Make It a Double? Sobering Results from Simulations Using Single-Moment Microphysics Schemes

Single-moment microphysics schemes have long enjoyed popularity for their simplicity and efficiency. However, in this article it is argued through theoretical considerations, idealized thunderstorm simulations, and radiative–convective equilibrium (RCE) simulations that the assumptions inherent in these parameterizations can induce large errors in the proper representation of clouds and their feedbacks to the atmosphere. For example, precipitation is shown to increase by 200% through changes to fixed parameters in a singlemoment scheme and low-cloud fraction in the RCE simulations drops from about 15% in double-moment simulations to about 2% in single-moment simulations. This study adds to the large body of work that has shown that double-moment schemes generally outperform single-moment schemes. Therefore, it is recommended that future studies, regardless of their focus and especially those employing cloud-resolving models to simulate a realistic atmosphere, strongly consider moving to the exclusive use of multimoment microphysics schemes.