General Information

At GFZ Potsdam the GRACE release 05 (RL05) Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products are generated on a routine basis for the period January 1, 2001 till today (current status December 03, 2017). AOD1B RL05 is used - as all precursor models such as AOD1B RL04 - for correction of short-term non tidal atmospheric and oceanic mass variations for GRACE RL05 gravity products. AOD1B RL04 is based on 6-hourly ECMWF analysis data and output from the baroclinic ocean model for circulation and tides (OMCT). Details on OMCT RL05 outputs can be found here. Additionally, for a consistent processing of SLR data the RL05 time series has been extended back to January 1, 1979 based on ERA-Interim data and made available to the users on April, 2015.

All products for 1979 till today are stored as daily gnu-zipped ascii files (AOD1B_YYYY_MM_DD_X_05.asc.gz) at the GRACE archives at ISDC and PO.DAAC and contain spherical harmonic coefficients up to degree and order 100 for four 6-hourly time stamps (0, 6, 12 and 18 hours) and for each time stamp four different data types describing gravity variabilities w.r.t. a 2001+2002 mean field are provided:

For an a-posteriori correction over land of the two jumps in January 2006 and 2010 (see known issues with AOD1B RL05) we have defined two new Level-2 data sets (called GAE and GAF). They were delivered to the GRACE SDS in terms of technical notes TN08 and TN09 in April 2014 (available at the GRACE archives at both GFZ and JPL). They have to be applied during the spherical harmonic synthesis in order to generate corrected monthly GSM grids for land applications.

Details on the GRACE AOD1B RL05 products (including GAE and GAF) as well as on the precursor releases can be found in the GRACE AOD1B Product Description Document for Product Releases 01 to 05 (Rev. 4.4, December 14, 2015) which can be downloaded here (1.7 MB).

A typical example for the variability in terms of geoid height for November 1, 2007 00:00 is shown in the following figure.

geoid ATM 1.11.2007 00:00
geoid OCN 1.11.2007 00:00

geoid GLO 1.11.2007 00:00
geoid OBA 1.11.2007 00:00

Figure 1: Geoid height variability [mm] for AOD1B RL05 components "atm", "ocn", "glo" and "oba" on November 1, 2007 00:00.

Quality Parameters

In order to check the quality of the GRACE mission period products different plots are routinely generated.

1. Geoid Height Variability

The minimum, maximum, mean and wRMS (cosine latitude weighted RMS) geoid heigth variability for all four data types and for the complete production period (2001-today) is derived from spherical harmonic coefficients of degree and order 0 to 100.

Generally, for a "nominal" AOD1B product, the

geoid ATM
geoid OCN

geoid GLO
geoid OBA

Figure 2: Geoid height variability [mm] for AOD1B RL05 components "atm", "ocn", "glo" and "oba" since January 1, 2001.

2. Individual Coefficient Statistics

The individual degree 0 to 2 spherical harmonics 6-hourly time series for the "atm", "ocn", "glo" and "oba" variabilities are shown in colour and high pass filtered (after subtraction of the daily mean) in black. These high pass filtered Cnm and Snm should show no jumps in amplitude.

Interestingly, the atmospheric mass is increasing till 2005 by about 1.9 10^14 kg/year and is then again decreasing till 2008 by about 4.7 10^14 kg/year (see "atm" C00 time series). Since 2008 the mass seems more or less constant. But, as the AOD1B degree 0 and 1 terms are - as for all other background models - not used (fixed to 1 and 0) for GRACE gravity field determination, this does not influence the quality of the GRACE level-2 products.

View routinely updated figures for the degree 0 coefficient

View routinely updated figures for the degree 1 coefficients

View routinely updated figures for the degree 2 coefficients


December 07, 2017, J.-C.Raimondo