An Energy Balance Model for Low--Level Clouds Based on a Simulation Resolving Mesoscale Motions

Abstract

This study proposes a new energy balance model to determine the cloud fraction of low-level clouds. It is assumed that the horizontal cloud field consists of several individual cloud cells with a similar structure. Using a high–resolution simulation dataset with a wide numerical domain, we conducted an energy budget analysis. Here we show that the energy injected into the domain by surface flux is approximately balanced with that loss due to radiation and advection due to large–scale motion. The analysis of cloud cells within the simulated cloud field showed that the cloud field consists of a number of cloud cells with similar structures. We developed a simple model for the cloud fraction from the energy conservation equation. The cloud fraction determined using the model developed in this study was able to quantitatively captured the simulated cloud fraction.