scholarly journals IGS Combined and Contributed Earth Rotation Parameter Solutions

2000 ◽  
Vol 178 ◽  
pp. 277-302
Author(s):  
Jan Kouba ◽  
Gerhard Beutler ◽  
Markus Rothacher
Keyword(s):  
Angular Momentum ◽  
Earth Rotation ◽  
Polar Motion ◽  
Rotation Parameter ◽  
Atmospheric Angular Momentum ◽  
Length Of Day ◽  
Earth Rotation Parameter ◽  
Average Correlation ◽  
Precision Level

AbstractSince January 1995 the International GPS Service (IGS) has been combining and analyzing daily polar motion (PM) series, produced and submitted by seven IGS analysis centers (ACs) for the IGS Final orbit/clock combinations. Since June 30, 1996 the IGS Earth Rotation Parameter (ERP) series that accompany the IGS combined orbits, also include combined PM rates. Furthermore, since March 1997, the IGS LOD (Length of Day) solutions are based on separate combinations of AC LOD solutions calibrated and weighted according to the IERS Bulletin A definite values. Similar to AC orbit solutions, the PM solutions have improved considerably since 1995, so that currently the IGS combined and the best AC PM solutions are at or below the 0.1 mas precision level, although PM biases may exceed .1 mas. Comparisons of AC ERP and PM rate solutions with the IGS Final combined ERP series revealed signals with 7 and 14-day periods for some AC solutions.During 1998, the IGS Final and the best AC PM rate solutions compared with Atmospheric Angular Momentum (AAM) at 0.3 mas/day (rms) with an average correlation of about 0.8 and 0.6 for the PM x and PM y rate components. The correlation varied considerably with time and frequency, though significant correlation already started from 6-day periods and reaching maxima within 10 to 50 day period bands. Most of the remaining signal in the PM rate solutions could likely be accounted for by Ocean Angular Momentum (OAM) as seen from the comparisons of combined OAM and AAM with the IGS PM series during 1995 and early 1996 when also OAM data were made available. During this period the IGS PM rates agreed with the combined OAM + AAM series with 0.3 and 0.2 mas/day (rms) for the PM x and y components and with an average correlation of about 0.8 for both PM components.

scholarly journals The influence of global warming in Earth rotation speed

1999 ◽  
Vol 17 (6) ◽  
pp. 806-811 ◽  
Author(s):  
R. Abarca del Rio
Keyword(s):  
Angular Momentum ◽  
Surface Temperature ◽  
Earth Rotation ◽  
Rotation Speed ◽  
Atmospheric Angular Momentum ◽  
Time Interval ◽  
Dynamical Response ◽  
Earth System ◽  
Length Of Day ◽  
Data Set

Abstract. The tendency of the atmospheric angular momentum (AAM) is investigated using a 49-year set of monthly AAM data for the period January 1949-December 1997. This data set is constructed with zonal wind values from the reanalyses of NCEP/NCAR, used in conjunction with a variety of operationally produced AAM time series with different independent sources and lengths over 1976-1997. In all the analyzed AAM series the linear trend is found to be positive. Since the angular momentum of the atmosphere-earth system is conserved this corresponds to a net loss of angular momentum by the solid earth, therefore decreasing the Earth rotation speed and increasing the length of day (LOD). The AAM rise is significant to the budget of angular momentum of the global atmosphere-earth system; its value in milliseconds/century (ms/cy) is +0.56 ms/cy, corresponding to one-third of the estimated increase in LOD (+1.7 ms/cy). The major contribution to this secular trend in AAM comes from the equatorial Tropopause. This is consistent with results from a previous study using a simplified aqua-planet model to investigate the AAM variations due to near equatorial warming conditions. During the same time interval, 1949-1997, the global marine + land-surface temperature increases by about 0.79 °C/cy, showing a linear correspondence between surface temperature increase and global AAM of about 0.07 ms per 0.1 °C. These results imply that atmospheric angular momentum may be used as an independent index of the global atmosphere's dynamical response to the greenhouse forcing, and as such, the length of day may be used as an indirect indicator of global warming.Key words. Meteorology and atmospheric dynamics (general circulation) · Geodesy

Atmospheric angular momentum fluctuations, length-of-day changes and polar motion

1983 ◽  
Vol 387 (1792) ◽  
pp. 31-73 ◽  
Keyword(s):  
Angular Momentum ◽  
Solid Earth ◽  
Polar Motion ◽  
Meteorological Data ◽  
Liquid Core ◽  
Atmospheric Angular Momentum ◽  
Axial Component ◽  
Length Of Day ◽  
Momentum Exchange ◽  
Geophysical Research

Variations in the distribution of mass within the atmosphere and changes in the pattern of winds, particularly the strength and location of the major mid-latitude jet-streams, produce fluctuations in all three components of the angular momentum of the atmosphere on timescales upwards of a few days. In a previous study (Hide et al . 1980) it has been shown that variations in the axial component of atmospheric angular momentum during the Special Observing Periods in 1979 of the First GARP Global Experiment (FGGE, where GARP is the Global Atmospheric Research Program) are well correlated with changes in length-of-day. This would be expected if the total angular momentum of the atmosphere and ‘solid’ Earth were conserved on short timescales (allowing for lunar and solar effects) but not if angular momentum transfer between the Earth’s liquid core and solid mantle, which is accepted to be substantial and even dominant on timescales upwards of several years, were significant on timescales of weeks or months. Fluctuations in the equatorial components of atmospheric angular momentum should contribute to the observed wobble of the instantaneous pole of the Earth’s rotation with respect to the Earth’s crust, but this has not been shown conclusively by previous studies. In this paper we re-examine some aspects of the underlying theory of non-rigid body rotational dynamics and angular momentum exchange between the atmosphere and solid Earth. Since only viscous or topographic coupling between the atmosphere and solid Earth can transfer angular momentum, no atmospheric flow that everywhere satisfied inviscid equations (including, but not solely, geostrophic flow) could affect the rotation of a spherical solid Earth. Currently available meteorological data are not adequate for evaluating the usual wobble excitation functions accurately, but we show that partial integration leads to an expression involving simpler functions ─ here called ‘equatorial angular momentum functions’ ─ which can be reliably evaluated from available meteorological data. The length-of-day problem is treated in terms of a similar ‘axial angular momentum function’ ; and ‘effective angular momentum functions’ are defined in order to allow for rotational and surface loading deformation of the Earth. Daily values of these atmospheric angular momentum functions have been calculated from the ‘initialized analysis global database’ of the European Centre for Medium-Range Weather Forecasts (ECMWF). They are presented for the period 1 January 1981─30 April 1982, along with the corresponding astronomically observed changes in length-of-day and polar motion, published by the Bureau International de l’Heure (BIH). Changes in length-of-day during this period can be accounted for almost entirely by angular momentum exchange between the atmosphere and solid Earth, and the existence of a persistent fluctuation in this exchange, with a timescale of about 7 weeks, is confirmed. We also demonstrate that meteorological phenomena provide an important contribution to the excitation of polar motion. Our work offers a theoretical basis for future routine determinations of atmospheric angular momentum fluctuations for the purposes of meteorological and geophysical research, including the assessment of the extent to which movements in the solid Earth associated with very large earthquakes contribute to the excitation of the Chandlerian wobble.

scholarly journals Assimilation of Earth rotation parameters into a global ocean model: excitation of polar motion

2011 ◽  
Vol 18 (5) ◽  
pp. 581-585 ◽  
Author(s):  
J. Saynisch ◽  
M. Wenzel ◽  
J. Schröter
Keyword(s):  
Angular Momentum ◽  
Mass Distribution ◽  
Earth Rotation ◽  
Polar Motion ◽  
Ocean Model ◽  
Current Speed ◽  
Global Ocean ◽  
Length Of Day ◽  
Motion Generation ◽  
Ocean Mass

Abstract. The oceanic contribution to Earth rotation anomalies can be manifold. Possible causes are a change of total ocean mass, changes in current speed or location and changes in mass distribution. To derive the governing physical mechanisms of oceanic Earth rotation excitation we assimilate Earth rotation observations with a global circulation ocean model. Before assimilation, observations of length of day and polar motion were transformed into estimates of ocean angular momentum. By using the adjoint 4D-VAR assimilation method we were able to reproduce these estimated time series. Although length of day was assimilated simultaneously the analysis in this paper focuses on the oceanic polar motion generation. Our results show that changes in mass distribution and currents contribute to oceanic polar motion generation. Both contributions are highly correlated and show similar amplitudes. The changes in the model done by the assimilation procedure could be related to changes in the atmospheric forcing. Since for geometrical reasons the change of total ocean mass does not project on polar motion, we conclude that the polar motion is mainly generated by a geostrophic response to atmospheric momentum forcing. In geostrophic currents mass displacement and current speed entail each other. This way the large similarity of mass and current generated ocean angular momentum can be explained.

scholarly journals Atmospheric Effects on Earth Rotation and Polar Motion

1988 ◽  
Vol 129 ◽  
pp. 401-410
Author(s):  
David A. Salstein
Keyword(s):  
Time Scales ◽  
Earth Rotation ◽  
Polar Motion ◽  
Atmospheric Effects ◽  
Length Of Day ◽  
Wind Fields ◽  
Wind Variability ◽  
Body Tides ◽  
Wind Distribution

The variability in the earth's rotation rate not due to known solid body tides is dominated on time scales of about four years and less by variations in global atmospheric angular momentum (M), as derived from the zonal wind distribution. Among features seen in the length of day (Δl.o.d.) record produced by atmospheric forcing are the strong seasonal cycle, quasi-periodic fluctuations around 40–50 days, and an interannual signal forced by a strong Pacific warming event, known as the El Niño. Momentum variations associated with these time scales arise in different latitudinal regions. Furthermore, winds in the stratosphere make a particularly important contribution to seasonal variability.Other related topics discussed here are (i) comparisons of the M series from wind fields produced at different weather centers, (ii) the torques that dynamically link the atmosphere and earth, and (iii) longer-term non-atmospheric effects that can be seen upon removal of the atmospheric signal. An interesting application for climatological purposes is the use of historical earth rotation series as a proxy for atmospheric wind variability prior to the era of upper-air data. Lastly, results pertaining to the role of atmospheric pressure systems in exciting rapid polar motion are presented.

scholarly journals On High Frequency Polar Motion and Length of Day Variations

2000 ◽  
Vol 178 ◽  
pp. 545-554
Author(s):  
K. Arfa-Kaboodvand ◽  
E. Groten
Keyword(s):  
Frequency Spectrum ◽  
Earth Rotation ◽  
High Frequency ◽  
Polar Motion ◽  
Length Of Day ◽  
Physical Processes ◽  
Earth Orientation ◽  
Tidal Forces ◽  
Diurnal Range ◽  
Insight Into

AbstractThe 0.042-day Earth rotation data (diurnal and semidiurnal) computed by the International GPS Service were used to analyze the daily/sub-daily variations of polar motion (PM) and length of day (LOD). Systematic and advanced spectral analytical investigations of the degree of periodic variability have been carried out. They show that the prominent periodical components can be found at the tidal frequencies of zonal, tesseral and sectorial waves. These investigations should give better insight into the physical processes, which influence Earth orientation (i.e. due to the atmospheric and oceanic motions, tidal forces etc.). It should be the basis for the detailed modeling of excitation functions in the sub-diurnal range of the high-frequency spectrum.

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
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