Environmental & Climate Sciences Department Seminar

Using observations collected at the ARM Eastern North Atlantic (ENA) site, we examine the relationship between the large-scale environment and the properties of low-level clouds that occur in conditions of subsidence. The cloud boundary cloud properties correlate well with the difference in potential temperature between the 800 hPa level and the surface, a measure of the degree of boundary layer instability. Moreover, consistent relationships are found between near-surface stability, surface energy fluxes, and cloud fraction, optical thickness, and top temperature in various regions of strong post-cold frontal activity. To help understand these mechanisms, we use the Weather Research Forecast (WRF) model to explore post-cold frontal clouds with a case study. The modeled cloud properties are sensitive to the interactions between the shallow convection and the boundary layer parameterizations. We will report how this sensitivity is related to boundary layer decoupling, vertical shear in the horizontal winds at cloud top, and drizzle. We also test the robustness of these conclusions by analyzing a perturbed initial conditions ensemble using WRF. A comparison of the perturbed physics and the perturbed initial condition ensembles explores the relative impact of circulation changes and physical processes on low-level cloud in the model.