## 3 Results
If selecting the period from August 2002 to July 2016, as provided in Table 5, the replacement of \(C_{30}\) terms after March 2012 affects the trend of mass variations over the GrIS and the AIS, respectively, by 0.2 and 1.0 Gt/yr. Finally, we compare mass change time series computed by the combination of degree one terms, the corresponding SLR-based \(C_{20}\) and \(C_{30}\) estimates over both ice sheets (experiment 4). As depicted by Figure 5, for combinations including the same SLR-based \(C_{20}\) estimates, mass change time series from the three data processing centers agree well with each other, except for the time span after July \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Mass Change Caused by SLR-based \(C_{20}\) Estimates**} \\ \cline{2-5}
**2002.08–2016.07** & **Trend [G/yr]** & **Annual Amp. [Gt]** & **Annual Phase** \\  & & & **[Degree]** \\ \hline \multirow{4}{*}{GrIS} & TN07 & \(-3.8\pm 0.2\) & 24 & 8 \\  & TN11 & \(-4.1\pm 0.2\) & 25 & 10 \\  & TN14 & \(-6.0\pm 0.2\) & 16 & 3 \\  & GFZ-SLR & \(-4.0\pm 0.2\) & 20 & 356 \\ \hline \multirow{4}{*}{AIS} & TN07 & \(-22.6\pm 1.4\) & 146 & 8 \\  & TN11 & \(-24.7\pm 1.5\) & 152 & 10 \\ \cline{1-1}  & TN14 & \(-36.1\pm 1.3\) & 97 & 3 \\ \cline{1-1}  & GFZ-SLR & \(-24.0\pm 1.3\) & 122 & 356 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The linear trend, annual amplitude and annual phase of mass change time series caused by SLR-based \(C_{20}\) estimates over the GrIS and the AIS during the time span from August 2002 to July 2016, using SLR-based \(C_{20}\) estimates in TN07, TN11, TN14, and GFZ. Figure 3: Mass change time series computed by only using SLR-based \(C_{20}\) estimates from TN07, TN11, TN14, and GFZ over **(a)** the GrIS and **(b)** the AIS during the GRACE mission span. 2016. The linear trend of mass variations computed from degree one terms, SLR-based \(C_{20}\) and \(C_{30}\) estimates in TN14 (green lines), is more negative over the GrIS, as compared to those associated with TN07 and TN11 corresponding to GRACE RL05 and RL06 data after March 2012. The mean value of linear trends of mass variations caused by these low degree spherical harmonics corresponding to GRACE RL05 (SW + TN07 + GRACE \(C_{30}\)), RL06 (SUN11 + TN11 + GRACE \(C_{30}\)), and RL06 (SUN14 + TN14 + GSFC) is \(-8.1\pm 0.7\), \(-12.3\pm 0.7\), \(-14.7\pm 0.7\) Gt/yr over the GrIS, respectively (Table 6). That is, the trend of mass variations computed from SUN11 + TN11 + GRACE \(C_{30}\) in absolute value is 50% larger than SW + TN07 + GRACE \(C_{30}\) over the GrIS. Compared with SUN11 + TN11 + GRACE \(C_{30}\), the linear trend of mass variations caused by SUN14 + TN14 + GSFC in absolute value is 20% larger over the GrIS. Over the AIS, as provided by Table 6, the signs of linear trends of mass variations caused by these low degree terms corresponding to GRACE RL05 (SW + TN07 + GRACE \(C_{30}\)) for CSR, GFZ, and JPL are not the same, while more consistent linear trends can be seen from mass change time series corresponding to GRACE RL06 (SUN11 + TN11 + GRACE \(C_{30}\)), RL06 (SUN14 + TN14 + GSFC). The difference between the two positive linear trends of the mass change time series caused by these low degree terms corresponding to GRACE RL06 (SUN11 + TN11 + GRACE \(C_{30}\)) and RL06 (SUN14 + TN14 + GSFC) is about 8 Gt/yr over the AIS. Figure 4: Mass change time series caused by \(C_{30}\) from CSR/GFZ/JPL-published GRACE RL05 and RL06 data and by SLR-based \(C_{30}\) in TN14 from GSFC over (**a**) the GrIS and (**b**) the AIS during the GRACE mission span. CSR/GFZ/JPL means that time series of mass change caused by \(C_{30}\) are separately calculated and shown for GRACE data published by CSR, GFZ, and JPL.