correlated with the preceding aaHmin (r=0.80). The maximum amplitude of the sunspot cycle (Rm) is much better correlated with high geomagnetic activity (aaHmax, r=0.79) than with low geomagnetic activity (aaLmax, r=0.37). The rise time from aaHmin to aaHmax is weakly anti-correlated to the following aaHmax (r=-0.42). Similar correlations are also found for the 13-month smoothed monthly mean aa index. These results are expected to be useful in understanding the geomagnetic activity intensity of solar cycle 25.

A stress test to evaluate the usefulness of Akaike information criterion in short-term earthquake prediction

Akaike information criterion (AIC) has been recently adopted to identify possible earthquake precursors in ionospheric total electron content (TEC). According to the authors of this methodology, their technique allows finding abrupt increases (positive breaks) in vertical TEC rate of change 25–80 min before the occurrence of large earthquakes, highlighting a promising implication of AIC method in Mw > 8 earthquakes alert strategies. Due to the relevance of this matter, a lively scientific debate ensued from these results. In this study, we carefully evaluate AIC method potentiality in searching earthquake TEC precursory signatures. We first investigate the dependence of the detected breaks number on the adjustable AIC method parameters. Then, we show that breaks occurrence clusters around specific local times and around moderate and high solar and geomagnetic activity. The outcome of this study is that AIC method is not concretely usable for issuing large earthquakes alerts.

Seasonal Effect on Hemispheric Asymmetry in Ionospheric Horizontal and Field‐Aligned Currents

AbstractWe present a statistical investigation of the seasonal effect on hemispheric asymmetry in the auroral currents during low (Kp &lt; 2) and high (Kp ≥ 2) geomagnetic activity. Five years of magnetic data from the Swarm satellites has been analyzed by applying the spherical elementary current system (SECS) method. Bootstrap resampling has been used to remove the seasonal differences between the hemispheres in the data set. In general, the currents are larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Asymmetry is larger during low than high Kp and during local winter and local autumn than local summer and local spring. For all Kp conditions together, the NH/SH ratio for FACs in winter, autumn, spring, and summer are 1.17 ± 0.05, 1.14 ± 0.05, 1.07 ± 0.04, and 1.02 ± 0.04, respectively. The largest asymmetry is observed during low Kp in local winter, when the excess in the NH currents is 21 ± 5% in FAC, 14 ± 3% in curl‐free (CF) and 10 ± 3% in divergence‐free (DF) current. We also find that evening sector (13–24 MLT) contributes more to the high NH/SH ratio than the morning (01–12 MLT) sector. The physical mechanisms producing the hemispheric asymmetry are not presently understood. We calculated the solar‐induced ionospheric conductances during low Kp conditions from the IRI model. The model conductance NH/SH ratios are above 1 in autumn and spring, similar to the currents, but below 1 for winter, which is in contradiction with the currents. Therefore, we do not consider solar‐induced conductances as the main explanation for hemispheric asymmetry.

Impact of solar irradiance and geomagnetic activity on polar NOx, ozone and temperature in WACCM simulations

The response of the atmosphere to solar irradiance and geomagnetic activity is analyzed in experiments with the Whole Atmosphere Community Climate Model (WACCM) under idealized forcings. Four experiments are carried out combining high (H) and low (L) solar radiative forcing with high (7) and low (3) geomagnetic activity: H7 (with high radiative forcing and high geomagnetic activity), H3, (high/low), L7 (low/high), and L3 (low/low). The comparison between these experiment is used to assess the effects of solar radiative forcing and geomagnetic activity mainly on the stratosphere. A two-step Monte Carlo-based statistical test, which defines an impact score, is used to assess statistically significant impacts on regional scales, on pressure levels, for a few key model variables, like NOx, ozone, and temperature.Under low solar forcing (L7/L3), a statistically significant relationship between geomagnetic activity and NOx is found in both hemispheres and for all seasons. An equally strong relationship is lacking for ozone and temperature when analyzing these fields on isobaric levels. A statistically significant impact on stratospheric ozone is only seen in austral winter and spring. However, vertical cross sections show statistically significant impact on temperature and ozone mainly in the southern hemisphere (SH) during austral winter and the following spring.Significant and persistent signals in both SH NOx and ozone concentrations are only produced when the effect of high solar forcing is added to high geomagnetic activity (H7). In this case, statistically significant differences are also found for mesospheric temperatures, ozone and NOx. This latter result appears also under low geomagnetic activity as a result of solar forcing alone, suggesting that solar irradiance significantly affects NOx, ozone and stratospheric temperatures and, in some seasons, even tropospheric temperature.In summary, geomagnetic activity primarily affects NOx and ozone concentrations in the SH. Solar maximum conditions can reduce the amount of NOx in the stratosphere because of higher ozone production. Thus, we conclude that correlations between changes in solar irradiance and geomagnetic activity are important with respect to their effects on the atmosphere. In particular, geomagnetic activity can modulate atmospheric ozone concentrations and other associated stratospheric and tropospheric variables under conditions of high solar activity.

Asymmetric behaviour and geomagnetic dependencies of zonal winds in the middle latitude upper thermosphere

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.

Study of ionospheric scintillation during geomagnetic storms at equatorial anomaly region Bhopal

GPS L-band signals get affected by ionospheric scintillation; as a result, satellite navigation too gets affected. The most extreme scintillation activity is expected to occur near the equatorial region during geomagnetic storms. The behavior and morphology of low-latitude ionosphere are different from the other latitudes. The space weather conditions in low latitude show different nature because of the geomagnetic field. Due to penetration of soft, high energetic particles, the plasma density increases, which is the main source of generation of ionospheric irregularities scintillation. GPS scintillation at low latitudes is primarily associated with equatorial spread F. Equatorial spread F is caused by ionospheric irregularities with a spatial spectrum extending from 100 km to less than 1 m. When GPS signals encounter the ionospheric irregularities of various sizes produced during high geomagnetic and solar activity, they undergo drastic changes in their phase and amplitude scintillation indices. The accuracy and reliability of GPS system get affected by scintillation. Also the atmosphere air molecule’s content and deviation of electrons, protons, neutrons according to flow rate are observed. In the present paper, we have studied the scintillation activity at low-latitude station Bhopal.

Role of the Outer Ionosphere in the Winter/Summer Asymmetry of Auroral Electron Precipitations

This paper analyzes the role of the outer ionosphere in the occurrence of a large difference in the frequency of accelerated electron fluxes in the auroral region in the premidnight sector for winter and summer conditions, which are associated with discrete auroras. Simulation indicates that the critical value JEIC of the longitudinal current of the Alfven wave for the development of electrostatic ion–cyclotron instability at heights around the Earth’s radius (h ~ RE) for winter almost coincides with the upper limit of average values of the stationary large-scale longitudinal current. Therefore, weak fluctuations of the longitudinal current associated with the Alfven wave are sufficient in winter for the development of processes leading to accelerated electron fluxes, which are associated with discrete auroras. The summer value of JEIC is four to five times higher than that for winter, and a stimulated precipitation of auroral electrons is likely to be possible only at high geomagnetic activity. The winter/summer asymmetry in the JEIC value is mainly associated with specific changes in the parameters of the outer ionosphere along the geomagnetic field. The difference in electron density reaches a maximum at heights h ~ RE, where the summer values of this density are five to six times higher than the winter ones, which, in turn, is associated with higher summer temperatures of electrons and ions. The important role of these temperatures in the winter/summer asymmetry in the frequency of accelerated electrons has been noted, it would seem, for the first time.

Extremely-low frequency magnetic field exposure for simulating geomagnetic pulsations in Alexandrium pacificum and Gymnodinium catenatum cultures

Growth and chain formation in cultures of the chain-forming dinoflagellates Alexandrium pacificum and Gymnodinium catenatum were previously found to be susceptible to space weather variables. A clock drive was used to deliver a frequency of 0.5 Hz and central amplitude of 7 µT in order to perform in vitro simulation of geomagnetic pulsations (composed of extremely low-frequency magnetic fields, ELFMF) which occur during high geomagnetic activity (GMA) periods. Short-term exposure (hours) to this ELFMF increased relative cell growth around 10 nT of naturally occurring GMA. Relative growth outside these intervals gradually approached 0% or was negative for G. catenatum. Differential survival to a subsequent shock was inversely related to growth, and minimal survival coincided with the same 10 nT interval. Relative growth and survival displayed opposite hormetic curves towards GMA: inverted U-shaped for growth, and J-shaped for survival. After exposure to this ELFMF, positive phototaxis response was not lost, but the percentage of cells swimming was slightly reduced. Long-term exposure (days) increased relative growth in A. pacificum but reduced in G. catenatum when low GMA was taking place. These alterations in growth were both associated with a reduction in the cellular pool of mycosporine-like amino acids (MAAs). MAAs that are more susceptible to oxidation were more reduced than those resistant, highlighting that an ELFMF can act by increasing cellular oxidative stress status. The higher susceptibility of G. catenatum found is in compliance with the previous association of its natural populations at the western Iberia coast with periods of solar activity minima and GMA minima.

Statistical Analysis of the Main Ionospheric Trough Using Swarm in Situ Measurements

AbstractA statistical analysis of the topside main ionospheric trough is implemented by using the Swarm constellation in situ plasma density measurements from December 2013 to November 2019. The key features of the main trough, such as the occurrence rate, minimum position, width, and depth, are characterized and quantified. The distribution patterns of these parameters are investigated with respect to magnetic local time, season, longitude, solar activity, and geomagnetic activity levels, respectively. The main results are as follows: (1) The diurnal variation of the trough occurrence rate usually exhibits a primary peak in the early morning, a subsidiary peak in the late evening, and a slight reduction around midnight especially in the Northern Hemisphere. (2) The seasonal variation of the nighttime trough has maximum occurrence rates around equinoxes, higher than those in local winter. (3) The trough distribution has an evident hemispherical asymmetry. It is more pronounced in the Northern Hemisphere during the winter and equinoctial seasons, with its average nighttime occurrence rate being 20–30% higher than that in the Southern Hemisphere. The trough minimum position and the trough width also exhibit more significant fluctuation in the Northern Hemisphere. (4) The longitudinal pattern of the trough shows clear east‐west preferences, which has a higher occurrence rate in eastern (western) longitudes around the December (June) solstice. (5) Conditions for the trough occurrence are more favored in low solar activity and high geomagnetic activity periods.

Immediate and delayed responses of power lines and transformers in the Czech electric power grid to geomagnetic storms

Eruptive events of solar activity often trigger abrupt variations of the geomagnetic field. Through the induction of electric currents, human infrastructures are also affected, namely the equipment of electric power transmission networks. It was shown in past studies that the rate of power-grid anomalies may increase after an exposure to strong geomagnetically induced currents. We search for a rapid response of devices in the Czech electric distribution grid to disturbed days of high geomagnetic activity. Such disturbed days are described either by the cumulative storm-time Dst or d(SYM-H)/dt low-latitude indices mainly influenced by ring current variations, by the cumulative AE high-latitude index measuring substorm-related auroral current variations, or by the cumulative ap mid-latitude index measuring both ring and auroral current variations. We use superposed epoch analysis to identify possible increases of anomaly rates during and after such disturbed days. We show that in the case of abundant series of anomalies on power lines, the anomaly rate increases significantly immediately (within 1 day) after the onset of geomagnetic storms. In the case of transformers, the increase of the anomaly rate is generally delayed by 2–3 days. We also find that transformers and some electric substations seem to be sensitive to a prolonged exposure to substorms, with a delayed increase of anomalies. Overall, we show that in the 5-day period following the commencement of geomagnetic activity there is an approximately 5–10% increase in the recorded anomalies in the Czech power grid and thus this fraction of anomalies is probably related to an exposure to GICs.

Statistical Distribution of Whistler Mode Waves in the Radiation Belts With Large Magnetic Field Amplitudes and Comparison to Large Electric Field Amplitudes

AbstractWe present a statistical analysis with 100% duty cycle and non‐time‐averaged amplitudes of the prevalence and distribution of high‐amplitude &gt;50‐pT whistler mode waves in the outer radiation belt using 5 years of Van Allen Probes data. Whistler mode waves with high magnetic field amplitudes are most common above L=4.5 and between magnetic local time of 0–14 where they are present approximately 1–6% of the time. During high geomagnetic activity, high‐amplitude whistler mode wave occurrence rises above 25% in some regions. The dayside population are more common during quiet or moderate geomagnetic activity and occur primarily &gt;5° from the magnetic equator, while the night‐to‐dawn population are enhanced during active times and are primarily within 5° of the magnetic equator. These results are different from the distribution of electric field peaks discussed in our previous paper covering the same time period and spatial range. Our previous study found large‐amplitude electric field peaks were common down to L=3.5 and were largely absent from afternoon and near noon. The different distribution of large electric and magnetic field amplitudes implies that the low‐L component of whistler mode waves observed previously are primarily highly oblique, while the dayside and high‐L populations are primarily field aligned. These results have important implications for modeling radiation belt particle interactions with chorus, as large‐amplitude waves interact nonlinearly with electrons, resulting in rapid energization, de‐energization, or pitch angle scattering. This also may provide clues regarding the mechanisms which can cause significant whistler mode wave growth up to more than 100 times the average wave amplitude.

Spatially Resolved Neutral Wind Response Times During High Geomagnetic Activity Above Svalbard

AbstractIt has previously been shown that in the high‐latitude thermosphere, sudden changes in plasma velocity (such as those due to changes in interplanetary magnetic field) are not immediately propagated into the neutral gas via the ion‐drag force. This is due to the neutral particles (O, O2, and N2) constituting the bulk mass of the thermospheric altitude range and thus holding on to residual inertia from a previous level of geomagnetic forcing. This means that consistent forcing (or dragging) from the ionospheric plasma is required, over a period of time, long enough for the neutrals to reach an equilibrium with regard to ion drag. Furthermore, mesoscale variations in the plasma convection morphology, solar pressure gradients, and other forces indicate that the thermosphere‐ionosphere coupling mechanism will also vary in strength across small spatial scales. Using data from the Super Dual Auroral Radar Network and a Scanning Doppler Imager, a geomagnetically active event was identified, which showed plasma flows clearly imparting momentum to the neutrals. A cross‐correlation analysis determined that the average time for the neutral winds to accelerate fully into the direction of ion drag was 75 min, but crucially, this time varied by up to 30 min (between 67 and 97 min) within a 1,000‐km field of view at an altitude of around 250 km. It is clear from this that the mesoscale structure of both the plasma and neutrals has a significant effect on ion‐neutral coupling strength and thus energy transfer in the thermosphere.