Global Simulations of Low Clouds in Tropical and Subtropical Oceans Using Two Methodologies to Compute the PBL Height

This work analyzed simulations of low clouds over the eastern tropical Pacific, generated using two WRF model configurations. These configurations are in global mode and differ only in the atmospheric boundary-layer scheme. One used the Yonsei University PBL scheme, while the other used a modified version of this scheme in which, for convectively unstable PBL regimes, the PBL height was predicted using a mass balance closed by an entrainment formulation. The main interest was to compare how these configurations simulate low clouds over the eastern tropical and subtropical oceans, along with their effects on shortwave radiation at the ocean surface. This work also explored how both configurations simulated the transition from Scu to deep convection regimes. Both configurations realistically reproduced high incidences of low clouds in the regions of interest, suggesting that both setups have good potential for simulations coupled with OGCMs. This study identified aspects requiring improvement before the tested PBL schemes and WRF model configurations can be used in coupled atmosphere–ocean general circulation model simulations. In particular, improvements are needed to reduce the biases in net surface shortwave radiation flux over the eastern tropical and subtropical oceans and in regions of transition to shallow convection, especially over the Pacific Ocean.