Blocking in a perturbed physics ensemble of HadGEM3

We investigate winter and summer blocking in a large ensemble of atmosphere-only and coupled simulations with perturbed parameters in a range of physical parameterisation schemes. The model is found to give a reasonable simulation of blocking; some biases remain but some of the mechanisms involved in very persistent blocks are found to be well represented. Some parameter sensitivity is found in the atmosphere-only simulations, revealing the importance of drag processes in winter and convective processes in summer. However, these sensitivities were not found to extend to the coupled simulations, highlighting the wide range of processes upon which blocking depends. Some sensitivity of projected future blocking changes to model biases is found, consistent with previous studies.