Hasil untuk "Geomagnetism"

ابوالفضل نیستانی

سیگنال­های دورپیوند باعث نوسان در سامانه اقلیم می­شوند. در این زمینه شاخص­هایی مانند الگوی دورپیوند شرق اطلس-غرب روسیه (EA-WR)، نوسان مدیترانه(MO)، نوسان اطلس شمالی (NAO)، نوسان شبه دوسالانه(QBO) و نوسان ENSO می­توانند بر وردایی کمیت­های جوی در منطقه ایران تأثیر قابل‌توجه داشته باشند. در این تحقیق با استفاده از پالایه­های رقومی سیگنال­های خامِ ماهانه در نوارهای بسامدی گوناگون جداسازی و موردمطالعه قرار گرفته­اند و با استفاده از تحلیل همبستگی، ارتباط خطی بین نوسان­های هم­بسامدِ شامل در این سیگنال­ها مورد آزمایش قرار گرفت. علاوه‌بر این، توان هر سیگنال بر اساس روش چگالی طیف توان در نوارهای بسامدی انتخاب شده استخراج شد و نوسان­های با بیشترین توان در هر سیگنال شناسایی شد. نتایج گویای همبستگی قابل‌توجه و معنادار بین وردشِ موجود در سیگنال­ها در بعضی از مقیاس­های زمانی است. به‌طور نمونه در مقیاس زمانی سالانه، مؤلفه متناظر در سیگنال­های EA-WR و NAO همبستگی مستقیم و بااهمیتی را در تأخیر زمانی صفر نشان می­دهند (ضریب همبستگی: 564/0). علاوه‌بر این، توزیع توانِ وردش برای هر کدام از شاخص­ها در هر نوار بسامدی کاملاً منحصر به فرد است. به‌طور خاص، بیش از %80 وردایی سیگنال ماهانه QBO در مقیاس زمانی 14 ماه تا 3 سال به‌طور شبه­چرخه­ای رخ می­دهد. برای سیگنال­های EA-WR و NAO بخش زیادی از وردایی (%45-55%) در مقیاس 2-5 ماه روی می­دهد که همبستگی ناچیزی بین این نوسان­های تصادفی مشاهده شد. اُفت و خیزهای بالابسامد در سیگنال MO غالب هستند و برای سیگنالSOI  به استثنای مقیاس سالانه، باقی مقیاس­های زمانی دارای اهمیت قابل ملاحظه‌ای در تعیین اقلیم منطقه ایران هستند.

Hanpeng Lu, Fengji Wang, Gang Zhang et al.

This study provides an overview of the seismic geological characteristics of the MS5.5 earthquake in Pingyuan, Shandong. In this study, the rapid response and disposal capabilities after the earthquake, including mobile gravity and geomagnetic emergency observations, were elaborated, and encrypted observations after the earthquake were conducted. It analyzes the changes in gravity and magnetic data before and after the earthquake. The primary use of mobile gravity data in recent years has been to systematically analyze the dynamic evolution characteristics of the half-year scale difference change and the 1～3 year scale cumulative change in the gravity field before the MS5.5 earthquake in Pingyuan. It better reflects the abnormal precursor information of the rapid increase in mobile gravity during the development and occurrence of the MS5.5 earthquake in Pingyuan and the effective theory of reverse recovery of the gravity field after the earthquake. Finally, the emergency observation results of mobile gravity and magnetism were analyzed, and the relationship between the gravitational field, stress field, and earthquakes was discussed. Through post-earthquake emergency observation and analysis, we should continue to strengthen the capability of gravity and magnetic fusion analysis, improve the reliability of the analysis results, provide a feasible basis for subsequent observation and further analysis and judgment after the earthquake, provide a reference basis for post-earthquake summaries, and strengthen mobile monitoring and earthquake risk zone identification in the Shandong region.

José Roberto de Abreu Junior, Wagner Carrupt Machado

Among the methods for mitigating the first-order effects of the ionosphere, the Klobuchar model and final Global Ionosphere Maps (GIM) produced by the International GNSS Service (IGS) are widely used. Previous studies have looked at their effectiveness in discrete periods and locations of Brazil, but this may have led to incomplete conclusions. Aiming to contribute to this discussion, this paper presents a more comprehensive evaluation of the Klobuchar model and IGS GIM performances in single-point positioning using data from the whole year of the solar cycle 24 peak from six stations of Brazilian Network for Continuous Monitoring of the GNSS Systems (RBMC). When compared to the solution without using correction for the ionosphere, improvements of approximately 39% and 52% were obtained with the Klobuchar model and the GIM, respectively. The results suggest that the lower intensity of solar cycle 24, the location of the GNSS station relative to the geomagnetic equator, and the occurrence of post-sunset ionospheric irregularities contribute to the worse performance of the assessed models when compared to research done with GNSS data from solar cycle 23.

Yude Tong, Xiaoying Huang, Yongbing Chen et al.

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

Geeta Vichare, Ankush Bhaskar, Rahul Rawat et al.

In 2023 April, a low-latitude aurora observed by the all-sky camera at Hanle, Ladakh, India (33°14’N geographic latitude), generated significant interest. This was the first such aurora recorded from the Indian region in the space era and occurred during a moderate solar storm. This study explores this low-latitude auroral sighting, which happened during the sheath-region passage of an interplanetary coronal mass ejection. We analyze in situ multispacecraft particle measurements and geomagnetic field observations from both ground-based and satellite-based magnetometers. The auroral observations at Hanle coincided with intense substorm activity. Our findings indicate that the aurora did not actually reach India; the equatorward boundary was beyond 50°N geographic latitude. Enhanced electron fluxes with energies below 100 eV were detected at 54°N geographic latitude at about 830 km altitude in the predawn sector (4–5 hr local time). In the midnight sector, the equatorward boundary is estimated to be around 52°N geographic latitude, based on Hanle observations and considering emission altitudes of 600–650 km due to low-energy electrons. Thus, the low-latitude red aurora observed from India resulted from the emissions at higher altitudes due to low-energy electron precipitation in the auroral oval and a slight equatorward expansion of the auroral oval. The low-energy electrons likely originated from the plasma sheet and were precipitated due to enhanced wave–particle interactions from strong magnetosphere compression during high solar wind pressure. This study is crucial in understanding low-latitude auroras in the modern space era.

Amrutha, S. V. Singh, K. C. Barik et al.

A comprehensive theoretical model for a homogeneous plasma system of hot, tenuous Maxwellian ring-distributed protons and the cold background of Maxwellian ions and electrons is used to study the resonant instabilities of magnetosonic (MS) waves. The perpendicular velocity integrals associated with the Maxwellian ring distribution have no analytical solution, hence, are solved numerically, while the parallel velocity integrals are solved analytically by invoking series expansion of the plasma dispersion function. For the plasma parameters relevant to Earth’s inner magnetosphere, the theoretical model generates MS waves with frequencies from 5 times the local proton cyclotron frequency to above the lower hybrid frequency for a propagation angle of 89.5°. Hydrogen (H ^+ ) band electromagnetic ion cyclotron waves are also excited by the Maxwellian ring protons for the same set of plasma parameters. A detailed analysis reveals that a sufficiently large ring velocity, as well as a smaller perpendicular and parallel thermal velocity, can enhance the MS wave growth. The study also explores the role of background plasma parameters in modulating the waves. The present theoretical model reproduces the harmonics of the MS waves observed by the Van Allen Probes in the Earth’s inner magnetosphere. Further, the model can generate MS waves in other plasma environments, e.g., Mars, where the presence of ring protons has been established by MAVEN in connection with the MS wave observations.

Arne Døssing, Mick Emil Kolster, Eduardo L. S. da Silva et al.

Abstract The active rift zones in Iceland provide unique insight into the geodynamic processes of divergent plate boundaries. The geodynamics of Iceland are studied intensively, particularly, by geophysical methods sensitive to active and/or visible structures such as earthquake seismic and Synthetic Aperture Radar observations or aerial photographs. However, older and less active structures, that may exert a strong control on the presently active geodynamics, are often buried beneath recent volcanic or sedimentary deposits and are—due to their passive mode—overseen by the typical geophysical investigations. Aeromagnetic surveys provide spatial information about subsurface magnetization contrasts relating to both active and inactive structures. However, the aeromagnetic data in Iceland were collected in the 1970-80s and are relevant only to large-scale regional rift studies. With the availability of reliable drones and light-weight atomic scalar sensors, high-quality drone magnetic surveys can provide an unprecedented spatial resolution of both active and passive structures of rift systems as compared to conventional airborne surveys. Here, we present the results of a drone-towed magnetic scalar field and scalar gradiometry study of the north-northeast trending Bárðarbunga spreading center to the north of the Vatnajökull ice cap, Iceland. Our results provide new information about the structural complexity of rift zones with evidence of densely-spaced, conjugate and oblique faults throughout the area. Evidence is shown of a hitherto unknown and prominent east-northeast trending fault structure that coincides with the northern tip of the main eruption edifice of the 1797 and 2014-15 Holuhraun volcanic events. We suggest that this pre-existing structure controlled the locus of vertical magma migration during the two Holuhraun events.

Xiong Chao, Lühr Hermann

In this study we make use of the Swarm counter-rotation constellation for estimating the typical scale length of the post-sunset equatorial plasma bubbles (EPBs) along fluxtubes. The close approaches between Swarm spacecraft near the equator occurred in September and October 2021, covering the magnetic local time from 19:00 to 23:00, which is favorable for the occurrence of EPBs. It is the first time to show the quasi-simultaneously samplings by Swarm A/C and B of the same fluxtube but at different altitude. The observations frequently reveal plasma density depletions only at one spacecraft altitude, confirming that EPBs extend only over finite parts of the fluxtube. Based on a statistical analysis of double and single EPB detections on the same fluxtube, our results imply the typical field-aligned scale length of the depletion structures associated with EPBs of the order of 550 km. Our detections are from the lower part of the depleted fluxtubes, and they coincide well with the latitudes of the equatorial ionization anomaly. In the upper part of the fluxtube near the magnetic equator, our estimation technique does not work well because of too large field-aligned spacecraft separation of the Swarm satellites.

Robert R. Downs, Alicia Urquidi Díaz, Qi Xu et al.

Minimally, a research data repository exists to make a collection of data assets available to potential users. If a dataset cannot be discovered and found, it cannot be reused (Garnett et al. 2017). Harvestable metadata catalogues are a key strategy for achieving greater global findability of data assets, as they create a surveyable access point to discover data products within large data collections. Such catalogues can be especially effective if they are tailored for interoperability with feature-rich infrastructures (e.g. meta-catalogues, see Kapiszewski & Karcher 2020; CRFCB 2014) that are highly visible and widely used, and also themselves integrated within the larger ecosystem of research infrastructures. This study offers insight into a set of World Data System (WDS) research data repositories ongoing and successful implementations of harvestable metadata services, which apply established and emerging research data standards and practices to fit global, local and domain-specific interoperability contexts. Establishing a harvestable metadata service involves making choices in a space where standards and technologies are continuously evolving. The repositories in this study leverage the resources they have, within the policy and funding constraints of their institution, to serve the changing needs of heterogeneous user groups. This document encapsulates and completes the work that was carried out by the WDS International Technology Office (ITO) Harvestable Metadata Services Working Group (HMetS-WG).

Dmytro Kotov, Phil G. Richards, Maryna Reznychenko et al.

This study explores the impact of the exosphere hydrogen (H) density on the ionosphere-plasmasphere system using a model whose key inputs are constrained by ionosphere observations at both ends of the magnetic field line with an L-value of 1.75 in the American longitudinal sector during a period with low solar and magnetic activities. This study is the first to be validated by ground-based and satellite data in the plasmasphere and both hemispheres. The main finding is that the entire ionosphere-plasmasphere system is very sensitive to the neutral hydrogen density in the lower exosphere. It was found that an increase in the H density by a factor of 2.75 from the commonly accepted values was necessary to bring the simulated plasma density into satisfactory agreement with Arase satellite measurements in the plasmasphere and also with DMSP satellite measurements in the topside ionospheres of the northern and southern hemispheres. A factor of 2.75 increase in the H density increases the simulated plasma density in the afternoon plasmasphere up to ∼80% and in the nighttime topside ionosphere up to ∼100%. These results indicate prominently that using the commonly accepted empirical model of the H density causes unacceptable errors in the simulated plasma density of the near-Earth plasma shells. We alert the space science community of this problem.

Songtong Han, Bo Zhang, Zhu Wen et al.

After wars, some unexploded bombs remained underground, and these faulty bombs seriously threaten the safety of people. The ability to accurately identify targets is crucial for subsequent mining work. A deep learning algorithm is used to recognize targets, which significantly improves recognition accuracy compared with the traditional recognition algorithm for measuring the magnetic moment of the target and the included geomagnetism angle. In this paper, a ResNet-18-based recognition system is presented for classifying metallic object types. First, a fluxgate magnetometer cube arrangement structure (FMCAS) magnetic field feature collector is constructed, utilizing an eight-fluxgate magnetometer sensor array structure that provides a 400 mm separation between each sensitive unit. Magnetic field data are acquired, along an east–west survey line on the northern side of the measured target using the FMCAS. Next, the location and type of targets are modified to create a database of magnetic target models, increasing the diversity of the training dataset. The experimental dataset is constructed by constructing the magnetic flux density tensor matrix. Finally, the enhanced ResNet-18 is used to train the data for the classification recognition recognizer. According to the test findings of 107 validation set groups, this method’s recognition accuracy is 84.1 percent. With a recognition accuracy rate of 96.3 percent, a recall rate of 96.4 percent, and a precision rate of 96.4 percent, the target with the largest magnetic moment has the best recognition impact. Experimental findings demonstrate that our enhanced RestNet-18 network can efficiently classify metallic items. This provides a new idea for underground metal target identification and classification.

Daniel A. Frost, Margaret S. Avery, Bruce A. Buffett et al.

Abstract Heat flux from the core to the mantle provides driving energy for mantle convection thus powering plate tectonics, and contributes a significant fraction of the geothermal heat budget. Indirect estimates of core‐mantle boundary heat flow are typically based on petrological evidence of mantle temperature, interpretations of temperatures indicated by seismic travel times, experimental measurements of mineral melting points, physical mantle convection models, or physical core convection models. However, previous estimates have not consistently integrated these lines of evidence. In this work, an interdisciplinary analysis is applied to co‐constrain core‐mantle boundary heat flow and test the thermal boundary layer (TBL) theory. The concurrence of TBL models, energy balance to support geomagnetism, seismology, and review of petrologic evidence for historic mantle temperatures supports QCMB ∼15 TW, with all except geomagnetism supporting as high as ∼20 TW. These values provide a tighter constraint on core heat flux relative to previous work. Our work describes the seismic properties consistent with a TBL, and supports a long‐lived basal mantle molten layer through much of Earth's history.

B. Remya, D. G. Sibeck, J. M. Ruohoniemi et al.

Abstract Electromagnetic ion cyclotron (EMIC) waves tend to occur during geomagnetic storms and solar wind pressure pulses. However, they have also been regularly observed even in the absence of these two drivers. These non‐storm time and non‐pressure pulse EMIC events are very well associated with individual nightside injections (Remya et al., 2018, https://doi.org/10.1029/2018JA025354). Nevertheless, not all substorm injections elicit wave activity. We examine the EMIC events excited during two substorm injections on 4 September 2015 and 1 October 2015. We find that injections that are associated with EMIC waves are also associated with enhanced ionospheric convection. The convective signatures occur at local times similar to those of the observed wave activity.

Wen Li, Dongyan Wei, Qifeng Lai et al.

Wi-Fi radio-map construction is an important phase in indoor fingerprint localization systems. Traditional methods for Wi-Fi radio-map construction have the problems of being time-consuming and labor-intensive. In this paper, an indoor Wi-Fi radio-map construction method is proposed which utilizes crowdsourcing data contributed by smartphone users. We draw indoor pathway map and construct Wi-Fi radio-map without requiring manual site survey, exact floor layout and extra infrastructure support. The key novelty is that it recognizes road segments from crowdsourcing traces by a cluster based on magnetism sequence similarity and constructs an indoor pathway map with Wi-Fi signal strengths annotated on. Through experiments in real world indoor areas, the method is proved to have good performance on magnetism similarity calculation, road segment clustering and pathway map construction. The Wi-Fi radio maps constructed by crowdsourcing data are validated to provide competitive indoor localization accuracy.

A. Hausoel, M. Karolak, E. Şaşιoğlu et al.

A first principles understanding of the origins of the Earth's magnetic field requires the study of iron and nickel at high temperatures and pressures. Here, the authors find anomalies in the electronic properties of nickel and iron-nickel alloys, which may be important for the physics of geomagnetism.

Guillaume St-Onge, Joseph S. Stoner

Along with the dramatic decrease in global geomagnetic field intensity, recent observations demonstrate that the geomagnetic field in the Arctic has dramatically changed over the last century. This change is best illustrated by the recent migration of the North Magnetic Pole (which has been in the Canadian Arctic for the last 400 years) into the Arctic Ocean. Because historical records are short, paleomagnetic studies are needed to put these recent Arctic geomagnetic changes into a proper temporal context. This paper presents an overview of Arctic geomagnetism, paleomagnetism, and recent efforts to move our understanding forward by looking at recent or emerging high-resolution Holocene records from the Low and the High Arctic. These paleomagnetic records attest to the unique nature of the geomagnetic field in the High Arctic. They also highlight how the Arctic, and especially the High Arctic, is a unique vantage point for studying geodynamo processes associated with the tangent cylinder model of convective flow within Earth's core that could lead to differences in the behavior of the geomagnetic field observed at Earth's surface, and possible relationships to paleomagnetic secular variations at mid-latitudes.

W. Elsasser

L. Lanci

W. Malkus

H. Ashton