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We consider quantum field theoretic systems subject to a time-dependent perturbation, and discuss the question of defining a time dependent particle number not just at asymptotic early and late times, but also during the perturbation. Naively, this is not a well-defined notion for such a non-equilibrium process, as the particle number at intermediate times depends on a basis choice of reference states with respect to which particles and anti-particles are defined, even though the final late-time particle number is independent of this basis choice. The basis choice is associated with a particular truncation of the adiabatic expansion. The adiabatic expansion is divergent, and we show that if this divergent expansion is truncated at its optimal order, a universal time dependence is obtained, confirming a general result of Dingle and Berry. This optimally truncated particle number provides a clear picture of quantum interference effects for perturbations with non-trivial temporal sub-structure. We illustrate these results using several equivalent definitions of adiabatic particle number: the Bogoliubov, Riccati, Spectral Function and Schrodinger picture approaches. In each approach, the particle number may be expressed in terms of the tiny deviations between the exact and adiabatic solutions of the Ermakov-Milne equation for the associated time-dependent oscillators.

Spectral analysis of ionospheric disturbances of seismic origin will aid for the detection and prediction of the unavoidable natural disasters like Earthquakes. These disturbances for an earthquake occurred in Kawalu, West Java Indonesia with a magnitude of 4.3 on Richter scale was analyzed. The earthquake has occurred on 12th December 2013 at 7:02 hours universal time coordinate i.e at 12:32 hours local time coordinate. Maximum entropy method was applied on the ionopsheric disturbances seen on the earthquake day. The enhancement in the energy of the ionosphere has a high value at the beginning. It had a slow initial decrement and then a rapid fall down is observed. The method may profoundly represent the effect impending earthquake.

A reference system is a theoretical concept of coordinates, and includes the time and the standards necessary to specify the bases for giving positions and motions in the system. There are celestial and terrestrial reference systems

The spectrum of high frequency Earth rotation variations contains strong harmonic signal components mainly excited by ocean tides along with much weaker non-harmonic fluctuations driven by irregular processes like the diurnal thermal tides in the atmosphere and oceans. In order to properly investigate non-harmonic phenomena a representation in time domain is inevitable. We present a method, operating in time domain, which is easily applicable within Earth rotation estimation from Very Long Baseline Interferometry (VLBI). It enables the determination of diurnal and subdiurnal variations, and is still effective with merely diurnal parameter sampling. The features of complex demodulation are used in an extended parameterization of polar motion and universal time which was implemented into a dedicated version of the Vienna VLBI Software VieVS. The functionality of the approach was evaluated by comparing amplitudes and phases of harmonic variations at tidal periods (diurnal/semidiurnal), derived from demodulated Earth rotation parameters (ERP), estimated from hourly resolved VLBI ERP time series and taken from a recently published VLBI ERP model to the terms of the conventional model for ocean tidal effects in Earth rotation recommended by the International Earth Rotation and Reference System Service (IERS). The three sets of tidal terms derived from VLBI observations extensively agree among each other within the three-sigma level of the demodulation approach, which is below 6 μas for polar motion and universal time. They also coincide in terms of differences to the IERS model, where significant deviations primarily for several major tidal terms are apparent. An additional spectral analysis of the as well estimated demodulated ERP series of the ter- and quarterdiurnal frequency bands did not reveal any significant signal structure. The complex demodulation applied in VLBI parameter estimation could be demonstrated a suitable procedure for the reliable reproduction of high frequency Earth rotation components and thus represents a qualified tool for future studies of irregular geophysical signals in ERP measured by space geodetic techniques.

This paper introduces briefly international standard time scale---theCoordinated Universal Time (UTC) and its realization, the time references and their traceability of Global Navigation Satellite System (GNSS). GNSS is based on precision time measurement, an uniform internal time reference is necessary to ensure all parts in a GNSS run synchronously. All GNSS system have precision time reference systems, at the same time, it is necessary that the time reference should be traced to the international legal time standard, UTC, to ensure global time synchronous and uniform, it can be realized by establishing time comparison link with national time standard. A possible solution of GNSS time reference and its traceability for COMPASS is discussed.

The celestial-mechanics approach (the spatial version of the problem for the Earth-Moon system in the field of gravity of the Sun) is used to construct a mathematical model of the Earth’s rotational-oscillatory motions. The fundamental aspects of the processes of tidal inhomogeneity in the Earth rotation and the Earth’s pole oscillations are studied. It is shown that the presence of the perturbing component of gravitational-tidal forces, which is orthogonal to the Moon’s orbit plane, also allows one to distinguish short-period perturbations in the Moon’s motion. The obtained model of rotational-oscillatory motions of the nonrigid Earth takes into account both the basic perturbations of large amplitudes and the more complicated small-scale properties of the motion due to the Moon short-period perturbations with combination frequencies.

Results of using the mode of automated data transmission from the very long baseline interferometry (VLBI) observatory complex of the Radiointerferometric Network Quasar-KVO, Russian Academy of Sciences correlation processing center are presented. The automated data exchange mode ensures a substantial reduction (∼30%) in the delivery times of observation data as compared to the nonautomated mode, in which the data transmission starts after the hour session completion. The automated data transmission and data exchange algorithm optimization allowed us to increase the efficiency in obtaining the universal time (UT) for the GLONASS global navigation system.

The intensity–time profile of Forbush decrease (FD) events observed by neutron monitors (NMs) looks like that of a geomagnetic storm as defined by the Dst index. Oh, Yi, and Kim (J. Geophys. Res. 113, A01103, 2008) and Oh and Yi (J. Geophys. Res. 114, A11102, 2009) classified FD events based on the amount of overlap and simultaneity of their main phase in Universal Time (UT). Oh and Yi define an FD event as simultaneous if the main phases observed by NMs distributed evenly around the Earth overlap in UT, and nonsimultaneous if they overlap only in the local time of some stations. They suggested that the occurrence mechanisms of two types of FD events may be related to interplanetary (IP) magnetic structures such as IP shocks and magnetic clouds. In their model, the simultaneity of FD events depends on the strength and propagation direction of magnetic structures overtaking the Earth. Recently, the Solar Terrestrial Relations Observatory (STEREO) mission has been able to visualize the emergence and propagation direction of coronal mass ejections (CMEs) in three dimensions in the heliosphere; thus, it is now possible to test the suggested mechanisms. One simultaneous FD event observed on 18 February 2011 may have been caused by a CME heading directly toward the Earth, which was observed on 15 February 2011 by the STEREO mission. Therefore, the simultaneity of FD events is proven to be a useful analysis tool in understanding the geoeffectiveness of solar events such as interplanetary CMEs and IP shocks.

A new approach to defining universal time in terms of observed intervals of pulsar time and measured parameters of the earth’s rotation is proposed. The identity of pulsar scales of universal time UT1 determined from equivalent parameters of the earth’s rotation is demonstrated. Computational relationships are derived for determining the parameters of pulsar scales of universal time and evaluating their errors.

The hardware and software upgrades to the Quasar VLBI network have allowed one to increase the measurement accuracy of the Earth orientation parameters (EOPs) and to improve the quality of geodynamic observations. At present, the observations are performed within two national programs: 24-h sessions on three radio telescopes of the network to determine all five EOPs (the Ru-E program) and 1-h sessions on the Zelenchukskaya-Badary and Svetloe-Badary baselines (the Ru-U program) for a prompt determination of the Universal Time. The results of processing the observations from January 2009 to November 2011 are presented. The rms deviations of the EOPs obtained in the Ru-E program from the IERS 08 C04 series are 1 mas for the coordinates of the Earth’s pole, 0.38 mas for the coordinates of the celestial pole, and 34 µs for the Universal Time. The rms deviations of the Universal Time obtained in the Ru-U program are 53 µs.

In experimental investigations of artificial and natural signals in extremely-low frequency (ELF) and ultra-low frequency (ULF) ranges, it is necessary to measure amplitudes and relative phases of the electromagnetic field components in a network of stations. The phase measurement includes accurate synchronization of data with the universal time. In this work, the geophysical data acquisition system, which allows one to synchronize measurement results and the coordinated universal time with an accuracy of a few microseconds, is described. Methods for processing the electromagnetic field components of the harmonic signal source, recorded by this data acquisition system, are proposed.

In the present work we model the global ionospheric total electron content (TEC) with the analysis of empirical orthogonal functions (EOF). The obtained statistical eigen modes, which makeup the modeled TEC, consist of two factors: the eigen vectors mapping TEC patterns at latitude and longitude (or local time LT), and the corresponding coefficients displaying the TEC variations in different time scales, i.e., the solar cycle, the yearly (annual and semiannual) and the diurnal universal time variations. It is found that the EOF analysis can separate the TEC variations into chief processes and the first two modes illustrate the most of the ionospheric climate properties. The first mode contains both the semiannual component which shows the semiannual ionospheric anomaly and the annual component which shows the annual or non-seasonal ionospheric anomaly. The second mode contains mainly the annual component and shows the normal seasonal ionospheric variation at most latitudes and local time sectors. The annual component in the second mode also manifests seasonal anomaly of the ionosphere at higher mid-latitudes around noontime. It is concluded that the EOF analysis, as a statistical eigen mode method, is resultful in analyzing the ionospheric climatology hence can be used to construct the empirical model for the ionospheric climatology.

The previously constructed mathematical model of the Earth’s axial rotation irregularity is refined with the methods of celestial mechanics by considering secondary terms in the expansion of the lunisolar gravitational tidal torque and by using corrections (residuum) for zonal tidal perturbations. The diurnal and sub-diurnal variations in the Earth’s axial rotation were investigated; namely, a celestial mechanics model adequately describing the observation data and revealing the cause of the diurnal and sub-diurnal oscillations of the angular velocity of the Earth’s rotation was constructed. Some examples of predicting the Earth’s axial rotation are given.

The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes in 1996 and 2000 at Grahamstown (33.32 °S, 26.50 °E) and Madimbo (22.38 °S, 30.88 °E) respectively. This study is intended to quantify the probability of occurrence of F region disturbances associated with SF over South Africa. A study was conducted using data for 8 years (2001–2008) over Madimbo (with a time resolution of 30 min) and Grahamstown (with a variable time resolution of 15 and 30 min). In this study, SF has been classified into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The SF events were identified by manually identifying ionograms showing SF and tabulating them according to type for further statistical analysis. The results show that the diurnal pattern of SF peaks strongly between 01:00 and 02:00 local time, LT (LT = UT + 2 h), where UT is the universal time. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown in 2001 and 2005, except for RSF which had peaks during autumn and spring in 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing solar activity, with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study, SF was evident in ∼0.03% and ∼0.06% of the available ionograms at Madimbo and Grahamstown respectively during the 8 years.

Universal Time (ut) is a non-uniform time-scale based on the rotation of the Earth around its axis. Another time-scale based on the duration of the SI second that was originally defined by the revolution of the Earth in its orbit around the Sun, is called Terrestrial Time (tt). As tt is a uniform time designed to provide continuity with the former Ephemeris Time (et), the difference between tt and ut is known as delta-T (ΔT). The time series of ΔT values shows the variations in Earth rotation. There are several mathematical models to represent ΔT used in astronomical software and calculations. This paper discusses a new model for values of ΔT from 1620 to 2010 that uses artificial neural networks. The maximum absolute error in this model is about 0.5 SI second. The accuracy of the new model is compared with that of four prior models.

A combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) observations was developed on the basis of homogeneous normal equation systems. The emphasis and purpose of the combination was the determination of sub-daily polar motion (PM) and universal time (UT1) for a long time-span of 13 years. Time series with an hourly resolution and a model for tidal variations of PM and UT1-TAI (dUT1) were estimated. In both cases, 14-day nutation corrections were estimated simultaneously with the ERPs. Due to the combination procedure, it was warranted that the strengths of both techniques were preserved. At the same time, only a minimum of de-correlating or stabilizing constraints were necessary. Hereby, a PM time series was determined, whose precision is mainly dominated by GPS observations. However, this setup benefits from the fact that VLBI delivered nutation and dUT1 estimates at the same time. An even bigger enhancement can be seen for the dUT1 estimation, where the high-frequency variations are provided by GPS, while the long term trend is defined by VLBI. The estimated combined tidal PM and dUT1 model was predominantly determined from the GPS observations. Overall, the combined tidal model for the first time completely comprises the geometrical benefits of VLBI and GPS observations. In terms of root mean squared (RMS) differences, the tidal amplitudes agree with other empirical single-technique tidal models below 4 μas in PM and 0.25 μs in dUT1. The noise floor of the tidal ERP model was investigated in three ways resulting in about 1 μas for diurnal PM and 0.07 μs for diurnal dUT1 while the semi-diurnal components have a slightly better accuracy.

Numerical celestial-mechanical models are used to compare (andg interpolate and forecast) near-diurnal tidal variations in the Earth’s axial rotation and oscillations in the global angular momentum of the atmosphere using the IERS data and NCEP/NCAR meteorological data. In order to improve the accuracy of interpolations and forecasts made for short and intraday time intervals, it is expedient to include the effect of small perturbations in short-term zonal tides, which influence fluctuations in Universal Time UT1 directly related to the Earth’s rotation. Due to the quasi-static formulation of the problem, it is assumed that the dynamics of the thin surface atmosphere are completely determined by the gradient of the tide-generating geopotential, which supports forced oscillations of the entire subsystem (i.e., of the mantle and atmospheric envelope). A comparison of the numerical simulations with the NCEP/NCAR data shows that the model is effective for applications in forecasting atmospheric tides.

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the traditional astronomical basis of civil time. International Atomic Time (TAI) is also maintained as a fundamental time scale based on the output of atomic frequency standards. Coordinated Universal Time (UTC) is an atomic scale for worldwide civil timekeeping, referenced to TAI, but with epoch adjustments via so-called leap seconds to remain within one second of UT1. A review of the development of the time scales, the status of the leap-second issue, and user considerations and perspectives are discussed. A description of some more recent applications for time usage is included.

The International Conference held in 1884 at Washington defined a universal time as the mean solar time at the Greenwich meridian (GMT). Now, the Universal Time, version UT1, is strictly defined as proportional to the angle of rotation of the Earth in space. In this evolution, the departure of UT1 from GMT does not exceed one or two seconds. This is quite negligible when compared with the departure between the solar time and the legal time of citizens, which may exceed two hours without raising protests.

We have established a regional ionospheric model (RIM) for investigating changes in the total electron content (TEC) over South Korea using 38 Korean GPS reference stations. The inverse distance weighted (IDW) interpolation method was applied to create a two-dimensional ionospheric map of vertical TEC units (TECU) based on a grid. To examine the diurnal patterns of ionospheric TEC over South Korea, we first processed the GPS data from a geomagnetically quiet period of 10 days. In a second step, we compared the estimated GPS-TEC variations with the changes in geomagnetic activity indices (the Kp and Dst indices) and the auroral electrojet index (AE) as a function of universal time (UT) on 4 and 20 November, 2003. The GPS-TEC responses for those storm events were proportional to the geomagnetic activity at this mid-latitude location. The sudden increases in ionospheric TEC (SITEC) caused by the geomagnetic storms were detected. The variations in GPS-TEC may help reveal the processes of ionospheric disturbances caused by geomagnetic storms.

The results of a prompt determination of the Universal Time corrections in the e-VLBI mode on the Quasar VLBI network in 2009–2011 are presented. For this purpose, the hardware-software tools for observational data transfer from the Svetloe, Zelenchukskaya, and Badary Observatories to the Correlation Processing Center (St. Petersburg) over fiber-optic communication lines in a mode close to real time using the specialized Tsunami protocol have been developed. The rms error in the UTC-UT1 corrections with respect to the combined IERS series is 60 µs.

Pulsars are unique celestial sources that produce distinctive, periodic signals. Since their discovery, they have been considered as potential navigation aids and timing beacons to form a reference coordinate system and universal time scale. Further study of these astronomical objects has shown that their pulse timing can achieve sub-microsecond level performance, and interest and research into these sources has grown to conceive a fully autonomous navigation and timing system for deep space vehicles. Sources that radiate within the X-ray band of the electromagnetic spectrum have high potential for creating a practical spacecraft navigation solution, which includes accurate time and position determination onboard a space vehicle using the precisely periodic sources, and precise attitude determination using both pulsating and steady sources. This paper provides an overview of spacecraft navigation methods and various research and results that have evolved since the concept of X-ray pulsar-based navigation was first proposed.

International audience; Real-time orbit determination and interplanetary navigation require accurate predictions of the orientation of the Earth in the celestial reference frame and in particular that for Universal Time UT1. Much of the UT1 variations over periods ranging from hours to a couple of years are due to the global atmospheric circulation. Therefore, the axial atmospheric angular momentum (AAM) forecast series may be used as a proxy index to predict UT1. Our approach taking advantage of this fact is based on an adaptive procedure. It involves incorporating integrations of AAM estimates into UT1 series. The procedure runs on a routine basis using AAM forecasts that are based on the two meteorological series, from the US National Centers for Environmental Prediction and the Japan Meteorological Agency. It is pertinent to test the prediction method for the period that includes the special CONT08 campaign over which we expect a significant improvement in UT1 accuracy. The studies we carried out were aimed both to compare atmospheric forecasts and analyses, as well as to compare the skills of the UT1 forecasts based on the method with atmospheric forecasts and that using current statistical processes, as applied to the C04 Earth orientation parameters series derived by the International Earth rotation and Reference Systems service (IERS). Here we neglect the oceanic sub-diurnal and diurnal variations, as these signals are expected to be smaller than the UT1-equivalent of 100 mu s, when averaged over a few days. The prediction performances for a 2-day forecast are similar, but at a forecast horizon of a week, the AAM-based forecast is roughly twice as skillful as the statistically based one.

Geomagnetic measurements during the total solar eclipse of August 1, 2008 in Novosibirsk (Klyuchi Observatory, NVS) and at the Burmistrovo station located on the total eclipse axis revealed eclipse-induced changes against the background of the normal daily variation. The main changes are a decrease in the X (north) component and an increase in the inclination I. Similar changes were recorded at the LZH observatory in China. Analysis of data on the eclipse of August 11, 1999 in Europe failed to unambiguously reveal eclipse effects against intense variations of ionospheric origin which occurred at the same universal time (UT). The geomagnetic effect of the solar eclipse may be due to a decrease in the electron concentration in the ionosphere and the corresponding decrease in the ionospheric current density.

VLBI is the only space-geodetic technique which gives direct access to the Earth’s phase of rotation, i.e. universal time UT1. Beside multi-baseline sessions, regular single baseline VLBI experiments are scheduled in order to provide estimates of UT1 for the international space community. Although the turn-around time of such sessions is usually much shorter and results are available within one day after the data were recorded, lower latency of UT1 results is still requested. Based on the experience gained over the last two years, an automated analysis procedure was established. The main goal was to realize fully unattended operation and robust estimation of UT1. Our new analysis software, named c5++, is capable of interfacing directly with the correlator output, carries out all processing stages without human interaction and provides the results for the scientific community or dedicated space applications. Moreover, the concept of ultra-rapid VLBI sessions can be extended to include further well-distributed stations, in order to obtain the polar motion parameters with the same latency and provide an up-to-date complete set of Earth orientation parameters for navigation of space and satellite missions.

SUMMARY A new simulation tool is introduced for extracting Earth conductivity information from geomagnetic satellites in low Earth orbit (LEO) such as CHAMP, Swarm and potential follow-on missions. Theoretical reconstruction of spherical harmonic spectra of global universal time (UT) geomagnetic field maps is analysed. An idealized regular solar daily variation field is assumed, along with its induced counterpart from a radially stratified Earth. Solar-quiet (Sq) spectra can be reliably reconstructed from discrete time-series of measurements sampled daily within a fixed UT window. A single LEO satellite should be in orbit for at least 1 yr under quiet-time conditions to ensure accurate spectral reconstruction of an Sq geomagnetic spectrum. The length of the daily sampling window and random day-to-day variability in the Sq source strength have only minor effects on spectral reconstruction. The shape of the spectra, and spectral ratios, are independent of radial mantle conductivity. Further research employing 3-D forward modelling of induction in a laterally heterogeneous earth, with more realistic and complete external source descriptions, is advocated. The new simulation tool should prove valuable to planners of future multisatellite geomagnetic missions, as well as scientists interested in analysing and interpreting satellite induction signals.

After publication of the Hipparcos catalogue (in 1997), a few new astrometric catalogues have appeared (TYCHO-2, ARIHIP, etc.), as a good combination of the Hipparcos satellite and ground-based data, to get more accurate coordinates and proper motions of stars than the Hipparcos catalogue ones. There are also investigations on improving the Hipparcos coordinates and proper motions by using the astrometric observations of latitude and universal time variations (via observed stars referred to Hipparcos catalogue), together with Hipparcos data, carried out during the last few years. These kind of ground-based data were collected at the end of the last century by J. Vondrak. There are about 4.4 million optical observations made worldwide at 33 observatories and with 47 instruments during 1899.7–1992.0; our Belgrade visual zenith telescope data (for the period 1949.0-1986.0) were included. First of all, these data were used to determine the Earth Orientation Parameters – EOP, but they are also useful for the opposite task – to check the accuracy of coordinates and proper motions of Hipparcos stars which were observed from the ground over many decades. Here, we use the latitude part of ten Photographic Zenith Tubes – PZT data (more than 0.9 million observations made at 6 observatories during the time interval 1915.8–1992.0), and combine them with the Hipparcos catalogue ones, with suitable weights, in order to check the proper motions in declination for 807 common PZT/Hipparcos stars (and to construct the PZT catalogue of μδ for 807 stars). Our standard errors in proper motions in declination of these stars are less than or equal to the Hipparcos ones for 423 stars. The mean value of standard errors of 313 stars observed over more than 20 years by PZT is 0.40 mas/yr. This is 53% of 0.75 mas/yr (the suitable value from the Hipparcos catalogue). We used the Least Squares Method – LSM with the linear model. Our results are in good agreement with the Earth Orientation Catalogue – EOC-2 and the new Hipparcos ones. The main steps of the method and the investigations of systematic errors in determined proper motions (the proper motion differences with respect to the Hipparcos values, the EOC-2 ones and the new Hipparcos ones, as a function of α, δ, and magnitude) are presented here. A comparison of the four catalogues by pairs shows that there is no significant relationship between the differences of their μδ values and magnitudes and color indices of the common 807 stars. All catalogues have relatively small random and systematic errors which are close to each other. However, the comparison shows that our formal errors are too small. They are underestimated by a factor of nearly 1.7 (for EOC-2, it is 2.0) if we take the new Hipparcos (or Hipparcos) data as reference (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)