Sensitivity of Radiative‐Convection Equilibrium to Divergence Damping in GFDL‐FV3‐Based Cloud‐Resolving Model Simulations

Abstract

Using a nonhydrostatic model based on a version of Geophysical Fluid Dynamics Laboratory's FV3 dynamical core at a cloud‐resolving resolution in radiative‐convective equilibrium (RCE) configuration, the sensitivity of the mean RCE climate to the magnitude and scale‐selectivity of the divergence damping is explored. Divergence damping is used to reduce small‐scale noise in more realistic configurations of this model. This sensitivity is tied to the strength (and width) of the convective updrafts, which decreases (increases) with increased damping and acts to organize the convection, dramatically drying out the troposphere and increasing the outgoing longwave radiation. Increased damping also results in a much‐broadened precipitation probability distribution and larger extreme values, as well as reduction in cloud fraction, which correspondingly decreases the magnitude of shortwave and longwave cloud radiative effects. Solutions exhibit a monotonic dependence on the strength of the damping and asymptotically converge to the inviscid limit. While the potential dependence of RCE simulations on resolution and microphysical assumptions are generally appreciated, these results highlight the potential significance of the choice of subgrid numerical diffusion in the dynamical core.

Application of the Cyclone Phase Space to Extratropical Transition in a Global Climate Model

“…The spots of increased geopotential height are confined to a few grid points and typically last on the order of 6 hr or less. We expect that their presence is the result of vigorous grid-scale updrafts, whose occurrence in the model is controlled in part by how strongly the divergent component of the horizontal flow is damped (e.g., Anber et al, 2018;Zhao & Held, 2012). This so-called divergence damping is used in numerical models to prevent the buildup of shortwave energy.…”

Updraft Constraints on Entrainment: Insights from Amazonian Deep Convection

“…11). It is possible that the models' subgrid diffusion or turbulent mixing schemes could play a major role in modifying the strength of updraft velocities (e.g., Jeevanjee 2017;Anber et al 2018).…”

On the Resolution Sensitivity of Equatorial Precipitation in a GFDL Global Atmospheric Model

“…On the other hand, the simulations by Anber et al. (2018) are limited to a small domain of 32 km × 32 km so that convective organization on the larger scales are ignored. The sensitivity to diffusion settings found in their model may not hold in a global simulation.…”

“…Besides model resolution, the precipitation extremes and convective organization are also sensitive to the diffusive damping setting in the dynamical core. Anber et al (2018) evaluated the sensitivity in convection organization and precipitation extremes to the damping settings in a radiative-convective equilibrium (RCE) configuration based on the same FV3 dynamical core used here. They found a weaker damping setting (either by using a higher order damping or a weaker damping coefficient) leads to weaker extremes in the 6-hourly averaged precipitation.…”

“…If higher order damping and/or weaker damping coefficients to be used in the finer resolution runs, we expect the daily precipitation extremes to reduce even more in the finer resolution runs, leading to a further departure from the estimation based on vertical velocity. On the other hand, the simulations by Anber et al (2018) are limited to a small domain of 32 km × 32 km so that convective organization on the larger scales are ignored. The sensitivity to diffusion settings found in their model may not hold in a global simulation.…”