DOI: 10.1594/pangaea.763431
title: Gravity potential spherical harmonic series

description: Time variable gravity fields, reflecting variations of mass distribution in the system Earth is one of the key parameters to understand the changing Earth. Mass variations are caused either by redistribution of mass in, on or above the Earth's surface or by geophysical processes in the Earth's interior. The first set of observations of monthly variations of the Earth gravity field was provided by the US/German GRACE satellite mission beginning in 2002. This mission is still providing valuable information to the science community. However, as GRACE has outlived its expected lifetime, the geoscience community is currently seeking successor missions in order to maintain the long time series of climate change that was begun by GRACE. Several studies on science requirements and technical feasibility have been conducted in the recent years. These studies required a realistic model of the time variable gravity field in order to perform simulation studies on sensitivity of satellites and their instrumentation. This was the primary reason for the European Space Agency (ESA) to initiate a study on ''Monitoring and Modelling individual Sources of Mass Distribution and Transport in the Earth System by Means of Satellites''. The goal of this interdisciplinary study was to create as realistic as possible simulated time variable gravity fields based on coupled geophysical models, which could be used in the simulation processes in a controlled environment. For this purpose global atmosphere, ocean, continental hydrology and ice models were used. The coupling was performed by using consistent forcing throughout the models and by including water flow between the different domains of the Earth system. In addition gravity field changes due to solid Earth processes like continuous glacial isostatic adjustment (GIA) and a sudden earthquake with co-seismic and post-seismic signals were modelled. All individual model results were combined and converted to gravity field spherical harmonic series, which is the quantity commonly used to describe the Earth's global gravity field. The result of this study is a twelve-year time-series of 6-hourly time variable gravity field spherical harmonics up to degree and order 180 corresponding to a global spatial resolution of 1 degree in latitude and longitude. In this paper, we outline the input data sets and the process of combining these data sets into a coherent model of temporal gravity field changes. The resulting time series was used in some follow-on studies and is available to anybody interested.
description: &lt; Monitoring and Modelling individual Sources of Mass Distribution and Transport in the Earth System by Means of Satellites &gt;Project Partners:- Institute of Astronomical and Physical Geodesy, Technical University Munich, Germany- Bristol Glaciology Centre, University of Bristol, United Kingdom- Department of Physical Geography, Utrecht University, The Netherlands- Deutsches GeoForschungsZentrum Potsdam, Germany- University of Luxembourg, Luxembourg- Delft Institute of Earth Observation and Space Systems, Delft University of Technology, The NetherlandsIn 2006 the European Space Agency (ESA) initiated a study on "Monitoring and Modelling individual Sources of Mass Distribution and Transport in the Earth System by Means of Satellites". The goal of this interdisciplinary study was to create as realistic as possible simulated time variable gravity fields based on coupled geophysical models, which could be used in the simulation processes in a controlled environment. For this purpose global atmosphere, ocean, continental hydrology and ice models were used. The coupling was performed by using consistent forcing throughout the models and by including water flow between the different domains of the Earth system. In addition gravity field changes due to solid Earth processes like continuous glacial isostatic adjustment (GIA) and a sudden earthquake with co-seismic and post-seismic signals were modelled. All individual model results were combined and converted to gravity field spherical harmonic series, which is the quantity commonly used to describe the Earth's global gravity field. The result of this study is a twelve-year time-series (1995 to 2006) of 6-hourly time variable gravity field spherical harmonics up to degree and order 180 corresponding to a global spatial resolution of 1 degree in latitude and longitude. On this Website the resulting time series is made available to the public.Various combinations of mass fields were computed and converted to gravity field spherical harmonics. Details are described in the reference given below. 6-hourly gravity potential spherical harmonics for each data combination scenario are combined to yearly batches (see table below linking to 60 files together, each file is a compressed tar archive with about 480 MB file size).The format of the gravity potential spherical harmonic series follows the conventions used by the International Center for Global Earth Models (ICGEM) see: http://icgem.gfz-potsdam.de/ICGEM/ICGEM.htmlWeb page with format description as pdf-file see Further details.
description: Supplement to: Gruber, Thomas; Bamber, Jonathan L; Bierkens, Marc F P; Dobslaw, Henryk; Murböck, M; Thomas, M; van Beek, L P H; van Dam, T; Vermeersen, L L A; Visser, P N A M (2011): Simulation of the time-variable gravity field by means of coupled geophysical models. Earth System Science Data, 3(1), 19-35