Universal Time Research Articles

HUB-GA: A heuristic for universal lists broadcasting using genetic algorithm

Broadcasting is a fundamental problem in the information dissemination area. In classical broadcasting, a message must be sent from one network member to all other members as rapidly as feasible. Although this problem is NP-hard for arbitrary graphs, it has several applications in various fields. As a result, the universal lists model, which replicates some real-world restrictions like the memory limits of nodes in large networks, is introduced as a branch of this problem in the literature. In the universal lists model, each node is equipped with a fixed list and has to follow the list regardless of the originator. As opposed to various applications for the problem of broadcasting with universal lists, the literature lacks any heuristic or approximation algorithm. In this regard, we suggest HUB-GA: A heuristic for universal lists broadcasting with genetic algorithm, as the first heuristic for this problem. HUB-GA works toward minimizing the universal lists broadcast time of a given graph with the aid of genetic algorithm. We undertake various numerical experiments on frequently used interconnection networks in the literature, graphs with clique-like structures, and synthetic instances with small-world model in order to cover many possibilities of industrial topologies. We also compare our results with state-of-the-art methods for classical broadcasting, which is proved to be the fastest model among all. Nevertheless of the substantial memory reduction in the universal list model compared to the classical model, our algorithm finds the same broadcast time as the classical model in diverse situations.

RRVPE: A Robust and Real-Time Visual-Inertial-GNSS Pose Estimator for Aerial Robot Navigation

Self-localization and orientation estimation are the essential capabilities for mobile robot navigation. In this article, a robust and real-time visual-inertial-GNSS(Global Navigation Satellite System) tightly coupled pose estimation (RRVPE) method for aerial robot navigation is presented. The aerial robot carries a front-facing stereo camera for self-localization and an RGB-D camera to generate 3D voxel map. Ulteriorly, a GNSS receiver is used to continuously provide pseudorange, Doppler frequency shift and universal time coordinated (UTC) pulse signals to the pose estimator. The proposed system leverages the Kanade Lucas algorithm to track Shi-Tomasi features in each video frame, and the local factor graph solution process is bounded in a circumscribed container, which can immensely abandon the computational complexity in nonlinear optimization procedure. The proposed robot pose estimator can achieve camera-rate (30 Hz) performance on the aerial robot companion computer. We thoroughly experimented the RRVPE system in both simulated and practical circumstances, and the results demonstrate dramatic advantages over the state-of-the-art robot pose estimators.

Estimation of Earth Rotation Parameters and Prediction of Polar Motion Using Hybrid CNN–LSTM Model

The Earth rotation parameters (ERPs), including polar motion (PMX and PMY) and universal time (UT1-UTC), play a central role in functions such as monitoring the Earth’s rotation and high-precision navigation and positioning. Variations in ERPs reflect not only the overall state of movement of the Earth, but also the interactions among the atmosphere, ocean, and land on the spatial and temporal scales. In this paper, we estimated ERP series based on very long baseline interferometry (VLBI) observations between 2011–2020. The results show that the average root mean square errors (RMSEs) are 0.187 mas for PMX, 0.205 mas for PMY, and 0.022 ms for UT1-UTC. Furthermore, to explore the high-frequency variations in more detail, we analyzed the polar motion time series spectrum based on fast Fourier transform (FFT), and our findings show that the Chandler motion was approximately 426 days and that the annual motion was about 360 days. In addition, the results also validate the presence of a weaker retrograde oscillation with an amplitude of about 3.5 mas. This paper proposes a hybrid prediction model that combines convolutional neural network (CNN) and long short-term memory (LSTM) neural network: the CNN–LSTM model. The advantages can be attributed to the CNN’s ability to extract and optimize features related to polar motion series, and the LSTM’s ability to make medium- to long-term predictions based on historical time series. Compared with Bulletin A, the prediction accuracies of PMX and PMY are improved by 42% and 13%, respectively. Notably, the hybrid CNN–LSTM model can effectively improve the accuracy of medium- and long-term polar motion prediction.

Single station bias calculation using data from calibrated GNSS station for various baseline distances

Precise ionospheric TEC can be derived from dual-frequency GNSS carrier phase leveled pseudorange measurements. However, differential code biases (DCB) of satellite and receiver are the main errors that cannot be ignored for precise TEC calculation. We have proposed a method of calculating station DCB using calibrated STEC data from a baseline GNSS station. The method is simply based on the understanding that the ionosphere observed by two baseline GNSS stations at the same universal time (UT) can be considered similar and would pose similar delay to the signals propagating to the two stations. The method is tested for different baseline distances of 250–1000 km and in different latitudinal regions. For 500 km baseline, the average DCB calculation error for one year data is less than 0.22 ns, 0.11 ns, and 0.25 ns for low, mid and high latitude regions, respectively. The most consistent results were obtained from high latitudes where the standard deviation remains less than 0.22 ns. The least accurate were the low latitude results where the spread of error were between 0.29 to 0.50 ns. Results showed that the accuracy and consistency of the DCB estimation reduced with the increasing baseline distance between the two participating GNSS stations. This was specifically true for low latitude regions.

Aeronomic and Dynamic Correction of the Global Model GTEC for Disturbed Conditions

An aeronomic and dynamic correction of the GTEC median global model of the total electroncontent for disturbed conditions (Ap ≥ 15 nT) is proposed. The GTEC global median model is developedfor quiet conditions (Ap 15 nT) as a function of the geographic coordinates, universal time UT, day of theyear, and solar activity level (the solar radio emission flux F10.7). The model is based on a spherical harmonicanalysis of the GIM-TEC Global Ionospheric Maps (1996–2019) provided by the Jet PropulsionLaboratory (NASA). The proposed GDMTEC global dynamic model (Global Dynamic Model of TEC)consists of the GTEC median model updated with several dynamic and aeronomic corrections related toformation of the main ionospheric trough, position of the auroral ionization maximum and changes of thethermospheric temperature and composition. The advantage of the proposed corrections of the medianmodel is the independence of forecast of the data in real time from assimilation of the current observationaldata. Testing of the model for disturbed conditions shows an improvement of the forecast compared to theIRI-Plas ionospheric reference model

Comparative Ontology of Theories of Space and Time

With a few exceptions, physics theories are based in a conception of time and space; our two major theories, general relativity, and quantum field theory, differ in their conceptions. Key issues herein include mathematics, logic, intuition, experiment, and ontology, with emphasis on simultaneity and dimensionality of the world. The treatment is through ontological comparison of two theories, space-time theory (special relativity) and energy-time theory (local absolute space and universal time). These two theories share many of the same equations but have different ontology.

Mathematical model of the global ionospheric electric field generated by thunderstorms

A model is created for the thunderstorm-related ionospheric part of the global electric circuit in January. This current system consists of both mid-latitude currents and equatorial electrojets, day-time and night-time, westward and eastward, up to 120 A. Data on the atmospheric fair weather electric field obtained during Carnegie cruise VII are plotted as a two dimensional map in Universal Time and month coordinates to show both time and seasonal variations.

Анализ вариаций в движении Северного полюса для повышения точности координатно-временных определений

This article considers a method for predicting the coordinates of the north pole, taking into account the influence of trend, quasi-periodic, regular and high-frequency variations. The necessary graphic material is given, illustrating the picture of the listed variations from 2000 to the present. In particular, a regular change in the amplitude of the Chandler period (СP) is shown. So, from 2006 to 2017, the amplitude of the СP gradually decreases from the maximum to zero, and from 2020 to the present, it has been steadily increasing. Based on the analysis of the behavior of trend changes in the pole coordinates, it is shown that at present the movement of the average pole is directed towards the Greenwich meridian, and not towards North America, as it is given in a number of literary sources. The practical implementation of the proposed method resulted in the creation of programs for predicting the coordinates of the pole and Universal Time for periods from one to 90 days. At the same time, the accuracy of forecasts calculated using these programs exceeds the accuracy of similar forecasts posted on the website of the International Earth Rotation Service. The problem of high-precision prediction of the coordinates of the pole and the Universal Time has now acquired particular relevance, especially in the light of the adopted Federal Target Program for the development of GLONASS up to 2030. In the field of improving the accuracy of ephemeris-time support (ETS).

Концепции универсального времени и множественности времен в понимании существования прошлой реальности

Abstract. The purpose of the article is to identify and determine the dependence of ontological ideas about the existence of past reality on thinking within the framework of competing concepts of universal time and multiplicity of times. The methods of research were the representation, comparison and ontological analysis of various ideas about the essence and nature of time, synthesis and philosophical criticism of the consequences arising from competing concepts of the multiplicity of times and the concept of a single universal time in relation to the definition of ontological characteristics of past reality. The article gives a representation of several versions of the concepts of multiplicity of times, some of which are based on the theory of relativity, others proceed from ontological differences in the processes of various forms of being — being material, spiritual, personal and social. It has been shown that in some cases, in the concepts of multiplicity of times, time itself and the idea of time as a construct of the mind are mistakenly identified, which serves as the reason for the incorrect attribution of time to atypical paradoxical properties, such as inversion — the possibility of its movement to reverse, the uncertainty of the past, present and future, the variability of the past and others. The author gives critical arguments refuting ideas about the possibility of changing the places of events and states of reality in the time relationship “earlier/later,” that is, in the sequence of their appearance and disappearance, as well as incorrect opinions about the possibility of variability of the past under the influence of processes that take place in the present and have to be in the future. The study justifies the idea that a clear and unambiguous distinction between past and present objective reality is impossible from the point of view of ideas about the multiplicity of times and is possible only in the conceptual field of theories, recognizing the unity of the world and using a single scale of universal time common to processes and events, having different ontological characteristics and flowing in arbitrarily distant places of space in different inertial reference systems.

Sensorium Dei

The problem of space in philosophy is as old as the problem of time. It comes down to an alternative: whether the three-dimensional volume of the surrounding space exists by itself, as Newton argued, or is associated with the bodies filling it (Leibniz). In the history of philosophy, the dispute between them is qualified as the opposition of the substantial and relational concepts of time and space. It is rarely mentioned, however, that Newton’s “in itself” meant the divine establish­ment of time and space. Euler got rid of the religious solution to the problem of space, who accepted the material universe as a source of formation of a three-dimensional volume. Thus, in mechanics, which began to be called classical, the Newtonian version was replaced by the relativistic one. This is how everyone interpreted the theory of relativity, including the author himself. But in fact, in its depth, Einstein’s solution returned Newton’s version to science, Henri Bergson convincingly argued, only in place of the Newtonian Creator one should put liv­ing nature as a source of universal time and absolute space. Bergson understood life as a new kind of movement, not reducible to mechanics. Bergson’s theoreti­cal positions have been scientifically proven by Vladimir Vernadsky in the con­cept of the proper state of the space of living matter, as well as by biophysicist Erwin Bauer in the principle of non-equilibrium of living systems. The internal energy of living organisms allows them to do work due to entropy. Newton’s conjecture about the sensorium of God turned out to be fruitful.

Rapid Fault Analysis by Deep Learning-Based PMU for Smart Grid System

Smart Grids (SG) is a power system development concept that has received significant attention nationally. SG signifies real-time data for specific communication requirements. The best capabilities for monitoring and controlling the grid are essential to system stability. One of the most critical needs for smart-grid execution is fast, precise, and economically synchronized measurements, which are made feasible by Phasor Measurement Units (PMU). PMUs can provide synchronized measurements and measure voltages as well as current phasors dynamically. PMUs utilize GPS time-stamping at Coordinated Universal Time (UTC) to capture electric phasors with great accuracy and precision. This research tends to Deep Learning (DL) advances to design a Residual Network (ResNet) model that can accurately identify and classify defects in grid-connected systems. As part of fault detection and probe, the proposed strategy uses a ResNet-50 technique to evaluate real-time measurement data from geographically scattered PMUs. As a result of its excellent signal classification efficiency and ability to extract high-quality signal features, its fault diagnosis performance is excellent. Our results demonstrate that the proposed method is effective in detecting and classifying faults at sufficient time. The proposed approaches classify the fault type with a precision of 98.5% and an accuracy of 99.1%. The long-short-term memory (LSTM), Convolutional Neural Network (CNN), and CNN-LSTM algorithms are applied to compare the networks. Real-world data tends to evaluate these networks.

Low latitude monthly total electron content composite correlations

Spatial correlations of total electron content (TEC) variability are compared among two SAMI3 model runs and Jet Propulsion Laboratory Global Ionospheric Maps (JPL/GIM). Individual monthly correlation maps are constructed with Equatorial reference points at 12 evenly spaced longitudes and 12 universal times. TEC composite correlations (TCCs) are then calculated by averaging the individual maps, shifted zonally to synchronize local time. The TCC structures are quantified using Gaussian fits in the zonal and meridional directions. A non-zero large-scale “base correlation” is found in all three datasets for 2014, a year with high solar activity. Higher base correlations generally occur in the SAMI3 runs than in JPL/GIM. The SAMI3 run driven with climatological neutral fields shows higher correlations than the run driven with neutrals from a Whole Atmosphere Community Climate Model with thermosphere–ionosphere eXtension (WACCM-X) simulation. Base correlation values strongly correlate with monthly F10.7 standard deviations. Empirical orthogonal function (EOF) analyses confirm that large-scale correlations are usually, although not always, related to solar forcing. Strong correlations between the Ap index and EOF modes are also observed, consistent with the geomagnetic forcing of the TEC field. The widths of the correlation structures are also examined, and these vary considerably with local time, month, and dataset. Off-Equator conjugate point correlations are also calculated from each dataset and variations with the month and local time are analyzed. Analysis of TCCs for 2010, a year with low solar activity, shows that base correlations as well as correlations of the first EOF mode with F10.7 are generally weaker than in 2014.

Double rupture event in the Tianshan Mountains: A case study of the 2021 Mw 5.3 Baicheng earthquake, NW China

Abstract On March 23, 2021 (21:14 universal time coordinated), an Mw 5.3 earthquake occurred in Baicheng County in Xinjiang, northwestern China, according to the United States Geological Survey. The earthquake produced a 4-km-long surface rupture at the epicenter, which is generally rare for earthquakes of magnitude 5.3. Thus, investigating the Baicheng earthquake is crucial for understanding the seismogenic structure of the region. We obtained the interferometric synthetic aperture radar deformation field and inverted the slip distribution of the Baicheng earthquake using Sentinel-1A satellite data and surface rupture data. The results indicate that the surface deformation area was elliptical, with long and short axes of approximately 20 and 10 km, respectively. The seismogenic structure is a left-lateral strike-slip fault with a small dip-slip component and strike and dip angles of 248° and 70°, respectively. Two other slip centers were also observed at 2 and 8 km beneath the surface in the dip direction. The maximum slip at 2 km was 0.45 m. Shear deformation between the Tarim Basin and Southern Tianshan Mountains was responsible for the strike-slip features of the Baicheng earthquake.

Zymography: developing of the enzyme soil activity visualization method

The enzymes produced by the soil biota are a key link in the regulation of biochemical processes. The soil enzyme activity can be visualized with zymography, a method based on using fluorescent substrates and obtaining two-dimensional images (zymograms). A variant of a zymographic measuring system has been proposed. Characteristics of lighting, photographic equipment and shooting modes, reagents preparation and calibration are presented. Preparing and analyzing soil samples of different texture (sand and clay loam) and processing the study results have been described. The ways of introducing the substrate are considered in this study, namely pipetting, short-time dipping, and saturation. An analysis of the kinetics of incubation of samples was carried out. The possibilities and disadvantages of the method were also considered and options for solving possible methodological problems during the analysis were proposed. The zymography is a promising method that allows comparing data with the results of other methods. The use of neural network technologies makes it possible to obtain the volumetric distribution of soil enzymes with high reliability. The soil zymography requires qualitative preparatory work and extreme accuracy during the analysis. It is necessary to ensure maximum contact between the substrate and the soil, as this is one of the key factors determining the quality of the results. The most optimal way to introduce the substrate is to saturate the membranes with substrate solution for 60 minutes. At this stage of the development of the method, it is not possible to establish a universal sample incubation time, since this depends on characteristics of both the studied soils and the experiment conditions. Also, it is necessary to document the conditions in detail for discussion the study results.

82. Incidence rates of invasive aspergillosis among lung transplant recipients in timeperiods with universal and targeted antifungal prophylaxis - a nationwide cohort study

Abstract Background The best stategy for prevention of invasive aspergillosis (IA) after lung transplantation (LTX) has not been determined. In 2016, Danish guidelines for IA prophylaxis was changed from 12 weeks of universal prophylaxis with voriconazole to targeted prophylaxis with posaconazole and inhaled amphotericin B for high risk patients. In a previous study we found significantly higher rates of adverse events in the period with universal prophylaxis. The objectives of this study were to compare rates of IA 1) in time periods before and after change of guidelines; 2) during persontime on vs. persontime without antifungal prophylaxis in the total study period. Methods In a Danish nationwide study we included all adult lung transplant recipients (LTXr), 2010–2019. Proven and probable IA were defined using ISHLT criteria. Patients were censored at the first of following events: death, retransplantation, end of 2019, or one year after LTX. The cumulative hazard of IA was calculated using the Nelson Aalen estimator. Rates of IA were analyzed in bi- and multivariate Poisson regression models adjusted for the time period after LTX (0–6 and 6–12 months). Persontime on protocol prophylaxis (start to end + 14 days) was treated as time-updated variable. Results A total of 295 LTXr were followed for 245 person-years, of whom 183/193 vs. 6/102 initiated antifungal prophylaxis during the universal vs. the targeted prophylaxis period (Table 1). IA was diagnosed in 34/193 (17.6%) vs. 15/102 (14.7%) LTXr the first year after transplantation in the universal vs. targeted prophylaxis period. Overall, similar cumulative hazards of IA were observed between the universal and targeted prophylaxis period (p=0.59, Figure 1). The adjusted incidence rate ratio (aIRR) of IA during the universal vs. targeted prophylaxis period was 1.30 (95% CI 0.69–2.44), (Table 2). In the total study period, the aIRR of IA during persontime on vs. persontime without antifungal prophylaxis was 0.87 (95% CI 0.40–1.88), (Table 2). Characteristics of lung transplant recipients in time periods with universal voriconazole and targeted posaconazole and inhaled amphotericin B prophylaxis. Proven and probable invasive aspergillosis including anastomosis infection, trakeobronkitis and pneumonia according to ISHLT criteria. *) Underlying diseases categorized as high risk of invasive aspergillosis. Incidence rates (IR) and incidence rate ratios (IRR) of invasive aspergillosis in lung transplant recipients in two multivariate models. Poisson regression models comparing rates of IA in model 1) during universal prophylaxis time period versus targeted prophylaxis time period and in model 2) during persontime on prophylaxis (start to end + 14 days) versus persontime without prophylaxis in the total study period 2010–2019. Adjusted for time after LTX IRR: Bivariable model including the listed variables in bold and adjustment for time after transplantation (time-updated). Fully adjusted IRR: Multivariable model with adjustment for sex, age, high risk underlying disease, single/double lung transplant, Aspergillus prior to transplantation and time after transplantation (time-updated). Abbreviations: LTX = lung transplant recipients; CI = confidence interval; IR = incidence rates per 100 person-years; IRR = incidence rate ratio; Ref. = reference. Cumulative hazards of invasive aspergillosis the first year after lung transplantation in time periods with universal voriconazole versus targeted posaconazole and inhaled amphotericin B prophylaxis. Conclusion A strategy of targeted prophylaxis, for high risk patients only, may be preferred over universal voriconazole prophylaxis after LTX due to similar rates of IA and lower rates of adverse events. Disclosures Maiken C. Arendrup, DMSci, PhD, MD, Chiesi, Gilead: Honoraria|F2G, Cidara, Scynexis: Grant/Research Support Michael Perch, MD, Boeringer-Ingelheim: Travel grant|PulmonX: Expert Testimony|Roche: Grant/Research Support|Takeda: Expert Testimony|Therakos: Honoraria|Zambon: Advisor/Consultant|Zambon: Expert Testimony Marie Helleberg, PhD, DMSc, AstraZeneca: Advisor/Consultant|Gilead: Advisor/Consultant|Gilead: Honoraria|GSK: Advisor/Consultant|GSK: Honoraria|Janssen: Advisor/Consultant|Roche: Advisor/Consultant|Sobi: Advisor/Consultant.

Longitudinal Evolution of Storm-Enhanced Densities: A Case Study

Due to the limitations on observational data, most storm-enhanced density (SED) studies have focused on the North American sector. The complete picture of the longitudinal evolution of SEDs is still not clear. In this study, we investigated the dynamic evolution of SEDs from the European sector to the North American sector during a geomagnetic storm that occurred on the 15 July 2012, the main phase of which lasted nearly 30 h, maintaining the stable interplanetary magnetic field (IMF) and solar wind input conditions. Multiple data sets were analyzed, including convection data from the Super Dual Auroral Radar Network (SuperDARN), total electron contents (TECs) from the Madrigal database, plasma data from the Millstone Hill incoherent scatter radar (MHISR), solar wind and geomagnetic indices from OMNIWeb, and regional auroral electrojet indices from SuperMAG. The observations showed that the positions of SEDs shifted from local noon over the European sector towards dusk over the American sector and simultaneously moved to lower latitudes. The peak values of SED TECs were found to be greater in the European sector and to decrease with universal time. A double SED phenomenon appeared in the North American sector, which is the first of its kind to be reported. Further analysis showed that the temporal and spatial changes in the SEDs were associated with the eastward auroral electrojet.

Storm-Time Relative Total Electron Content Modelling Using Machine Learning Techniques

Accurately predicting total electron content (TEC) during geomagnetic storms is still a challenging task for ionospheric models. In this work, a neural-network (NN)-based model is proposed which predicts relative TEC with respect to the preceding 27-day median TEC, during storm time for the European region (with longitudes 30°W–50°E and latitudes 32.5°N–70°N). The 27-day median TEC (referred to as median TEC), latitude, longitude, universal time, storm time, solar radio flux index F10.7, global storm index SYM-H and geomagnetic activity index Hp30 are used as inputs and the output of the network is the relative TEC. The relative TEC can be converted to the actual TEC knowing the median TEC. The median TEC is calculated at each grid point over the European region considering data from the last 27 days before the storm using global ionosphere maps (GIMs) from international GNSS service (IGS) sources. A storm event is defined when the storm time disturbance index Dst drops below 50 nanotesla. The model was trained with storm-time relative TEC data from the time period of 1998 until 2019 (2015 is excluded) and contains 365 storms. Unseen storm data from 33 storm events during 2015 and 2020 were used to test the model. The UQRG GIMs were used because of their high temporal resolution (15 min) compared to other products from different analysis centers. The NN-based model predictions show the seasonal behavior of the storms including positive and negative storm phases during winter and summer, respectively, and show a mixture of both phases during equinoxes. The model’s performance was also compared with the Neustrelitz TEC model (NTCM) and the NN-based quiet-time TEC model, both developed at the German Aerospace Agency (DLR). The storm model has a root mean squared error (RMSE) of 3.38 TEC units (TECU), which is an improvement by 1.87 TECU compared to the NTCM, where an RMSE of 5.25 TECU was found. This improvement corresponds to a performance increase by 35.6%. The storm-time model outperforms the quiet-time model by 1.34 TECU, which corresponds to a performance increase by 28.4% from 4.72 to 3.38 TECU. The quiet-time model was trained with Carrington averaged TEC and, therefore, is ideal to be used as an input instead of the GIM derived 27-day median. We found an improvement by 0.8 TECU which corresponds to a performance increase by 17% from 4.72 to 3.92 TECU for the storm-time model using the quiet-time-model predicted TEC as an input compared to solely using the quiet-time model.

Assessment of the influences of post-construction facilities on pedestrian-level wind environment: An experimental study in Changsha, China

With continuous urbanisation, an increasing number of post-construction facilities (such as high-rise buildings and green plants) have altered the original layout of the community. Which has resulted in deterioration of the wind environment. However, there is a deficiency of qualitative studies on the pedestrian-height wind environment that focus on the influence of post-construction facilities. The presents research takes Changsha universal time community as a case study. A wind tunnel test at a scale of 1:250 was performed to analyse the wind environment by considering the post-construction facilities. 81 sets of cases with different inflow patterns, wind directions, adjacent high-rise buildings, and plants were examined to reveal the flow field distribution characteristics. Furthermore, the exceedance probability method was introduced to assess the wind environment of the community in different cases. The results indicate that the index distribution coefficient of wind velocity and the turbulence intensity profile inside the practical community is significantly larger than the code values. A roughness distance of 800 m can generate highly effective mean wind profiles. However, it is unable to generate the desired turbulence profiles. Considering the post-construction facilities, high-rise buildings cause acceleration effects on the average wind velocity and the acceleration effects are inversely proportional to the distance of the post-construction facilities. Large, medium, and small trees cause deceleration effects of the average wind speed and improve the wind environment comfort quality of the community.

The Adriatic Thrust Fault of the 2021 Seismic Sequence Estimated from Accurate Earthquake Locations Using sP Depth Phases

ABSTRACT An earthquake sequence occurred in the Central Adriatic region during March–June 2021. This sequence started on 27 March with a mainshock of moment magnitude (Mw) 5.2 occurring at 13:47 coordinated universal time (UTC). No foreshock was observed before this mainshock. The sequence lasted approximately three months, until the end of June 2021. Approximately 200 seismic events were recorded by the regional seismic network during this time, including four M ≥ 4.0 earthquakes. The 27 March 2021 earthquake was one of the strongest instrumentally recorded events in the area bounded approximately by the Ancona–Zadar line to the north and the Gargano–Dubrovnik line to the south. The mainshock originated at a focal depth of 9.9 km. The seismicity spread from the mainshock up-dip and down-dip along a northeast-dipping plane. Here, we investigate the geometry of the fault activated by this seismic sequence by using sP depth phases. We aim to significantly reduce the large uncertainties associated with the hypocentral locations of offshore earthquakes beneath the Adriatic Sea—an area that plays a fundamental role in the geodynamics of the Mediterranean. These refined earthquake locations also allow us to make inferences with regards to the seismotectonic context responsible for the analyzed seismicity, thus identifying a structure (here referred to as the Mid-Adriatic fault) consisting of a northwest–southeast-striking thrust fault with a ∼35° northeast-dipping plane. The use of depth-phase arrival times to constrain off-network event locations is of particular interest in Italy due to both the peculiar shape of the peninsula and the extreme scarcity of seafloor stations, the cost and management of which are very expensive and complex. Here, we present the first attempt to apply this off-network locating technique to the Italian offshore seismicity research with the aim of improving hazard estimations in these hard-to-monitor regions.

Global Gridded Ionospheric Electron Density Derivation During 2006–2016 by Assimilating COSMIC TEC and Its Validation

AbstractThe long‐term accurate specification of the Earth's ionospheric states is crucial to scientific research and applications in the space weather community. In the current work, a global monthly mean three‐dimensional (3‐D) ionospheric electron density product has been obtained during one solar cycle from 2006 to 2016. Specifically, an accurate 3‐D product is reconstructed monthly by assimilating the Constellation Observing System for Meteorology, Ionosphere and Climate slant total electron content (TEC) into an empirical background model via the Kalman filter data assimilation algorithm. The outputs of the results have spatial resolutions of 2° in latitude, 5° in longitude, and 20 km in height, and temporal resolution of 1 hr in universal time. The accuracy and reliability of the results are systematically validated by the critical frequency at the F2 layer from global ionosonde stations, the in situ electron density from the CHAllenging Minisatellite Payload Planar Langmuir Probe, the TEC from the Massachusetts Institute of Technology, and Gravity Recovery and Climate Experiment. We found that the products agree well with the independent observations. Some well‐known ionospheric climatological patterns, including the solar and seasonal variation, annual asymmetry, the Weddell Sea Anomaly, and the longitudinal wave structure, can be well illustrated. The advantages of the products are its 3‐D and gridded electron density and continuous one solar cycle time series (2006–2016). It is useful to study the spatial‐temporal variations in ionospheric states from seasons to decades, which can also be used as the background parameters for atmospheric and ionospheric‐related scientific research and applications.