Evaluating Gravimetric Polar Motion Excitation Estimates from the RL06 GRACE Monthly-Mean Gravity Field Models

Abstract

Over the last 15 years, the Gravity Recovery and Climate Experiment (GRACE) mission has provided measurements of temporal changes in mass redistribution at and within the Earth that affect polar motion. The newest generation of GRACE temporal models, are evaluated by conversion into the equatorial components of hydrological polar motion excitation and compared with the residuals of observed polar motion excitation derived from geodetic measurements of the pole coordinates. We analyze temporal variations of hydrological excitation series and decompose them into linear trends and seasonal and non-seasonal changes, with a particular focus on the spectral bands with periods of 1000–3000, 450–1000, 100–450, and 60–100 days. Hydrological and reduced geodetic excitation series are also analyzed in four separated time periods which are characterized by different accuracy of GRACE measurements. The level of agreement between hydrological and reduced geodetic excitation depends on the frequency band considered and is highest for interannual changes with periods of 1000–3000 days. We find that the CSR RL06, ITSG 2018 and CNES RL04 GRACE solutions provide the best agreement with reduced geodetic excitation for most of the oscillations investigated.

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

“…We do not distinguish between GAO series with GIA removed and GAO series without GIA removed as post-glacial rebound mainly affects trends. The time series plots show that the χ 2 component is characterized by bigger amplitudes than χ 1 (note that there are different scales on y axis for χ 1 and χ 2 ), which has been already demonstrated in other works (e.g., Nastula et al 2019;Seoane et al 2011;, 2020aWińska et al 2016Wińska et al , 2017 and arises from continent-ocean distribution (Fig. 1).…”

“…This is not surprising, because, on the one hand, post-glacial rebound has the greatest impact on areas of the Northern Hemisphere-Fennoscandia and the northern part of North America. On the other hand, the χ 2 component is more sensitive than the χ 1 component to mass changes over these areas (Śliwińska et al 2020a;Youm et al 2017). In general, removing signals from post-glacial rebound reduces the GAO trend for the χ 1 component, but increases the trend for χ 2 .…”

“…Bizouard (2016), Lambeck (1980), and Munk and MacDonald (1960) showed that PM has an elliptic character with two circular terms: retrograde (clockwise) and prograde (counter-clockwise). Therefore, phasor diagrams are usually shown separately for prograde and retrograde oscillations (Brzeziński et al 2009;Dobslaw et al 2010;Nastula et al 2011;Seoane et al 2009Seoane et al , 2011, 2020aWińska et al 2016). Non-seasonal oscillations are obtained after removing trends and seasonal oscillations from the time series and they are presented as time series plots of χ 1 and χ 2 components of non-seasonal oscillation.…”

“…In the studies on PM variations due to global mass redistribution, particular emphasis was placed on determining the contribution of the continental hydrosphere and cryosphere (e.g., Göttl et al 2018;Jin et al 2010Jin et al , 2012Meyrath and van Dam 2016;Nastula and Śliwińska 2020;Nastula et al 2007Nastula et al , 2011Nastula et al , 2019Seoane et al 2011Seoane et al , 2012, 2020aWińska et al 2016Wińska et al , 2017. The sum of land hydrosphere and cryosphere components, which include soil water, surface water, groundwater, water in snow cover and ice, and water in vegetation, is commonly known as terrestrial water storage (TWS).…”

Evaluating Processing Choices for the Geodetic Estimation of Earth Orientation Parameters With Numerical Models of Global Geophysical Fluids

“…Atmospheric reanalyses produced by Meteorological Services like the European Centre for Medium‐Range Weather Forecasts (ECMWF) are now routinely available (Dee et al, 2011). Particularly, the mass component estimates of ocean and land hydrosphere models have benefited from the availability of time‐variable gravity field obtained with the GRACE mission (Göttl et al, 2019; Śliwińska et al, 2020). We therefore consider it nowadays as a viable option to use a geophysical model data set as the reference against which different geodetic combination time series are compared.…”