Convection Parameterizations (CPs) are components of atmospheric models that aim to represent the statistical effects of a sub-grid scale ensemble of convective clouds. This is done in models in which the spatial resolution is not sufficient to resolve the associated convective circulations. Although CPs have been under development for over 50 years, many challenges remain. These parameterizations often differ fundamentally in closure assumptions and parameters used to solve the interaction problem, leading to a large spread and uncertainty in possible solutions. Additionally, more complexity is being added with almost every new development. On the other hand, increasing resolution in Numerical Weather Prediction models introduced additional challenges, since models can now partially resolve convection. We will discuss basic ideas and constraints of parameterizations, challenges with treating gray-scales (when convection is partially resolved) and new ideas for future developments. Simulations with FV3GFS, GEOS-5, and WRF (with and without the Grell-Freitas convection scheme) will be used to illustrate some of the issues.
