Combination of geodetic space observations for estimating cryospheric mass changes and their impact on Earth rotation (CIEROT)
This project focuses on the determination of the effect of mass changes within the cryosphere on Earth rotation from a combination of geometric and gravimetric space observations.
The redistribution and motion of masses in the Earth System causes variations of Earth rotation via the exchange of angular momentum. The impact of variations of angular momentum in the Earth's subsystems is commonly expressed in terms of so-called excitation functions. While the integral excitation can be determined from the observations of geometric space techniques with high accuracy, their separation into individual contributions from the Earth's subsystems is a big a challenge. Especially the quantification of the effects of mass changes within the cryosphere is afflicted with large uncertainties due to the absence of (1) precise geodetic information on global scale and (2) reliable cryosphere models. Since 2002 gravity field changes of the Earth have been observed by the satellite mission GRACE (Gravity Recovery and Climate Experiment). The separation of the measurements, in particular into the contribution of ice mass changes, poses a special challenge because the signal of ice mass changes is superposed by the effect of postglacial land uplift.
Since 2003 and 2010 respectively ice height changes can be observed by the altimeter satellite ICESat (Ice, Cloud, and land Elevaion Satellite) and CryoSat-2 with high accuracy. The transformation of these measurements into ice mass changes requires knowledge of the ice dynamics and its density. Within this project, for the first time, geometric and gravimetric space observations will be combined in order to estimate the cryospheric mass effect on Earth rotation. By the combination of different geodetic space observations, weaknesses of individual observations can be compensated, and technique-specific strengths can be optimally accounted for. The findings will also provide information about the influence of increased ice melting and the corresponding sea level change on Earth rotation. Vice versa, the changes in Earth rotation will be analyzed with respect to their impact on the mean annual temperature of the Earth. The resulting changes of mass and angular momentum within the cryosphere will also contribute to improve cryosphere models.