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The Role of SCMs and CRMs for Investigating Biases in NWP and Climate Models

The Role of SCMs and CRMs for Investigating Biases in NWP and Climate Models

Jon Petch, Steve Derbyshire, Anna Maidens, Martin Willett and Ricky Wong

Single column versions of climate and NWP models (SCMs)are a powerful tool for investigating the behaviour of the physical parametrizations in large scale models. This is because they use very little computer time and allow the parametrizations to be tested in isolation of the large scale dynamics. They also provide a good method for a direct comparison with a cloud-resolving model (CRM). However, through isolating the parametrization from the dynamics, an SCM is unlikely to show all the biases seen in the full model and may well have different biases of its own. It is therefore important to understand when an SCM is, and is not, an appropriate tool for better understanding a particular model bias.

In this presentation I will show results from the latest GCSS deep WG case study where a single column from a full NWP simulation is compared with SCM and CRM simulations of observed convective systems. I will also present results from idealised SCM and CRM experiments. In each case I will discuss how the behaviour of the SCM can be linked to understanding biases in the full model and also where the SCM behaviour is a red herring and not linked to biases seen in the full model.