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The paper presents results of modeling various variations of the Universal Time (UT1). To develop a variation models, UT1 observations from 1901 to 2020 published by the International Earth Rotation and Reference Systems Service (IERS) were used. Using the developed method, the main variations are identified from the diverse spectrum of irregularities in the Earth’s rotation, the models of which are presented as a superposition of a limited number of harmonic components. The results obtained in this paper are important for improving the accuracy of predictions of Universal Time.

There are remarkable ionospheric discrepancies between space-borne (COSMIC) measurements and ground-based (ionosonde) observations, the discrepancies could decrease the accuracies of the ionospheric model developed by multi-source data seriously. To reduce the discrepancies between two observational systems, the peak frequency (foF2) and peak height (hmF2) derived from the COSMIC and ionosonde data are used to develop the ionospheric models by an artificial neural network (ANN) method, respectively. The averaged root-mean-square errors (RMSEs) of COSPF (COSMIC peak frequency model), COSPH (COSMIC peak height model), IONOPF (Ionosonde peak frequency model) and IONOPH (Ionosonde peak height model) are 0.58 MHz, 19.59 km, 0.92 MHz and 23.40 km, respectively. The results indicate that the discrepancies between these models are dependent on universal time, geographic latitude and seasons. The peak frequencies measured by COSMIC are generally larger than ionosonde’s observations in the nighttime or middle-latitudes with the amplitude of lower than 25%, while the averaged peak height derived from COSMIC is smaller than ionosonde’s data in the polar regions. The differences between ANN-based maps and references show that the discrepancies between two ionospheric detecting techniques are proportional to the intensity of solar radiation. Besides, a new method based on the ANN technique is proposed to reduce the discrepancies for improving ionospheric models developed by multiple measurements, the results indicate that the RMSEs of ANN models optimized by the method are 14–25% lower than the models without the application of the method. Furthermore, the ionospheric model built by the multiple measurements with the application of the method is more powerful in capturing the ionospheric dynamic physics features, such as equatorial ionization, Weddell Sea, mid-latitude summer nighttime and winter anomalies. In conclusion, the new method is significant in improving the accuracy and physical characteristics of an ionospheric model based on multi-source observations.

The present work uses the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), under geomagnetically disturbed conditions that are closely related to the southward interplanetary magnetic field (IMF), to investigate how the nighttime poleward wind (30°–50° magnetic latitude and 19–22 magnetic local time) responds to subauroral polarization streams (SAPS) that commence at different universal times (UTs). The SAPS effects on the poleward winds show a remarkable UT variation, with weaker magnitudes at 00 and 12 UT than at 06 and 18 UT. The strongest poleward wind emerges when SAPS commence at 06 UT, and the weakest poleward wind develops when SAPS occur at 00 UT. A diagnostic analysis of model results shows that the pressure gradient is more prominent for the developing of the poleward wind at 00 and 12 UT. Meanwhile, the effect of ion drag is important in the modulation of the poleward wind velocity at 06 and 18 UT. This is caused by the misalignment of the geomagnetic and geographic coordinate systems, resulting in a large component of ion drag in the geographically northward (southward) direction due to channel orientation of the SAPS at 06 and 18 UT (00 and 12 UT). The Coriolis force effect induced by westward winds maximizes (minimizes) when SAPS commence at 12 UT (00 UT). The centrifugal force due to the accelerated westward winds shows similar UT variations as the Coriolis force, but with an opposite effect.

On September 6, 2017, the solar active region AR 2673 emitted two solar flares: the first at 08:57 UT (X2.2) and the second at 11:53 UT (X9.3); both were powerful enough to black-out high and low frequency radio waves (where UT is universal time). The X9.3 was the strongest solar flare event in the past decade. In this study, we took the advantage of these two extreme flare events to investigate corresponding effects on the ionosphere using multi-instrument observations from magnetometers, Global Positioning System – Total Electron content (GPS-TEC) receivers, ionosondes and Swarm satellites over a large geographical extent covering South American, African and European sectors. During the X2.2 flare, European and African sectors were sunlit and during X9.3 European, African, and South American sectors were sunlit and exposed to the solar flare radiation. During the X2.2 flare, there was an ionosonde blackout for a duration of about 45 min, while during the X9.3 flare this blackout lasted for 1 h and 30 min. The blackout are seen over a large global extent which demonstrates the severity of solar flare events in disrupting the radio communication. The horizontal component of Earth’s geomagnetic field has shown ripples and enhancements during these flare events. The ionospheric Vertical Total Electron Content (VTEC) showed a positive phase along with an intensification of the Equatorial Ionization Anomaly (EIA) over the South American and African sectors. The dynamical and physical processes associated with the TEC and EIA variabilities due to solar flare are discussed.

Earthquake (EQ) anomalies in the form of enhancement and depletion in ionospheric Total Electron Content (TEC) from Global Positioning System (GPS) may considerably alarm about short and long term precursors of the impending main shock. In this paper, TEC anomalies are investigated from permanent GPS ground-stations in Turkey associated to Mw ≥ 6.0 EQs occurred in 2011–2012. Temporal and spatial analyses of TEC at 2 h sampling have shown significant evidences about EQ induced ionospheric anomalies during 10–14 h of UT (Universal Time) within 5 days before Mw 6.0 Greece, and Mw 7.1, Turkish EQ. Spatial analyses have manifested arrival of TEC anomalies at UT = 10 h to epicenter of both EQs, which linger above epicenter during UT = 12–14 h and left seismogenic zone after UT = 14 h before every EQ during Kp

A well-known property of the classical least squares (LS) extrapolation is that a fit is best in the middle of the time span of observed data, but worse near the beginning and end of the time span. This phenomenon is called the edge effect in data processing. The goal of this work is to reduce the edge effect to improve predictions of the Earth rotation parameters (ERP), which comprise the Earth’s polar motion and rotation angle (the difference between the smoothed principal form of universal time UT1 and the coordinated universal time UTC) because a best LS fitting near the end of the data used is better for extrapolation. We first use the LS extrapolation for models consisting of one polynomial and two sinusoids in combination with an autoregressive (AR) technique to extend the observed time series forward. We then re-estimate the LS extrapolation model from the extended time series to reduce the edge-effect. ERP predictions are subsequently generated by combining of the edge effect reduced LS extrapolation and AR technique, denoted as ERLS + AR. Through an example, we demonstrate that the edge-effect in the observed data fitting can be reduced by re-estimating the LS extrapolation model with the extended time series. To validate the ERLS + AR method, we calculate the ERP predictions up to 365 days into the future year-by-year for the 4-year period from 2014 to 2017 using the data from the previous 8 years. The results show that the accuracy of the short-term predictions obtained by the ERLS + AR method is comparable with that achieved by the LS + AR approach in terms of the mean absolute error (MAE). However, an accuracy improvement is found mostly for long-term predictions based on the ERLS + AR method. The MAE for the UT1 ? UTC and polar motion predictions can decrease by approximately 15% to 20%, respectively. It is therefore suggested embedding the ERLS extrapolation algorithm into the existing ERP prediction procedure.

The results of the work on the improvement of programs and methods for the joint processing (combining) of measurement results of various types (radio-interferometry with extra-long bases, satellite laser ranging, measurements based on the results of receiving signals from global navigation satellite systems) at the Main Metrology Center of the State Service for Time, Frequency, and Earth’s Rotation Parameters Evaluation are described. Methods of combining the results of various measurements at the measurement levels and time series level are considered. The accuracy of determining universal time was improved by the post-correlation- processing of measurement results obtained from new 13-meter antennas of a two-element radio interferometer at the colocation assemblies of the Institute of Applied Astronomy of the Russian Academy of Sciences. The accuracy of determining the combined values of the Earth’s rotation parameters was increased due to the following: improvement in the accuracy of the individual series obtained by processing various measurements determined by different data processing and analysis centers and improvement of combination algorithms.

As part of the operation of the military segment of the Service of Universal Time and Reference Frequencies, the results of the pilot operation of the subsystem for providing universal time for military consumers are presented, which is built on the basis of the national measurement standard of time and frequency, the output standard of the Armed Forces of Ukraine of time and frequency using precise time servers (Microsemi Time Provider 4100) and fiber-optic technologies for transmitting time synchronization signals via PTP and NTP protocols over packet data networks – Ethernet. Studies have confirmed the possibility of transmitting reference signals of time and frequency synchronization using modern digital and fiber-optic technologies from the national measurement standard of time and frequency to the reference standard of the units of time and frequency of the Armed Forces of Ukraine with the root mean square deviation (RMS) of error not exceeding 30 ns. RMS from the mean value of the reference signal of frequency 1 РРS of the slave server of the communication center (Kyiv) when transmitting reference signals for synchronizing time from the reference standard of the units of time and frequency of the Armed Forces of Ukraine (Kharkiv) in the observation interval of 30 days (with periodic daily switching on the servers located in the ICEC of the Armed Forces of Ukraine) did not exceed 100 ns. With a continuous operating mode (2 days), the RMS was not more than 65 ns. The research results make it possible to formulate basic requirements for the composition, technical characteristics, functional capabilities and operating modes of the equipment of the military consumer time synchronization system using the PTP and NTP protocols over packet data networks – Ethernet in order to ensure its reliability and accuracy.

2019 marked the 20th anniversary of the International VLBI Service for Geodesy and Astrometry (IVS). This service is the largest and most authoritative organization that coordinates international activities in radio astrometry and VLBI sub-system of space geodesy. Currently, about 60 antennas located in many countries on all continents participate in the IVS observing programs. The IVS Data Centers have accumulated more than 18 million observations obtained during more than 17'000 sessions, including more than 10,000 Intensive sessions for rapid determination of Universal Time. The paper traces the dynamics of IVS development based on statistical processing of the array of observations collected in the IVS Data Centers for the period of 1979-2018. Various statistics by the years, stations, baselines, and radio sources are provided. The evolution of the IVS observational data and the accuracy of results obtained from processing VLBI observations is considered., Comment: Incorporated corrections submitted and accepted for publication in Astronomy Reports

A resolution about continuing Coordinate Universal Time (UTC) is drafted by Commission A of URSI. When soliciting advices before submitting the resolution to ITU-R, China Commit of URSI delivered an opposition comment. This opposition comment raised highly concern and a further debate upon whether the leap second should be added into UTC. Here, the issue of the UTC's leap second and time continuity is revealed, the views of supportive and oppositive are introduced, the initial and final drafts of statement by URSI are compared.

The article deals with the issues of time synchronization using the Internet protocols NTP and PTP. These issues are considered as an example of the state of affairs and the prospects of development of the Service of Universal Time and Reference Frequencies (hereinafter referred to as the Time and Frequency Service) in terms of the dissemination of time and frequency via the Internet and increase of the reliability and immunity of the entire system as a whole. With the development of information technology and communication systems 3G, 4G, 5G, network synchronization has become more important than ever before. The need for synchronization for some sectors of the economy has come close to existing possibilities. Today, there are several options for device synchronization in Ukraine: via the Internet, using PTP, NTP, and locally using GNSS. The latter option provides high-precision synchronization up to 40 ns, but has a major disadvantage: poor noise immunity. According to some experts, our dependence on GPS is becoming very dangerous, given the extreme unreliability of this technology. The problem is that the signal from the satellite is very weak, and it is extremely easy to muffle it with generating noise at the same frequency. At the same time, as the needs increase, the bandwidth of existing NTP and PTP servers will not be able to process all requests. This requires a major reorganization and implementation of organizational measures, such as: firstly, the rendering of the nodes of time synchronization with UTC (UA) by Ukraine’s national measurement standard of time, and secondly, the development of NTP and PTP servers controlled by the Time and Frequency Service of Ukraine as an alternative to GPS synchronization, that is the best way to develop the Time and Frequency Service.

The work examines diurnal variations in the statistical characteristics of the variability of the electron number density NmF2 of the maximum of the ionspheric F2 layer during quiet geomagnetic conditions at low solar activity based on hourly ionosonde measurements of the critical frequency of the ionspheric F2 layer from 1957 to 2017 over Moscow. The statistical parameters of NmF2 are calculated for each month M of each year at the universal time UT = 0, 1, … 23 h: the mathematical expectation NmF2E; the most probable value NmF2MP; the average monthly median NmF2MED; the arithmetic mean NmF2A; the standard deviations of NmF2 from NmF2E, NmF2MP, and NmF2MED; and the coefficients of variation CVE, CVMP, and CVMED of NmF2 relative to NmF2E, NmF2MP, and NmF2MED, respectively. It follows from the calculations that the CVE, CVMED, and CVMP values vary within the intervals of 12–43%, 12–60%, and 13–75%, respectively, and, in the vast majority of cases, CVE(UT, M) < CVMED(UT, M) and CVE(UT, M) < CVMP(UT, M). If the coefficient CVE in each month of each year is compared for different time points, the lowest CVE value varies from 12% (July) to 19% (December) and occurs during daytime, while the highest CVE value lies in the interval from 26% (June) to 43% (December). For each UT, the lowest and highest values of this coefficient in the autumn, winter, and spring months are greater than those for the summer months. It was found that the difference of NmF2A(UT, M) from NmF2E(UT, M) does not exceed 0.2%.