Southern Ocean Cloud Controlling Factors and Their Connections to Cloud Radiative Effects in CMIP6 Models

Clouds and their associated radiative effects present a large source of uncertainty in global climate models, and one particular region where this uncertainty is large is the Southern Ocean. Previous research has shown that dynamical “cloud-controlling factors” influence clouds and their radiative effects. For example, in the Southern Ocean, previous research has shown that two important cloud-controlling factors are vertical velocity and boundary layer estimated inversion strength (EIS), and that upward vertical velocity anomalies and enhancement of EIS were associated with increased cloud reflection (negative SWCRE). CMIP5 models were shown to generally capture the observed anomalies in the dynamical cloud controlling factors associated with midlatitude jet shifts however a fraction of models underestimated the sensitivity of shortwave cloud radiative effects to perturbations in EIS. This could therefore lead to a fraction of the models incorrectly estimating midlatitude cloud feedbacks in regions with appreciable changes in the dynamical cloud controlling factors, such as with a poleward shift of the midlatitude jet in the Southern Ocean, as a result of the incorrect sensitivity of the cloud radiative effects to the dynamical cloud controlling factors. This work aims to assess whether a fraction of CMIP6 models continue to incorrectly estimate the sensitivity to perturbations in the cloud controlling factors or have improved from the previous generation of global climate models in this regard.