GRACE non-tidal high-frequency atmospheric and oceanic mass variation models are routinely generated at GFZ as so-called Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products to be added to the background static gravity model during GRACE monthly gravity field determination. AOD1B products are 3-hourly series of spherical harmonic coefficients up to degree and order 180 which are routinely provided to the GRACE Science Data System and the user community with only a few days time delay. These products reflect spatio-temporal mass variations in the atmosphere and oceans deduced from an operational atmospheric model and corresponding ocean dynamics provided by an ocean model. The variability is derived by subtraction of a long-term mean of vertical integrated atmospheric mass distributions and a corresponding mean of ocean bottom pressure as simulated with the ocean model.
The latest release 06 (RL06) of AOD1B is available since the year 1976 with a temporal resolution of 3 h. The product is provided in Stokes coefficients up to degree and order 180. RL06 separates tidal and non-tidal signals, and has an improved long-term consistency due to the introduction of a time-invariant reference orography in continental regions.
Release 05 (RL05) is identical to RL04 what concerns the atmospheric mass variability which is, as all other previous releases, based on 6-hourly meteorological analysis fields of the Integrated Forecast System of the European Centre for Medium-Range Weather Forecasts (ECMWF). The oceanic mass variability is – as for RL03 and RL04 - based on output of GFZ’s Ocean Model for Circulation and Tides (OMCT), but with updated parameterization and spatial resolution which significantly improved the quality of AOD1B product over the oceans. Statistics and further details on OMCT RL05 outputs and derived AOD1B RL05 products are regularly updated.
- OMCT simulations for AOD1B RL05
- Statistics for AOD1B RL05 coefficients
- Known Issues with AOD1B RL05
Previous AOD1B releases (RL00 – RL04) are no longer produced. For AOD1B RL00 and RL01 the JPL provided barotropic ocean model PPHA (developed by Pacanowski, Ponte, Hirose and Ali) based on a 2001 mean field was used. Unfortunately, this model had deficiencies which influenced the quality of the GRACE gravity field solutions. Therefore the production of RL01 has been stopped on June 30, 2007 and since RL03 the OMCT model is used for operational AOD1B model generation (RL02 was an intermediate test series which was only made available for some dedicated months). Also, the mean field to define variability was extended with RL02 to the period 2001+2002. AOD1B RL04 has also been reprocessed back to 1976 based on ERA40 (ECMWF re-analysis) data for a consistent processing of and combination with Satellite Laser Ranging data. The GFZ Scientific Report STR08/12 is providing further information. As it was shown e.g. by Bonin and Chambers, 2012 ) that AOD1B RL04 has deficiencies especially over the ocean the production of RL04 has been stopped on April 30, 2012 and was substituted by RL05. AOD1B RL04 statistics and further details can be found here (note: This page is no longer updated!).
- OMCT simulations for AOD1B RL04 (outdated, processed until May 2012)
- Statistics for AOD1B RL04 coefficients
- Known Issues with AOD1B RL04
Data Access and Documentation
AOD1B products are publicly available at GFZ’s Information System and Data Center (ISDC).
Before using the AOD1B products please read the GRACE AOD1B Product Description Document for Product Releases 01 to 04 (Rev. 3.1, April 13, 2007, 1.7 MB) resp. GRACE AOD1B Product Description Document for Product Release 05 (Rev. 4.3, April 23, 2015, 1.7 MB).
AOD1B are GGFC Operational Products
The GRACE AOD1B products were accepted by the International Earth Rotation and Reference Systems Service (IERS) Global Geophysical Fluid Center (GGFC) as Provisionary Products in 2009 and have been given the status of GGFC Operational Products in May 2012.
Further GGFC Operational Products from GFZ
In addition to the AOD1B Products, GFZ also provides Effective Angular Momentum Functions based on ECMWF atmospheric data and OMCT ocean circulation simulations for studies of the time-variable rotation of the Earth.
Information on those products can be found here.
- Effective Angular Momentum Functions from ECMWF and OMCT