The GRACE M-SSA solution is a Level-3 product, provided as monthly grids of equivalent water height (EWH) in cm from August 2002 to January 2016.
The method used to calcute these monthly solutions is explained in Prevost et al. (2019).
The data can be find in the Matlab format (.mat) in grace_mssa_matlab.zip or in text format (one file per month) in grace_mssa_grids.zip.
When using these data, please cite : Prevost, P., Chanard, K., Fleitout, L., Calais, E., Walwer, D., van Dam,T., & Ghil, M. (2019). Data-adaptive spatio-temporal filtering of GRACE data. Geophysical Journal International, 219(3), 2034-2055.