Horizontal Component Of Magnetic Field Research Articles

Rapid Geomagnetic Variations During High‐Speed Stream, Sheath and Magnetic Cloud‐Driven Geomagnetic Storms From 1996 to 2023

AbstractThe most detrimental geomagnetically induced currents (GICs) documented to date have all taken place during geomagnetic storms. Yet, the probability of GICs throughout geomagnetic storms driven by different solar wind transients, such as high‐speed streams/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejection (ICME) sheaths and magnetic clouds (MC), is poorly understood. We present an algorithm to detect geomagnetic storms and storm phases, resulting in a catalog of 755 geomagnetic storms from January 1996 to June 2023 with the solar wind drivers. Using these storms and the IMAGE magnetometer network, we study the temporal and spatial evolution of spikes in the time derivative of the horizontal component of the external magnetic field, , greater than 0.5 nT/s during geomagnetic storms driven by HSS/SIR, sheaths and MCs. Spikes occur more often toward the end of the storm main phase for HSS/SIR and MC‐driven storms, while sheaths have spikes throughout the entire main phase. During the main phase most spikes occur in the morning sector around 05 magnetic local time (MLT) and the extent in MLT is narrowest for MCs and widest for sheaths. However, spikes in the pre‐midnight sector during the main and recovery phases are most prominent for HSS/SIR‐driven storms. During the storm sudden commencement (SSC), three MLT hotspots exist, the post‐midnight at 04 MLT, pre‐noon at 09 MLT and afternoon at 15 MLT. The pre‐noon hotspot has the highest probability of spikes and the widest extent in magnetic latitude.

Variability of Ionospheric Total Electron Content Over Morocco During the Godzilla Sand and Dust Storm of June 2020

During sand and dust storm (SDS) events, atmospheric suspension and transport of sand and dust brings a reasonable amount of electrification in the atmosphere which plays a very important role in the atmosphere-ionosphere coupling. The Godzilla SDS began on 5<sup>th</sup> June 2020 in Algeria following a decrease in pressure and spread to other areas across the Sahara between 6<sup>th</sup> and 28<sup>th</sup> June 2020. Using SDS data from Copernicus Sentinel-5P satellite mission and Vertical Total Electron Content (VTEC) data from four GNSS receiver stations: IFR1 (Ifrane Seismic), MELI (Melilla), TETN (Tetouan) and OUCA (Ouca) over Morocco, we investigate the possible ionospheric TEC variability over the four GNSS receiver stations during the Godzilla SDS event which was tracked using the Sentinel-5P Satellite mission. Solar wind parameters: Horizontal component of Interplanetary Magnetic Field (IMF-Bz), interplanetary Electric Field (IEF-Ey) and solar wind speed (V) and geomagnetic indices: Disturbance Storm Time (Dst) and Planetary K (Kp) indices were examined and showed very minimal geomagnetic influence during the period. We observed major ionospheric disturbances over the four Global Navigation Satellite System (GNSS) receiver stations on 16<sup>th</sup>, 17<sup>th</sup>, 18<sup>th</sup>, 21<sup>st</sup>, 22<sup>nd</sup>, 23<sup>rd</sup> 25<sup>th</sup> and 26<sup>th</sup> June 2020: the period with the Sentinel-5P Aerosol Index (SAI) of more than 4 as recorded by the Sentinel-5P Satellite engine. The daily VTEC values over the four GNSS receiver stations recorded continuous electron density perturbations during these days. Apart from the ionospheric TEC perturbations, significant enhancements and decreases in daily maximum VTEC values over the four GNSS receiver stations were also noted. These were attributed to the changes in the atmospheric electric fields generated by the SDS event. The VTEC plots for each day exhibited similar trends, hence exhibited the same ionospheric dynamics. VTEC depletions of depths 3 to 6 TECU over all the four GNSS receiver stations were noted on 12<sup>th</sup>, 14<sup>th</sup>, 17<sup>th</sup>, 20<sup>th</sup> and 25<sup>th</sup> June 2020. Nighttime VTEC enhancements were also noted and majorly occurred between 20:00 and 21:00 UT on 9<sup>th</sup>, 13<sup>th</sup>, 15<sup>th</sup>, 17<sup>th</sup>, 19<sup>th</sup>, 20<sup>th</sup> and 21<sup>st</sup> June 2020. This was attributed to the development of the electron avalanche processes including dust and electron absorption or losses and the active conversion to electron dissociative attachment leading to electron excitation. In conclusion, the Godzilla SDS of June 2020 led to the electron density perturbations over Morocco.

Searching for Evidence of Subchromospheric Magnetic Reconnection on the Sun

Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low-FIP elements (the FIP effect) while more active stars such as M dwarfs have coronae generally characterized by the inverse-FIP (I-FIP) effect. Highly localized regions of I-FIP effect solar plasma have been observed by Hinode's EUV Imaging Spectrometer in a number of highly complex active regions (ARs), usually around strong light bridges of the umbrae of coalescing/merging sunspots. These observations can be interpreted in the context of the ponderomotive force fractionation model, which predicts that plasma with I-FIP effect composition is created by the refraction of waves coming from below the plasma fractionation region in the chromosphere. A plausible source of these waves is thought to be reconnection in the (high-plasma-β) subchromospheric magnetic field. In this study, we use the 3D visualization technique of Chintzoglou & Zhang combined with observations of localized I-FIP effect in the corona of AR 11504 to identify potential sites of such reconnection and its possible consequences in the solar atmosphere. We found subtle signatures of episodic heating and reconnection outflows in the expected places, in between magnetic flux tubes forming a light bridge, within the photosphere of the AR. Furthermore, on either side of the light bridge, we observed small antiparallel horizontal magnetic field components, supporting the possibility of reconnection occurring where we observe I-FIP plasma. When taken together with the I-FIP effect observations, these subtle signatures provide a compelling case for indirect observational evidence of reconnection below the fractionation layer of the chromosphere, however direct evidence remains elusive.

Micron-sized fiber diamond probe for quantum precision measurement of microwave magnetic field

Abstract We present a quantitative measurement of the horizontal component of the microwave magnetic field of a coplanar waveguide using a quantum diamond probe in fiber format. The measurement results are compared in detail with simulation, showing a good consistence. Further simulation shows fiber diamond probe brings negligible disturbance to the field under measurement compared to bulk diamond. This method will find important applications ranging from electromagnetic compatibility test and failure analysis of high frequency and high complexity integrated circuits.

New Concept Ocean-Bottom Multiphysics (OBMP) Nodes for Reservoir Monitoring

Marine-controlled source electromagnetics (CSEM) have been extensively applied to various exploration scenarios worldwide. However, its perceived value and cost relative to seismic and the scarcity of realistic case studies have limited the industry’s interest in time-lapse reservoir-monitoring (4D) applications. A feasible way to make demand for CSEM for 4D-monitoring programs would be to increase the value of information and reduce survey costs by performing joint operations where seismic and CSEM data are acquired during the same survey and at equivalent spatial densities. To this end, we propose a new multiphysics ocean-bottom nodes (OBN) concept and show the industry that CSEM can be a cost efficient and effective integrators to 4D seismic projects. To this end, we conducted a feasibility study demonstrating that horizontal magnetic field components have the required sensitivities and can be used instead of horizontal electric field components in mapping the 3D resistivity distribution and 4D fluid change responses in a given reservoir. This makes engineering a new OBN class simpler and cheaper, as various miniaturized magnetic field sensors are available off-the-shelf or readily working along with packaging and coupling solutions.

The Ionospheric Dynamics of the African Sector Responding to a Severe Geomagnetic Storm; the Storm of 3–5 November 2021

AbstractThe sudden storm commencement (SSC) of 3 November 2021, a severe storm was detected through disturbances in magnetospheric and ring current systems at around 1942 UT. We used a daily variation of total electron content (TEC) from ground‐based GNSS stations, ionosonde parameters and modeled zonal and meridional wind velocities to study the ionospheric response over the African region by comparing storm and quiet time variations. The equatorial GNSS station of NKLG recorded initial positive storm effects around the time of SSC, of which these effects spread over the whole African region during the main phase with positive and negative storm effects during the main and recovery phases respectively. The two disturbances at the SSC and the main phase were caused by the penetrating electric field and traveling atmospheric disturbances respectively. The analysis of TIMED Global UltraViolet Imager images revealed storm time‐induced changes in thermospheric composition during the main phase which resulted in a differential ionospheric response with intense, moderate, and weak positive storm effects in northern, equatorial, and southern regions respectively. The horizontal magnetic field components show two signatures of prompt penetration electric field that suppressed the formation of the equatorial anomaly at SSC and enhanced positive storm effects in the equatorial region at the main phase, Therefore, the ionospheric response was due to the relative contributions of prompt penetration electric field effects and equatorward traveling disturbances which depended on storm onset time, past ionospheric state, and storm phase.

The Nonpotentiality of Steady-state Coronal Magnetic Field Derived with Time-relaxation Magnetohydrodynamics Simulations Using Helioseismic and Magnetic Imager Three-component Magnetic Field Data

The steady states of the coronal magnetic field obtained with the magnetohydrodynamic (MHD) time-relaxation simulation model are examined. Our electric-field-driven model can introduce the three components of the solar surface magnetic field data maps as the boundary values of an MHD simulation, without violating the divergence-free condition of the magnetic field. The magnetic field in the simulated steady-state solar corona exhibits substantial nonpotentiality in the closed-field streamers. A few choices are allowed in our model, such as the criteria for determining whether or not the horizontal components at the weak-field region are included. The initial magnetic field configuration can be arbitrarily determined. In this work, we examined the differences between the steady states obtained with the information on the horizontal components and with several choices of the simulation setting, and compared the new steady states with those obtained without using the horizontal magnetic field components. We found that nonpotential magnetic structures in the derived steady states well correspond to the observed solar filament structures during a selected period of Carrington Rotation 2106. The difference in the steady state with different boundary treatments is found to be large. The difference caused by the initial magnetic configuration is found to be small.

Forecasting changes of the magnetic field in the United Kingdom from L1 Lagrange solar wind measurements

Extreme space weather events can have large impacts on ground-based infrastructure important to technology-based societies. Machine learning techniques based on interplanetary observations have proven successful as a tool for forecasting global geomagnetic indices, however, few studies have examined local ground magnetic field perturbations. Nowcast and forecast models which predict the magnitude of the horizontal geomagnetic field, |BH|, and its time derivative, dBHdt, at ground level would be valuable for assessing the potential space weather hazard. We attempt to predict the variation of the magnetic field at the three United Kingdom observatories (Eskdalemuir, Hartland and Lerwick) driven by L1 solar wind parameters. The horizontal magnetic field component and its time derivative are predicted from solar wind plasma and interplanetary magnetic field observations using Long Short-Term Memory (LSTM) networks and hybrid Convolutional Neural Network-LSTM models. A 5-fold grid search cross-validation is used for tuning the hyperparameters in each model. Forecasts were made with 5, 15 and 30-min lead times. Models were trained and validated with geomagnetic storm-only data from 1997 to 2016; their outputs were evaluated with the 7–9th September 2017 storms. The forecast models are only able to predict the directly driven parts of geomagnetic storms (not the substorms) and LSTM models generally perform best. We find the |BH| 15- and 30-min forecasts at Lerwick and Eskdalemuir have some predictive power. The 5-min |BH| forecast as well as all the dBHdt models for Eskdalemuir and all the Hartland models were found to have little or no predictive power. This suggests that the machine learning models have better forecasting power at higher latitude (closer to the auroral zones), where the ground magnetic variation field is larger and during storm onset, which is directly driven by changes in the solar wind.

Electromagnetic Seasons in Schumann Resonance Records

AbstractResults of 6‐year concurrent observations of Schumann resonance at the Ukrainian “Akademik Vernadsky” Antarctic station (65.25°N, 64.25°W) and at SOUSY Arctic facility (Svalbard 78.15°N, 16.05°E) are analyzed and compared. Measurements were performed simultaneously by using similar techniques and the calibrated digital equipment. The long‐term records of two orthogonal horizontal magnetic field components demonstrated seasonal and interannual changes in the peak frequency and intensity of the first Schumann resonance mode. The analysis of the annual variations of these parameters in different hemispheres allowed us to select the “electromagnetic seasons.” We suggest that each “electromagnetic season” corresponds to the characteristic pattern of diurnal peak frequency variation determined by lightning the source‐observer configuration. This configuration is unique for each observation point and varies from one season to another in line with the seasonal latitudinal north‐south drift of world thunderstorms. Our observation has demonstrated the different duration of “electromagnetic seasons” in the Arctic and Antarctic. To study the formal reason of this discrepancy, the final data were processed using the singular value decomposition (SVD) algorithm, which allowed us to identify the principal components (PCs) of the time series. The implementation of this technique to peak frequency variation showed the phase shift between the semiannual PCs at the Southern and Northern Hemispheres that explains the different duration of “electromagnetic seasons.” The SVD of the first Schumann resonance mode intensity demonstrated the phase shift between annual variations in different hemispheres and complicated the behavior of other PCs that deserve a separate study.

Forward model of metal magnetic memory testing based on equivalent surface magnetic charge theory

The magnetic dipole theory has been widely and successfully used to qualitatively analyze the testing signals of metal magnetic memory (MMM) testing. However, the magnetic charge density of the existing models is always an assumed value distributed uniformly or linearly along the defect section or in a stress concentration area, as a result the existing models are unsuitable for quantitatively analyzing the metal magnetic memory signal. In this work, a new forward model of MMM testing is established by considering the influence of uneven stress on magnetic charge density distribution, discretizing the specimen into numbers of micro elements firstly, assuming that the magnetic characteristic parameters of each element are evenly distributed and the magnetic charge density changes with stress in each element which can be determined by combining the modified magneto-mechanical model and the classical theory of magnetic charges. Compared with the experimental results of hole defect and crack defect specimen, the theoretical results calculated by the proposed model prove to be in good agreement with the testing results both qualitatively and quantitatively. Consequently, the proposed model is a new theoretical and quantitative model for analyzing the experimental change rule of metal magnetic memory testing. Then, the effects of stress concentration and macroscopic defects on the distribution of magnetic field are analyzed, showing that when there is only a stress concentration in the specimen, the horizontal component is negative valley, and the normal component changes from negative to positive valley peak in the stress concentration area; when there is a crack defect in the specimen, the distribution of magnetic field is just opposite to that when there is only a stress concentration. The distribution characteristics of the magnetic field can be used to judge the damage type in the specimen. Moreover, taking crack defect for example, the horizontal and normal component of magnetic field and their characteristic parameters changing with the size parameters of crack defect, such as width, length, depth and buried depth of crack defect, are analyzed in detail. The results show that the <inline-formula><tex-math id="M1">\begin{document}${W_{\Delta {H_x}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M1.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M2">\begin{document}${W_{\Delta {H_z}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M2.png"/></alternatives></inline-formula> increase lineally with the increase of the width of crack, <inline-formula><tex-math id="M3">\begin{document}$\Delta {H_x}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M3.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M4">\begin{document}$\Delta {H_z}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M4.png"/></alternatives></inline-formula>increase with the increase of the length and depth of crack, but gradually decrease with the increase of defect buried depth.

Characterization of seasonal and annual variation of horizontal component of magnetic field in africa and asia regions

This study considered the horizontal component of the magnetic field, H, which is a characteristic of Equatorial Electrojet (EEJ). Using Magnetic Data Acquisition System (MAGDAS) data preserved for the year 2009, variations in H strength were determined in 10 stations in Africa and Asia sector. The seasonal and annual fluctuations in the H-component of the Earth’s magnetic field were studied using hourly data of the horizontal magnetic field component. For the hourly fluctuation, the baseline values of H were estimated using the average values around local midnight hours between 2300 and 0200 local-time (LT) and subtracted from other hourly values; for seasonal and yearly analysis, the monthly and annual averages were computed. In all seasons, seasonal variations were higher in equatorial stations than in anti-equatorial stations, while maximum values of SqH were recorded in the equinoctial season, with an annual highest peak value of 70.96 nT in Langkawi (LKW; 6.30°S, 99.78°E) and the lowest peak value of 27.45 nT in Cooktown (CKT; 15.48°N, 145.25°E) both at 1300 LT.

Evolution of Global Lightning in the Transition From Cold to Warm Phase Preceding Two Super El Niño Events

AbstractMultistation observations of Schumann resonance (SR) intensity document common behavior in the evolution of continental‐scale lightning activity in two super El Niño events, occurring in 1997/98 and 2015/16. The vertical electric field component of SR at Nagycenk, Hungary and the two horizontal magnetic field components in Rhode Island, USA in 1997, and in 2014–2015, the two horizontal magnetic field components at Hornsund, Svalbard and Eskdalemuir, United Kingdom as well as in Boulder Creek, California and Alberta, Canada exhibit considerable increases in SR intensity from some tens of percent up to a few hundred percents in the transition months preceding the two super El Niño events. The UT time distribution of anomalies in SR intensity indicates that in 1997 the lightning activity increases mainly in Southeast Asia, the Maritime Continent and India, i.e. the Asian chimney region. On the other hand, a global response in lightning is indicated by the anomalies in SR intensity in 2014 and 2015. SR‐based results are strengthened by comparison to independent lightning observations from the Optical Transient Detector and the World Wide Lightning Location Network, which also exhibit increased lightning activity in the transition months. The increased lightning is attributable to increased instability due to thermodynamic disequilibrium between the surface and the midtroposphere during the transition. The main conclusion is that variations in SR intensity may act as a precursor for the occurrence and magnitude of these extreme climate events, and in keeping with earlier findings, as a precursor to maxima in global surface air temperature.

The Location of the Earth's Magnetic Poles From Circum‐Terrestrial Observations

AbstractThe magnetic poles or dip poles are the points on the Earth's surface and circum‐terrestrial area where the magnetic field is vertical, so the horizontal component vanishes. They are not coincident with geomagnetic poles, which are the points where the dipole axis, obtained by analytic models, intersects the Earth's surface, and their instrumental sampling determination from ad hoc ground surveys is difficult due to the harsh environmental conditions and remoteness of the areas where they are located. In this work, we use magnetic field measurements from ESA's Swarm satellites covering 5 years (2015–2019), and determine the position of the magnetic poles by modeling the yearly average horizontal magnetic field component through analytic two‐dimensional Taylor polynomial fit and finding the locations where this component is minimum. The yearly dip poles positions at average satellites geocentric altitudes are also projected at ground level based on WGS84 geodetic reference system. Reliability of our method is evaluated by an optimized Monte Carlo test applied to combined International Geomagnetic Reference Field (IGRF) model and Swarm data. The availability of several years of data allows us to investigate the long term variation and dynamics of the magnetic poles, also in comparison with the results provided by IGRF model (both IGRF12 and IGRF13). Our results agree with the model, in better accordance in the north hemisphere with IGRF13, indicating that both magnetic poles move in the north‐west direction, with a speed of ∼37–72 km/y (lower in year 2016) for the north dip pole and of ∼5–9 km/y for the south one.

Evaluation of errors in estimating the azimuth of powerful lightning discharges from measurements of Q-burstst

In this work, we study the variability of errors in determining the azimuth of Q-bursts’ sources on a daily time scale. Qbursts are electromagnetic pulse radiation in the extremely low frequency (ELF) range, excited by powerful lightning discharges, and they are used to locate lightnings over the world. We estimated the errors from data collected for two horizontal orthogonal magnetic field components of Q-bursts. Experimental records of Q-bursts were made at Akademik Vernadsky station from March to April 2019, which covers the vernal equinox day. We determined the azimuth of a Q-bursts’ source by digital rotation of the coordinate system until the signal in one magnetic component would drop to its minimum value. The absolute value of the azimuth error was estimated from the ratio of the Q-burst’s amplitude to the standard deviation of the residual signal. With an automated processing procedure, we analyzed over 800 thousand Q-bursts with amplitude over 10 picotesla. A characteristic diurnal pattern has been discovered in the estimated azimuth errors variations. The night level of the azimuth error exceeded the day level by about two degrees on average. The decrease-rise-decrease И-shaped swing during transition from night to day and mirror-symmetric Nshaped swing during transition from day to night were identified. Each of those transitional swings takes about four hours. A comparison of the daily variations in the total intensity of ELF background noise with the estimated daily azimuth error diagrams demonstrates the opposite character: maximal level of the ELF background noise was observed during the daytime while the estimated azimuth errors take minimal values at this time. This contradicts the generally accepted notion that increasing the noise increases the error. Thus, we suppose that the residual magnetic component in a Q-burst occurs not only from the background noise but can also result from nonlinear polarization of the incident wave due to gyrotropy of the nighttime lower ionosphere. Coherent waves resulting from diffraction of the incident field on the day-night interface in the Earth-ionosphere cavity could explain the И- and N-shaped swings of the azimuth error during the passage of the solar terminator.

Reflection of the solar activity Hale cycles on the geomagnetic field secular variations

The effect of dramatic decaying of solar activity in the twentieth cycle on secular variations of the Earth’s geomagnetic field has been investigated. Solar activity decay leads to reduction of the number of magnetic storms on the Earth. During the years of large-scale solar activity negative variations from external sources of the field — circular magnetospheric current, increase, as well as amplitudes of changes of auroral and equatorial ionospheric electrojets. Circular current reduces the horizontal component of the Earth’s magnetic field in low and medium latitudes and increases the vertical component in the high latitudes. In auroral latitudes the intensity of auroral electrojets increases during a magnetic storm. Therefore in more active years average annual absolute values of horizontal component of magnetic field will be smaller at the observatories situated in low and medium latitudes and average annual absolute values of the vertical component of magnetic field will be higher in the high latitudes of the Earth. As far as secular variations are determined as the difference between average annual values of the field, the effect of external sources of the field increases with the growth of solar activity.At the observatories of the northern hemisphere of the Earth (West Europe and North America) decaying of solar activity leads to the increase of average annual values of the field, i.e., to positive secular variations. The effect is maximal in the region of the magnetic pole. The amplitude of the effect decreases with the decrease of the latitude of the observatory. The sign of the effect changes (i.e. negative values of secular variations for the northern hemisphere) at the longitudes 60°Е («Kazan») and 150—160°E («cape Uellen», «Barrov»). Amplitudes of negative secular variations are maximal at the magnetic observatory «Irkutsk». The effect is not observed at the insular observatories as well as the observatories in South America. It is evidently a result of superposition of variations with different signs from the external and internal sources such as variations from the currents in the oceanic flows and the equality by the value of amplitude of secular variations from external and internal sources.

A Portable Magnetometer for Magnetic Measurements of Meter‐Sized Meteorites

AbstractMeteorites contain records of past magnetic fields in the form of natural remanent magnetization (NRM). A key property of meteorite magnetization that provides information about its origin is its dependence on spatial scale. In particular, understanding how the mean remanent magnetization varies from the scale of meteorites to the global scale of their parent bodies would aid in the interpretation of spacecraft magnetometry data. However, the vast majority of meteorite samples whose remanent magnetization have been measured have sizes <10 cm due to the limited size range accommodated by laboratory magnetometers. To address this limitation, we developed a portable magnetometer array that enables remanence measurements of meter‐size meteorites in a non‐magnetically shielded environment. The instrument measures both NRM and induced magnetization using two orthogonal square Helmholtz coil pairs that compensate the vertical and horizontal components of the background magnetic field. An array of four magnetometers mounted on a movable aluminum rail measures the magnetic field at multiple locations around the sample. The instrument is transportable and can be adapted to different sample sizes. After distinguishing the induced component from the remanent component of a sample's total field, the remanence can be estimated from a multipole field inversion combined with nonlinear least squares method. We validated the instrument and data processing on a magnet of known magnetic moment and measured the NRM of a meter‐sized iron meteorite.

A Gray‐Box Model for a Probabilistic Estimate of Regional Ground Magnetic Perturbations: Enhancing the NOAA Operational Geospace Model With Machine Learning

AbstractWe present a novel algorithm that predicts the probability that the time derivative of the horizontal component of the ground magnetic field dB/dt exceeds a specified threshold at a given location. This quantity provides important information that is physically relevant to geomagnetically induced currents (GICs), which are electric currents associated with sudden changes in the Earth's magnetic field due to space weather events. The model follows a “gray‐box” approach by combining the output of a physics‐based model with machine learning. Specifically, we combine the University of Michigan's Geospace model that is operational at the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center, with a boosted ensemble of classification trees. We discuss the problem of recalibrating the output of the decision tree to obtain reliable probabilities. The performance of the model is assessed by typical metrics for probabilistic forecasts: Probability of Detection and False Detection, True Skill Statistic, Heidke Skill Score, and Receiver Operating Characteristic curve. We show that the ML‐enhanced algorithm consistently improves all the metrics considered.

Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations

Abstract. Geomagnetically induced currents (GICs) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents and the three-dimensional (3D) distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH∕dt) is closely related to the electric field via Faraday's law and provides a convenient proxy for the GIC risk. However, forecasting dH∕dt still remains a challenge. We use 25 years of 10 s data from the northern European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that, instead of the primary ionospheric currents, the measured dH∕dt is dominated by the signature from the secondary induced telluric currents at nearly all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to high-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the stations involved. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible (i.e., a dense observation network is available).

English

Variations of equatorial electrojet (EEJ) in six Magnetic Data Acquisition System (MAGDAS) stations (four stations within the magnetic equator region and two stations outside the region) on the 210oMagnetic Meridian (MM) chain were examined. Data of hourly values of horizontal component of magnetic field, H in the year 2007 for Cooktown (CKT), Amami-oh-Shima (AMA), Davao (DAV), Langkawi (LKW), Yap- Island (YAP) and Cebu (CEB) were used in the study. The electrojet current was studied using both the estimation method and Fambitakoye simulation model to determine the correlation between their results. The strength of equatorial electrojet in the stations were estimated with respect to Cooktown (CKT; 15.48°N, 145.25°E), a station located outside the electrojet region. The maximum electrojet strength was observed in the month of March in Davao (DAV), Cebu (CEB) and Langkawi (LKW) with values of 107.5, 88.5 and 64.08 nT, respectively. The model simulation of EEJ current presents maximum values of 237.9, 207 and 160 nT in DAV, CEB and LKW, respectively in the same month. This result establishes a similarity in the performance of the methods but with higher values in the model performance. A linear correlation analysis between them showed average correlation coefficient values of 0.81 in Yap-Island (YAP), 0.84 in LKW, 0.6 in DAV and 0.54 in CEB. The data also show variability in EEJ, with results showing higher EEJ current magnitude for stations closer to the dip equator. The Root Mean Square Error (RMSE) was carried out to determine the suitability of the model for in the four seasons for each station. Result shows that the model performed better for March equinox in Cebu (3.58) and Yap-Island (5.97), December solstice (8.96) and September equinox in Davao and Langkawi (6.55), respectively. Key words: Equatorial electrojet, dip equator, magnetic data acquisition system (MAGDAS), Fambitakoye model, E-region, solar quiet.

Investigation of the Influence of Distant Parameters on Horizontal Component of Ground Magnetic Field.

The influence of distant parameters on the horizontal component of magnetic field was investigated for two years within two locations in Africa. The measure of storm occurrence (Dst-index) was used to select successful storm days. The effect of distant parameters on residual field was investigated using filter analysis. This study was considered on both time domain and frequency domain. The results showed very close correspondence of rapid changes in amplitudes between residual H–component and the selected IMF parameters especially the solar wind velocity, proton density and Bz. The correlation analysis between the distant parameters and residual H–component completely revealed effective dependence of the depression of residual field on the selected parameters. The value of the correlation coefficient (r) with solar wind velocity, proton density and Bz showed significant values of the range of 0.5 and above. This is direct evidence that Solar wind velocity, proton density and Bz are more effective in causing geomagnetic fluctuations at equatorial low latitude stations.