Uncertainties in cloud-radiative heating within an idealized extratropical cyclone

Abstract. Cloud radiative heating (CRH) within the atmosphere affects the dynamics and predictability of extratropical cyclones. However, CRH is uncertain in numerical weather prediction and climate models, and this could affect model predictions of extratropical cyclones. In this paper, we present a systematic quantification of CRH uncertainties. To this end, we study an idealized extratropical cyclone simulated at a convection-permitting resolution of 2.5 km, and combine large-eddy simulations at 300 m resolution with offline radiative transfer calculations. We quantify four factors contributing to the CRH uncertainty in different regions of the cyclone: 3D cloud radiative effects, parameterization of ice-optical properties, cloud horizontal heterogeneity, and cloud vertical overlap. The two last factors can be considered to be essentially resolved at 300 m but need to be parametrized at 2.5 km resolution. Our results indicate that the parameterization of ice-optical properties and the cloud horizontal heterogeneity are the two factors contributing most to the uncertainty in CRH. On the other hand, 3D cloud radiative effects are much smaller, especially for stratiform clouds within the warm conveyor belt of the cyclone. Our analysis in particular highlights the potential to improve the simulation of CRH by better representing ice-optical properties. Future work should in particular address how uncertainty in ice-optical properties affects the dynamics and predictability of extratropical cyclones.