# SLR, GRACE and Swarm Gravity Field Determination and Combination
## 3 Results and Discussion  
Figure 4 shows the integrated secular effect of glacial isostatic adjustment (GIA), ice mass and snow mass change in the polar regions during the period 2010 to 2014 as derived from un-smoothed degree 60 monthly gravity field models determined from GRACE GPS and K-band observations. Figure 3: Integrated mass within Greenland reconstructed at different truncation degrees, (**a**) without filter or (**b**) smoothed by a 300 km Gaussian filter. The mass loss is mainly related to ice loss (dynamic or by melting and run-off). GIA, i.e., the relaxation of the crust in reaction to the large scale ice melt after the last ice age, counteracts ice mass loss and therefore the actual ice mass loss is even larger (estimates for the mass change induced by GIA vary from 1 Gt/year to 20 Gt/year for Greenland and from 55 Gt/year to 110 Gt/year for Antarctica [32]) than indicated by the figures, while snow mass depends on the season and largely cancels out in a multi-year mean. The observation coverage is densest near the poles due to the polar orbits of the GRACE satellites and consequently the noise is lowest near the poles. At lower latitudes, the noisy striping typical for GRACE becomes visible. For comparison to SLR-derived gravity field models the GRACE results are truncated at degree/order 10 and the corresponding EWH trends are shown in Figure 5. The trend signal that is well localized over the continents in Figure 4 leaks out over the oceans in Figure 5, as predicted by our simulation (Figure 3). In Figure 6, global plots of GRACE-derived trends 2010-2014 in EWH (left) and the amplitudes of seasonal variations (right) are provided, both truncated at degree/order 10. Trends are mainly visible at high latitudes, where large scale ice mass loss is the main reason for negative trends, GIA for positive trends in North America and Fennoscandia. At this low spherical harmonic resolution, it is difficult to state if negative trends near the west coast of North America are related to drought. Positive trends in the Amazon region probably are related to inter-annual variability that is not strictly seasonal. Figure 4: Trends in equivalent water height (EWH) as observed by GRACE in the Arctic (**left**) or Antarctic (**right**) region in the period 2010-2014, derived from unfiltered d/o 60 solutions. Figure 5: Trends in equivalent water height (EWH) in polar regions derived from GRACE gravity fields truncated at d/o 10. Seasonal variations (Figure 6, right) are related to hydrology and are strongest in the tropical and subtropical regions with strong seasonal variation in rainfall. Figure 7 provides the same information as Figure 6, but derived from SLR. In the top row, the unconstrained degree 6 gravity field models, and, in the bottom row, the constrained degree/order 10 solutions are evaluated. Especially in the case of the EWH trends, the improvement of the localization with a higher maximum degree is obvious. In the case of seasonal variations, the amplitudes in all but the Amazon basin are heavily attenuated compared to GRACE (Figure 6, right). Figures 8 and 9 focus on EWH trends derived from SLR for the time periods 1995-1999, 2000-2004, 2005-2009 and 2010-2014 in polar regions. The trends are determined either from unconstrained degree 6 solutions (top row) or from regularized monthly gravity field models up to spherical harmonic degree and order 10 (bottom row). While we can confirm the findings of [PERSON] et al. (2018) based on simulations that with degree 5 gravity fields, the correct localization of mass variations in Greenland and Antarctica is not granted; we observe rather precise localization of the SLR-derived mass trends in Greenland or Antarctica for the regularized degree 10 solutions (compare the sub-figures for the time-period 2010-2014 in Figures 8 and 9 with the corresponding results from GRACE in Figure 5).