On the usefulness of atmospheric and oceanic angular momentum in recovering polar motion and gravity field variations in a unified process

AbstractObserved polar motion consists of uniform circular motions at both positive (prograde) and negative (retrograde) frequencies. Generalized Euler–Liouville equations of Bizouard, taking into account Earth's triaxiality and asymmetry of the ocean tide, show that the corresponding retrograde and prograde circular excitations are coupled at any frequency. In this work, we reconstructed the polar motion excitation in the Chandler band (prograde and retrograde). Then we compared it with geophysical excitation, filtered out in the same way from the series of the Oceanic Angular Momentum (OAM) and Atmospheric Angular Momentum (AAM) for the period 1960–2000. The agreement was found to be better in the prograde band than in the retrograde one.

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

Remote Sensing ◽

10.3390/rs12010138 ◽

2020 ◽

Vol 12 (1) ◽

pp. 138 ◽

Cited By ~ 3

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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Evaluation of hydrological and cryospheric angular momentum estimates based on GRACE, GRACE-FO and SLR data for their contributions to polar motion excitation

Earth Planets and Space ◽

10.1186/s40623-021-01393-5 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Justyna Śliwińska ◽

Jolanta Nastula ◽

Małgorzata Wińska

Keyword(s):

Angular Momentum ◽

Spherical Harmonic ◽

Polar Motion ◽

Spectral Band ◽

Water Storage ◽

Terrestrial Water Storage ◽

Terrestrial Water ◽

High Consistency ◽

Polar Motion Excitation

AbstractIn geodesy, a key application of data from the Gravity Recovery and Climate Experiment (GRACE), GRACE Follow-On (GRACE-FO), and Satellite Laser Ranging (SLR) is an interpretation of changes in polar motion excitation due to variations in the Earth’s surficial fluids, especially in the continental water, snow, and ice. Such impacts are usually examined by computing hydrological and cryospheric polar motion excitation (hydrological and cryospheric angular momentum, HAM/CAM). Three types of GRACE and GRACE-FO data can be used to determine HAM/CAM, namely degree-2 order-1 spherical harmonic coefficients of geopotential, gridded terrestrial water storage anomalies computed from spherical harmonic coefficients, and terrestrial water storage anomalies obtained from mascon solutions. This study compares HAM/CAM computed from these three kinds of gravimetric data. A comparison of GRACE-based excitation series with HAM/CAM obtained from SLR is also provided. A validation of different HAM/CAM estimates is conducted here using the so-called geodetic residual time series (GAO), which describes the hydrological and cryospheric signal in the observed polar motion excitation. Our analysis of GRACE mission data indicates that the use of mascon solutions provides higher consistency between HAM/CAM and GAO than the use of other datasets, especially in the seasonal spectral band. These conclusions are confirmed by the results obtained for data from first 2 years of GRACE-FO. Overall, after 2 years from the start of GRACE-FO, the high consistency between HAM/CAM and GAO that was achieved during the best GRACE period has not yet been repeated. However, it should be remembered that with the systematic appearance of subsequent GRACE-FO observations, this quality can be expected to increase. SLR data can be used for determination of HAM/CAM to fill the one-year-long data gap between the end of GRACE and the start of the GRACE-FO mission. In addition, SLR series could be particularly useful in determination of HAM/CAM in the non-seasonal spectral band. Despite its low seasonal amplitudes, SLR-based HAM/CAM provides high phase consistency with GAO for annual and semiannual oscillation.

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Interannual variations in the Earth's polar motion for 1963-1991: Comparison with atmospheric angular momentum over 1980-1991

Geophysical Research Letters ◽

10.1029/94gl02285 ◽

1994 ◽

Vol 21 (22) ◽

pp. 2361-2364 ◽

Cited By ~ 13

Author(s):

R. Abarca del Rio ◽

A. Cazenave

Keyword(s):

Angular Momentum ◽

Polar Motion ◽

Atmospheric Angular Momentum ◽

Interannual Variations

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Regional Atmospheric Angular Momentum Contributions to Polar Motion Excitation

Geodesy on the Move - International Association of Geodesy Symposia ◽

10.1007/978-3-642-72245-5_51 ◽

1998 ◽

pp. 333-338

Author(s):

Jolanta Nastula ◽

David Salstein

Keyword(s):

Angular Momentum ◽

Polar Motion ◽

Atmospheric Angular Momentum ◽

Polar Motion Excitation

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Gravity, Oceanic Angular Momentum, and the Earth’s Rotation

Gravity, Geoid and Geodynamics 2000 - International Association of Geodesy Symposia ◽

10.1007/978-3-662-04827-6_26 ◽

2001 ◽

pp. 153-158 ◽

Cited By ~ 5

Author(s):

Richard S. Gross

Keyword(s):

Angular Momentum ◽

Earth’S Rotation ◽

Earth's Rotation ◽

Oceanic Angular Momentum

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Determination of Polar Motion and Earth Rotation from Laser Tracking of Satellites

Symposium - International Astronomical Union ◽

10.1017/s0074180900036287 ◽

1979 ◽

Vol 82 ◽

pp. 231-238 ◽

Cited By ~ 4

Author(s):

David E. Smith ◽

Ronald Kolenkiewicz ◽

Peter J. Dunn ◽

Mark Torrence

Keyword(s):

Gravity Field ◽

Radiation Pressure ◽

Orbit Determination ◽

Earth Rotation ◽

Polar Motion ◽

Ocean Tides ◽

Earth’S Gravity Field ◽

Laser Tracking ◽

Order Of Magnitude

Laser tracking of the Lageos spacecraft has been used to derive the position of the Earth's pole of rotation at 5-day intervals during October, November and December 1976. The estimated precision of the results is 0.01 to 0.02 arcseconds in both x and y components, although the formal uncertainty is an order of magnitude better, and there is general agreement with the Bureau International de l'Heure smoothed pole path to about 0.02 arcseconds. Present orbit determination capability of Lageos is limited to about 25 cm rms fit to data over periods of 5 days and about 50 cm over 50 days. The present major sources of error in the perturbations of Lageos are Earth and ocean tides followed by the Earth's gravity field, and solar and Earth reflected radiation pressure. Ultimate accuracy for polar motion and Earth rotation from Lageos after improved modeling of the perturbing forces appears to be of order ± 5 cm for polar motion over a period of about 1 day and about ± 0.2 to ± 0.3 milliseconds in U.T. for periods up to 2 or 3 months.

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