Diverse Cloud Regimes in the Northeast Pacific: Evaluating a Mesoscale NWP Model With Shipborne Observations

Abstract

As marine clouds play an important role in Earth's radiation budget, it is important that global climate and numerical weather prediction (NWP) models accurately simulate them. These clouds are challenging to represent within models due to the incomplete understanding of the processes that control their evolution, as well as the wide range of scales (spatial and temporal) that those processes occur. Here we evaluate simulations of clouds over the northeast Pacific Ocean using the Weather Research and Forecasting (WRF) model with a quasi-operational configuration to assess the model's representation of diverse cloud regimes in order to inform future model physics development. The simulations are evaluated with shipborne observations from the Marine ARM GCSS Pacific Cross-Section Intercomparison (GPCI) Investigation of Clouds (MAGIC) campaign in 2013, where stratocumulus, transitional, and cumulus regimes were present. The stratocumulus to cumulus transition observed during Leg 15A (20–25 July 2013) is well simulated in space and time, but the stratocumulus cloud base and top are too low, a flaw partially inherited from the ERA5 initialization. Four different vertical grids are tested to determine requirements for simulation of stratocumulus. The size of simulated cumulus cloud systems depends on the model grid spacing (13 km baseline vs. 3 km) and on tuning of the Mellor-Yamada-Nakanishi-Niino eddy diffusivity-mass flux (MYNN-EDMF) boundary layer and shallow cloud scheme. The model shortfalls identified in this study have helped to distinguish multiple avenues for future analysis that will guide development of the scheme.