Large Eddy Simulations Driven by Large Scale Models

Large eddy simulations (LES) of boundary layer clouds will play an important role in reducing uncertainties in equilibrium climate sensitivity. However, care must be taken to design LES to yield the greatest benefit. This not only includes the design of LES codes, but also the types of problems posed to LES. Here we discuss LES that are driven by large scale models, including atmospheric reanalysis and idealized climate models. We begin by showing that LES driven by reanalysis can capture observable features of marine boundary layer clouds. This serves as a verification step for the LES formulation. Next, we turn to LES driven by an idealized climate model. Here, effort is made to ensure that the LES remains energetically consistent in terms of both the large scale forcing and the surface boundary conditions. As a means of avoiding potentially confounding effects, the same, albeit simplified, representation of cloud microphysics is used in both the LES and climate model. LES designed in this manner allow the exploration of the physical mechanisms of marine boundary layer cloud feedbacks in an energetically consistent, physically realizable setting, and provide a computational laboratory for designing the next generation of cloud parameterizations.