Journal Article

Vertical Resolution Impacts Explicit Simulation of Deep Convection

Pritchard, M. S., Ferretti, S. L., Jenney, A. M.

2023

Overview

The aggregation of tropical convection greatly influences the mean‐state of the atmosphere, altering humidity distributions, total atmospheric radiative cooling, and cloud amounts. Although studies have demonstrated the sensitivity of convective aggregation to horizontal resolution and domain size, few studies have explored the impact of vertical resolution on convective aggregation. Here, we investigate the impact of vertical resolution on simulations of deep convection and convective aggregation using the System for Atmospheric Modeling convection resolving model. We analyze simulations of tropical radiative‐convective equilibrium with varying vertical levels (32, 64, 128, and 256) across small (100 km), medium (700 km) and large (1,500 km) domains. We demonstrate that relative humidity and cloud fraction decrease with increasing vertical resolution as a result of reduced turbulent mixing. Vertical resolution also influences the occurrence of, onset time, and equilibrium intensity of aggregated convection, and also appears to affect the sensitivity of convective aggregation to domain size. Understanding how simulated convection aggregates, as well as its simulated sensitivity to model formulation, is critical for making and interpreting future predictions of global climate change. Plain Language Summary We study the simulation of clouds and storms in simple computer models of the tropical atmosphere. These models calculate air movement on a grid. Large grid boxes result in a very coarse, pixelated representation of the atmosphere, while smaller grid boxes offer a much clearer, high‐resolution video. Ideally, the average air movement, cloud formation, and rainfall simulated by these models shouldn't be affected by the size of the grid boxes, with smaller boxes just providing additional detail. However, here we show that the height of grid boxes influences average properties of the simulations, such as the total cloud amount, the amount of rain that falls, and the relative humidity. Key Points The relative humidity and high cloud fraction both decrease with increasing vertical resolution in System for Atmospheric Modeling Vertical resolution impacts convective aggregation occurrence, onset time, and equilibrium intensity The sensitivity of convective aggregation to domain size may depend on vertical resolution

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Aggregation / Atmospheric cooling / Climate change / Clouds / Convection / convection resolving model / convective aggregation / Cooling / Equilibrium / Global climate / Humidity / Radiative cooling / Relative humidity / SAM / Simulation / Temperature / Tropical convection / Turbulent mixing / vertical resolution