Środowiskowe Seminarium Fizyki Atmosfery

Formation and growth of cloud and precipitation particles (“cloud microphysics”) affect such macroscopic cloud field properties as the mean surface rainfall, cloud cover, and liquid/ice water paths. Indirect aerosol effects (e.g., through different CCN concentrations) are examples of the impact on shallow convection. For deep convection, hypothesized convective invigoration in polluted environments (because of additional latent heating due to freezing of the liquid water advected above the freezing level) is another example. In-situ and remote–sensing observations cannot provide sufficiently accurate estimates of such effects and are not capable in distinguishing between correlation and causality. Numerical modeling is then the only reliable approach to study the impacts. However, traditional approaches that rely on parallel simulations (i.e., contrasting cloud fields developing in different CCN or IN environments) are not reliable because of natural variability of a cloud field that is affected by the feedback between cloud microphysics and dynamics. We propose a novel modeling approach to assess the impact of cloud microphysics on macroscopic cloud field characteristics. The main idea is to use two microphysical schemes or the same scheme with different parameters, with one scheme coupled to the dynamics and driving the simulation, and the other scheme applied as in the kinematic model, that is, responding to the simulated flow but not affecting it. We will discuss application of this methodology to cloud field simulations of shallow and deep convection and show that the methodology allows assessing the impact of cloud microphysics on cloud field macroscopic properties with unprecedented accuracy.