Observation-based evaluation of DestinE Climate DT simulations

Climate projections are widely used to inform about potential future climate. The current cutting edge in decadal-scale projections is at kilometre-scale global atmosphere-ocean models, which resolve finer parts of motion spectra as compared to the previous generation models. This imposes new challenges for evaluation of climate simulations. The question is which reference materials are adequate to evaluate the rich process-level variability present in the new-generation models. Common reanalyses, for instance, do not provide proper quidance in this respect. Here, we advocate the use of raw Earth observations for this purpose.
 
The architecture in the DestinE Climate DT (https://destination-earth.eu/) in highly synergetic with numerical weather prediction (NWP). Specifically, the so-called streaming approach enables run-time access for observation models to consume the near-native state vector and compute observation-space quantities, such as brightness temperature. Thereby, Climate DT opens the pathway for direct observation-space evaluation using, in principle, any set of Earth observations and potentially resolves the open question about adequante process-level reference materials. In Climate DT, these are used for online monitoring of ongoing simulations and their posterior evaluation. The synergy aspect here is the extensive sharing of observation modelling infrastructure with data assimilation in NWP, foremost with ECMWF.
 
We showcase early examples of statistical Earth observation-based evaluation of kilometre-scale climate simulations produced in Destination Earth Climate DT. All three kilometre-scale models contained in Climate DT simulate the mean climate well. At process-level, however, significant systematic errors appear. For instance, the diurnal range of 2-metre temperature and 10-metre wind speed variability are not well simulated. The examples demonstrate how direct use of Earth observations help to evaluate simulation results, especially at the process level. Such finding can accelerate model development, especially regarding the physical process parametrizations.
 
Finally, observation data base files, augmented with model counterparts, are generated online for all Climate DT simulations and they are accessible via the DestinE data lake. This presentation has a companion in ESSI1.8 about the technical implementation aspects.