Monthly mean of background models
=================================

During the gravity field recovery process, the following background models are
reduced from the data:
  - ocean tide: FES2014b, co-estimated
  - pole tide: IERS 2010
  - ocean pole tide: Desai 2004 (IERS 2010)
  - atmospheric tides: AOD1B RL06
  - atmosphere and ocean dealiasing: AOD1B RL06
  - sub-monthly continental hydrology: LSDM
  - relativistic corrections: IERS 2010

These effects are not present in the monthly solutions, which is consistent with the
RL06 of the official GRACE processing centers. We provide monthly means of these models,
so that the full tidal/non-tidal gravity can be restored and/or signal separation can
be performed.

Standard GRACE solutions (GSM) contain
  - terrestrial water storage
  - cryosphere
  - errors in the AOD1B product (residual atmosphere and ocean signal)
  - solid earth (e.g. earthquakes)
  - Glacial Isostatic Adjustment (GIA)

and are given in center of mass. We provide monthly means of geocenter motion (degree one)
derived from SLR (Cheng et al. 2010) consistent and with the GSM definition, to transform
the solution into center of figure.
Another common post-processing step is to replace the GRACE C20 coefficients as these are
typically less reliable than SLR derived values (Cheng et al. 2011), of which a GSM compatible
time series is also provided.

To restore reduced signals (e.g. atmosphere and ocean, long-periodic ocean tides) or separate individual
geophysical subsystems, monthly means of
 - Glacial Isostatic Adjustment (GIA, Steffen 2017)
 - Atmosphere (AOD1B RL06)
 - Ocean (AOD1B RL06)
 - Ocean bottom pressure (AOD1B RL06)
 - Hydrology (LSDM)
 - Earth-, pole and ocean pole tide (IERS2010, Desai 2004)
 - Ocean tides (FES2014b)
are provided.

References
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Dobslaw, H., Bergmann-Wolf, I., Dill, R., Poropat, L., Thomas, M., Dahle, C., Esselborn, S., König, R., Flechtner, F.: A New High-Resolution Model of Non-Tidal Atmosphere and Ocean Mass Variability for De-Aliasing of Satellite Gravity Observations: AOD1B RL06. Geophysical Journal International, 211(1), 263-269, DOI: doi.org/10.1093/gji/ggx302.
Dill, R. (2008): Hydrological model LSDM for operational Earth rotation and gravity field variations. GFZ ScientificTechnical Report STR08/09.
Cheng, M., J. C. Ries, and B. D. Tapley (2011), Variations of the Earth's figure axis from satellite laser ranging and GRACE, J. Geophys. Res., 116, B01409, doi:10.1029/2010JB000850.
Cheng, M.K., B.D. Tapley, J.C. Ries (2010) Geocenter Variations from Analysis of SLR data, IAG Commission 1 Symposium 2010, Reference Frames for Applications in Geosciences (REFAG2010), Marne-La-Vallee, France, 4-8 October 2010.