Fig. 3.

Schematic representation of the correspondence between daily time series and the irregular—quasi-monthly—temporal resolution of the GRACE time series. For daily time steps, $t=\left\{t_1,\dots ,t_i,\dots ,t_n\right\}$ going from the 1st to the nth day. For quasi-monthly time steps, $t^{\ast }=\left\{t_1^{\ast },\dots ,t_j^{\ast },\dots ,t_m^{\ast }\right\}$ going from the 1st to the mth month, $a_j$ and $b_j$ denoting the first and last days of a given month