GRACE AOD1B RL04 (since 30 April 2012 no longer updated)


 

General Information

At GFZ Potsdam the GRACE release 04 (RL04) Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products have been generated on a routine basis for the period January 1, 2001 until April 30, 2012 to be used for correction of short-term non tidal atmospheric and oceanic mass variations for GRACE RL04 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 RL04 outputs can be found here. Additionally, for a consistent processing of SLR data the RL04 time series has been extended back to January 1, 1976 based on ERA40 data and made available to the users on January 19, 2009.

All products for 1976 till today are stored as daily gnu-zipped ascii files (AOD1B_YYYY_MM_DD_X_04.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:

Details on the GRACE AOD1B RL04 products as well as on the precursor releases can be found in the GRACE AOD1B Product Description Document for Product Releases 01 to 04 (Rev. 3.1, April 13, 2007) which can be downloaded here (1.7 MB). Details on the additional time series for 1976-2000 based on ERA40 are described in a Scientific Technical Report (4.5 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 RL04 components "atm", "ocn", "glo" and "oba" on November 1, 2007 00:00.

Important Note 30 November 2007

If you downloaded AOD1B RL04 products for the period June 23, 2006 until September 20, 2007 prior to November 30, 2007 please be sure to download these files again because the oceanic contributions to these products are wrong (by mistake twice reduction of atmospheric S2 tide from surface pressure data used to force the OMCT model). The correct AOD1B RL04 products for this range of dates have to have a product creation date later than November 2007 within the header information, e.g.

PRODUCT CREATE START TIME(UTC): 2007-11-08 10:51:24.000

PRODUCT CREATE END TIME(UTC) : 2007-11-08 13:19:25.000

The influence of the wrong AOD1B products on the GAA/B/C/D products is negligible, thus these products need only to be redistributed if the number of days to generate the GSM-products have been changed. The influence on the gravity field result is unfortunately drastic (especially over the oceans). Therefore the SDS centers have reprocessed the corresponding GSM products. Please read the SDS newsletters and the L2 Release Notes (both available at the GRACE archives) regularly.

Quality Parameters

In order to check the quality of the GRACE mission period products different plots are routinely generated and shown on this page (plots for the period 1976-2008 are included in the STR0812). First, 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. Second, 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.

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid

Generally, for a "nominal" AOD1B product, the

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.

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


geoid ATM
geoid OCN

geoid GLO
geoid OBA

Figure 2: Geoid height variability [mm] for AOD1B RL04 components "atm", "ocn", "glo" and "oba" since January 1, 2001.

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


c00 ATM
c00 OCN

c00 GLO
c00 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


c10 ATM
c10 OCN

c10 GLO
c10 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


c11 ATM
c11 OCN

c11 GLO
c11 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


s11 ATM
s11 OCN

s11 GLO
s11 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


c20 ATM
c20 OCN

c20 GLO
c20 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


c21 ATM
c21 OCN

c21 GLO
c21 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


c22 ATM
c22 OCN

c22 GLO
c22 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


s21 ATM
s21 OCN

s21 GLO
s21 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid


s22 ATM
s22 OCN

s22 GLO
s22 OBA

top | C00 | C10 | C11 | S11 | C20 | C21 | C22 | S21 | S22 | geoid




GRACE

July 24, 2012, F.Flechtner