Combination of modeled short-term angular momentum function forecasts from atmosphere, ocean, and hydrology with 90-day EOP predictions

2013 ◽  
Vol 87 (6) ◽  
pp. 567-577 ◽  
Author(s):  
R. Dill ◽  
H. Dobslaw ◽  
M. Thomas
Keyword(s):  
Angular Momentum ◽  
Short Term ◽  
Momentum Function

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

1994 ◽  
Vol 99 (B4) ◽  
pp. 6981 ◽  
Author(s):  
A. P. Freedman ◽  
J. A. Steppe ◽  
J. O. Dickey ◽  
T. M. Eubanks ◽  
L.-Y. Sung
Keyword(s):  
Angular Momentum ◽  
Universal Time ◽  
Atmospheric Angular Momentum ◽  
Length Of Day ◽  
Short Term ◽  
Term Prediction ◽  
Short Term Prediction

IERS Rapid Service/Prediction Center Use of Atmospheric and Ocean Angular Momentum for Earth Orientation

2020 ◽  
Author(s):  
Nicholas Stamatakos ◽  
David Salstein ◽  
Dennis McCarthy
Keyword(s):  
Angular Momentum ◽  
Sea Level ◽  
Ocean Model ◽  
Data Series ◽  
Earth System ◽  
Short Term ◽  
Combined System ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Orientation Parameters

<p>The accuracy of near real-time estimates and short-term predictions of Earth orientation parameters (EOPs) can be enhanced by the use of Atmospheric Angular Momentum (AAM) and Ocean Angular Momentum (OAM) information, by accounting for the global conservation of angular momentum in the Earth system. The US Navy analysis and forecast scheme is named the Navy Earth System Prediction Capability (NAVY ESPC)  and is comprised of the Navy Global Environmental Model (NAVGEM) atmospheric and Hybrid Coordinate Ocean Model (HYCOM) ocean systems (along with ice forecasts). GOFS is being improved continually, and the resultant motion and mass fields are potentially useful for operational Earth orientation applications.  Consistency between the NAVGEM and HYCOM fields is required for calculations of the total angular momentum of the combined system of geophysical fluids. However, they might not include land-based Hydrological Angular Momentum functions (HAM) and the additional amount due to sea-level variability, the Sea-Level Angular Momentum (SLAM), both of which may be accounted for separately. We investigate various combination and optimal estimation processes using these data series, in conjunction with existing EOP observations to improve accuracy and robustness of short-term EOP predictions. Results are compared with those from other fluid models, particularly from those of the GeoForschungsZentrum (GFZ), the German Research Center for Geosciences. We also estimate power spectral density as a measure of error, for NAVGEM and HYCOM-based AAM/OAM series and similar series from other centers, comparing them to equivalent measures calculated from Earth orientation parameters.</p>

scholarly journals Balance training improves feedback control of perturbed balance in older adults

2021 ◽  
Author(s):  
Leila Alizadehsaravi ◽  
Sjoerd M. Bruijn ◽  
Jaap H. van Dieen
Keyword(s):  
Older Adults ◽  
Angular Momentum ◽  
Feedback Control ◽  
Center Of Mass ◽  
Balance Training ◽  
Rate Of Change ◽  
The Body ◽  
Balance Performance ◽  
Short Term

Recovering balance after perturbations becomes challenging with aging, but an effective balance training could reduce such challenges. In this study, we examined the effect of balance training on feedback control after unpredictable perturbations by investigating balance performance, recovery strategy, and muscle synergies. We assessed the effect of balance training on unipedal perturbed balance in twenty older adults (>65 years) after short-term (one session) and long-term (3-weeks) training. Participants were exposed to random medial and lateral perturbations consisting of 8-degree rotations of a robot-controlled balance platform. We measured full-body 3D kinematics and activation of 9 muscles (8 stance leg muscles, one trunk muscle) during 2.5 s after the onset of perturbation. The perturbation was divided into 3 phases: phase1 from the onset to maximum rotation of the platform, phase 2 from the maximum rotation angle to the 0-degree angle and phase 3 after platform movement. Balance performance improved after long-term training as evidenced by decreased amplitudes of center of mass acceleration and rate of change of body angular momentum. The rate of change of angular momentum did not directly contribute to return of the center of mass within the base of support, but it reoriented the body to an aligned and vertical position. The improved performance coincided with altered activation of synergies depending on the direction and phase of the perturbation. We concluded that balance training improves control of perturbed balance, and reorganizes feedback responses, by changing temporal patterns of muscle activation. These effects were more pronounced after long-term than short-term training.

scholarly journals Short-term variation of the Earth's rotation and the solar activity

1988 ◽  
Vol 128 ◽  
pp. 353-358 ◽  
Author(s):  
D. Djurovic ◽  
P. Paquet
Keyword(s):  
Spectral Analysis ◽  
Angular Momentum ◽  
Solar Activity ◽  
Earth Rotation ◽  
Cyclic Variation ◽  
The Sun ◽  
Physical Processes ◽  
Short Term ◽  
The Earth ◽  
Term Variation

In 1980, Feissel et al. identified a quasi–cyclic variation of 55 days in the irregularities of the Earth Rotation (ER) later detected in the Atmospheric Angular Momentum (AAM) (Langley et al., 1981). The purpose of this work is to analyse whether the causes of this cycle could lie in the physical processes of the Sun. The Wolf Numbers (WN) are used as parameters of the solar activity. Their spectral analysis over the period 1967–1985 shows such a component at 51 days. Analysis of three other periods, among which is the MERIT campaign, confirms it as well as during low or increasing solar activity periods.

scholarly journals Forecasting short-term changes in the Earth's rotation

1988 ◽  
Vol 128 ◽  
pp. 287-288 ◽  
Author(s):  
Raymond Hide
Keyword(s):  
Angular Momentum ◽  
Solid Earth ◽  
Weather Forecasting ◽  
Meteorological Data ◽  
Earth’S Rotation ◽  
Momentum Exchange ◽  
Short Term ◽  
Earth's Rotation ◽  
Tidal Changes ◽  
Geophysical Processes

Summary of PosterIt has long been appreciated that atmospheric motions must contribute to the excitation of fluctuations in the Earth's rotation (Munk and MacDonald 1960, Lambeck 1980, Rochester 1984) but the exploitation of modern meteorological data, collected largely to meet the demands of daily global weather forecasting, in the routine evaluation of angular momentum exchange between the atmosphere and the solid Earth was not initiated until comparatively recently (Hide et al. 1980). This procedure constitutes a necessary step towards the accurate separation of these features of the observed non-tidal changes in the length of day and polar motion and that are of meteorological origin from those that must be attributed to other geophysical processes, such as angular momentum transfer between the solid Earth and other fluid regions of the Earth (liquid metallic core, oceans, etc.), and to changes in the inertia tensor of the solid Earth associated with earthquakes, melting of ice, etc.

scholarly journals Interdecadal oscillations in Atmospheric Angular Momentum variations

2012 ◽  
Vol 2 (1) ◽  
pp. 42-52 ◽  
Author(s):  
R. Abarca-del-Rio ◽  
D. Gambis ◽  
D. Salstein
Keyword(s):  
Angular Momentum ◽  
Time Scales ◽  
Secular Trend ◽  
Atmospheric Angular Momentum ◽  
Positive Trend ◽  
Short Term ◽  
The Pacific ◽  
Time Signals

Interdecadal oscillations in Atmospheric Angular Momentum variationsGlobal Atmospheric Angular Momentum (AAM) is an intrinsic index for describing processes that affect the atmospheric circulation on time scales ranging from intraseasonal to secular. It is associated with length-of-day (LOD) variability through conservation of global angular momentum in planet Earth and thus is of considerable importance for quantifying how the Earth acts as a system. The availability of lengthy AAM time series computed from the recent 20th Century atmospheric reanalyses (1870-2008), complemented by the NCAR-NCEP reanalysis in the overlapping period of 1948-2008 allows the investigation of the role of decadal and interdecadal cycles as well as the recent overall trend in AAM. Thus, we extend to the entire 20th century (and prior, back to 1870) results concerning decadal time scales and a secular positive trend detected over recent decades by different authors. In addition, we also note that AAM has features of interdecadal time scales that modulate the lower frequency variability. These interdecadal time signals oscillate with periods of about 30-50 years, and we found an indication of an 80-90 year period. Short term signals interact with the long-term (secular) trend. Particularly over the years 1950-1985 the global positive trend in AAM appears to result from a conjunction of constructive positive slopes from all lower frequency signals (interdecadal short-term trends and the long-term positive secular trend). Since the mid 1980s, however, the interdecadal oscillation short-term trend contribution decreases, as does the total signal in global AAM. These oscillations appear as two interdecadal modes originating within the Pacific (associated principally with the Pacific Decadal Oscillation and also ENSO) from which they propagate poleward, with differing characteristics in each hemisphere.

scholarly journals Prograde and Retrograde Terms of Gravimetric Polar Motion Excitation Estimates from the GRACE Monthly Gravity Field Models

2020 ◽  
Vol 12 (1) ◽  
pp. 138 ◽  
Author(s):  
Jolanta Nastula ◽  
Justyna Śliwińska
Keyword(s):  
Angular Momentum ◽  
Gravity Field ◽  
Polar Motion ◽  
Temporal Variations ◽  
Short Term ◽  
Grace Data ◽  
Hydrological Angular Momentum ◽  
Gravity Field Models ◽  
Polar Motion Excitation

From 2002 to 2017, the Gravity Recovery and Climate Experiment (GRACE) mission’s twin satellites measured variations in the mass redistribution of Earth’s superficial fluids, which disturb polar motion (PM). In this study, the PM excitation estimates were computed from two recent releases of GRACE monthly gravity field models, RL05 and RL06, and converted into prograde and retrograde circular terms by applying the complex Fourier transform. This is the first such analysis of circular parts in GRACE-based excitations. The obtained series were validated by comparison with the residuals of observed polar motion excitation (geodetic angular momentum (GAM)–atmospheric angular momentum (AAM)–oceanic angular momentum (OAM) (GAO)) determined from precise geodetic measurements of the pole coordinates. We examined temporal variations of hydrological excitation function series (or hydrological angular momentum, HAM) in four spectral bands: seasonal, non-seasonal, non-seasonal short-term, and non-seasonal long-term. The general conclusions arising from the conducted analyses of prograde and retrograde terms were consistent with the findings from the equatorial components of PM excitation studies drawn in previous research. In particular, we showed that the new GRACE RL06 data increased the consistency between different solutions and improved the agreement between GRACE-based excitation series and reference data. The level of agreement between HAM and GAO was dependent on the oscillation considered and was higher for long-term than short-term variations. For most of the oscillations considered, the highest agreement with GAO was obtained for CSR RL06 and ITSG-Grace2018 solutions. This study revealed that both prograde and retrograde circular terms of PM excitation can be determined by GRACE with similar levels of accuracy. The findings from this study may help in choosing the most appropriate GRACE solution for PM investigations and can be useful in future improvements to GRACE data processing.

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