Geomagnetic Field Measurements Research Articles

Investigation of low-latitude nighttime geomagnetic pulsation events occurred under variable IMF and solar conditions

Disturbances in the Interplanetary Magnetic Field (IMF) and solar conditions can affect the geomagnetic field measurements. In the current study, the influence of IMF and solar fluctuations on the nighttime Pc3-5 and Pi2 pulsations at low latitudes is investigated. Geomagnetic data recorded by the Egyptian geomagnetic observatories are used to examine the occurrence of nighttime pulsation events in Egypt. The corresponding daytime data from the Honolulu (HON) INTERMAGNET observatory were used for comparison between nighttime and daytime pulsation activity aiming for a better understanding of their sources. Two pulsation activities occurred on 7 and 27 February 2014 under different IMF and solar conditions were examined. Results of data analysis indicate that geomagnetic field fluctuations (Pc3-5 and Pi2 pulsations) are affected by changes in the IMF and solar conditions. The occurrence of space weather events such as geomagnetic storms and Coronal Mass Ejections (CMEs) can significantly affect the coherence and correlations between the pulsation wave-packets observed at nighttime and daytime suggesting different generation mechanisms for each pulsation event.

A Compensation Method for the Geomagnetic Measurement Error of an Underwater Ship-Borne Magnetometer Based on Constrained Total Least Squares.

When magnetic matching aided navigation is applied to an underwater vehicle, the magnetometer must be installed inside the vehicle, considering the navigation safety and concealment of the underwater vehicle. Then, the interference magnetic field will seriously affect the accuracy of geomagnetic field measurement, which directly affects the accuracy of geomagnetic matching aided navigation. Therefore, improving the accuracy of geomagnetic measurements inside the vehicle through error compensation has become one of the most difficult problems that requires an urgent solution in geomagnetic matching aided navigation. In order to solve this problem, this paper establishes the calculation model of the internal magnetic field of the underwater vehicle and the geomagnetic measurement error model of the ship-borne magnetometer. Then, a compensation method for the geomagnetic measurement error of the ship-borne magnetometer, based on the constrained total least square method, is proposed. To verify the effectiveness of the method proposed in this paper, a simulation experiment of geomagnetic measurement and compensation of a ship-borne three-axis magnetometer was constructed. Among them, to be closer to the real situation, a combination of the geomagnetism model, the elliptic shell model and the magnetic dipole model was used to simulate the internal magnetic field of the underwater vehicle. The experimental results indicated that the root mean square error of geomagnetic measurement in an underwater vehicle was less than 5 nT after compensation, and the accuracy of geomagnetic measurement met the requirements of geomagnetic matching aided navigation.

Daily geomagnetic variations under variable IMF/solar conditions and their connection with underground conductivity changes in Japan

Fluctuations in Solar Wind (SW) and Interplanetary Magnetic Field (IMF) significantly affect the Geomagnetic Field (GF) measurements particularly during extreme space weather events. The current study investigates the variations of horizontal (H), vertical (Z) geomagnetic components under quiet and disturbed IMF and solar conditions as well as the effect of underground conductivity on the stationary geomagnetic measurements in Japan. Results of data analysis show that the response of the GF to IMF and solar parameters fluctuations is variable. The H- and Z-components were in good harmony with high visual correlation along a latitudinal profile across Japan during quiet times. On the other hand, during the disturbed times related to a Coronal Mass Ejection (CME) launched on 13 May 2005, the GF components varied with the disturbance of IMF and solar parameters. The H-components showed highly correlated variations with a significant reduction along the examined profile due to intensified ionospheric currents, while the Z-components recorded in the northern part of Japan showed abnormal daily variations pattern (positive daily variations) with an enhanced amplitude which is opposite to the normal behavior of daily variations recorded in the central and southern parts of Japan (negative daily variations). The observed enhanced and abnormal daily variation of Z-components in north Japan, which we consider a remarkable observation here, is possibly linked with underground conductivity anomaly in this region.

Predictability of Magnetic Field Reversals

Geomagnetic field measurements indicate that at present we may be on the brink of the Earth’s magnetic field reversal, potentially resulting in all the accompanying negative consequences for the mankind. Mathematical modelling is necessary in order to find precursors for reversals and excursions of the magnetic field. With this purpose in mind, following the Podvigina scenario for the emergence of the reversals, we have studied convective flows not far (in the parameter space) from their onset and the onset of magnetic field generation, and found a flow demonstrating reversals of polarity of some harmonics comprising the magnetic field. We discuss a simulated regime featuring patterns of behaviour that apparently indicate future reversals of certain harmonics of the magnetic field. It remains to be seen whether reversal precursors similar to the observed ones exist and might be applicable for the much more complex geomagnetic dynamo.

A novel magnetic calibration method based on an extended shaping filter

During maneuvering of high-speed aircraft, the eddy-current magnetic field has a significant impact on the real-time geomagnetic field measurement accuracy. However, it is difficult to estimate the eddy-current component directly when it is considered in the magnetic distortion model. In this paper, we proposed a geomagnetic field estimation method based on a shaping filter. Soft-iron, hard-iron and eddy-current field distortions were considered in the compensation system. In the estimation process, a higher-order shaping filter is designed to coincide the higher-order statistics of the alternative system with the input of the original system. Simulation results showed that our proposed method could accurately estimate the eddy-current field. Compared with methods that do not consider the eddy-current field, the root-mean-square error of the geomagnetic field could be reduced by more than 50%, thus significantly improving the accuracy of geomagnetic field measurement.

Uncertainty of Low‐Degree Space Gravimetry Observations: Surface Processes Versus Earth's Core Signal

AbstractSpace gravity measurements have been mainly used to study the temporal mass variations at the Earth's surface and within the mantle. Nevertheless, mass variations due to the Earth's core might be observable in the gravity field variations as measured by Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On satellites. Earth's core dynamical processes inferred from geomagnetic field measurements are characterized by large‐scale patterns associated with low spherical harmonic degrees of the potential fields. To study these processes, the use of large spatial and inter‐annual temporal filters is needed. To access gravity variations related to the Earth's core, surface effects must be corrected, including hydrological, oceanic or atmospheric loading (Newtonian attraction and mass redistribution). However, these corrections for surface processes add errors to the estimates of the residual gravity field variations enclosing deep Earth's signals. As our goal is to evaluate the possibility to detect signals of core origin embedded in the residual gravity field variations, a quantification of the uncertainty associated with gravity field products and geophysical models used to minimize the surface process signatures is necessary. Here, we estimate the dispersion for GRACE solutions as about 0.34 cm of equivalent water height (EWH) or 20% of the total signal. Uncertainty for hydrological models is as large as 0.89–2.10 cm of EWH. We provide estimates of Earth's core signals whose amplitudes are compared with GRACE gravity field residuals and uncertainties. The results presented here underline how challenging is to get new information about the dynamics of the Earth's core via high‐resolution, high‐accuracy gravity data.

Determining ULF Wave Contributions to Geomagnetically Induced Currents: The Important Role of Sampling Rate

AbstractPast studies found that large‐amplitude geomagnetically induced current (GIC) related to magnetospheric Ultra Low Frequency (ULF) waves tend to be associated with periods >120 s at magnetic latitudes >60°, with comparatively (a) smaller GIC amplitudes at lower latitudes and shorter wave periods and (b) fewer reports of waves associated with GIC at lower latitudes. ULF wave periods generally decrease with decreasing latitude; thus, we examine whether these trends might be due, in part, to the undersampling of ULF wave fields in commonly available measurements with 60 s sampling intervals. We use geomagnetic field (B), geoelectric field (E), and GIC measurements with 0.5–10 s sampling intervals during the 29–31 October 2003 geomagnetic storm to show that waves with periods <∼120 s were present during times with the largest amplitude E and GIC variations. These waves contributed to roughly half the maximum E and GIC values, including during times with the maximum GIC values reported over a 14‐year monitoring interval in New Zealand. The undersampling of wave periods <120 s in 60 s measurements can preclude identification of the cause of the GIC during some time intervals. These results indicate (a) ULF waves with periods ≤120 s are an important contributor to large amplitude GIC variations, (b) the use of 0.1–1.0 Hz sampling rates reveals their contributions to B, E, and GIC, and (c) these waves' contributions are likely strongest at magnetic latitudes <60° where ULF waves often have periods <120 s.

The decrease in diurnal oxygen production in Elodea under the influence of high geomagnetic variability: the role of light, temperature and atmospheric pressure

Epidemiological studies have indicated adverse effects of geomagnetic disturbance on human health, including increased mortality. There is evidence from plant and animal studies that help to elucidate this interaction. This study tests the hypothesis that geomagnetic disturbance affects living systems, by modifying the metabolic process of photosynthesis, in the natural environment.Continuous 24-h measurements of dissolved oxygen in flasks containing Holtfreiter’s solution and strands of healthy Elodea were recorded from May 1996, until September 1998, in an electromagnetically quiet, purpose built, garden shed environment, without mains electricity. Sensormeter recordings of oxygen, light, temperature and air pressure were uploaded weekly to a PC. The hourly total geomagnetic field measurements were obtained from the nearest observatory.Significant decrease in oxygen (diurnal volume of oxygen divided by plant mass and diurnal light), (O/WL), was found on days of high geomagnetic field variability throughout 11 recorded months of the year 1997. This result was independent of temperature and atmospheric pressure. No significant decrease in O/WL during high geomagnetic variability was found for the 7 months recorded in 1996. The 1996 and 1997 data both showed a significant decrease in the diurnal time lag between peak light and peak oxygen for diurnal high geomagnetic variability compared with low geomagnetic variability. Cross correlation analysis for 1997 and 1998 data showed a decrease in positive correlation of oxygen with light in high geomagnetic variability, compared with low geomagnetic variability, and increased positive correlation with the geomagnetic field instead. These experiments support a hypothesis of high geomagnetic field variability as a weak zeitgeber, and a metabolic depressant for photosynthetic oxygen production in plants.

Electrically tunable magnetic sensor for satellite-free global positioning

Navigation and positioning technologies play a key role in modern human activities. Currently, navigation devices are mostly dependent on the global navigation satellite systems, for example, the global positioning system (GPS). However, it is known that GPS signals can be jammed or spoofed or otherwise fail. As the need for GPS independent navigation increases in some practical application scenarios, novel navigation techniques based on the geomagnetic field have been developed. A main task of geomagnetic navigation is to obtain the amplitude and direction of the geomagnetic field accurately. Here, we introduce an alternative scheme for vectorial measurements of the local geomagnetic field for magnetic positioning based on the biological ferric sulfide cluster, which exists in the magnetoreceptor protein/cryptochrome complex in certain avian species. We find that by observing the number of peaks and the proportional rate of spectrum on resonance, both the direction and intensity of the magnetic field can be determined. Therefore, our findings may provide a fresh insight into magnetic field measurement and also suggest further guidelines for the design and operation of satellite-free navigation systems based on the electrically tunable inorganic biological molecules.

Signature of Tidal Sea Level in Geomagnetic Field Variations at Island Lampedusa (Italy) Observatory

In this work, we analyze the geomagnetic field measurements collected from 2017 to 2020 at the Italian observatories of Lampedusa and Duronia (an island and inland site, respectively) for investigating a possible signature of the tidal sea water level changes on the local magnetic variations. We obtain the following main results: (a) evidence of the geomagnetic power spectral peaks at the solar and lunar tidal main frequencies at both sites is found; (b) by using a robust fit procedure, we find that the geomagnetic field variations at Lampedusa are strongly influenced by the lunar tidal variations in the sea level, while at Duronia, the main effects on the geomagnetic field variations are associated with diurnal solar ionospheric tides; (c) a single-station induction arrows (SSIAs) investigation reveals different behaviors between Lampedusa and Duronia. Specifically, Lampedusa shows that the induction arrows in different frequency ranges point toward different directions with different amplitudes, probably related to the surrounding regions with different water depths, while Duronia shows a persistent coast effect, with the induction arrows pointing toward the Adriatic sea; and (d) a Superposed Epoch Analysis reveals, only for Lampedusa, a close relationship between SSIAs with a frequency of >2 mHz (<1.3 mHz) and the sea level variations driven by the astronomical O1 tide, indicating an amplitude intensification of ∼4×10−3 (∼5×10−3) and an azimuthal angle increment of ∼3∘ ( ∼9∘), in correspondence to a 1 cm sea level increase.

Power-law dependence of the wavelet spectrum of ground magnetic variations during magnetic storms

We show that time variations in the ring current and auroral electrojets in 2015, during which three major magnetic storms (MSs) occurred, are recorded in several specific ways by ground magnetometers. Specifically, we show that the time variations in magnetic field intensity have power-law wavelet spectra. The variations in ring current intensity are detected in geomagnetic field measurements of ground stations at magnetic mid-latitudes between λ=-50° and +50°. We confirmed the results of Balasis et al. (2006), who had shown that the Dst index wavelet spectrum follows a power law of the form f-β, where f is the frequency, and β is the exponent of the power law, by applying the same wavelet analysis to the SYM-H index version of the Dst index, and also to ground magnetic field measurements. Balasis et al. (2006) also showed that the critical exponent β of the power law, obtains values greater than 2 (or equivalently that the Hurst exponent H>0.5), shortly before the onset and during the main phase of the storms. Here, using wavelet transforms on the Earth’s magnetic field as measured at different magnetic latitudes (MLAT), we showed that at mid-geomagnetic latitudes, where the Earth’s magnetic field is determined mainly by the ring current, the resulting Hurst exponent is greater than 0.5 several hours before and during magnetic storms. Geomagnetic field variation at higher magnetic latitudes between λ=+50° and +73°, also show power-law wavelet spectra. However, here we find a more complex dependence with two power-law exponents. We interpret this double power law as the effect of both the ring current and the auroral electrojets. Finally, for polar latitudes, between λ=+73° and +85°, we find the same complex dependence with two power-law exponents. Our results show that the geomagnetic field at auroral latitudes has much lower power and very different wavelet spectra compared to the geomagnetic field at ranges of lower magnetic latitude. Our results show how wavelet-based measures of ground geomagnetic variations reflect the time evolution of several magnetospheric current systems.

Application of Magneto‐Impedance (MI) Sensor to Geomagnetic Field Measurements

AbstractThe magneto‐impedance (MI) effect was discovered about 30 years ago and a microsize magnetic sensor utilizing this effect has become commercially available. We make some modifications to the commercially available MI sensors to cover the dynamic range of the geomagnetic field. The total cost of three MI sensors for the two horizontal components and one vertical component including the modification is approximately one‐third of the standard price of triaxial fluxgate magnetometer sensors. For the period of 30 March to 27 April 2018, we conducted experimental observations of geomagnetic field variations with the MI sensor magnetometer (MIM) at the Mineyama observatory, which is located about 100 km northwest of Kyoto, Japan. Data obtained with the MIM are compared with those from the fluxgate magnetometer (FGM) that has been working at the observatory. Results show that the MIM can record geomagnetic field variations such as geomagnetic storm, solar quiet variations, low‐latitude positive bays, storm sudden commencement, and long‐period geomagnetic pulsations with a peak‐to‐peak amplitude of ≤1 nT that is also detected with the FGM. Power spectra of the geomagnetic field variations measured with the MIM and FGM are almost the same. It is found that the MIM has a larger temperature drift than the FGM. The present study reveals that the MIM is comparable to the FGM in measuring the geomagnetic field variations in a period from a few tens of seconds to a few hours and is useful for researches in upper atmospheric physics or space physics.

Direct Determination of Geomagnetic Baselines During Quiet Periods for Low‐ and Mid‐Latitude Observatories

AbstractThe geomagnetic field is composed of a variety of sources that act on a wide range of timescales and amplitudes. The separation of magnetic storm effects from quiet variations is needed to accurately quantify impacts of space weather events. The extraction of such quiet contributions within geomagnetic measurements is achieved by the determination of baselines, which, ideally, is done by a simple algorithm which captures quiet sources suitably well, while being applicable to an extensive network of magnetic observatories independent of the period of time. In this work, we apply signal filtering techniques on the horizontal components of geomagnetic field measurements from low‐ and mid‐latitude observatories to determine baselines. The variations within the baseline are investigated for magnetically quiet periods between 1991 and 2019, focusing on long‐term trends, seasonal and local time dependencies, and day‐to‐day variability. The analysis confirms that the contributing quiet sources include the secular variation and the solar quiet (Sq) current system. The non‐negligible day‐to‐day variability, that is typical for Sq in low‐ and mid‐latitudes, is embedded within the baseline. Thus, the filter approach extracts quiet magnetic field variations well. Comparisons with other baseline methods show good agreements. We conclude that the filter approach can be used to determine baselines automatically during magnetically quiet periods without the need of further apriori information and is applicable on a wide network of magnetic observatories. It marks the first step for deriving magnetic indices for (near) real‐time space weather applications.

Analysis of local geomagnetic index under the influence of equatorial electrojet (EEJ) at the equatorial Phuket geomagnetic station in Thailand

The local K-index is an important proxy to monitor geomagnetic disturbances due to the solar wind in space weather study. The diurnal variation of geomagnetic fields observed in the magnetic equatorial region is dominated by the equatorial electrojet (EEJ), and the variation of EEJ is directly related to the local ionospheric dynamics; therefore, in this work, the local K-index is generated by based on the geomagnetic field measurement at an equatorial geomagnetic station in Phuket, Thailand and the effects of EEJ on the computed local K-indices are analyzed. At each station, an L9 (the lower limit for K = 9) value is set to develop a conversion table between the magnetic range scales and K-indices, and that L9 value must be assigned based on the characterization of the geomagnetic variations at that station. In this work, suitable L9 values are determined by analyzing the distributions of the local K-index and the planetary geomagnetic index, Kp-index. According to the results in the present study, the L9 value of 500 nT can provide local K-indices that can classify the geomagnetic disturbances more correctly. The results show that 40% of the local K-index is consistent with the Kp-index, and about 45% of the local K indices are ±1 deviated from Kp-indices. It is found that using the suitable L9 value can partially control the EEJ’s dominance on K-index. Moreover, we investigated the seasonal and day-to-day variability of the diurnal variation of the geomagnetic fields from the Phuket station. Upon reviewing the data, the equatorial geomagnetic field variations were consistent with the planetary geomagnetic activity levels, and the day-to-day changes of the daytime field amplitudes were relatively high in the high solar activity year and moderate in the low solar activity year.

Adaptations to a geomagnetic field interpolation method in Southern Africa

Space weather and its impact on infrastructure presents a clear risk in the modern era, as evidenced by the adverse effects of geomagnetically induced currents (GICs) in power networks. To model GICs, ground-based geomagnetic field (B-field) measurements are critical and need to be available in the region of interest. A challenge globally lies in the sparse distribution of magnetometer arrays, which are seldom located near critical power network nodes. Interpolation of the geomagnetic field (B-field) is often needed, with the spherical elementary current system (SECS) approach developed for high-latitude regions favoured. We adapt this interpolation scheme to include low-cost variometers to interpolate dB/dt directly and increase interpolation accuracy. A further adaptation to the scheme is to physically represent the mid-latitude context where most power networks and pipelines lie. The driving current systems in these regions differ from their high-latitude counterparts. Using a physics-consistent mid-latitude version of SECS, we show why previous implementations in Southern Africa are incorrect but still result in useful interpolation. The scope of these adaptations not only has direct application to research in general, but also to utilities, where effective low-cost instrumentation can be used to improve GIC modelling accuracy.

Pressure-Gradient Current at High Latitude from Swarm Measurements

The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. Using geomagnetic field, plasma density and electron temperature measurements recorded on board ESA Swarm A satellite from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes characterized by well defined flow patterns, which can cause artifacts in the main field models. Our findings can be used to correct magnetic field measurements for diamagnetic current effect, to improve modern magnetic field models, as well as to understand the impact of ionospheric irregularities on ionospheric dynamics at small-scale sizes of a few tens of kilometers.

Forecasting GICs and Geoelectric Fields From Solar Wind Data Using LSTMs: Application in Austria

AbstractThe forecasting of local GIC effects has largely relied on the forecasting of dB/dt as a proxy and, to date, little attention has been paid to directly forecasting the geoelectric field or GICs themselves. We approach this problem with machine learning tools, specifically recurrent neural networks or LSTMs by taking solar wind observations as input and training the models to predict two different kinds of output: first, the geoelectric field components Ex and Ey; and second, the GICs in specific substations in Austria. The training is carried out on the geoelectric field and GICs modeled from 26 years of one‐minute geomagnetic field measurements, and results are compared to GIC measurements from recent years. The GICs are generally predicted better by an LSTM trained on values from a specific substation, but only a fraction of the largest GICs are correctly predicted. This model has a correlation with measurements of around 0.6, and a root‐mean‐square error of 0.7 A. The probability of detecting mild activity in GICs is around 50%, and 15% for larger GICs.

Katz Fractal Dimension of Geoelectric Field during Severe Geomagnetic Storms.

We are concerned with the time series resulting from the computed local horizontal geoelectric field, obtained with the aid of a 1-D layered Earth model based on local geomagnetic field measurements, for the full solar magnetic cycle of 1996–2019, covering the two consecutive solar activity cycles 23 and 24. To our best knowledge, for the first time, the roughness of severe geomagnetic storms is considered by using a monofractal time series analysis of the Earth electric field. We show that during severe geomagnetic storms the Katz fractal dimension of the geoelectric field grows rapidly.

Design of a suspended high-stability fluxgate sensor

To achieve long-term geomagnetic vector field measurements, high resolution, low noise, reliability, and great stability are required, relative to the recording instrument. In this paper, we report the design and production of a high-performance magnetometer based on the fluxgate effect. To avoid drift due to the tilt of the observation pillar, which is often the main cause of baseline drift, and leveling error due to the installation process, the developed sensor was fixed to a suspended platform for automatic horizontal leveling. A special gimbaled construction was used, which allowed automatic leveling of the vertical position of the z-axis within tilts of ±6° of arc. The performance of the proposed sensor was tested in a zero-magnetic-field device, and the results showed that the accuracy of the scale factor was 0.01%, the standard deviation of the residuals was 0.1723, and the noise was ⩽0.08 nT (Peak-Peak). At the time of this research, the developed instrument had been in continuous operation for >6 months in the Jinghai geomagnetic observatory. The monthly residual standard deviation maximum values of the D, H, and Z components were 0.68 nT, 0.58 nT, and 0.44 nT respectively, which were smaller than the requirements of the China Geomagnetic Network. Therefore, the observational data and the baseline values indicated that the prototype was stable and reliable. Additionally, owing to its integrated design, the prototype was easy to carry and set up, so it was very suitable for short-term earthquake tracking and the intensive monitoring of magnetic anomaly areas.

Tetrahedral satellite formation: Geomagnetic measurements exchange and interpolation

This note presents a study of a four-satellite tetrahedral formation to collect, process, and exchange multipoint measurements of geomagnetic field in a near-polar orbit. The study is conducted as a series of numerical experiments based on simulated spacecraft orbits and corresponding geomagnetic field models output. The four satellites are assumed to move in near-circular orbits specifically chosen to maintain the tetrahedron quality. The satellites exchange their simulated magnetometers readings and the collected multipoint measurements are processed on board of any of them thus creating an instantaneous interpolated map of the geomagnetic field in the interior of the tetrahedron. Interpolation is carried out with the use of Kriging algorithms, known in geostatistics for capturing spatial correlation of the data and taking into account statistical properties of the interpolated variables. We propose a concept of a servicing formation, and analyze interpolation accuracy for different formation sizes. It is then discussed how the processed multipoint measurements can be provided as a service to other nearby satellites. Finally, we show that using the existing COTS magnetometers it is possible to obtain real-time interpolation data, which are more precise at a given point and time than a conventional onboard magnetic field model, thus ensuring better attitude determination routines performance in the serviced spacecraft.