From Grid to Cloud: Understanding the Impact of Grid Size on Simulated
Anvil Clouds and Atmospheric Profiles
Abstract
In this study, we explore the relationship between anvil cloud fraction
and horizontal model resolution in small domain radiative-convective
equilibrium (RCE) simulations, building on the findings of
\citeA{jeevanjee22}. Using the System of Atmosphere
Modeling (SAM) model, we find that finer resolutions yield higher anvil
cloud fractions due to larger convective updrafts mass flux and
increased mass detrainment at anvil levels. Employing two different
microphysics schemes, we illustrate that finer resolution can enhance
mass flux through either stronger cloud evaporation or weaker
upper-troposphere stability, as the consequence of enhanced horizontal
mixing. Moreover, we refine an analytical zero-buoyancy plume model to
investigate the effects of adjusting entrainment rate and evaporation
rate on vertical atmosphere profiles in a simple theoretical framework.
Our solutions of the zero-buoyancy plume model suggest that stronger
horizontal mixing can lead to larger convective updraft mass flux,
consistent with the analysis in numerical simulations. We also observe
the likelihood of atmospheric profiles converging at a grid size of
approximately 100m, potentially as a result of converging entrainment
rate and mixing strength. These insights have implications for global
storm-resolving simulations, implying a possible convergence of high
cloud and deep convection properties as the horizontal resolution
approaches around 100m.