TY - JOUR

T1 - Significance of secular trends of mass variations determined from GRACE solutions

AU - Steffen, Holger

AU - Petrovic, Svetozar

AU - Müller, Jürgen

AU - Schmidt, Roland

AU - Wünsch, Johann

AU - Barthelmes, Franz

AU - Kusche, Jürgen

N1 - Funding information: We would like to thank the GRACE science team for the overall support, CSR, University of Texas, JPL Pasadena, ITG Bonn , and CNES Toulouse for providing the GRACE monthly solutions, and Petra Döll and her group for making the WGHM data available. We would also like to thank Andreas Güntner (GFZ), Sean Swenson (University of Colorado), Wouter van der Wal (TU Delft), and Matthias Weigelt (Universität Stuttgart) for helpful discussions. We are very grateful for the excellent reviews and numerous valuable suggestions of two anonymous referees, which have greatly improved this manuscript. This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through research grant MU1141/8-1 (SPP 1257) and by the German Ministry of Education and Research (BMBF) within the geoscientific R + D programme GEOTECHNOLOGIEN under grant 03F0424A .

PY - 2009/9/30

Y1 - 2009/9/30

N2 - Since 2002 the Earth's gravity field is globally observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission. The GRACE monthly gravity field solutions, available from several analysis centres, reflect mass variations in the atmosphere, hydrosphere and geosphere. Due to correlated noise contained in these solutions, it is, however, first necessary to apply an appropriate filtering technique. The resulting, smoothed time series are applied not only to determine variations with different periodic signatures (e.g., seasonal, short and medium-term), but to derive long-periodic mass variations and secular trends as well. As the GRACE monthly solutions always show the integral effect of all mass variations, for separation of single processes, like the GIA (Glacial isostatic adjustment)-related mass increase in Fennoscandia, appropriate reduction models (e.g. from hydrology) are necessary. In this study we show for the example of the Fennoscandian uplift area that GRACE solutions from different analysis centres yield considerably different secular trends. Furthermore, it turns out that the inevitable filtering of the monthly gravity field models affects not only the amplitudes of the signals, but also their spatial resolution and distribution such as the spatial form of the detected signals. It also becomes evident that the determination of trends has to be performed together with the determination of periodic components. All periodic terms which are really contained in the data, and only such, have to be included. The restricted time span of the available GRACE measurements, however, limits the separation of long-periodic and secular signals. It is shown that varying the analysis time span affects the results considerably. Finally, a reduction of hydrological signals from the detected integral secular trends using global hydrological models (WGHM, LaDWorld, GLDAS) is attempted. The differences among the trends resulting from different models illustrate that the state-of-the-art hydrology models are not suitable for this purpose as yet. Consequently, taking the GRACE monthly gravity field solutions from one centre, choosing a single filter and applying an insufficiently reliable reduction model leads sometimes to a misinterpretation of considered geophysical processes. Therefore, one has to be cautious with the final interpretation of the results.

AB - Since 2002 the Earth's gravity field is globally observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission. The GRACE monthly gravity field solutions, available from several analysis centres, reflect mass variations in the atmosphere, hydrosphere and geosphere. Due to correlated noise contained in these solutions, it is, however, first necessary to apply an appropriate filtering technique. The resulting, smoothed time series are applied not only to determine variations with different periodic signatures (e.g., seasonal, short and medium-term), but to derive long-periodic mass variations and secular trends as well. As the GRACE monthly solutions always show the integral effect of all mass variations, for separation of single processes, like the GIA (Glacial isostatic adjustment)-related mass increase in Fennoscandia, appropriate reduction models (e.g. from hydrology) are necessary. In this study we show for the example of the Fennoscandian uplift area that GRACE solutions from different analysis centres yield considerably different secular trends. Furthermore, it turns out that the inevitable filtering of the monthly gravity field models affects not only the amplitudes of the signals, but also their spatial resolution and distribution such as the spatial form of the detected signals. It also becomes evident that the determination of trends has to be performed together with the determination of periodic components. All periodic terms which are really contained in the data, and only such, have to be included. The restricted time span of the available GRACE measurements, however, limits the separation of long-periodic and secular signals. It is shown that varying the analysis time span affects the results considerably. Finally, a reduction of hydrological signals from the detected integral secular trends using global hydrological models (WGHM, LaDWorld, GLDAS) is attempted. The differences among the trends resulting from different models illustrate that the state-of-the-art hydrology models are not suitable for this purpose as yet. Consequently, taking the GRACE monthly gravity field solutions from one centre, choosing a single filter and applying an insufficiently reliable reduction model leads sometimes to a misinterpretation of considered geophysical processes. Therefore, one has to be cautious with the final interpretation of the results.

KW - Filtering

KW - Glacial isostatic adjustment

KW - Global hydrology models

KW - GRACE

KW - Mass variation

UR - http://www.scopus.com/inward/record.url?scp=72149106817&partnerID=8YFLogxK

U2 - 10.1016/j.jog.2009.09.029

DO - 10.1016/j.jog.2009.09.029

M3 - Article

AN - SCOPUS:72149106817

VL - 48

SP - 157

EP - 165

JO - Journal of geodynamics

JF - Journal of geodynamics

SN - 0264-3707

IS - 3-5

ER -