Abstract
AbstractClouds interact with atmospheric radiation and substantially modify the Earth's energy budget. Cloud formation processes occur over a vast range of spatial and temporal scales, which make their thorough numerical representation challenging. Therefore, the impact of parameter choices for simulations of cloud‐radiative effects is assessed in the current study. Numerical experiments are carried out using the ICOsahedral Nonhydrostatic (ICON) model with varying grid spacings between 2.5 and 80 km and with different subgrid‐scale parameterization approaches. Simulations are performed over the North Atlantic with either one‐moment or two‐moment microphysics and with convection being parameterized or explicitly resolved by grid‐scale dynamics. Simulated cloud‐radiative effects are compared to products derived from Meteosat measurements. Furthermore, a sophisticated cloud classification algorithm is applied to understand the differences and dependencies of simulated and observed cloud‐radiative effects. The cloud classification algorithm developed for the satellite observations is also applied to the simulation output based on synthetic infrared brightness temperatures, a novel approach that is not impacted by changing insolation and guarantees a consistent and fair comparison. It is found that flux biases originate equally from clear‐sky and cloudy parts of the radiation field. Simulated cloud amounts and cloud‐radiative effects are dominated by marine, shallow clouds, and their behavior is highly resolution dependent. Bias compensation between shortwave and longwave flux biases, seen in the coarser simulations, is significantly diminished for higher resolutions. Based on the analysis results, it is argued that cloud‐microphysical and cloud‐radiative properties have to be adjusted to further improve agreement with observed cloud‐radiative effects.
Highlights
Clouds are very effective in cooling the Earth
We investigate the impact of subgrid-scale parameterization choices regarding convection and cloud microphysics on cloud-radiative effects and the radiation budget
Observations are provided by measurements of the imaging radiometer SEVIRI (Spinning Enhanced Visible and InfraRed Imager) on board the geostationary satellites of the Meteosat Second Generation (MSG) series operated by EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites)
Summary
Clouds are very effective in cooling the Earth. Clouds scatter sunlight back to space before it can be absorbed by the Earth's surface. High-resolution modeling might break the so-called cloud parameterization “deadlock” (Randall et al, 2003) and promises to lead to more reliable simulations of cloud and precipitation responses to future climate change (Collins et al, 2018; Roberts et al, 2018; Stevens et al, 2020) Motivated by these advances, we consider the radiative effects of mid-latitude cloud systems in simulations with a large range of horizontal resolutions, with three different treatments of atmospheric convection and with two different treatments of cloud microphysics in this study. A more detailed description of the modifications of the cloud classification software and supporting information is provided in the supplement
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