Hasil untuk "Geomagnetism"

C. Finlay, S. Maus, C. Beggan et al.

Ipsita Katual, Gopi K. Seemala, Chinmaya Nayak et al.

This study reports an event-specific longitudinal asymmetry of ionospheric irregularities during 23-24 April 2023 geomagnetic storm (SYM-H: −233 nT), utilizing multi-instrument observations (ground-based GNSS and magnetometer along with space-borne Swarm and GOLD satellites). The rate of change of total electron content index (ROTI) is used as a proxy for ionospheric irregularities. Irregularities were largely absent over most western longitudes, except over the Western African sector, where they persisted from 22 to 26 April. On 24 April, these were restricted to 90 °–70 °W during post-midnight hours. On the contrary, over eastern longitudes, irregularities were observed on all days except 24 April. Electron density depletions near ∼12 °W and ∼35 °W reached beyond ∼40 °N and 30 °S Glat on 23 April. Persistence of irregularities observed at GNSS stations YKRO, ACRG, and NKLG over the African longitude sector suggests a decoupling from storm-time magnetospheric electric fields, however suggests dominance of local-time control, background electrodynamics, or trans-equatorial winds, which is relatively a rare observation and strengthens the regional resilience of EPB generation mechanisms. By applying a moving average filter to the magnetic H-component, contributions of prompt penetration (DP2) and disturbance dynamo (Ddyn) currents are separated, with peak activity during southward IMF Bz. Simultaneous DP2 across different local time sectors and anti-Sq patterns illustrate the roles of storm time ionospheric currents. There is a clear sector-dependent phase reversal (main vs. recovery phase) within the storm, highlighting the roles of storm-time drivers, and storm phase alone cannot predict irregularities occurrence without longitude context.

Sidorenko Klim, Vasenina Alena

This paper presents the results of a study on the behavior of parameters of the ionospheric F2 layer, such as the critical frequency (f₀F2) and the peak height of the layer (hₘF2), under geomagnetic storms of varying intensities. The study is based on vertical sounding measurements from the DIDBase database and the Dst index calculated by the World Data Center for Geomagnetism. We examine a methodology for identifying the presence of a geomagnetic storm using Dst-index time series. The main patterns of f₀F2 and hₘF2 variations for different geographic latitudes, seasons, and storm intensities are identified and analyzed. The obtained results can be useful for forecasting and modeling ionospheric conditions, which is of great importance for various applications, including satellite communications, global positioning systems, and shortwave radio communications.

بهرام آصفی, قاسم عزیزی, مصطفی کریمی et al.

جت استریم‌ یکی از کلیدی‌ترین اجزای گردش جو بوده و نقش بسیار مهمی در سامانه‌های جوی و شرایط اقلیمی دارد. در این مطالعه با استفاده از داده‌‌های بازتحلیل روزانه باد NCEP/NCAR (1985 تا 2015) در تراز 250 هکتوپاسکال و تحلیل خوشه‌ای سلسه‌مراتبی، آرایش روزانه الگوهای جریان جت در محدوده‌ای از غرب اقیانوس اطلس شمالی تا غرب آسیا استخراج شد. همچنین با هدف شناسایی محدوده عمل، فراوانی و انحراف‌معیار جت در مقیاس ماهانه محاسبه شد. نتایج نشان داد که فراوانی و پراکنش مکانی جریان جت در دوره سرد سال بیش از دوره گرم بوده که می‌تواند بیانگر حوزه عمل متغییر و رخداد بیشتر جت در دوره سرد سال باشد. نتیجه تحلیل خوشه‌ای استخراج 9 خوشه مشخص از آرایش زمانی-مکانی جت بود. بیشترین فراوانی متعلق به خوشه 6 (الگوی تابستانه) و نمایانگر ثبات نسبتاً بالای جت با استقرار جت جنب‌حاره‌ای در شمالی‌ترین موقعیت خود برروی دریای خزر در دوره گرم سال است. خوشه‌های 2، 4، 8 و 9 که با دو جریان جت قطبی برروی اقیانوس اطلس و اروپا و جنب‌حاره برروی شمال افریقا و جنوب غرب آسیا مشخص شده، نمایانگر الگوی رخداد دوره سرد سال با تنوع بالا می‌باشند. قوی‌ترین جت‌ها در ماه‌های انتهای تابستان و زمستان دیده می‌شوند. افزایش در فراوانی خوشه کم‌تکرار ۳ (الگوی زمستانی جت قطبی قوی و جنوبی‌تر) و روند کاهشی خوشه‌های ۱ و ۸ (الگوهای پاییزه و زمستانه)، می‌تواند حاکی از تغییر آرایش جت استریم‌ها و رژیم‌های گردش جوی منطقه باشد. این تغییرات می‌تواند افزایش بی‌هنجاری‌های دمایی و بارشی سال‌های اخیر در منطقه را توجیه کند.

Ilya Firsov, Dmitry Kudin, Anatoly Soloviev et al.

Abstract We present candidate models for the 14th generation of the International Geomagnetic Reference Field (IGRF-14), specifically the Definitive Geomagnetic Reference Field (DGRF) for epoch 2020.0 and the IGRF for epoch 2025.0. These models were developed using high-quality magnetic measurements from the European Space Agency’s Swarm satellite mission, including data from three low-Earth orbiting satellites equipped with Absolute Scalar Magnetometers and Vector Field Magnetometers. These models are first GC RAS candidates in the IGRF series, where we aim on methodological clarity and incremental innovation, and are part of the CAMPUS project, which is devoted to the construction of a series of Earth’s magnetic field models. Our methodology employs rigorous data selection criteria to minimize contamination from external sources and with strict scalar-vector consistency constraints. The internal magnetic field is parameterized using spherical harmonic functions up to degree 13, with coefficients determined through a two-stage inversion process involving linear inversion of vector measurements followed by nonlinear refinement including absolute scalar intensity data. For the DGRF 2020 model, we utilized data collected between January 2019 and December 2020, while the IGRF 2025 model incorporates measurements from January 2023 to September 2024. Comparison between the models indicates changes in field structure over the 5-year interval, particularly in the South Atlantic Anomaly (SAA) region. These candidate models effectively capture the main features of Earth’s core-generated magnetic field and are consistent with long-term trends observed in previous IGRF generations, contributing to the collective scientific effort to maintain accurate descriptions of Earth’s magnetic field. Graphical Abstract

M. Ankita, S. Tulasi Ram, T. Yokoyama et al.

Abstract Satellite Traces (STs) are the important ionogram signatures for the presence of upwellings in the bottom‐side ionosphere, which provide the necessary seed perturbation for the development of equatorial plasma bubbles (EPBs). In this study, a virtual ionosonde experiment is simulated to investigate the various ST signatures under the presence of shallow, deep, overhead, and off‐centered upwellings in the bottom‐side ionosphere. It is shown that STs occur at higher and lower virtual heights than the main ionogram trace for the off‐centered and overhead upwellings, respectively. The height separation between the main trace and STs increases with the deepening of overhead upwellings. Further, a proof‐of‐concept is demonstrated that multiple STs from ionograms can be used to reconstruct the spatial structure of bottom‐side upwellings, if the precise Angle‐of‐Arrival information can be resolved from the wide beam Ionosonde systems, and can have potential applications in predicting the occurrence of EPBs.

Francesco Antonelli, Rodoilton Stevanato, Angela Rodizes et al.

The gold exploration in the Castro Basin, Brazil, has been hampered by complex geology, disseminated low-grade ore, and the subsurface nature of quartz-adularia veins. To address these challenges, this study applied airborne geophysical techniques (gamma-ray spectrometry and magnetometry) to identify hydrothermal alteration zones and related structures. Radiometric parameters and magnetic gradient variations were analyzed to correlate with gold occurrences. Results indicated a strong association between potassium enrichment and magnetic lineaments, which was confirmed by geochemical samples. Based on these results, the Torre Target was selected for ground geophysical surveys. Electrical resistivity, induced polarization and magnetometry data were collected and integrated with digital elevation models. Geoelectrical sections and maps delineated the main ore body characterized by high chargeability anomalies associated with argillic alteration and disseminated sulfides. Resistivity data highlighted potential vertical contacts and fault structures indicative of an epithermal system. Magnetic techniques identified areas of magnetite concentrations within breccias and rhyolite, suggesting a connection to the mineralization events. In addition, magnetic data helped differentiate chargeability anomalies associated with the ore body from those associated with residual soil from diabase dikes. Results were validated by drilling, confirming the accuracy of the targets identified. This study demonstrates the effectiveness of geophysical techniques for the exploration of challenging gold deposits in the Castro Basin.

S. Sathishkumar, S. Sridharan, K. Krishnapriya et al.

Upper mesospheric wind data acquired by the medium frequency radar at Kolhapur (16.7oN, 74.2oE) and Modern–Era Retrospective analysis for Research and Application version 2 (MERRA-2) temperature and wind reanalysis datasets are used to investigate the dynamical response of the low-latitude middle atmosphere to the sudden stratospheric warming (SSW) events that occurred during the 2017–18 and 2018–19 winters. When the amplitude of the high-latitude stratospheric planetary wave (PW) of zonal wavenumber one reduces considerably with the onset of the SSW event, the low-latitude mesospheric PW over Kolhapur also shows a considerable reduction in the PW activity. It is noteworthy that the upper mesospheric winds are eastward for approximately 3 weeks after the onset of SSW. The reduced PW activity is associated with the enhanced gravity wave activity in the meridional wind during the SSW 2018–19 event. The plane of propagation of gravity waves obtained from the perturbation ellipse method suggests that their predominant plane of propagation is in the north–south direction. The persistence of the eastward winds is suggested to be due to the interaction of the northward propagating gravity waves with the mean flow, leading to the eastward acceleration due to the Coriolis force.

Mick Emil Kolster, Mark David Wigh, Eduardo Lima Simões da Silva et al.

Using Uncrewed Aerial vehicles (UAVs) to rapidly scan areas for potential unexploded ordnance (UXO) can provide an efficiency increase while minimizing detonation risks. We present a complete overview of how such mappings can be performed using scalar magnetometers, including initial sensor testing, time stamping validation, data positioning, noise removal, and source model inversion. A test survey was performed across disarmed UXO targets, during which three scalar magnetometers were towed in an airframe (“bird”) 10 m below a small (<25 kg) high speed (∼10 m/s) UAV to avoid magnetic disturbances from the UAV itself. Data were collected across ∼58 min of flight, with each sensor traversing ∼31.7 km to acquire dense data coverage across a 600 m × 100 m area. By using three individual magnetometers in the bird, UXO detection results across single-sensor data and several different multi-sensor configurations can be compared. The data obtained exhibited low apparent noise floors (on the order of tens of picoTesla) and retained a precision that enabled targeted modelling and removal of high-frequency noise with amplitudes of ±5 picoTesla. All of the different gradiometer configurations tested enabled recovery of most targets (including all major targets), although the horizontal configuration performed significantly worse in comparison.

K. K. Ajith, S. Tulasi Ram, GuoZhu Li et al.

The occurrence of midnight Equatorial Plasma Bubbles (EPBs) during the June solstice period of the ascending phase of solar cycle 24, from 2010 to 2014, was studied using data from the 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia. The analysis shows that the occurrence of midnight hour EPBs was at its maximum during the low solar activity year 2010 and monotonically decreased thereafter with increasing solar activity. Details of the dependence of midnight hour EPB occurrence on solar activity were investigated using SAMI2 model simulation with a realistic input of E × B drift velocity data obtained from the CINDI-IVM onboard the C/NOFS satellite. Results obtained from term-by-term analysis of the flux tube integrated linear growth rate of RT instability indicate that the formation of a high flux tube electron content height gradient (steep vertical gradient) region at higher altitudes, due to the elevated F layer, is the key factor enhancing the growth rate of RT instability during low solar activity June solstices. Other factors are discussed in light of the relatively weak westward zonal electric field in the presence of the equatorward neutral wind and north-to-south transequatorial wind around the midnight hours of low solar activity June solstices. Also discussed are the initial seeding of RT instability by MSTIDs and how the threshold height required for EPB development varies with solar activity.

Fuyang Tian, Jun Wang, Benhai Xiong et al.

The behaviors of dairy cows, such as feeding, ruminating, running, resting (standing, lying), head-shaking, drinking, and walking, can indicate their health status. In this study, a multi-sensor was used to collect data of cow&#x2019;s multi-behaviors for research on behavior recognition. Firstly, a collar style data acquisition system equipped with geomagnetic and acceleration sensors to collect the behavioral data of dairy cows during their daily activities was designed. Secondly, the dairy cow behavioral recognition fusion model based on K-Nearest-Neighbors (KNN) and Random Forest (RF) models were used for behavior classification. To verify the accuracy of the fusion model, the algorithms of KNN, RF, Gradient Boosting Decision Tree (GBDT), Support Vector Machine (SVM), and Learning Vector Quantization (LVQ) were introduced for comparative recognition experiments with different algorithms. The KNN-RF fusion model had the highest average recognition accuracy of 98.51&#x0025;, followed by the KNN model with an average recognition accuracy of 95.37&#x0025;, and the LVQ model had the lowest average recognition accuracy of 80.81&#x0025;. For the recognition and verification of each behavior, the KNN-RF fusion model had the most obvious improvement in the recognition of dairy cow feeding behavior, with a recognition accuracy of 99.34&#x0025;, followed by the KNN model with a recognition accuracy of 95.07&#x0025;. All six models had the lowest recognition accuracy for cow head-shaking behavior: a recognition accuracy of 89.11&#x0025; with the KNN-RF model followed by the RF model with a recognition accuracy of 85.14&#x0025;. The system can quickly and continuously collect cow behavior information, accurately recognize individual behaviors, and provide a scientific basis for the optimal design and efficient management of digital facilities and equipment for dairy cows.

B. J. Jackel, C. Unick, F. Creutzberg et al.

Observations of astronomical sources provide information that can significantly enhance the utility of auroral data for scientific studies. This report presents results obtained by using Jupiter for field cross calibration of four multispectral auroral meridian scanning photometers during the 2011–2015 Northern Hemisphere winters. Seasonal average optical field-of-view and local orientation estimates are obtained with uncertainties of 0.01 and 0.1°, respectively. Estimates of absolute sensitivity are repeatable to roughly 5 % from one month to the next, while the relative response between different wavelength channels is stable to better than 1 %. Astronomical field calibrations and darkroom calibration differences are on the order of 10 %. Atmospheric variability is the primary source of uncertainty; this may be reduced with complementary data from co-located instruments.

Viljanen Ari, Myllys Minna, Nevanlinna Heikki

We analyse geomagnetic recordings at four subauroral and midlatitude Russian observatories in 1850–1862. The data consist of spot readings made once in hour of the north and east components of the magnetic field. We use the hourly change of the horizontal field vector as the measure of activity. We compare these values to data from modern observatories at corresponding magnetic latitudes (Nurmijärvi, Finland, magnetic latitude ~57 N; Tartu, Estonia, ~54.5 N; Dourbes, Belgium, ~46 N) by reducing their data to the 1-h format. The largest variations at the Russian observatories occurred during the Carrington storm in September 1859 and they reached about 1000 nT/h, which was the instrumental off-scale limit. When the time stamp for the spot readings happens to be optimal, the top variation in the Nurmijärvi data is about 3700 nT/h (July 1982), and at Tartu the maximum is about 1600 nT/h (November 2004). At a midlatitude site Nertchinsk in Russia (magnetic latitude ~45 N), the variation during the Carrington storm was at the off-scale limit, and exceeded the value observed at Dourbes during the Halloween storm in October 2003. At Nertchinsk, the Carrington event was at least four times larger than any other storm in 1850–1862. Despite the limitations of the old recordings and in using only hourly spot readings, the Carrington storm was definitely a very large event at midlatitudes. At higher latitudes, it remains somewhat unclear whether it exceeds the largest modern storms, especially the one in July 1982.

M. C. Brown, B. R. Jicha, B. S. Singer et al.

We obtain new 40Ar/39Ar ages for three lavas that record part of the Matuyama‐Brunhes geomagnetic field reversal process on Guadeloupe. These lavas record a reversed‐transitional‐reversed magnetostratigraphy and yield a weighted mean isochron age of 785.2 ± 5.2 ka (2σ analytical uncertainty) relative to an age for the Fish Canyon sanidine standard of 28.201 Ma. This age is of greater accuracy than ages obtained previously by K‐Ar dating. These lavas may record directional fluctuations occurring between the Matuyama‐Brunhes precursor and the final directional reversal. Such variations have been observed in some globally distributed coupled paleomagnetic and oxygen isotope marine sedimentary records of the Matuyama‐Brunhes reversal. Previous paleointensity estimates from these lavas indicate reduced, but fluctuating field strength during this time.

Mario Brkić, Danko Markovinović, Enio Jungwirth

<p>After more than half a century, scientific book Basic Geomagnetic Network of the Republic of Croatia 2004 – 2012, with Geomagnetic Field Maps for 2009.5 epoch describes the recent geomagnetic field on Croatian territory. A review of research in the past decade as well as the original solutions makes the book a document of contribution to geodesy and geomagnetism in Croatia.</p><p>The book’s introduction gives an overview of two centuries of history and the strategic, security, economic and scientific significance of knowing the geomagnetic field on the Croatian territory. All the activities related to the updating of the geomagnetic information, which took place in the last decade, signified a big step toward the countries where geomagnetic survey is a mature scientific and technical discipline, and a scientific contribution to understanding of the nature of the Earth's magnetism.</p><p>The declination, inclination and total intensity maps (along with the normal annual changes) for the epoch 2009.5 are given in the Appendix. The book Basic Geomagnetic Network of the Republic of Croatia 2004 – 2012, with Geomagnetic Field Maps for 2009.5 epoch (ISBN 978-953-293-521-9) is published by the State Geodetic Administration of the Republic of Croatia. Beside editor in chief, M. Brkić, the authors are: E. Vujić, D. Šugar, E. Jungwirth, D. Markovinović, M. Rezo, M. Pavasović, O. Bjelotomić, M. Šljivarić, M. Varga and V. Poslončec-Petrić. The book contains 48 pages and 3 maps, and is published in 200 copies. CIP record is available in digital catalogue of the National and University Library in Zagreb under number 861937.</p>

Ge Zhi-lei

Masako Miki, Aya Taniguchi, M. Yokoyama et al.

Xinying Han, H. Seki, Y. Kamiya et al.

In this paper an efficient technique using magnetic field is proposed for wearable handwriting input. This device requires mounting a permanent magnet onto fingertip and detecting the magnetic field generated by the magnet through magnetic sensors at the wrist of the other hand. The position of magnet is calculated by the vector of the magnetic field. And a method is proposed to avoid geomagnetic influence, using two magnetic sensors. Numerical methods are used to calculate the position of magnet with geomagnetism cancellation. Two numerical methods have been adopted and compared. A prototype device is made and we succeeded to get the trajectory of handwriting input character.

Cui Shuai

S. Gokarn, G. Gupta, D. Walia et al.