Journal Article

Intercomparison of large‐eddy simulations of Arctic mixed‐phase clouds: Importance of ice size distribution assumptions

Fridlind, Ann M., Cheng, Anning, Ackerman, Andrew S., Solomon, Amy, Ghan, Steven, Korolev, Alexei, Hoose, Corinna, Ovchinnikov, Mikhail, Shipway, Ben J., Morrison, Hugh, Savre, Julien, Fan, Jiwen, Sulia, Kara, Avramov, Alexander, Paukert, Marco, McFarquhar, Greg M., Shupe, Matthew D., Harrington, Jerry

2014

Overview

Large‐eddy simulations of mixed‐phase Arctic clouds by 11 different models are analyzed with the goal of improving understanding and model representation of processes controlling the evolution of these clouds. In a case based on observations from the Indirect and Semi‐Direct Aerosol Campaign (ISDAC), it is found that ice number concentration, Ni, exerts significant influence on the cloud structure. Increasing Ni leads to a substantial reduction in liquid water path (LWP), in agreement with earlier studies. In contrast to previous intercomparison studies, all models here use the same ice particle properties (i.e., mass‐size, mass‐fall speed, and mass‐capacitance relationships) and a common radiation parameterization. The constrained setup exposes the importance of ice particle size distributions (PSDs) in influencing cloud evolution. A clear separation in LWP and IWP predicted by models with bin and bulk microphysical treatments is documented and attributed primarily to the assumed shape of ice PSD used in bulk schemes. Compared to the bin schemes that explicitly predict the PSD, schemes assuming exponential ice PSD underestimate ice growth by vapor deposition and overestimate mass‐weighted fall speed leading to an underprediction of IWP by a factor of two in the considered case. Sensitivity tests indicate LWP and IWP are much closer to the bin model simulations when a modified shape factor which is similar to that predicted by bin model simulation is used in bulk scheme. These results demonstrate the importance of representation of ice PSD in determining the partitioning of liquid and ice and the longevity of mixed‐phase clouds. Key Points Constrained LES of mixed‐phase Arctic clouds from 11 models are analyzed Ice water path differences are attributed to assumed ice size distributions Bulk schemes with gamma size distributions agree better with bin schemes

• Publisher: John Wiley & Sons, Inc
• Subject: American Recovery & Reinvestment Act 2009-US / Arctic clouds / Capacitance / Climate / cloud microphysics / Cloud structure / Clouds / Evolution / Experiments / Grants / Growth rate / Ice / ice size distribution / Intercomparison / Laboratories / large-eddy simulations / Mass / mixed-phase clouds / Parameterization / Radiation / Scale models / Shape / Simulation / Size distribution