Hasil untuk "Geomagnetism"

Dayanand Bhaskar, Rajat Tripathi, Mahesh N. Shrivastava et al.

We present lightning-induced ionospheric perturbations in narrowband very-low-frequency (VLF) signals from the transmitters NWC (21.82° S, 114.17° E, 19.8 kHz) and VTX (8.4° N, 77.8° E, 18.6 kHz) recorded at the low-latitude station Dehradun (DDN; 30.3° N, 78.0° E) over a 12-month period from September 2020 to October 2021. Early/slow VLF events, VLF LOREs, and step-like VLF LOREs associated with lightning were analyzed for their onset and recovery times. This study utilized data from the World Wide Lightning Location Network (WWLLN), which provides lightning locations and energy estimates. The results show that early/slow VLF events occur most frequently, accounting for approximately 68% of cases, followed by VLF LOREs at 12%, and step-like VLF LOREs at 10%. Furthermore, we observed that 100% of the VLF perturbing events occurred during the nighttime, which is not entirely consistent with previous studies. Moreover, more than 60% of VLF LOREs were associated with lightning energies of approximately 1 kJ, and about 40% were associated with lightning energies of ~10 kJ. Step-like VLF LOREs were linked to WWLLN energies between 1 and 5 kJ. The observed WWLLN energy range is somewhat lower than the energies reported in previous studies. Scattering characteristics revealed that 87.3% of events were associated with wide-angle scattering, while approximately 12.6% were linked to narrow-angle scattering. LWPC version 2.1 was used to simulate these perturbing events and to estimate the reflection height (H′, in km) and the exponential sharpness factor (β, in km⁻¹) corresponding to changes in D-region electron density. The reflection height (H′, in km) and the exponential sharpness factor (β, in km⁻¹) of the D-region varied from 83 to 87 km and from 0.42 to 0.79 km⁻¹ for early/slow VLF events, from 83 to 85 km and from 0.5 to 0.75 km⁻¹ for step-like VLF LOREs, and from 81 to 83 km and from 0.75 to 0.81 km⁻¹ for VLF LOREs, respectively.

مجتبی شکوهی, مهدی مصری زاده, ابراهیم اسعدی اسکویی

گرمایش زمین، سبب افزایش شدت و فراوانی پدیده‌های حدی از جمله امواج گرمایی شده است. میزان تأثیرات امواج گرمایی وابسته به پارامترهای تداوم، فراوانی، شدت و وسعت منطقه درگیر پدیده است. در این پژوهش شاخص شدت موج گرمایی با استفاده از مفهوم آنتروپی، متناسب با انحراف از آستانه دمایی و احتمال وقوع آن در هر منطقه از ایران تعریف شد. برای محاسبه این شاخص، از توابع پارامتریک توزیع احتمال دمای متوسط روزانه، در ماهای گرم سال متناسب با هر منطقه استفاده شد. از یک شبکه منظم برای متوسط دمای طی دوره 2011-2021 استفاده شد. توابع توزیع احتمال مختلفی مورد آزمون قرار گرفت و نتایج نشان داد در اغلب مناطق ایران تابع توزیع احتمال ویبول مناسب است. احتمال وقوع این پدیده در اغلب مناطق ایران یکبار در سال است. به غیر از مناطق جنوب‌شرقی ایران، بیشترین فراوانی و گسترده‌ترین امواج گرمایی در ماه جولای رخ داده است. به غیر از یک ناحیه مرکزی، در اکثر نواحی ایران میانگین تداوم امواج گرمایی حداکثر 4 روز است. میانگین هندسی اندازه شدت موج گرمایی نشان داد، مقدار شدت در مناطق مختلف کشور متفاوت و بیشترین مقادیر آن در سواحل جنوبی به بیش از 80 درصد می­رسد. وسعت مناطق درگیر رخداد پدیده موج گرمایی در سال­های اخیر علاوه‌بر افزایش، با شدت بزرگ‌تری همراه بوده است. بیشترین وسعت مناطق در برگیرنده پدیده­های امواج گرمایی، اکثرا مناطق مرکزی و نوار شرقی کشور را در برمی‌گیرند.

ZhaoJin Rong, Yong Wei, Fei He et al.

Many planets, including the Earth, possess a global dipolar magnetic field. To diagnose the interior source of the dipolar field, researchers usually adopt a dipole model consisting of six parameters to fit the observed dataset of the magnetic field. However, the simultaneous fitting of these parameters often leads to multiple local optimal parameter sets. To address this fitting dilemma, Rong ZJ et al. (2021) recently developed a current loop model. This technique can successively separate and invert the loop parameters. Here, we further show how this technique can be reduced and modified to fit a dipole model. Applications of this reduced technique to the International Geomagnetic Reference Field model and the Martian crustal field model highlight its unique ability to diagnose both the planetary global dipolar field and the local crustal field anomaly, a capability that sets it apart from existing methods. The potential impact of this technique on geomagnetism and planetary magnetism is significant, given its unique ability to diagnose both the planetary global dipolar field and the local crustal field anomaly.

Olsen Nils, de Geeter Chiara, Alken Patrick et al.

The Equatorial Electrojet (EEJ) is a spatially localized electric current in the ionospheric dynamo region, flowing along the magnetic dip equator at an altitude of about 110 km, mainly on the dayside. Previous empirical models of the EEJ were based on magnetic intensity observations from the Ørsted, CHAMP, and SAC-C satellites. However, with the launch of the Swarm satellite trio in November 2013, a considerable amount of new data is available. We use latitudinal profiles of EEJ sheet current densities based on magnetic intensity measurements of the Swarm A and B satellites to construct a climatological model of the EEJ. This model describes sheet current density variations with local time, longitude, season, lunar phase, and the F10.7 solar flux. We validate our model with independent EEJ current density estimates from the Swarm C and CSES satellites.

Parkhomov Vladimir Alexandrovich, Eselevich Victor Grigorieivich, Eselevich Maksim Victorovich et al.

We address the sequence of Sun-to-Earth phenomena, that enables to study the mechanism for geoefficiency of eruptive prominences propagating from the Sun inside coronal mass ejections (CMEs). An eruptive prominence ejected in the solar wind (SW) moves at the SW velocity Earthward like adiamagnetic structure of eruptive prominence (DSEP).The key feature of the latter is a largesharp plasma concentration jump N inside the DSEP at a simultaneous sharp drop in the interplanetary magnetic field (IMF) modulus B. It is the anti-correlation between the N and B profiles in DSEP, due to which its contact with the magnetosphere may lead not only to magnetosphere compression, but also to penetration of DSEP substance into the magnetosphere. The duration of the magnetospheric disturbance (in the form of dayside auroras), global increase in the current systems, charged particle flux enhancement in the radiation belts, and generation of the irregular Pi2-3 oscillations aredetermined by the DSEP size. We present statistical investigations into DSEPs observed in different years of solar activity and builta qualitative modelfor DSEP geoefficiency.

Bahadur Singh Kotlia, Neha Kholia, David Porinchu et al.

We present results of our investigations on 7.65 m long core sediments from the Khajjiar lake, Himachal Pradesh, aimed at reconstructing palaeoclimate variability in the climatically sensitive region affected by both ISM (Indian Summer Monsoon) and IWM (Indian Winter Monsoon). Based on the multi-proxy approach, including organic geochemistry (carbon isotopes), magnetic susceptibility as primary proxies and inorganic geochemistry (major oxides) with grain size analysis as secondary proxies, climate of the mid-late Holocene (∼4600 yr) has been established on centennial to millennial scale. The chronology of the sediments is constrained by five AMS radiocarbon dates. The sedimentological data reveal variations in sediment grain size related to palaeo-precipitation. The first high resolution multi-proxy record from the Khajjiar lake core indicates less humid conditions during ∼4600–4185 cal yr BP except an extreme peak of dry and arid climate at around ∼4370 cal yr BP. Intensified monsoon with more wet and humid conditions has been interpreted during ∼4185–3790 cal yr BP. ∼3790–3300 cal yr BP, ∼2845–2115 and ∼1555–405 cal yr BP, and ∼2990–2845 cal yr BP and fluctuations are observed from ∼2115 to 1555 cal yr BP. The results suggest two major climatic phases corresponding with the 4.2 ka and Roman Warm Period (RWP). A regional comparison of mid-late Holocene climate records reveals a broad synchronicity, but with considerable spatial variation. The timing and duration of climate events varied across regions.

Eva Weiler, Christian Möstl, Emma E. Davies et al.

Forecasting the geomagnetic effects of solar coronal mass ejections (CMEs) is currently an unsolved problem. CMEs, responsible for the largest values of the north-south component of the interplanetary magnetic field, are the key driver of intense and extreme geomagnetic activity. Observations of southward interplanetary magnetic fields are currently only accessible directly through in situ measurements by spacecraft in the solar wind. On 10-12 May 2024, the strongest geomagnetic storm since 2003 took place, caused by five interacting CMEs. We clarify the relationship between the CMEs, their solar source regions, and the resulting signatures at the Sun-Earth L1 point observed by the ACE spacecraft at 1.00 AU. The STEREO-A spacecraft was situated at 0.956 AU and 12.6° west of Earth during the event, serving as a fortuitous sub-L1 monitor providing interplanetary magnetic field measurements of the solar wind. We demonstrate an extension of the prediction lead time, as the shock was observed 2.57 hours earlier at STEREO-A than at L1, consistent with the measured shock speed at L1, 710 km/s, and the radial distance of 0.04 AU. By deriving the geomagnetic indices based on the STEREO-A beacon data, we show that the strength of the geomagnetic storm would have been decently forecasted, with the modeled minimum SYM-H=-478.5 nT, underestimating the observed minimum by only 8%. Our study sets an unprecedented benchmark for future mission design using upstream monitoring for space weather prediction.

Wenqi Bai, Xiaohui Zhang, Shiliang Zhang et al.

Geomagnetic navigation has drawn increasing attention with its capacity in navigating through complex environments and its independence from external navigation services like global navigation satellite systems (GNSS). Existing studies on geomagnetic navigation, i.e., matching navigation and bionic navigation, rely on pre-stored map or extensive searches, leading to limited applicability or reduced navigation efficiency in unexplored areas. To address the issues with geomagnetic navigation in areas where GNSS is unavailable, this paper develops a deep reinforcement learning (DRL)-based mechanism, especially for long-distance geomagnetic navigation. The designed mechanism trains an agent to learn and gain the magnetoreception capacity for geomagnetic navigation, rather than using any pre-stored map or extensive and expensive searching approaches. Particularly, we integrate the geomagnetic gradient-based parallel approach into geomagnetic navigation. This integration mitigates the over-exploration of the learning agent by adjusting the geomagnetic gradient, such that the obtained gradient is aligned towards the destination. We explore the effectiveness of the proposed approach via detailed numerical simulations, where we implement twin delayed deep deterministic policy gradient (TD3) in realizing the proposed approach. The results demonstrate that our approach outperforms existing metaheuristic and bionic navigation methods in long-distance missions under diverse navigation conditions.

Xiaohui Zhang, Xingming Li, Songnan Yang et al.

This paper proposes a geomagnetic and inertial combined navigation approach based on the flexible correction-model predictive control algorithm (Fc-MPC). This approach aims to overcome the limitations of existing combined navigation methods that require prior geomagnetic maps and the inertial navigation drift of long-range missions. The proposed method uses geomagnetic gradient information and the model predictive control (MPC) algorithm with heading control and state constraints, eliminating the dependence on prior geomagnetic maps. Instead, the proposed method achieves real-time measurements of the geomagnetic declination, geomagnetic inclination, and inertial navigation data and introduces uniform compensation conditions to adjust and correct the predictive results in real-time. Simulation and real experiment results demonstrate that the proposed Fc-MPC algorithm significantly improves the precision, efficiency, and stability of the geomagnetic and inertial combined navigation system.

Yali Wang, Weiyu Ma, Binbin Zhao et al.

The purpose of this work is to investigate the responses of multiple parameters to the Madoi earthquake preparation. A new method is employed to extract anomalies in a geomagnetic field. The results show that there were abnormal changes in the lithosphere, atmosphere, and ionosphere near the epicenter before the earthquake. Despite the differences in spatial and temporal resolutions, the increase in geomagnetic residuals in the lithosphere exhibits similar temporal characteristics to the enhancement of thermal infrared radiation in the atmosphere. Two high–value regions are present in the ground–based geomagnetic high residuals and the ionospheric disturbances. The northern one is around the epicenter of the Madoi earthquake. Near the southern one, an M6.4 Yangbi earthquake occurred four hours before the Madoi earthquake. In this study, we have observed almost all of the physical phenomena that can occur during the preparation of an earthquake, as predicted using the electrostatic channel model. It can be inferred that the electrostatic channel is a possible mechanism for coupling between the lithosphere, atmosphere, and ionosphere during the Madoi earthquake.

Pablo Rivera, F. Javier Pavón-Carrasco, María Luisa Osete

Abstract The Levantine Iron Age anomaly (LIAA) is a regional short-decadal geomagnetic strength field variation located at the Levantine region characterized by high intensities with maximum virtual axial dipole moments around 190 ZAm2. It has been constrained by archeomagnetic data coming from Eastern Europe and Western Asia between 1050 and 700 BC. The LIAA can be related to a fast and spatially localized geomagnetic positive anomaly (spike) at the Earth’s surface. In this study, we model the LIAA by using a Fisher–von Mises function that fits the most recent archeomagnetic intensity database in the region. A spherical harmonic analysis is implemented for this spike function to perturb a base model in order to build a global reconstruction (perturbed-model) that reproduces the spatial and temporal characteristics of the LIAA. Our results show the importance of harmonic degrees from n = 3–4 to n = 20 to reconstruct the anomaly extension suggested by the database. Two maxima linked with the LIAA are reproduced by our global perturbed-model at the Levantine region at 950 BC and 750 BC. A third maxima in intensity around 500 BC is also observed, affecting the whole Europe. Graphical Abstract

Somayeh Tarana, Nasibe Alipoura, Kourosh Roknia et al.

Solar activities may disturb the geomagnetic field and impact the power grid via geomagnetically induced currents. We study active and reactive powers as well as the power factor of Iran's power grid transformers (230 kV and 400 kV) and their correlations with geomagnetic disturbances indices (SYM-H < -30 nT and sizable horizontal geomagnetic field fluctuation) from 19 March 2018 to 20 March 2020. Out of 128,627 cases with a transformer power factor of less than 0.7, we observe that 12,112 samples correlated with SYM-H. Our investigation shows that about 4 percent of two years, the SYM-H has values less than -30 nT. Analysis of high-performance transformers (a power factor greater than 0.7 at 95 percent of working time) shows at least a 55 percent correlation of power factor less than 0.7 and SYM-H less than -30 nT. We observe that the transformers' power factor of Rafsanjan-Kerman and Sarcheshmeh-Kerman (wye connection on 230 kV side) substations decreased to less than 0.7 and correlated with SYM-H. We show that the reactive power of the Sefidrood-Guilan and Shahid Beheshti-Guilan transformers (wye configurations) increased considerably on 9 January 2020 and positively correlated with SYM-H may produce large GICs at this part of the grid. We observe that the increase in reactive power at the Shahid Beheshti-Guilan substation correlated with the sizable changes in the horizontal field recorded by the Jaipur station. However, more details (temperature and current of transformers) need records to estimate the impact of geomagnetic induction current on the power grid.

Kevin Styp-Rekowski, Ingo Michaelis, Claudia Stolle et al.

Abstract Additional datasets from space-based observations of the Earth’s magnetic field are of high value to space physics and geomagnetism. The use of platform magnetometers from non-dedicated satellites has recently successfully provided additional spatial and temporal coverage of the magnetic field. The Gravity and steady-state Ocean Circulation Explorer (GOCE) mission was launched in March 2009 and ended in November 2013 with the purpose of measuring the Earth’s gravity field. It also carried three platform magnetometers onboard. Careful calibration of the platform magnetometers can remove artificial disturbances caused by other satellite payload systems, improving the quality of the measurements. In this work, a machine learning-based approach is presented that uses neural networks to achieve a calibration that can incorporate a variety of collected information about the satellite system. The evaluation has shown that the approach is able to significantly reduce the calibration residual with a mean absolute residual of about 6.47nT for low- and mid-latitudes. In addition, the calibrated platform magnetometer data can be used for reconstructing the lithospheric field, due to the low altitude of the mission, and also observing other magnetic phenomena such as geomagnetic storms. Furthermore, the inclusion of the calibrated platform magnetometer data also allows improvement of geomagnetic field models. The calibrated dataset is published alongside this work. Graphical Abstract

Antonio Mecozzi

There is a growing concern that a big coronal mass ejection event will induce perturbations on the power supply of fiber optic transoceanic cables that may produce a global internet blackout. In this paper we give the expression of the voltage variations that a transient change of the geomagnetic field induces on the voltage of the power supply of a transoceanic fiber optic cable. We show that the transient voltage change is proportional to the magnitude of the magnetic field deviations and not to its time derivative as a direct application of Faraday's law would imply, and this suggests design criteria to protect transoceanic fiber optic systems against big geomagnetic storm events. The presented analysis also enables the classification of existing systems into some that are less sensitive to the weakening of the geomagnetic field occurring during strong geomagnetic storms and others that are more prone to experience an outage when a weakening of the geomagnetic field occurs.

Igor Aleshin, Kirill Kholodkov, Ivan Malygin et al.

This paper portrays the method of UAV magnetometry survey data interpolation. The method accommodates the fact that this kind of data has a spatial distribution of the samples along a series of straight lines (similar to maritime tacks), which is a prominent characteristic of many kinds of UAV surveys. The interpolation relies on the very basic Nearest Neighbours algorithm, although augmented with a Machine Learning approach. Such an approach enables the error of less than 5 percent by intelligently adjusting the Nearest Neighbour algorithm parameters. The method was pilot tested on geomagnetic data with Borok Geomagnetic Observatory UAV aeromagnetic survey data.

Benjamin S. Murphy, Greg M. Lucas, Jeffrey J. Love et al.

Abstract At present, the most reliable information for inferring storm‐time ground electric fields along electrical transmission lines comes from coarsely sampled, national‐scale magnetotelluric (MT) data sets, such as that provided by the EarthScope USArray program. An underlying assumption in the use of such data is that they adequately sample the spatial heterogeneity of the surface relationship between geomagnetic and geoelectric fields. Here, we assess the degree to which the density of MT data sampling affects geoelectric hazard assessments. For electrical transmission networks in each of four focus regions across the contiguous United States, we perform two parallel band‐limited (101–103 s) hazard analyses: one using only USArray‐style (∼70‐km station spacing) MT data, and one incorporating denser (≪70‐km station spacing) MT data. We find that the use of USArray‐style MT sampling alone provides a useful first‐order estimate of integrated geoelectric fields along electrical transmission lines. However, we also find that the use of higher density MT data can in some areas lead to order‐of‐magnitude differences in line‐averaged electric field estimates at the level of individual transmission lines and can also yield significant differences in subregional hazard patterns. As we demonstrate using variogram plots, these differences reflect short‐spatial‐scale variability in Earth conductivity, which in turn reflects regional lithotectonic structure and history. We also provide a cautionary example in the use of electrical conductivity models to predict dense MT data; although valuable for hazard applications, models may only be able to reproduce surface geoelectric fields as captured by the MT data from which they were derived.

G. Zhang, J. Songwadhana, H. Lu et al.

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator (LS) detector for neutrino mass ordering and other neutrino physics research. The detector uses large-size $20$ inches photomultiplier tubes to detect photons from a liquid scintillator. The large PMTs are sensitive and easily affected such that the detection efficiency loses about 60$\%$ under the geomagnetic field intensity ($\sim$500 mG). It has a significantly negative effect on the detector performance, and a compensation system is necessary for geomagnetic field shielding. As permalloys are easily rusted in water, a better way for the geomagnetic shielding is to apply an active compensation coils system. The simulations show that a set of 32 circular coils can meet the experiment requirement. The residual magnetic field is less than 0.05 G in the Central Detector Photomultiplier Tube (CD-PMT) region (38.5-39.5 m in diameter). A prototype coil system with a 1.2 m was built to validate the simulation and the design. The measured data of prototype and simulation results are consistent with each other, and geomagnetic field intensity is effectively reduced by coils, verifying the shielding coils system design for JUNO. This study is expected to provide practical guidance for the PMT magnetic field shielding for future large-scale detector designs.

Aditi Upadhyay, Bharati Kakad, Amar Kakad et al.

Abstract We present a statistical study of electromagnetic ion cyclotron (EMIC) waves observed at Antarctic station (geographic $$70.7{^\circ }\,\hbox {S}$$ 70.7 ∘ S , $$11.8{^\circ }\,\hbox {E}$$ 11.8 ∘ E , $$L=5$$ L = 5 ) on quiet and disturbed days during 2011–2017. The data span a fairly good period of both ascending and descending phases of the solar cycle 24, which has witnessed extremely low activity. We noted EMIC wave occurrence by examining wave power in different frequency ranges in the spectrogram. EMIC wave occurrence during ascending and descending phases of solar cycle 24, its local time, seasonal dependence and durations have been examined. There are total 2367 days for which data are available. Overall, EMIC waves are observed for 3166.5 h ( $$\approx 5.57\%$$ ≈ 5.57 % of total duration) which has contributions from 1263 days. We find a significantly higher EMIC wave occurrence during the descending phase ( $$\approx$$ ≈ 6.83%) as compared to the ascending phase ( $$\approx$$ ≈ 4.08%) of the solar cycle, which implies nearly a twofold increase in EMIC wave occurrence. This feature is attributed to the higher solar wind dynamic pressure during descending phase of solar activity. There is no evident difference in the percentage occurrence of EMIC waves on magnetically disturbed and quiet days. On ground, EMIC waves show marginally higher occurrence during winter as compared to summer. This seasonal tendency is attributed to lower electron densities and conductivities in the ionosphere, which can affect the propagation of EMIC waves through ionospheric ducts. In local time, the probability distribution function of EMIC wave occurrence shows enhancement during 11.7–20.7 LT (i.e., afternoon–dusk sector). Daily durations of EMIC waves are in the range of 5–1015 min and it is noted that the longer duration (240–1015 min) events are prevalent on quiet days and are mostly seen during the descending phase of solar cycle.

Rajat K. Dey, Sabyasachi Ray, Sandip Dam

The paper aims to explore the asymmetry of the muon content of non-vertical and very high energy Monte Carlo showers due to the influence of Earth's geomagnetic field. Simulations have shown that the geomagnetic field modifies the trajectories of muons in a shower producing a polar asymmetry in the density/number of positive and negative muons in the shower front plane. The asymmetry is quantified by a transverse separation between the positive and negative muons barycentric positions through opposite quadrants across the shower core. The dependence of this transverse muon barycenter separation (TMBS) on polar position shows a clear maximum at a position that is correlated with the primary composition and geomagnetic activities. It is noticed that the maximum TMBS parameter exhibits sensitivity to any transient weakening of Earth's magnetic shield caused by geomagnetic storm originated from bursting solar processes. Obtained simulation results are quite important to design any possible new experiment based on these features of muons in extensive air showers.

S. Chakraborty, S. K. Morley

Geomagnetic activity is often described using summary indices to summarize the likelihood of space weather impacts, as well as when parameterizing space weather models. The geomagnetic index $\text{K}_\text{p}$ in particular, is widely used for these purposes. Current state-of-the-art forecast models provide deterministic $\text{K}_\text{p}$ predictions using a variety of methods -- including empirically-derived functions, physics-based models, and neural networks -- but do not provide uncertainty estimates associated with the forecast. This paper provides a sample methodology to generate a 3-hour-ahead $\text{K}_\text{p}$ prediction with uncertainty bounds and from this provide a probabilistic geomagnetic storm forecast. Specifically, we have used a two-layered architecture to separately predict storm ($\text{K}_\text{p}\geq 5^-$) and non-storm cases. As solar wind-driven models are limited in their ability to predict the onset of transient-driven activity we also introduce a model variant using solar X-ray flux to assess whether simple models including proxies for solar activity can improve the predictions of geomagnetic storm activity with lead times longer than the L1-to-Earth propagation time. By comparing the performance of these models we show that including operationally-available information about solar irradiance enhances the ability of predictive models to capture the onset of geomagnetic storms and that this can be achieved while also enabling probabilistic forecasts.