Assimilation and Modelling
Our work related to modeling is concerned with data assimilation in the ocean-sea ice system, but also with forward oriented process-modeling with highest possible resolution. A newly emerging effort is concerned with coupled climate modeling and assimilation in a coupled system.
Most remote sensing sensors are not capable to measure directly any parameter of, e.g., the ocean interior. However, knowledge about conditions in the ocean interior and about interaction processes between ocean and atmosphere and in the ocean is of substantial importance for understanding the Earth climate system. The perfect tool to gain maximum knowledge about such processes is the usage of numerical models in combination with assimilation of remote sensing and in situ data.
Used is the GECCO environment to perform long (up to 60+ years) global and regional assimilation runs, including the Atlantic and Arctic ocean-atmosphere systems. The assimilation infrastructure is also being used to investigate ocean and sea ice sensitivities to specific forcing factors.
Ocean syntheses are needed to perform decadal climate predictions with coupled climate models for the initialization of the ocean components. The results of the GECCO2 ocean syntheses can be obtained from the 'Integrated Climate Data Center' (ICDC) for the period from 1948 until present.
For an accurate understanding of the ocean’s role in climate variability and ongoing trends, the representation of eddy dynamics and associated transports in ocean numerical simulations is crucial since eddies are major players in tracer (physical or bio- geochemical) transport and thus in the maintenance of ocean stratification.
The process modeling effort is concerned in particular with achieving the highest-possible resolution in the simulation of the ocean at the mesoscale and sub-mesoscale. To that end, a hierarchy of model simulations of the Atlantic-Arctic system is being conducted with spatial resolutions varying form 1 degree down to 3 km. Results are being used to investigate the sensitivity of the ocean circulation to model resolution, but especially, to investigate small-scale ocean phenomena (e.g., current instabilities, eddy generation, filamentation) and their relevant physical mechanisms.
A newly emerging effort is concerned with coupled climate modeling and assimilation in a coupled system. For that purpose a new coupled model was constructed which consists out of the MITogcm and the atmosphere model of the University of Hamburg PLASIM. Both models where coupled into a new unique model for which also the adjoint can be generated using the TAF adjoint compiler.
This new model (CESAM = CEN Earth System Assimilation Model) is now being used in process studied, for climate system sensitivity analysis and will serve as the basis for coupled data assimilation.