ANU monthly mascon estimates are provided in hdf5 format, either on the native mascon geometry or on a regular grid. The following solutions are available:

ANU mascon fingerprint files

Below are links to the sea level fingerprint files that relate changes in mass on our continental mascons to changes in ocean height on our ocean mascons. These files are used during the calculations of the degree-1 loading effects (see below) as well as in the assessment of the effects of continental hydrology on ocean mass changes (McGirr et al., 2024).

mascons_stage5_V010_200km.fingerprints.gz

Corrections applied

Degree-1

We use the approach of Swenson et al. (2008) to calculate the degree-1 (geocentre) signals compatible with our monthly mascon estimates. The total degree-1 correction is calculated for each mascon using barystatic sea level fingerprints to define the ocean mass component of degree-1 as per Sun et al. (2016). To calculate the degree-1 correction, we use our GRACE/GRACE-FO mascon estimates rather than a spherical harmonic representation, we therefore do not use the optimal parameter values as suggested by Sun et al. (2016). The degree-1 correction is calculated relative to the AOD1B (e.g. GAC and GAD) degree-1 coefficients. 

C_2,0 and C_3,0 replacement:

We replace the C₂₀ terms of our monthly temporal gravity field for the entire time span, and the C₃₀ terms for the GRACE Follow-On period (2018-present) using values derived from Satellite Laser Ranging, defined in Technical Note #14 (Loomis et al., 2019). Spherical harmonic coefficients are not explicitly estimated when deriving our mascon solutions; rather, changes to the water mass of each mascon are the parameters estimated. We therefore convert our mascon solutions to spherical harmonics, remove the mascon estimates C₂₀ and C₃₀ and replace them with values derived from Loomis et al. (2019) represented on our mascon geometry. 

Glacial Isostatic Adjustment

We correct the monthly mascon adjustments for glacial isostatic adjustment (GIA) using the ICE6G-D model (Peltier et al., 2018). Adjustments are applied in units of equivalent water height anomalies using 2008.0 as the reference epoch.

Atmosphere and Ocean Dealiasing

We add back the AOD1B RL06 GAD product to our mascon estimates, by doing so, the corrected ocean mascons represent ocean bottom pressure anomalies. To calculate estimates of ocean mass anomalies from our corrected mascons, atmospheric loading (GAC) must be removed. See the GRACE-FO Mission Documentation for Technical Note #12 and the AOD1B product description document for further information.

Removing the corrections

The component files used to create the corrected mascon estimates are provided below in netcdf format. Each correction grid is provided relative to the 2004 to 2010 mean epoch. The component files are combined to generate the corrected grid:

Corrected_GRACE[GRACE-FO] = Uncorrected + Degree1 - GIA + GAD - Mascon_C20 + SLR_C20 [- Mascon_C30 + SLR_C30]

Experimental solutions

Here we provide links to solution files that are "experimental" and/or don't relate to data used in any specific publication. The data below do not relate to a doi but provide a means for us to provide access to and to share our solutions.

ACG_2023_0.25deg.nc : monthly mascon estimates for 2023 generated using the accelerometer transplant data from TU Graz (available from TU-Graz)

ACH_2023_0.25deg.nc : monthly mascon estimates for 2023 generated using the ACH1B accelerometer transplant data from JPL

ANU_GRACEFO_2018_2024.nc : monthly GRACE-FO mascon estimates 2018-06 to 2024-12 generated using the ACH1B accelerometer transplant data from JPL

References

Loomis, B. D., Rachlin, K. E., Wiese, D. N., Landerer, F. W., & Luthcke, S. B. (2020). Replacing GRACE/GRACE-FO C_3,0 with satellite laser ranging: Impacts on antarctic ice sheet mass change. Geophysical Research Letters, 47(3), e2019GL085488. https://doi.org/10.1029/2019GL085488

Sun, Y., Riva, R., & Ditmar, P. (2016). Optimizing estimates of annual variations and trends in geocenter motion and J₂ from a combination of GRACE data and geophysical models. Journal of Geophysical Research: Solid Earth, 121(11), 8352–8370. https://doi.org/10.1002/2016JB013073

Swenson, S., D. Chambers, and J. Wahr (2008), Estimating geocenter variations from a combination of GRACE and ocean model output, J. Geophys. Res., 113, B08410, doi:10.1029/2007JB005338.