Length Of The Day Research Articles

The Scale-Invariant Vacuum Paradigm: Main Results and Current Progress Review (Part II)

This is a summary of the main results within the Scale-Invariant Vacuum (SIV) paradigm based on Weyl integrable geometry. We also review the mathematical framework and utilize alternative derivations of the key equations based on the reparametrization invariance as well. The main results discussed are related to the early universe; that is, applications to inflation, Big Bang Nucleosynthesis, and the growth of the density fluctuations within the SIV. Some of the key SIV results for the early universe are a natural exit from inflation within the SIV in a later time texit with value related to the parameters of the inflationary potential along with the possibility for the density fluctuations to grow sufficiently fast within the SIV without the need for dark matter to seed the growth of structure in the universe. In the late-time universe, the applications of the SIV paradigm are related to scale-invariant dynamics of galaxies, MOND, dark matter, and dwarf spheroidals, where one can find MOND to be a peculiar case of the SIV theory. Finally, within the recent time epoch, we highlight that some of the change in the length-of-the-day (LOD), about 0.92 cm/yr, can be accounted for by SIV effects in the Earth–Moon system.

Did atmospheric thermal tides cause a daylength locking in the Precambrian? A review on recent results

After the initial suggestion by Zahnle and Walker (1987) that the torque accelerating the spin rate of the Earth and produced by the heating of the atmosphere by the Sun could counteract the braking luni-solar gravitational torque in the Precambrian, several authors have recently revisited this hypothesis. In these studies, it is argued that the geological evidence of the past spin state of the Earth plays in favor of this atmospheric tidal locking of the length of the day (LOD). In the present review of the recent literature, we show that the drawn conclusions critically depend on LOD estimates based on stromatolite growth band data of Panella at 1.88 and 2.0 Ga which are subject to large uncertainties. When only the most robust cyclostatigraphic estimates of the LOD are retained, the LOD locking hypothesis is not supported. Moreover, our consideration of the published General Circulation Model numerical simulations and of a new analytical model for the thermal atmospheric tides suggest that the atmospheric tidal resonance, which is the crucial ingredient for the LOD locking in the Precambrian, was never of sufficiently large amplitude to allow for this tidal LOD lock.

Increased Caribbean seismicity and volcanism during minima in Earth’s rotation rate: Search for a physical mechanism and a 2030 forecast

Three quarters of all Mw ≥ 6.6 earthquakes and volcanic eruptions surrounding the Caribbean plate occur preferentially during periods of decadal minima in Earth’s angular spin velocity. This correlation is revealed most clearly as a 4–6 years phase lag following the first derivative of the length of the day (LOD), Earth’s angular deceleration. We show that local strains and displacements resulting from oblateness changes, or plate boundary stresses associated with changes in tropical rotation rates are orders of magnitude lower than those typically associated with earthquake or volcano triggering. Notwithstanding the absence of a satisfactory causal physical mechanism, the relationship permits decadal trends in Caribbean tectonic hazards to be anticipated many years before their occurrence. The next period of increased tectonic activity in the Caribbean, corresponding to a probable slowing in Earth’s spin rate, will occur in the decade starting on or about 2030.

Investigation of the Global Seismic Noise Properties in Connection to Strong Earthquakes

The global seismic noise, recorded on a network of 229 broadband seismic stations located around the globe for 25 years, from the beginning of 1997 to the end of 2021, has been investigated. To study the noise properties a set of statistics estimated daily have been used: the multifractal singularity spectrum support width, the minimum entropy of the squared wavelet coefficients, and the wavelet-based Donoho-Johnstone (DJ) index. It is shown that the time points of local extrema of the average values of the analyzed noise properties (minima for singularity spectrum support width and DJ-index and maxima for entropy) tend to occur before strong earthquakes. The time interval from the middle of 2002 to the middle of 2003 is determined, when the trend of decreasing the average coherence of the noise properties in the auxiliary network of 50 reference points changed to an increase. Along with an increase in the average coherence, there is an increase in the radius of the spatial maximum coherences of noise properties. Both of these trends continue until the end of 2021, which is interpreted as a general sign of an increase in the degree of criticality of the state of the planet and, as a result, an increase in global seismic danger. After two mega-earthquakes close in time: 27 February 2010, M=8.8 in Chile and 11 March 2011, M=9.1 in Japan, there was an increase in the spatial scales of the strong coherence of noise parameters, which is a sign of an increase in the critical state. The response of seismic noise properties to variations in the length of the day (LOD) has been studied. An estimate of the correlation function between the mean values of the response to LOD and the logarithm of the released seismic energy in a time window of 1 year indicates a delay in energy release with respect to the maxima of the response of noise properties to LOD with a delay time of about 500 days. In connection with this result, an additional intrigue is the extreme increase in the average value of the response to LOD in 2021.

Time series analysis of temperatures and insolation of the Earth's surface at Kara-Dag using satellite observation

This article discusses the results of a numerical analysis of the time series of the surface temperature, air temperature at a height of 2 m, as well as the total insolation falling to the earth at the Kara-Dag point over the past 38 years. Statistical analysis of observations and continuous time-frequency wavelet analysis are performed. Models of seasonal fluctuations in three time series of observations are compared. Coherent fluctuations were established between variations in total insolation data and data variations: of length of the day (LOD) (the period of variations is 11.8 years, the square of the coherence modulus is 0.85); of solar activity (the period of variations is 10.5 years, the squared modulus of coherence is 0.8; and the period of variations is 3.6 years, the squared modulus of coherence is 0.85); of global temperature indices (the period of variations is 2.3 years, the squared modulus of coherence is 0.7; and the period of variations is 3.5 years, the squared modulus of coherence is 0.9), respectively. The time evolution of observations in order to detect signs of chaotic oscillations is discussed.

Sagnac Gyroscopes and the GINGER Project

Large frame optical Sagnac gyroscopes, more commonly called ring laser gyroscopes, are considered the only device able to provide fast and very high sensitivity measurement of the length of the day (LOD), and of the Earth rotation axis variations. Several large frame Sagnac gyros are presently operative with high duty cycle and sensitivity well below fractions of nrad/s in 1 second measurement. At present other inertial angular rotation sensors are not competitive with ring laser gyroscopes. The feasibility depends on the so called hetero-lithic ring lasers. The present status of art is reported, and the feasibility of the main goals for geodesy discussed.

МОДЕЛЬ ИНСОЛЯЦИИ ПОВЕРХНОСТИ ЗЕМЛИ В ПУНКТЕ "КАРАДАГ" ПО ДАННЫМ SSE

Anomalous enhancement of solar insolation of the earth's surface in the presence of foci of excitation in its depths can cause a response at local sites. Such foci include, first of all, recent and past (retro) volcanoes, such as the ancient volcano on the territory of Kara-Dag in the Crimea. The authors of this article have found increased, in comparison with other localities of the Crimea, general insolation according to SSE. According to the 22-year linear trend, the rate of insolation growth falling on the earth's surface at Kara-Dag has been calculated, which is 2,69 kWh/m2 per century, being more than 2 times higher than insolation growth in other areas of the Crimea. This phenomenon has been the subject of discussion, and additional research is needed, both on the geological structure of Kara-Dag and on the impact of external and internal forces. At the stage of studying the structure of data on insolation of the earth's surface at Kara-Dag, we have built a 6-order sine-wave model. The most powerful (amplitudes more than an order of magnitude higher than the noise level) regular oscillations on the 22-year interval have periods of 365,3 and 365,7 days. Statistical estimates of the degree of approximation by a sinusoidal model (R2 = 0,9, RMSE = 0,7) indicate that, in addition to regular periodic oscillations, there are irregular fluctuations in the data at time intervals determined by a continuous time-frequency wavelet analysis. The wavelet transformation graph highlights the interval of insolation energy growth at Kara-Dag locality after 1995. In order to analyze the statistical relationship of changes in local insolation of the Earth's surface with the Earth's rotation around the axis and its orbital movement, solar activity and global temperature, autoregression models of the power spectral density were calculated using which coherent oscillations were found between variations in Kara-Dag paragraph and variations in the data: on the length of the day (LOD) with a period of 11,8 years and a square modulus of coherence of 0,85; about solar activity with periods of 10,5, 3,6 years and a squared coherence modulus of 0,8 and 0,85; about global temperature indices with periods of 2,3, 3,5 years and squares of coherence modulus 0,7 and 0,9, respectively. The increased growth of insolation and the temperature of the earth at Kara-Dag locality that we found requires additional research and observations.

Spectral coherence between climate oscillations and the M ≥ 7 earthquake historical worldwide record

We compare the NOAA Significant Earthquake Historical database versus typical climatic indices and the length of the day (LOD). The Pacific Decadal Oscillation (PDO) record is mainly adopted because most of the analyzed earthquakes occurred at the land boundaries of the Pacific Plate. The NOAA catalog contains information on destructive earthquakes. Using advanced spectral and magnitude squared coherence methodologies, we found that the magnitude $$M\ge 7$$ earthquake annual frequency and the PDO record share common frequencies at about 9-, 20-, and 50- to 60-year periods, which are typically found in climate records and among the solar and lunar harmonics. The two records are negatively correlated at the 20- and 50- to 60-year timescales and positively correlated at the 9-year and lower timescales. We use a simple harmonic model to forecast the $$M\ge 7$$ significant earthquake annual frequency for the next decades. The next 15 years should be characterized by a relatively high $$M\ge 7$$ earthquake activity (on average 10–12 occurrences per year) with possible maxima in 2020 and 2030 and a minimum in the 2040s. On the 60-year scale, the LOD is found to be highly correlated with the earthquake record ( $$r=0.51$$ for 1900–1994, and $$r=0.95$$ for 1910–1970). However, the LOD variations appear to be too small to be the primary earthquake trigger. Our results suggest that large earthquakes are triggered by crust deformations induced by, and/or linked to climatic and oceanic oscillations induced by astronomical forcings, which also regulate the LOD.

The Possible Explanation for Secondary Microseisms Seasonal and Annual Variations

Annual drift is typical for microseisms. We propose a model based on thermoelastic wave generation that explains the highest microseisms during winter using higher stress level at the same time. If we remove the average influence of the background stress from the microseisms, we obtain the residual microseisms, which show the semiannual periods with maxima in March and October. The histogram of anomalous microseisms has the same form as the variations in Length of the Day (LOD). This phenomenon is recognized as a secondary order mechanism after the annual drift. The synoptic situations and earthquakes were recognized as imminent triggers of anomalous microseisms. This synoptic situation is consistent with the uplift of the northern part of Europe after ice cap melting.

On the nonstationarity of the decadal periodicities of the length of day

Abstract. The Earth's rotation rate is not constant, but changes on all observable timescales, from subdaily to decadal and longer. These variations are usually discussed in terms of variations in the length of the day (LoD) and are caused by processes acting within the interior, at the surface and outside of the Earth. Here, we investigate the presence of long-standing decadal variations in yearly LoD data covering the period from 1832 to 2009 by applying the Hilbert–Huang transform (HHT). The HHT has been slightly modified here to take into account the uncertainty of LoD values that has changed greatly in time due to the use of different LoD measurement techniques. The LoD time series has been completely decomposed into five intrinsic mode functions (IMF) and a residual trend. The estimation of instantaneous frequencies and related amplitudes of the obtained IMFs has allowed us to compute the Hilbert spectrum that has been used as the starting point for studying and discussing the stationarity of typical LoD timescale stationarity. The obtained results while showing the presence of multiple periodicities also indicate the absence of really stationary periodicities. Therefore, rather than considering the processes taking place in the Earth's core as the result of a superposition of oscillations (i.e. stationary mechanisms) occurring on a discrete number of different timescales, it would be better to think of a superposition of fluctuations that are intermittent in both frequency and amplitude.

Did a change in tectonic regime occur between the Phanerozoic and earlier Epochs?

A compilation of palaeogeographical maps of the Neo Proterozoic (Ptz) and Phanerozoic (Pz) 0.6 Ga BP to the present is analyzed in the terms of the (a) ratio between continental to oceanic crust areas (in short continent-to-ocean ratio), (b) length of spreading centres and (c) length of subduction zones. The variation of these tectonic processes is then compared to the variations occurred during the Archean (Arc 3.8–2.5 Ga BP) and Proterozoic (Ptz 2.5–0.54 Ga BP). The discussion takes the geomagnetic field and changes in length of the day (LOD) into account as well. From the constancy of the continent-to-ocean ratio through Pz and from the small size of the continental area above sea level in Neoproterozoic it follows that at the border between Ptz and Pz there has been a large change of the length of the shelf zones. This change can explain contemporary change of the despinning rate from about 0.35 to about 1.79 ms/century. In general, our findings suggest a change in tectonic regime at the border between Ptz and Pz.

On modulations of the Chandler wobble excitation

We derive the Chandler wobble excitation from the polar motion (PM) observations by using the Panteleev corrective filtering. The latter method is based on inversion of the Euler–Liouville equation, with additional filtering in the Chandler frequency band. The excitation reconstruction reveals amplitude changes different from the one observed in the Chandler wobble itself. Their main feature, well observable over the length of the day (LOD), is the presence of a 18.6-year amplitude modulation synchronous with the lunar orbital precession cycle and tidal effects. The filtering of oceanic and atmospheric excitation in the Chandler frequency band also reveals a coherent 18.6-year oceanic pattern. Most probably the ocean provide a channel for the tidal energy transfer.

On the regime of the Earth’s polar motion based on data for the period 1962–2007

The view of the Earth’s polar motion as a completely deterministic process has been called into question in the past decades, because no long-term prediction can be made. At the same time, no fundamental restrictions currently exist in the problem of a long-term prediction of the Earth’s rotation. Determining the boundaries of predictability is related to identifying the regime of the Earth’s polar motion. IERS data for the period 1962–2007 have been used to study the regime of the Earth’s polar motion. Analysis of the plots of polhodes reveals peculiarities in the variations of the pole’s coordinates X and Y in certain intervals along the time axis. The data in the interval from 2003 to 2006 have been analyzed in greatest detail: a model for the Chandler and annual oscillations has been constructed and relations between the parameters of these oscillations have been determined; the shift of the instantaneous pole on the phase plane and the Poincare plane has been investigated. As a result, we have found features inherent in chaotic motion (intermittency) and calculated the period (32 years) of the possible repetitions of such anomalies, as confirmed by our analysis of the plots of polhodes. The intervals where the peculiarities in the motion of the Earth’s instantaneous pole manifest themselves are compared with the intervals of the inflections on the plots of variations in the length of the day (LOD).

Seasonal and inter-annual variations of length of day and polar motion observed by SLR in 1993–2006

A time series of length of the day (LOD) and polar motion (PM) were estimated from the range data measured by the satellite laser ranging technique (SLR) to LAGEOS 1/2 through 1993 to 2006. Compared with EOPC04 released by the International Earth Rotation and Reference Systems Service (IERS), the root mean squares errors for LOD, X and Y of PM are 0.0067 milliseconds (ms), 0.18 milli-arc-seconds (mas) and 0.20 mas, respectively. Then the time series are analyzed with the wavelet transformation and least squares method. Wavelet analysis shows that there are the obvious seasonal and inter-annual variations of LOD and PM, but the annual variation cannot be distinguished from the Chandler variation because these two frequencies are very close. The trends and periodic variations of LOD and PM are given in the least squares sense. LOD changes with the annual and semiannual periods. The annual and Chandler variations for PM are also detected, but the semiannual motion for PM is not found. The trend rate of the LOD change in 1993–2006 is −0.18 ms per year, and the difference from the well-known 1.7 ms per century showed that the trend rate is diverse in different periods possibly. The trend rates of PM in the X and Y directions are 2.25 and 1.67 mas per year respectively, and the North Pole moves to 36.5°E relative to the crust, which is different from the direction of Greenland.

Cycles, scaling and crossover phenomenon in length of the day (LOD) time series

The dynamics of the temporal fluctuations of the length of the day (LOD) time series from January 1, 1962 to November 2, 2006 were investigated. The power spectrum of the whole time series has revealed annual, semi-annual, decadal and daily oscillatory behaviors, correlated with oceanic–atmospheric processes and interactions. The scaling behavior was analyzed by using the detrended fluctuation analysis (DFA), which has revealed two different scaling regimes, separated by a crossover timescale at approximately 23 days. Flicker-noise process can describe the dynamics of the LOD time regime involving intermediate and long timescales, while Brownian dynamics characterizes the LOD time series for small timescales.

Long-term changes in atmospheric circulation, earth rotation rate and north–south solar asymmetry

Earlier studies have demonstrated a relation between long-term changes in the Earth's rotation rate and the prevalence of zonal or meridional types of circulation. The results, however, have been confined to the 20th century and to the Northern hemisphere. In the present paper we compare the long-term changes in the length of the day (LOD) and the temperature contrast between the equator and the pole in the Northern and the Southern hemispheres as an indirect measure for the zonality of the atmospheric circulation. In the 20th century in the Northern hemisphere we find a high negative correlation between the rotation rate and the equator/pole temperature contrast, while in the 19th century the correlation is positive. For the Southern hemisphere, the situation is opposite. The correlation changes when the North–South asymmetry of solar activity also changes sign. The decadal changes in LOD are shown to be related to the changes in the North–South asymmetry of solar equatorial rotation rate supposedly induced by planetary-driven changes in the angular momentum of the solar system, with both quantities showing pronounced periodicities and high squared coherence at 47 years. It is hypothesized that decadal changes in LOD are driven by core-mantle coupling processes regulated by solar wind transferring solar magnetic fields and angular momentum modulated by planetary influences. The atmospheric circulation in the Northern and Southern hemispheres is found to be different not only on decadal time-scales but also in the 11-year solar cycle, and different in even and odd cycles. While long-term changes in geomagnetic activity closely follow sunspot activity changes, the correlation between the two in the 11-year cycle has been decreasing in the last century with the increase of the North–South solar activity asymmetry which modulates also the asymmetry of galactic cosmic rays flux considered a candidate mediator between solar activity and climate.

Angular momentum fluctuations within the Earth's liquid core and torsional oscillations of the core-mantle system

Summary Non-steady differential rotation is one of the main characteristics of the buoyancy-driven flow within the Earth's liquid metallic outer core that generates the main geomagnetic field by magnetohydrodynamic (MHD) dynamo action. Concomitant fluctuations in angular momentum transfer both within the core and between the core and the overlying ‘solid’ mantle are investigated by assuming that average departures from ‘isorotation’ on coaxial cylindrical surfaces are negligibly small. The interval of time covered by the analysis is the 15 decades from 1840 to 1990, for which requisite determinations are available of decadal fluctuations of the length of the day (LOD) and also of flow velocities just below the core–mantle boundary (CMB), as inferred from geomagnetic secular variation (GSV) data. Core angular momentum (CAM) fluctuations are most pronounced in the mid-latitudes, where they are generally out of phase with those occurring in equatorial regions. They are roughly in phase with decadal LOD fluctuations, especially after about 1870, with a dominant variability period of approximately 65 years, in keeping with previous analyses based on GSV and/or LOD data. The largest positive correlations (0.8 when data before 1867.5 are excluded) are found in the mid-latitudes, with a maximum at zero lag and with secondary peaks at 67 years and at −64 years, again implying a mode of approximately 65 years. Propagation of CAM anomalies from the equatorial to polar regions is evident in both the time-latitude dependence of CAM and its latitudinal correlation with length of day fluctuations. Future work on excitation mechanisms should establish the connection, if any, between the dominant timescale of approximately 65 years seen in the data and the gravest of the theoretically possible subseismic modes of torsional MHD oscillations of the core.

Atmospheric changes caused By El Ni˜o slightly increase length of day

El Niño, which has dramatically altered the climate in many regions around the globe, also infinitesimally increases the length of the day (LOD), scientists at the 1998 AGU Spring Meeting reported on May 26. They say these tiny changes could affect global and interplanetary navigation, and provide an important clue about energy distribution within the Earth system and how components of the system work together.During the peak period of the current El Niño, LOD increased temporarily by about 600–700 microseconds, according to John Gipson, a scientist with NVI, Inc., based at the NASA Goddard Space Flight Center in Greenbelt, Md. He says the increase is not as much as the peak increase of about 800 microseconds, (less than l/1000ths of a second), registered during the strong 1982–1983 El Niño episode.

Historical eclipses and the rotation of the earth

This paper summarises recent research on long-term variations in the Earth's past rotation. A variety of ancient and medieval observations of both solar and lunar eclipses are investigated to determine changes in the length of the day (LOD) between 700 BC and AD 1600. These data originate from Babylon, China, Europe and the Arab world. In all, some 400 individual observations - both timed and untimed - are analysed. The results indicate an average rate of increase in the LOD by 1.7 milliseconds per century (ms/cy), considerably less than that calculated on the basis of lunar and solar tidal friction alone (i.e. 2.3 ± 0.1 ms/cy). The residual mean non-tidal decrease in the LOD by about 0.6 ms/cy is in good accord with that expected on the basis of post-glacial isostatic compensation. However, there is also some indication of long-term fluctuations in the LOD of amplitude some 4 ms on a time-scale of around 1500 years. Possible causes are core-mantle coupling and variations in global sea-level associated with climatic fluctuations.

The short‐term prediction of universal time and length of day using atmospheric angular momentum

The ability to predict short‐term variations in the Earth's rotation has gained importance in recent years owing to more precise spacecraft tracking requirements. Universal time (UT1), that component of the Earth's orientation corresponding to the rotation angle, can be measured by a number of high‐precision space geodetic techniques. A Kalman filter developed at the Jet Propulsion Laboratory (JPL) optimally combines these different data sets and generates a smoothed time series and a set of predictions for UT1, as well as for additional Earth orientation components. These UT1 predictions utilize an empirically derived random walk stochastic model for the length of the day (LOD) and require frequent and up‐to‐date measurements of either UT1 or LOD to keep errors from quickly accumulating. Recent studies have shown that LOD variations are correlated with changes in the Earth's axial atmospheric angular momentum (AAM) over timescales of several years down to as little as 8 days. AAM estimates and forecasts out to 10 days are routinely available from meteorological analysis centers; these data can supplement geodetic measurements to improve the short‐term prediction of LOD and have therefore been incorporated as independent data types in the JPL Kaiman filter. We find that AAM and, to a lesser extent, AAM forecast data are extremely helpful in generating accurate near‐real‐time estimates of UT1 and LOD and in improving short‐term predictions of these quantities out to about 10 days.