Geomagnetic Stations Research Articles

Analysis of coherence areas between conjugate stations affected by the South Atlantic Magnetic Anomaly

The South Atlantic Magnetic Anomaly (SAMA) is a region in the South Atlantic Ocean where the Earth's magnetic field is significantly weaker than in other parts of the world. This anomaly has been of interest to scientists and researchers studying the Earth's magnetic field. The SAMA can affect navigation systems and satellite operations, and it is an important area of study for understanding the dynamics of the Earth's magnetic field. This paper investigates the signal characteristics of conjugate stations influenced by the SAMA in a moderate geomagnetic storm through record analysis of geomagnetically conjugate stations interlinking both hemispheres. This study uses the horizontal magnetic components measured in the same time interval in two typical longitudes: the America-SAMA region and the Asia-Pacific one. This procedure allows us to do a comparative analysis between regions. Our procedure uses the data recorded simultaneously in four conjugate-station pairs to characterize the magnetic variability coherence domain surrounding conjugate stations. Here, we present and discuss the first maps of the SAMA region, which corresponds to the coherence area at low latitudes. Indeed, this coherence area concept refers to the edges (close-to-the-ground geometric area) around the conjugate point, where geophysical phenomena generally exhibit similar fluctuating behavior. The correlation coefficients technique was used to calculate those areas, using the H component of the geomagnetic field. Our main results indicate that the areas in the Asia-Pacific region are similar in size and shape, which characterize typical patterns. In the America-SAMA region, the coherence areas for the conjugate stations are not similar in shape and size. These differences between coherence areas could be due to the region's unique characteristics, i.e. it presents an enhanced ionospheric conductivity. Additionally, geomagnetic stations inside a large area of South America, involving the Santa Maria region, will present, in principle, magnetic fluctuations with similarity in the records.

Fast Fourier Transform (FFT) Application For Short-Term Earthquake Precursor Analysis Using Geomagnetic Data (Case Study of Kupang Geomagnetic Station, East Nusa Tenggara, Indonesia)

Abstract Earthquake (EQ) precursors have been identified from ULF geomagnetic enhancements related to a moderate EQ in Kupang, East Nusa Tenggara, Indonesia. Three components of geomagnetic data (X, Y, and Z) collected during January-June 2010 were analyzed. The EQ occurred on May 7, 2010, and its epicenter was 27.78 km from the KPG Geomagnetic Station. The magnitude and depth of the EQ were 5 and 11.3 km, respectively. This study investigated the energy of ULF geomagnetic signals in the frequency range of 0.03 to 0.04 Hz using SDR based on FFT. The results showed that the geomagnetic energy increased approximately three days before the EQ. Due to the significant magnitude and relative proximity of the EQ to the observation station, it can be concluded that the closer the geomagnetic station from the EQ source, the more likely it is to detect anomalies caused by the EQ. Despite the increase in geomagnetic energy, the Dst index which measures the global activity of the geomagnetic variation in low-latitude regions does not indicate any extraordinary global geomagnetic activity. This indicates that geomagnetic anomalies are most likely related to EQ events.

Identifying Ionospheric Small‐Scale Currents: A Spatial Correlation Study Using Closely‐Spaced Pairs of Ground Magnetometers

AbstractThe occurrence of small‐scale and intense ionospheric currents that can contribute to geomagnetically induced currents have recently been discovered. A difficulty in their characterization is that their signatures are often only observed at single widely spaced (typically 200–400 km) ground geomagnetic stations. These small‐scale structures motivate the examination of the maximum station separation required to fully characterize these small‐scale signatures. We analyze distributions of correlation coefficients between closely spaced mid‐latitude and auroral zone ground magnetometer stations spanning day to month long intervals to assess the separation distance at which geomagnetic signatures appear in only one station. Distributions were analyzed using periods that included low and high geomagnetic activity. We used data from pairs of magnetometer stations across North America within 200 km of each other, all of which were separated primarily latitudinally. Results show that while measurements remain largely similar up to separations of 200 km, large and frequent differences appear starting at around 130 km separation. Larger differences and lower correlations are observed during high geomagnetic activity, while low geomagnetic activity leads to frequent high correlation even past 200 km separation. Small but identifiable differences can appear in magnetometer data from stations as close as 35 km during high geomagnetic activity. We recommend future magnetometer array deployment in the auroral and sub‐auroral zone to have separations of 100–150 km. This enables the monitoring of large scale effects of geomagnetic storms, better temporal and spatial resolution of substorms, and observations of small‐scale current signatures.

Research on Subsurface Electrical Structure Based on a Dense Geomagnetic Array in Southern Yunnan.

The electrical resistivity of subsurface rocks is one of the important sensitive parameters characterizing the internal physics of the Earth. Currently, research on subsurface electrical structures using geomagnetic sounding methods primarily focuses on two approaches: the first is based on observations from a few geomagnetic stations, which have low spatial resolution and cannot effectively describe the distribution of anomalies; the second is based on mobile geomagnetic observations, which have low temporal resolution and cannot promptly reflect anomalies. To address these issues, this study deployed a dense geomagnetic array for long-term observation in the southern segment of the Xiaojiang Fault Zone in the Yuxi area of southern Yunnan. This setup aims to promptly capture seismic magnetic anomalies, providing more data support and fundamental information for short-term earthquake prediction. Based on the long-term observation data from the dense array, the study of the subsurface electrical structure is carried out. The results indicate that during the observation period, which was seismically quiet, the regional subsurface electrical structure remained stable. A large-scale subsurface low-resistivity body was observed in the region, and the electrical structures at the two ends of the southern segment of the Xiaojiang Fault Zone were found to be completely different.

Global mantle conductivity imaging using 3-D geomagnetic depth sounding with real earth surface conductivity constraint

The water content in the Earth's interior is of great significance for material circulation and the dynamic evolution of the planet. The water content in mantle minerals significantly affects their conductivities. By measuring the variations in conductivity within the Earth, we can infer the water content in the mantle and study the movement and processes of materials within the Earth. The geomagnetic depth sounding is a widely used method for imaging the mantle conductivity as it has large sounding depth. However, the ocean induction effects can seriously impact geomagnetic data that can't be well corrected using conventional methods. Here, we present a novel three-dimensional inversion method for geomagnetic depth sounding to overcome the ocean induction effects by directly adopt the real earth surface conductivity into the inverse model. In this method, the unstructured tetrahedral grids are used to represent the model in multi-scale and the vector finite-element method is adopted to accurately compute the geomagnetic responses. The synthetic model tests show that the earth surface conductivity has serious effect on the inversion results, but it can be well suppressed by directly modeling it in the inverse model. We further invert the data from 128 geomagnetic stations around the world and obtain a more accurate new model of global mantle conductivity.

Anomalous geomagnetic activities before the Karangasem - Bali, Indonesia earthquakes on December 13, 2022

Abstract A series of earthquakes occurred on Bali Island, Indonesia, on December 13, 2022. The United States Geological Survey (USGS) recorded four shallow earthquakes around Karangasem - Bali with magnitude (M) > 4 at that time. The largest was the M 5.2 earthquake, which occurred at 10:38:21.67 UTC with 10 km of depth. We analyzed the anomalous geomagnetic activities during these earthquakes by utilizing the geomagnetic data from the Bayan geomagnetic station located on Lombok Island, less than 100 km from the earthquake’s epicenters. We conducted the polarization ratio analysis by applying the Fast Fourier Transform (FFT) on the five hours of night geomagnetic data (16:00 - 21:00 UTC). The spectral power values of X, Y, and Z geomagnetic data at frequencies 0.04 - 0.06 Hz were calculated and compared with the disturbance storm time (Dst) to find their correlation. The Pearson correlation analysis indicates that they are significantly uncorrelated. Finally, we calculated the Sz/Sg to analyze the geomagnetic anomalies and found them 6 - 11 days before the earthquakes at frequencies 0.04 - 0.06 Hz. We consider that these anomalies are possibly caused by the M 5.2 earthquake since it had the highest magnitude, Es, and Kls values.

The Geomagnetic Stations Network of Mexico (REGMEX): The initial steps towards a real-time monitoring of geomagnetic activity in Mexico

In this paper we present our first steps towards the monitoring, in near real-time, of the geomagnetic activity in the continental territory of Mexico by the Space Weather National Laboratory (LANCE) via the Geomagnetic Stations Network of Mexico (REGMEX). REGMEX aims to monitor the geomagnetic field at five different sites in real-time. The collected data will be processed to promptly calculate and publish Mexico’s regional geomagnetic-activity indices (ΔH and K). Currently, Mexico lacks facilities to simultaneously monitor geomagnetic activity in real-time across its territory. This work shows the way in which LANCE endeavors to solve the lack of such geomagnetic data by presenting the REGMEX’s development plan and its current development status. In addition, we show geomagnetic storms as registered by our available regional geomagnetic indices and compare those records with their planetary counterparts.

Assessing the Solar Activity and Geomagnetic Disturbance during Minimum Phase of Solar Cycle 24 across the Globe.

Understanding solar activity and its implications on the Earth’s environment has become necessary. Most importantly, events that characterized the minimum phase of solar cycle 24 (2019) and geomagnetic disturbance experienced during this period calls for an assessment. To assess this, the study has therefore used INTERMAGNET data from geomagnetic stations across the globe during the solar minimum year of solar cycle 24. A total of nine geomagnetic stations data of five disturbed days in a month were used, and were averaged in a minute interval for year 2019. The stations were selected with reference to their geomagnetic locations (latitudes and longitudes) as well as analyzing their horizontal magnetic field (H-Component) from the X and Y component of the geomagnetic field to reveal the variance in the global pattern of solar variations. The seasonal variations were studied across various latitudes and longitudes to understand the impact of solar activities on the earth surface as a result of geomagnetic field disturbance on Earth’s magnetosphere at the end of cycle 24 (2019). The results of stations revealed ABK and DRV with 350nT and 150nT of H component respectively which are the highest while other stations have 60nT below. This study shows that low geomagnetic disturbance was witnessed during the end of the cycle due to the minimum solar activity which was as a result of low number of sunspot during this period.

Robust Estimation of C-response of Geomagnetic Data

C-response from geomagnetic data contain information on the geoelectric structure of the deep Earth, providing an effective way to study the deep Earth structure. How to obtain high accuracy C-response from geomagnetic data is an important step in the subsequent study of the deep Earth structure, and has important practical significance for the study of the deep geoelectric structure. In order to obtain stable C-response estimates and suppress the influence of noise, this paper proposes to use the Robust C-response estimation method and apply it to the C-response estimation of actual geomagnetic station data, and the results of this estimation are most comparatively analyzed with two other traditional C-response estimations to reflect the correctness of the Robust C-response estimation method. The implementation of this method provides a methodological basis for the subsequent processing and interpretation of geomagnetic station data.

Horizontal Magnetic Anomaly Accompanying the Co-Seismic Earthquake Light of the M7.3 Fukushima Earthquake of 16 March 2022: Phenomenon and Mechanism

A horizontal magnetic disturbance accompanying the co-seismic earthquake light (EQL) of the M7.3 Fukushima earthquake of 16 March 2022 was detected by a fluxgate magnetometer installed at the KAK station, which is 270 km south of the EQL and 210 km west of the epicenter. The instantaneous change of the declination component of the geomagnetic field reached about 1.7″, much exceeding the threshold of three-fold error (0.72″). Considering the direction information of the geomagnetic data, the horizontal magnetic disturbance vector was further analyzed, which manifested the normal of the horizontal magnetic disturbance vector passing through the position of the EQL. Combined with the experimental results of pressure-simulated rock current (PSRC), the mechanism of the EQL and the geomagnetic anomaly was proposed to interpret the spatiotemporal correlation between the EQL and the horizontal magnetic disturbance vector, which should be a manifest of the induced magnetic horizontal vector (IMHV), attributed to the upward seismic PSRC. Different from previous precursor studies on geomagnetic disturbance on the power spectrum, vertical component, or polarization, this paper focuses on the direction information of the horizontal magnetic disturbance vector, which could be further applied to locate potential seismogenic zones based on the IMHVs observed by multiple geomagnetic stations.

Ionospheric Currents in the Equatorial and Low Latitudes of Africa

The magnetometer data obtained for 2008 from geomagnetic stations installed across Africa by magnetic data acquisition set (MAGDAS) have been used to study the ionospheric Sq current system in the equatorial and lowlatitudes of Africa. The aim of this work is to separate the quiet-day feld variations obtained in the equatorial and low latitude regions of Africa into their external and internal feld contributions and then to use the paired external and internal coeffcients of the SHAto determine the source current and induced currents. The method used involved a spherical harmonic analysis (SHA). This was applied in the separation of the internal and external field/current contribution to the Sq variations. The result shows that the variation in the currents is seen to be a dawn-to-dusk phenomenon with the variation in the external currents different from that of the internal currents both in amplitude and in phase. Furthermore, the seasonal variation in the external current maximizes during the March equinox and minimizes during the December solstice. The maximum current observed in AAB and ILR is due to the Equatorial Electrojet Current present in the AAB and ILR stations. Seasonal variation was observed in the geomagnetic component variations as well as in the currents. This is attributed to the position of the sun with respect to the earth at different months of the year. The equinoctial maximum is observed in external current intensity which occurred mostly during the March Equinox.

A New Installation for Geomagnetic Field Monitoring at Talos Dome, a Remote Antarctic Site Away from Permanent Observatories

An automatic geomagnetic station for monitoring the Earth’s magnetic field variations was installed in December 2020 at Talos Dome, a remote site on the Antarctic Plateau, about 300 km away from the permanent geomagnetic observatory at Mario Zucchelli Station (MZS). Designed and assembled at the laboratory of electronics of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Rome, this autonomous station is formed by a vector magnetometer specifically manufactured by Lviv Institute (Ukraine) for very low temperatures and a low-power system supplied by batteries charged by a wind generator and solar panel. Data, sampled at 1 Hz, are locally stored and can be downloaded once a year during the Antarctic summer expeditions. The goal was to integrate observatory data for better monitoring the geomagnetic field from an uncovered Antarctic area. In fact, it is well known that the distribution of geomagnetic observatories strongly favors the northern hemisphere, and each new instrumental installation in Antarctica should be considered as a useful attempt to balance the geomagnetic monitoring in the two hemispheres. The achieved goal was to obtain a long data series, keeping the station working even during the austral winter when the temperature can reach −60 °C; we recorded almost 11 months of data in one year and the station is still operating. Data from the new station, jointly with data from permanent observatories, improve the analysis of the magnetospheric dynamics and the ionosphere–magnetosphere coupling. Talos Dome, together with the Italian geomagnetic observatory at Mario Zucchelli Station and New Zealand geomagnetic observatory at Scott Base, constitutes a network along the 80°S geomagnetic parallel, which is interesting for studying the longitudinal propagation of geomagnetic signals of external origin. In this work we present the characteristics of the station and of the data it provides, with the aim of them for analysis in the framework of space weather.

Responses of Water Temperature and Level to Large Earthquakes in Tibet

Well water levels can reflect the stress placed on a confined subsurface aquifer system in a similar manner to a strain meter. Based on observations of the geophysical field in Lhasa combined with digital data recorded at an underground fluid well at the Lhasa geomagnetic station in recent years, we comprehensively analyzed the characteristics of co-seismic changes caused by 14 different-magnitude M ≥ 5 earthquakes recorded in the well. The results show that (1) the co-seismic changes in water temperature and water level are different; the water level exhibits oscillation-type changes, while the water temperature variations indicate first heating and subsequent recovery. (2) The co-seismic changes are related to the epicentral distance, magnitude and focal depth of the earthquake. The closer the epicenter is to the well, the earlier the co-seismic responses occur, but the time interval between the co-seismic changes in the water level and temperature differs. (3) The co-seismic ratio of the water temperature is higher than that of the water level; this may be related to faulty water level instrumentation or segmented records.

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.

Nonlinear time series analysis of ionospheric electric current disturbance associated with geomagnetic storm

The wavelet power spectrum and nonlinear dynamics time series techniques were used to examine the ionospheric electric current disturbance (Diono) during the geomagnetic storms of 9–11 November 2004 and 14–16 May 2005. These storms were characterized by high solar wind speed from coronal mass ejections (CMEs). The time series of the solar wind parameters (interplanetary magnetic field, IMF Bz and solar wind speed, Vx) and geomagnetic indices (Symmetric disturbance field, SYM-H, eastward electrojet, AU and westward electrojet AL), were used to monitor solar wind conditions and the geomagnetic perturbation, respectively. The horizontal component of the geomagnetic field obtained from six ground-based magnetometer stations was also analyzed. The high latitudes stations (ESK, NUR, LER and SOD) show higher energy wavelet coefficient of Diono with high frequencies, due to the existence of ionospheric currents at high latitudes during geomagnetic storm. The mid and low latitude stations (HER and AAE) display low energy wavelet coefficient with low frequency. The low latitude geomagnetic stations display high values of Lyapunov exponent (LE) during 9–11 November 2004 and 14–16 May 2005 of the geomagnetic storm. The low values of Lyapunov exponent might be as result of the internal dynamics restructuring during geomagnetic storm. The electrodynamics of the magnetosphere-ionosphere due to solar wind influenced the chaotic signature of Diono. The solar wind is a stochastic driver which contributes in the generation of geomagnetic disturbance in the Earth’s magnetosphere due to CMEs that generates the geomagnetic storms.

NEW AND UPDATED GEOMAGNETIC REPEAT STATIONS IN THE REPUBLIC OF KOSOVO

Each country is good to have their own geomagnetic repeat stations for monitoring and defining the geomagnetic anomaly field. The paper present and define the network of geomagnetic stations in the Republic of Kosovo. A network of 10 geomagnetic stations has been define on the territory of the Republic and on the basis of the performed observations and measurements that were conducted during the SFRY, a new and updated network for monitoring the geomagnetic field in the Republic of Kosovo is defined. The researches for selection of locations for geomagnetic stations according to INTERMAGNET standards are presented.

Analysis of Ionospheric and Geomagnetic Response to the 2020 Patagonian Solar Eclipse

Total solar eclipses are unique opportunities to study how the ionospheric and external geomagnetic field responds to fast changes in the ionizing flux as the moon’s shadow travels through its path over the ionosphere at an average speed of 3,000 km/h. In this contribution, we describe our observing campaign in which we set up GNSS and geomagnetic stations at the city of Valcheta, Río Negro, Argentina (which was located right under the path of totality). We also describe the results obtained from the analysis of the combination of on-site data together with publicly available observations from geodetic and geomagnetic observatories. The large span in latitude of our data allowed us to analyze the different magnitudes of the drop in vertical total electron content (ΔVTEC) with varying occultation percentages. We found an expected reduction in this drop as we move away from totality path but we also detected a new increment in ΔVTEC as we got closer to Earth’s Magnetic Equator. We also compared our observations of the geomagnetic field variations with predictions that were based on the Ashour-Chapman model and we find an overall good agreement, although a ≈20 min delay with the eclipse maximum is evident beyond observing uncertainties. This suggests the presence of processes that delay the response of the lower ionosphere to the loss of the photoionization flux.

Search for dark-photon dark matter in the SuperMAG geomagnetic field dataset

In our recent companion paper [arXiv:2106.00022], we pointed out a novel signature of ultralight kinetically mixed dark-photon dark matter. This signature is a quasi-monochromatic, time-oscillating terrestrial magnetic field that takes a particular pattern over the surface of the Earth. In this work, we present a search for this signal in existing, unshielded magnetometer data recorded by geographically dispersed, geomagnetic stations. The dataset comes from the SuperMAG Collaboration and consists of measurements taken with one-minute cadence since 1970, with $\mathcal{O}(500)$ stations contributing in all. We aggregate the magnetic field measurements from all stations by projecting them onto a small set of global vector spherical harmonics (VSH) that capture the expected vectorial pattern of the signal at each station. Within each dark-photon coherence time, we use a data-driven technique to estimate the broadband background noise in the data, and search for excess narrowband power in this set of VSH components; we stack the searches in distinct coherence times incoherently. Following a Bayesian analysis approach that allows us to account for the stochastic nature of the dark-photon dark-matter field, we set exclusion bounds on the kinetic mixing parameter in the dark-photon dark-matter mass range $2\times10^{-18}\,\text{eV} \lesssim m_{A'} \lesssim 7\times10^{-17}\,\text{eV}$ (corresponding to frequencies $6\times 10^{-4}\,\text{Hz}\lesssim f_{A'} \lesssim 2\times 10^{-2}\,\text{Hz}$). These limits are complementary to various existing astrophysical constraints. Although our main analysis also identifies a number of candidate signals in the SuperMAG dataset, these appear to either fail or be in tension with various additional robustness checks we apply to those candidates. We report no robust and significant evidence for a dark-photon dark-matter signal in the SuperMAG dataset.

Applying Wavelet Analysis to Assess the Ultra Low Frequency (ULF) Geomagnetic Anomalies prior to the M6.1 Banten Earthquake (2018)

The M6.1 Banten earthquake (EQ) occurred on January 23, 2018. The EQ epicenter was in Lebak Regency, Banten. The epicenter distance from the ULF geomagnetic station installed in Banten Province is about 100 km. Applying wavelet analysis on the geomagnetic time series data, we assess the ultra-low frequency (ULF) geomagnetic anomaly related to the M6.1 Banten EQ. We focused on the frequency of 0.02 Hz for the analysis of the spectral density ratio based on wavelet. We applied the Morlet wavelet as the mother wavelet in this study. The spectral density ratio analysis based on the Morlet wavelet presents the existence of the ULF geomagnetic anomalies prior to the M6.1 Banten EQ. The global geomagnetic index, Dst, did not show any peculiarity when the anomalies prior to the EQ exist. Then, we concluded that the anomaly is possibly related to the Banten EQ.

Prediction of Equatorial Electrojet Based on the Neural Network during Quiet Time

In this study, BP neural network technology was used to predict the variations of Equatorial Electrojet (EEJ) of Indian sector, Peruvian sector and CHAMP satellite during the magnetic quiet pe-riod after 2008. The neural network training data is the corresponding observation data of EEJ during the period of magnetic quiet from 2000 to 2007. The input parameters are day of year, local time, solar zenith angle, solar activity index (<italic>F</italic>_10.7), lunar age and satellite geographic longitude, and the output parameters are EEJ. The EEJ prediction results are statistically analyzed and compared with the observation results. Results show that: BP neural network has good ability in predicting the variations of EEJ in the event, and the prediction results can reflect the important distribution characteristics of EEJ; there is very good correlation between the predicted values and the observed values of EEJ, and the correlation coefficient between the observed values and the predicted values of geomagnetic sta-tions can reach over 85%. In addition, the prediction results of BP neural network model are compared with those of Yamazakis empirical model, and the performance of BP neural network is equivalent with Yamazakis empirical model. The results show that BP neural network has excellent performance in predicting EEJ variations during quiet period, and has a good application prospect.