Section 1.3: Earth System Modelling

The many geodetic and geophysical measurements from satellites, airplanes, and terrestrial networks contain comprehensive information about Earth system dynamics. They are, however, only a snapshot of the dynamic status of our planet. Since these measurements reflect the effects of many different, concurrently active processes, they cannot be interpreted without additional contributions from theory and models. This is the focus of the work in Section 1.3. We concentrate on the modelling of transfer of mass, momentum and energy in the Earth system. This includes the simulation of the static and time-varying portions of the Earth's gravitational and magnetic fields, the deformation of the Earth's surface, changes in sea level and variations in Earth's rotation. 

The geodetic parameters and fields, like the Earth's shape, its gravitational field and its orientation in space, are affected by many dynamic processes. The causes for their variation stem from all different parts of the Earth system, from the upper atmosphere to the core. By means of numerical simulations we trace these influences and draw conclusions about the dynamic processes from measured changes. For example, we model how the changes in global atmospheric wind systems, ocean currents and continental water systems affect the Earth's rotation. We investigate the viscoelastic response of the Earth's crust to changes in continental ice masses and determine resulting changes in sea level. In contrast to short term elastic deformations, this isostatic adaptation to the decrease in ice loading can still be observed thousands of years after the last glacial ice has melted. We also model how variations of and interactions between convection currents in the Earth's mantle and its outer core produce the decadal oscillations in Earth rotation.

Our research falls into five categories

We develop and explore numerical codes rooted in the fundamental theories of fluid dynamics to aid geodetic and geophysical data analysis and interpretation for the benefit of an improved understanding of the System Earth. Central to our work are ocean general circulation models configured to cover global or regional domains that represent processes as ocean tides, self-attraction and loading feedbacks to the ocean dynamics, or surface pressure forcing in addition to the usually considered atmospheric fluxes. We further use numerical models of the terrestrial water cycle that consider vertical water and energy exchange with the atmosphere, and lateral water transport in the soil and through the river network.

This topic systematically combines observations and numerical models of Earth's systems. Observations are interpolated in time and space under consideration of modelled physical laws, not directly observed quantities are estimated and numerical models are reinitialized to improve the forecasts. By using models, data assimilation can invert causal connections to find the sources of observed changes. Likewise we try to relate sensitivities of hardly observable quantities to observable quantities with the goal to derive the former by observing the latter. Closely related is the estimation and optimization of the expected gain of future observation campaigns.

In this topic we concentrate on joint analysis of gravity, seismic and other geophysical, geodetic and geological data aiming for construction of comprehensive models of the lithosphere and underlying mantle and finding a connection of these models with ongoing tectonic processes and geodynamics.

We use observations and numerical simulations to understand the dynamics of the large ice sheets of Greenland and Antarctica in the past and predict their dynamics in the future. A particular focus is on the mass balance of these ice sheets, since it has a direct impact on the global sea level. Interactions of the ice sheets with the ocean, the atmosphere and the solid earth play a key role in understanding their dynamics and for meaningful modeling.

In this topic, we consider the solid earth response to mass redistributions at its surface in relation to geodynamic and geophysical problems like climate, ocean and ice-sheet dynamics. The focus is numerical modelling of instantaneous to long-term processes of ten thousand years and more.

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