PNNL

Abstract

Post-frontal clouds (PFC) are ubiquitous in the marine boundary layer, and their morphology is essential to estimating the radiation budget in weather and climate models. Here we examine the roles of sea surface temperature (SST) and meteorological factors in controlling the mesoscale morphology and evolution of shallow clouds associated with a cold air outbreak, which occurred on 1 March 2020 during Phase I of the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE). Our results show that the simulated PFC cloud structure and ambient conditions by the Weather Research and Forecasting (WRF) model are generally consistent with observations from GOES-16 and dropsonde measurements in terms of cloud amount, cloud structure, and boundary layer profiles. Detailed comparisons of cloud morphology between WRF simulation and GOES-16 are presented. We also examine the thermodynamical and dynamical influences in the cloud mesoscale morphology using WRF sensitivity experiments driven by two meteorological forcing datasets. We find that SST, wind, and water vapor mixing ratio from various forcing datasets impact the cloud dissipation, cloud size distribution and other characteristics of the mesoscale morphology of cloud streets. Two datasets with different domain-mean SST and spatial gradients, being used to drive the WRF simulations, lead to dissimilar values of hydrometeor water path and cloud core fraction. We also find that using the large-scale meteorological forcings from ERA5 leads to a different time evolution of wind direction shear in the inner domain, which favors the existence of longer cloud rolls. Our results provide new insights into the evolution of PFC clouds and their local boundary layer structure.