Picture: Cloudy Dawn. Credit: Josh Sorenson (Pexels).

The transport of heat up and down the atmosphere, called atmospheric convection, is a complex process. To simplify the representation of convection in global climate models (GCMs) scientists use “parameterization”, which is essentially mathematical equations of physical processes. However, there are many different ways to formulate these equations, and no agreement on which is better.

In this work CLEX researchers aim to understand a few popular ways to parameterize convection. They extracted one vertical column from five different GCMs and lightly tickled (perturbed) it and then observed the responses.

They found different models respond very differently to the same tickling, and this tells us a lot about the model. Importantly, the specific perturbation they used can single out the responses of convection-related equations from equations of other processes.

All models in the study have one thing in common: they are quite jumpy when tickled, especially at the top of the boundary layer where clouds start to form. The researchers suspect the culprits are switches placed in the models that sometimes lead to sudden changes in their response. This work highlights potentially problematic behaviour that can provide clues on how to make climate models better.

  • Paper: Hwong, Yi-Ling, Siwon Song, Steven Sherwood, Alison Stirling, Catherine Rio, Romain Roehrig, Chimene Laure Daleu, et al. “Characterizing Convection Schemes Using Their Responses to Imposed Tendency Perturbations.” Preprint. Earth and Space Science Open Archive. Earth and Space Science Open Archive, January 21, 2021. World. https://doi.org/10.1002/essoar.10505890.1.