We describe how convective vertical velocities w(c) vary in the "gray zone'' of horizontal resolution, using both hydrostatic and nonhydrostatic versions of GFDL's FV3 dynamical core, as well as analytical solutions to the equations of motion. We derive a simple criterion (based on parcel geometries) for a model to resolve convection, and find that O(100 m) resolution can be required for convergence of w(c). We also find, both numerically and analytically, that hydrostatic systems overestimate w(c), by a factor of 2-3 in the convection-resolving regime. This overestimation is simply understood in terms of the "effective buoyancy pressure'' of Jeevanjee and Romps (2015, 2016).

http://dx.doi.org/10.1002/2017ms001059

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