Melting of ice-sheets in the Tian-Shan Mountains observed by satellite gravity measurements

Continental ice sheets are frozen from fresh-water with volume change related to temperature, snowfall, river runoff and evapotranspiration, which affect and are affected by changes in Earth's climate. The ice sheets variations play an important role in global water cycle and understanding land and ocean water exchange and energy balance. However, it is very difficult to accurately monitor the continental ice-sheets variations due to the lack of in situ widespread measurements, particularly the Tian-Shan Mountains ice sheets with a mean elevation of more than 3000m. With the launch of the Gravity Recovery and Climate Experiment (GRACE) mission since 2002, it has been very successful to estimate global terrestrial water storage (TWS) changes. In this paper, the global total terrestrial water storage with monthly resolution are derived from approximate 10 years of monthly GRACE measurements (2002 August-2012 April), and the ice sheets storage variations in Tian-Shan Mountains are obtained by subtracting the terrestrial water storage from the hydrological models. The seasonal and long-term trend of Tian-Shan Mountains ice sheets variations are investigated from about 10 years of monthly ice sheets variation time series. Results show that significant seasonal variations of ice-sheets in Tian-Shan Mountains and the annual amplitudes and phases agree remarkably well for the two independent observations. The maximum annual ice sheets storage in Tian-Shan Mountains normally appears in September-October, and the minimum is around in March-April. The ice-sheets melting in Tian-Shan Mountains is significant since 2005 and accelerating in some areas.