Are there any linked Issues or Pull Requests?
No response
Brief description
If using the PC2 cloud-scheme, cloud water content and fraction are advected prognostic variables. Numerical diffusion of these variables can cause problems, especially when cloud diffuses downwards to well-below where cloud-base ought to be in the surface mixed-layer. Liquid-cloud appearing too-low within mixed-layers can easily cause spurious convective triggering in CoMorph, since it assumes the cloud must be saturated and neutrally-buoyant (which implies a higher MSE than the mixed-layer mean), and attempts to trigger convection from within the cloudy part of the grid-box as that is moist-unstable. A principal source of spurious numerical vertical diffusion of cloud is the compensating subsidence term in the convection scheme, since it applies vertical advection with a highly-diffusive linear-upwind numerical method.
We reduce this problem by applying a limiter to the vertical transport of cloud by the compensating subsidence term in CoMorph, so-as to approximate a less-diffusive higher-order scheme.
Further details of the issue.
No response
Are there any linked Issues or Pull Requests?
No response
Brief description
If using the PC2 cloud-scheme, cloud water content and fraction are advected prognostic variables. Numerical diffusion of these variables can cause problems, especially when cloud diffuses downwards to well-below where cloud-base ought to be in the surface mixed-layer. Liquid-cloud appearing too-low within mixed-layers can easily cause spurious convective triggering in CoMorph, since it assumes the cloud must be saturated and neutrally-buoyant (which implies a higher MSE than the mixed-layer mean), and attempts to trigger convection from within the cloudy part of the grid-box as that is moist-unstable. A principal source of spurious numerical vertical diffusion of cloud is the compensating subsidence term in the convection scheme, since it applies vertical advection with a highly-diffusive linear-upwind numerical method.
We reduce this problem by applying a limiter to the vertical transport of cloud by the compensating subsidence term in CoMorph, so-as to approximate a less-diffusive higher-order scheme.
Further details of the issue.
No response