Using GRACE/GRACE-FO and Swarm to estimate ice-sheets mass loss in Antarctica and Greenland during 2002-2020

The Intergovernmental Panel on Climate Change's (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) concluded that the Antarctica and Greenland ice sheets were major contributors to global sea-level rise. Satellite gravimetry, e. g. the Gravity Recovery and Climate Experiment (GRACE) and the GRACE Follow-on (GRACE-FO) missions, provides the direct observations of large-scale ice mass loss. However, there is a one-year data gap spanning from July 2017 to May 2018 between GRACE and GRACE-FO. Fortunately, operating from November 2013, the Swarm mission with a constellation of three LEO (Low Earth Orbit) satellites can be used to recover global large-scale temporal gravity fields. Meanwhile, the ARIMA-MC (Autoregressive Integrated Moving Average Model-Monte Carlo) method also makes forecasting the missing time-varied gravity possible. The main objective of this study is to determine ice mass variations in Antarctica and Greenland during the one-year gap between GRACE and GRACE-FO. Our results indicated that Swarm's results were comparable to the forecast from the ARIMA-MC method in space-time. From April 2002 to March 2020, the rates of ice mass loss were -119 +/- 23 Gt.a(-1) and -259 +/- 20 Gt.a(-1) over Antarctica and Greenland, respectively, which was equivalent to the global sea level rise at the rate of similar to 0. 33 mm.a(-1) and similar to 0. 72 mm.a(-1), respectively. The ice loss rate of Wilkes Land in Antarctica during 2010-2020 was accelerated by 10 times comparing to the period of 2002-2009. The major abrupt ablation of Greenland in the summer of 2019 was connected to the NAO (North Atlantic Oscillation) event.