ModE-Sim (short for Modern Era Simulations) is a medium-size ensemble of model simulations using the ECHAM6 atmosphere general circulation model (model version 6.3.5p2, doi:10.17617/2.1810480). Its setup is based on the PMIP4 experiments, but uses a forced AGCM rather than a fully coupled model.

                ModE-Sim was originally designed to form the a-priori state for a climate reconstruction (Modern Era Reanalysis, ModE-RA, to be found as separate experiment within this WDC project) that uses an offline data assimilation technique to combine the output of ModE-Sim with historical climate information. However, beyond its original purpose ModE-Sim on its own can be used as a tool to study climate variability, providing a high number of posible climate states that are physically plausible under the given forcings and boundary conditions. This might include, e.g. the separation of internal variability from the response to externally forced signals, understanding of teleconnection patterns, or the study of extreme events.

                The ensemble uses observed/reconstructed forcings and boundary conditions, while accounting in uncertainties in these. For 1420 to 1850 we provide a 60 member ensemble grouped in three subsets. The subset 1420-2 provided in this dataset group has 20 members and uses a 20-member ensemble of perturbed volcanic forcings from the easy volcanic aerosol (EVA) model to account for uncertainties in the strength and the timing of volcanic eruptions. As ocean boundary condition 20 different realizations of SST reconstructions were used and for sea ice analogues were picked from the HadISST2 sea ice, based on the reconstructed SST fields.