Hasil untuk "Geomagnetism"

K. M. R. Hunt, K. M. R. Hunt, J.-P. Baudouin et al.

<p>Western disturbances (WDs) are synoptic-scale weather systems embedded within the subtropical westerly jet. Manifesting as upper-level troughs often associated with a lower-tropospheric low over western or northern India, they share some dynamical features with extratropical cyclones. WDs are most common during the boreal winter (December to March), during which they bring the majority of precipitation – both rain and snow – to the western Himalaya, as well as to surrounding areas of north India, Pakistan, and the Tibetan Plateau. WDs are also associated with weather hazards such as heavy snowfall, hailstorms, fog, cloudbursts, avalanches, frost, and cold waves.</p> <p>In this paper, we review recent developments in understanding WDs and their impacts. Over the last decade, recent studies have collectively made use of novel data, novel analysis techniques such as tracking algorithms, and the increasing availability of high-resolution weather and climate models. This review is separated into six main sections – structure and thermodynamics, precipitation and impacts, teleconnections, modelling experiments, forecasting at a range of scales, and paleoclimate and climate change – each motivated with a brief discussion of the accomplishments and limitations of previous research.</p> <p>A number of step changes in understanding are synthesised. Use of new modelling frameworks and tracking algorithms has significantly improved knowledge of WD structure and variability, and a more frequentist approach can now be taken. Improved observation systems have helped quantification of water security over the western Himalaya. Convection-permitting models have improved our understanding of how WDs interact with the Himalaya to trigger natural hazards. Improvements in paleoclimate and future climate modelling experiments have helped to explain how WDs and their impacts over the Himalaya respond to large-scale natural and anthropogenic forcings. We end by summarising unresolved questions and outlining key future WD research topics.</p>

B. Nilam, S. Tulasi Ram, D. M. Oliveira et al.

Abstract A series of coronal mass ejections (CMEs) from the Sun, interacted with one another and formed a complex interplanetary‐CME (ICME) that impinged Earth's magnetosphere on 10 May 2024 and caused the strongest geomagnetic storm of the past two decades. We present a unique pulse‐like enhanced solar wind density structure associated with a giant Kelvin‐Helmholtz (KH) wave vortex formed within the ICME due to compression of sheath region by the surrounding ejecta. When impinged on the magnetosphere, it caused enhanced eastward and westward currents, leading to strong positive and negative geomagnetic field impulses at low and auroral latitudes, respectively. The negative disturbances extended to mid‐latitudes around the midnight sector. Interestingly, the westward current pulse (negative disturbance) penetrated deep into low‐latitudes (up to 24.49°N and 28.92°S) in both hemispheres, but exclusively on the dawn side. The mechanisms responsible for such an intensification and low‐latitude penetration of westward current pulse are discussed.

Alireza Goudarzi, Shadi Veisi, Seyed Hadi Dehghan-Manshadi et al.

Accurate seismic first arrival picking is fundamental for geophysical interpretation and subsurface imaging. This study evaluates the performance of wavelet-based denoising techniques combined with the Translation-Invariant Shrinkage (TIS) algorithm to enhance first arrival detection. The Higher Density Discrete Wavelet Transform (HDDWT) and Double Density Wavelet Transform (DDWT) are applied to synthetic and real seismic datasets with varying noise levels. Results indicate that HDDWT outperforms DDWT in preserving critical low-frequency components and maintaining signal fidelity, particularly under high noise conditions. The P-phase Picker algorithm, when integrated with HDDWT, achieves superior accuracy and reliability in first arrival detection. These findings underscore the potential of HDDWT and TIS as robust tools for improving seismic data quality and enhancing interpretation workflows.

Jayashree Bulusu, Rohit Kumar Jha, Amrita Yadav et al.

A unique two-dimensional gridded geomagnetic map of India is constructed using the geomagnetic field observations from 11 observatories of India, operated by the Indian Institute of Geomagnetism. In order to create the spatial grid, 11 spatial techniques are compared with observed magnetic field during 2011–2020. Out of the 11 known techniques of spatial interpolation, the Modified Shepard’s Method is selected as the best suitable method for interpolation. The spatial gird provides the hourly values of absolute and variations in horizontal (H) and vertical (Z) magnetic field over India. The spatial grid can be applied to higher temporal resolution of data sets as well. This map can be used to get the regional changes in the magnetic field during quiet and disturbed conditions. A user-friendly MATLAB based GUI is created for obtaining the spatial grid.

A. T. Chartier, J. Rodriguez‐Zuluaga, C. L. Waters et al.

Abstract The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) provides continuous global maps of Birkeland currents, using magnetic field perturbations (dB) obtained by calibrating and detrending data from engineering magnetometers on the 66 polar‐orbiting Iridium satellites in the communications constellation. Here, we provide an assessment of AMPERE dB accuracy, as compared with magnetic field observations from the Swarm satellite mission. The CHAOS v8.1 model (Finlay et al., 2020, https://doi.org/10.1186/s40623‐020‐01252‐9) was used to remove the main field and other non‐ionospheric contributions from both data sets. In a nearest‐neighbor comparison covering August 2022, AMPERE's calibrated and detrended dB data from the Iridium NEXT satellites are found to have root‐mean‐square deviations of 31 and 33 nT (for dBθ and dBφ, respectively) as compared with data from Swarm, while the biases are −7 and −2 nT. For the same interval, AMPERE's fitted maps have root‐mean‐square errors of <40 nT, rising to 109–185 nT in active conditions (defined as Swarm dB > 250 nT). However, there is evidence that small scale (<400‐km along Swarm track direction) dB structures are not fully resolved. Overall, we find that the AMPERE dB data and fitted products are unbiased and are typically in excellent agreement with the Swarm data.

Evângela Patrícia Alves da Silva, Alessandra Davolio, Marcos Sebastião dos Santos et al.

Brazilian pre-salt carbonates represent more than 70% of the produced hydrocarbons in Brazil, which makes them of great interest for 4D seismic studies. 4D seismic modeling is crucial to understand how production impacts the 4D seismic response. We propose including rock-fluid interaction on the traditional methodology for 4D petro-elastic modeling (generally considering only variations of pressure and fluid saturation) given the presence of CO2 in the injected fluid. To model the rock-fluid interaction, we consider expressing the dry rock bulk and shear moduli as a function of the porosity for the monitor data. In the modeling, we focus in observing changes in the rock due to dissolution of CaCO3 by the CO2-rich injected fluid. We perform the analysis in the region around the injector wells and the results show that rock-fluid interaction favors the 4D anomalies, considering the reservoir conditions in this study. The higher ∆AI values obtained in petro-elastic modeling with rock-fluid interaction present an optimistic scenario compared to a traditional petro-elastic modeling in 4D feasibility studies and as another hypothesis that supports the interpretation of 4D anomalies.

Wen Chen, Ding Yuan, Xueshang Feng et al.

Geomagnetically Induced Current (GIC) refers to the electromagnetic response of the Earth and its conductive modern infrastructures to space weather and would pose a significant threat to high-voltage power grids designed for the alternative current operation. To assess the impact of space weather on the power grid, one needs to calculate the GIC on a national or continental scale. In this study, we developed a smart and parallelized GIC modelling algorithm, Graph GIC. This algorithm deploys a graph representing a power grid in a single-line diagram, in which substations/transformers act as nodes and transmission lines as edges. With these denotations, a power grid and its electric parameters are mathematically represented with an adjacency matrix and an admittance matrix. We used sparse matrix and parallelisation techniques to expedite the intensive computation in cases of large-scale power grids. The Graph GIC was validated with a benchmark grid, applied to the GIC calculation of the 500 kV power grid of Guangdong, China, and conducted preliminary analysis on the grid's susceptibility to geomagnetic storms. The Graph GIC algorithm has the advantage of an intuitive and highly scalable graph representation of a power grid at any scale. It achieves high-accuracy calculation and a speedup of about 18 times after parallelisation. This algorithm could be applied to assess the impact of space weather on a power grid up to continental scales and could be incorporated into global space weather modelling frameworks.

Ayisha M Ashruf, Ankush Bhaskar, C Vineeth et al.

This study investigates the orbital decay and subsequent reentries of 12 Starlink satellites from 16 April to 15 May 2024. By examining Two-Line Element data, we observed a significant increase in orbital decay following the geomagnetic storm on 10 May 2024, consistent with expectations of increased thermospheric density. An unexpected increase in decay rates for 10 satellites was identified around 25 April 2024, while two lower-altitude satellites remained unaffected. Detailed analysis revealed that this enhanced decay rate prior to the storm was influenced by a spike in the O/N2 ratio and an increase in Extreme Ultra Violet (EUV) flux. Moreover, most of the satellites exhibited sharp decay during the early recovery phase of the geomagnetic storm. Based on the positions and local times of changes in decay rates, it is likely that the satellites were affected by various processes during elevated space weather activity, such as enhanced EUV flux, Joule heating, particle precipitation, and the equatorial neutral anomaly. This study highlights the complex role of preconditioning due to enhanced EUV flux and extreme space weather activity in the orbital dynamics of Low-Earth Orbit (LEO) satellites.

Anna Wawrzaszek, Agnieszka Gil, Renata Modzelewska et al.

High temporal and high spatial resolution geoelectric field models of two Mäntsälä, Finnish pipeline GIC intervals that occurred within the 7-8 September, 2017 geomagnetic storm have been made. The geomagnetic measurements with 10 s sampling rate of 28 IMAGE ground magnetometers distributed over the north Europe (from $52.07^\circ$ to $69.76^\circ$ latitude) are the bases for the study. A GeoElectric Dynamic Mapping (GEDMap) code was developed for this task. GEDMap considers 4 different methods of interpolation and allows a grid of $0.05^\circ$ (lat.)$\times 0.2^\circ$ (lon.) spatial scale resolution. The geoelectric field dynamic mapping output gives both spatial and temporal variations of the magnitude and direction of fields. The GEDMap results show very rapid and strong variability of geoelectric field and the extremely localized peak enhancements. The magnitude of geoelectric fields over Mäntsälä at the time of the two GIC peaks were 279.7 mV/km and 336.9 mV/km. The comparison of the GIC measurements in Mäntsälä and our modeling results show very good agreement with a correlation coefficient higher than 0.8. It is found that the auroral electrojet geoelectric field has very rapid changes in both magnitude and orientation causing the GICs. It is also shown that the electrojet is not simply oriented in the east-west direction. It is possible that even higher time resolution base magnetometer data of 1 s will yield even more structure, so this will be our next effort.

Yue-Kin Tsang, Chris A. Jones

The ratio of the Lowes spectrum and the secular variation spectrum measured at the Earth's surface provides a time scale $τ_{\rm sv}(l)$ as a function of spherical harmonic degree $l$. $τ_{\rm sv}$ is often assumed to be representative of time scales related to the dynamo inside the outer core and its scaling with $l$ is debated. To assess the validity of this surmise and to study the time variation of the geomagnetic field $\boldsymbol{\dot B}$ inside the outer core, we introduce a magnetic time-scale spectrum $τ(l,r)$ that is valid for all radius $r$ above the inner core and reduces to the usual $τ_{\rm sv}$ at and above the core-mantle boundary (CMB). We study $τ$ in a numerical geodynamo model. Focusing on the large scales, we find that $τ\sim l^{-1}$ at the CMB. Just below the CMB, $τ$ undergo a sharp transition such that the scaling becomes shallower than $l^{-1}$. This transition stems from the magnetic boundary condition at the CMB that ties all three components of $\boldsymbol{\dot B}$ together. In the interior of the outer core, the time variation of the horizontal magnetic field, which dominates $\boldsymbol{\dot B}$, has no such constraint. The upshot is $τ_{\rm sv}$ becomes unreliable in estimating time scales inside the outer core. Another question concerning $τ$ is whether a scaling argument based on the frozen-flux hypothesis can be used to explain its scaling. To investigate this, we analyse the induction equation in the spectral space. We find that away from both boundaries, the magnetic diffusion term is negligible in the power spectrum of $\boldsymbol{\dot B}$. However, $\boldsymbol{\dot B}$ is controlled by the radial derivative in the induction term, thus invalidating the frozen-flux argument. Near the CMB, magnetic diffusion starts to affect $\boldsymbol{\dot B}$ rendering the frozen-flux hypothesis inapplicable.

Kwon-Seok Chae, In-Taek Oh, Soo Hyun Jeong et al.

To resolve disputes or determine the order of things, people commonly use binary choices such as tossing a coin, even though it is obscure whether the empirical probability equals to the theoretical probability. The geomagnetic field (GMF) is broadly applied as a sensory cue for various movements in many organisms including humans, although our understanding is limited. Here we reveal a GMF-modulated probabilistic abstract decision-making in humans and the underlying mechanism, exploiting the zero-sum binary stone choice of Go game as a proof-of-principle. The large-scale data analyses of professional Go matches and in situ stone choice games showed that the empirical probabilities of the stone selections were remarkably different from the theoretical probability. In laboratory experiments, experimental probability in the decision-making was significantly influenced by GMF conditions and specific magnetic resonance frequency. Time series and stepwise systematic analyses pinpointed the intentionally uncontrollable decision-making as a primary modulating target. Notably, the continuum of GMF lines and anisotropic magnetic interplay between players were crucial to influence the magnetic field resonance-mediated abstract decision-making. Our findings provide unique insights into the impact of sensing GMF in decision-makings at tipping points and the quantum mechanical mechanism for manifesting the gap between theoretical and empirical probability in 3-dimensional living space.

Sumanjit Chakraborty, D. Chakrabarty

This investigation is directed to understand the asymmetry in $Δ$X variations caused due to the relative roles played by IMF Bz and IMF By in a particular interval (22:22 - 22:55 UT), during the main phase of a strong geomagnetic storm event of April 06, 2000 (Ap = 236). Two pairs of antipodal stations, being part of the SuperMAG network, are considered here. Ionospheric convection maps from SuperDARN network are used to understand spatio-temporal evolution of the DP2 ionospheric convection patterns over high-latitudes. The two-dimensional maps of equivalent currents are used to show signatures of global DP2 currents associated with the interplay effect between the two IMF components. Observations show increases in the difference in $Δ$X variations between nearly antipodal stations from the Japanese-European/African sector with respect to the same between the nearly antipodal stations from the Pacific/American-Indian sector. This asymmetry is observed during the period when the absolute magnitude of IMF By is larger than that of IMF Bz resulting in a significant and conspicuous enhancement in IMF |By/Bz|. It is suggested that the distortions in DP2 cells and associated rotation of electrodynamic day-night divider, bring one pair of stations under the same DP2 cell and one station of the other pair under a different DP2 cell and throat flow region leading to the asymmetry in $Δ$X variations between the antipodal stations. Therefore, the work highlights the importance of the interplay between IMF Bz and IMF By in determining the ionospheric impact over low latitudes during strong geomagnetic conditions.

Jianjun Quan, Yongtong Zheng, Shaoran Wang et al.

The tracking and analysis of precursor network observation data is comprehensively carried out at precursor stations and regional centers. The event records generated by the tracking and analysis of earthquake precursor data demonstrate the dynamic changes of precursor network observation data. This article starts from the current situation of data tracking and analysis, proposes precautions for data tracking and analysis in the field of geomagnetism, and discusses common problems in geomagnetic tracking and analysis through multiple aspects such as event leakage analysis and over analysis, data type selection, event start and end time, event analysis description, map drawing and annotation, event type classification, geophysical event analysis, and proposes corresponding solutions, measures are proposed for the promotion of data tracking and analysis in the field of geomagnetism. We hope to provide reference for the observation personnel of geomagnetic stations to better carry out data analysis research and output application work, provide a solid foundation for the prediction and scientific research of geomagnetic disciplines, and promote the shift of the focus of daily work of earthquake precursor networks from observation to both observation and application.

Zhaobo He, Xingxing Hu, Yuntian Teng et al.

In order to minimize interruptions to recording, geomagnetic observatories usually use a back-up instrument operating simultaneously with the primary instrument in order to obtain comparative observations. Based on the correction parameter calculation method established in the previous work, we focused on the effects of temperature and instrument drift on the comparative geomagnetic vector observations. The linear influence of temperature on the comparative data was shown to be variable. The relative temperature coefficient changed around the temperature inflection point and showed a V-type distribution in a scatter plot. This conclusion was verified in laboratory experiments. The long-term time drift between the comparative instruments exhibits a linear pattern, and the fitness of the correction model can be evaluated by the degree to which the residual distribution of the fitted straight line conforms to the normal distribution. However, the absolute value of the long-term time drift between variometers with the same type of probe is very small. Therefore, long-term time drift correction should be carried out with care. The associated analysis and conclusions have the potential to benefit data agreement correction of long-term comparative geomagnetic vector observations and comparative testing of the performance of vector instruments.

Jibrin A. Alhassan., Ogbonnaya Okike, Augustine E. Chukwude

Forbush decrease (FD), discovered by Scott E. Forbush about 80 years ago, is reffered to as the non-repetitive short-term depression in galactic cosmic ray (GCR) flux, presumed to be associated with large-scale perturbations in solar wind and interplanetary magnetic field (IMF). It is the most spectacular variability in the GCR intensity which appear to be the compass for investigators seeking solar-terrestrial relationships. The method of selection and validation of FD events are very important to cosmic ray scientists. We have deployed a new computer software to determine the amplitude and timing of FDs from daily-averaged cosmic ray (CR) data at OULU neutron monitor station. The code selected 230 FDs between 1998 and 2002. In an attempt to validate the new FD automated catalog, the relationship between the amplitude of FDs, and IMF, solar wind speed (SWS) and geomagnetic storm indices (Dst, kp, ap) is tested here. A two-dimensional regression analysis indicates significant linear relationship between large FDs (CR(\%) $\leq-3$) and solar wind data and geomagnetic storm indices in the present sample. The implications of the relationship among these parameters are discussed.

Valeriy G. Petrov, Tatyana N. Bondar

Abstract The International Geomagnetic Reference Field (IGRF) model is a combination of the several models developed by independent groups of scientists using different approaches for the selection of input data and methods for calculating harmonic coefficients. This approach allows for mutual comparison of individual models and for their combination to obtain the most reliable values of the harmonic coefficients. This letter provides a brief description of methods for building the IZMIRAN Earth’s main magnetic field model, submitted to the IAGA Working Group V-MOD for creating IGRF-13. Special efforts were made to obtain as uniform coverage of the entire Earth’s surface as possible with observations. The surface was divided into a grid of approximately equal cells. Then the data for geomagnetically quiet intervals were placed in the corresponding cells and a median filter was applied to select the data in each cell. Spherical harmonic coefficients up to degree 13 were calculated for the interval 2014-Jan to 2019-Aug with a time step of 10 days and extrapolated to 01.01.2010.

Jouni J. Takalo

We show that the time series of sunspot-group areas has a gap, the so-called Gnevyshev gap (GG), between ascending and descending phases of the cycle and especially so for the even-numbered cycles. For the odd cycles this gap is less obvious, and is only a small decline after the maximum of the cycle. We resample the cycles to have the same length of 3945 days (about 10.8 years), and show that the decline is between 1445-1567 days after the start of the cycle for the even cycles, and extending sometimes until 1725 days from the start of the cycle. For the odd cycles the gap is a little earlier, 1332-1445 days after the start of the cycles with no extension. We analyze geomagnetic disturbances for Solar Cycles 17-24 using the Dst-index, the related Dxt- and Dcx-indices, and the Ap-index. In all of these time series there is a decline at the time, or somewhat after, the GG in the solar indices, and it is as deepest between 1567-1725 days for the even cycles and between 1445-1567 days for the odd cycles. The averages of these indices for even cycles in the interval 1445-1725 are 46%, 46%, 18%, and 29% smaller compared to surrounding intervals of similar length for Dst, Dxt, Dcx, and Ap, respectively. For odd cycles the averages of the Dst- and Dxt-indices between 1322-1567 days are 31% and 12% smaller than the surrounding intervals, but not smaller for the Dcx-index and only 4% smaller for the Ap-index. The declines are significant at the 99% level for both even and odd cycles of the Dst-index and for Dxt-, Dcx- and Ap-indices for even cycles. For odd cycles of the Dxt-index the significance is 95%, but the decline is insignificant for odd cycles of the Dcx- and Ap-indices.

Sumanjit Chakraborty, Sarbani Ray, Abhirup Datta et al.

This paper presents the equatorial ionospheric response to eleven strong-to-severe geomagnetic storms that occurred during the period 2000-2005, the declining phase of the solar cycle 23. The analysis has been performed using the global ion density plots of Defense Meteorological Satellite Program (DMSP). Observations show that for about 91% of the cases, post-sunset equatorial irregularities occurred within 3h from the time of northward to southward transition of the Interplanetary Magnetic Field (IMF) clock angle, thus bringing out the importance of the role played by IMF By in the process of Prompt Penetration of Electric Field (PPEF) in addition to the IMF Bz. This is an improvement from the previously reported (Ray et al.,2015) 4h window of ESF generation from the southward IMF Bz crossing -10 nT.

Sumanjit Chakraborty, Abhirup Datta, Sarbani Ray et al.

This paper presents the storm time comparative analysis of the performances of latest versions of global ionospheric models: International Reference Ionosphere (IRI) 2016, NeQuick 2 (NeQ) and the IRI extended to Plasmasphere (IRI-P) 2017 with respect to Navigation with Indian Constellation (NavIC) and Global Navigation Satellite System (GNSS) derived ionospheric Total Electron Content (TEC). The analysis is carried out under varying geomagnetic storm conditions during September 2017-November 2018, falling in the declining phase of solar cycle 24. TEC data from Indore, located near the northern crest of the Equatorial Ionization Anomaly (EIA) along with data obtained from the International GNSS Service (IGS) stations at Lucknow, located beyond the anomaly crest; Hyderabad, located between anomaly crest and magnetic equator and Bangalore, located near the magnetic equator have been analysed. The models generally overestimated during the storm periods with the exception of IRI-P, which matched (with an offset of about 3-5 TECU) with the enhancement observed on September 7, 2017 (during the strong storm of September 2017), from stations around the anomaly crest. No significant match was observed by the other two models. This match of IRI-P is attributed to the plasmaspheric contribution as well as the capability of assimilating measured TEC values into this model. In the present study, to the best of our knowledge, first comparisons of the empirical model derived TEC with NavIC and GNSS measurements from an anomaly crest location, combined with the IGS observations from the magnetic equator to locations beyond the anomaly crest, are conducted during geomagnetically disturbed conditions. Since NavIC satellites are at higher altitudes(~ 36000 km), the inclusion of NavIC data to the existing model could give better ionospheric predictions over the Indian subcontinent.

M. E. Iglesias-Martínez, J. C. Castro-Palacio, F. Scholkmann et al.

In this work, we analyzed time-series of background radiation inside a multilayer interleaving structure, geomagnetic activity and cosmic-ray activity using the Pearson correlation coefficient and a new correlation measure based on the one-dimensional component of the fourth order cumulant. The new method is proposed based on the fact that the cumulant of a random process is zero if it is of Gaussian nature. The results show that this methodology is useful for detecting correlations between the analyzed variables.