Title: A High‐Resolution Simulation of Roll Convection Over the Yellow Sea During a Cold Air Outbreak.

Journal: Journal of Geophysical Research: Atmospheres, doi:10.1029/2019JD030968.

Authors: CHEN Y., H. -L. Yuan, and S. -H. Gao

Abstract: Horizontal convective rolls (HCRs) are significant for vertical transport of momentum, heat, and moisture, which is not fully understood partly due to lack of adequate observations. Previous high‐resolution modeling studies of roll convection mainly focused on idealized simulations. This study is one of the first simulations of HCRs with high‐resolution numerical weather prediction models in the real world, aiming to assess the modeling ability of realistic roll structure and investigate the characteristics of roll‐to‐cell transition. A real case of roll convection over the Yellow Sea during a cold air outbreak has been simulated, using the Weather Research and Forecasting (WRF) model at resolutions of 1 (WRF1) and 3 km (WRF3). Compared with the WRF3 simulation, the cloud water, vertical velocity, and the fine‐scale secondary circulations of HCRs are enhanced in WRF1 simulation, and the geometrical and physical parameters are consistent with the observations of satellite images (viewed as cloud streets) or previous studies. In this case, the 1‐km WRF simulation is able to reproduce the HCRs with a roll size of ~5 km. When the rolls transform to open cells downstream, the friction velocity and sensible heat flux gradually reduce following the prevailing wind, and the stability parameter –zi/L (the ratio of planetary boundary layer depth to Obukhov length) tends to increase with larger variances. During the roll‐to‐cell transition, the associated thermodynamic conditions are well simulated, with an average –zi/L ~ 22. In the future, reliable high‐resolution simulations can serve as an alternative to quantitatively investigate roll characteristics when observations are sparse or unavailable.