Environmental Science and Engineering Seminar
Traditional cloud modeling methodology applies continuous medium approach for all thermodynamic variables, that is, not only for the temperature and water vapor, but also for all forms of cloud condensate and precipitation. Continuous in time and space Eulerian variables used to represent cloud and precipitation particles are mass and sometimes number mixing ratios for bulk microphysical schemes and mass and/or number spectral density mixing ratios for bin schemes. Such a methodology has been the workhorse of the cloud-scale modeling from its early days, but also in numerical weather prediction and in climate simulation. However, practical application of such approaches face challenges due to numerical diffusion in the physical space and in the particle mass (or size) space for bin schemes, difficulty in representing aerosol processing by clouds, and inability to properly represent unresolved spatial scales that arguably play a significant role for the development of a particle spectrum. This lecture will discuss problems with Eulerian methodology and introduce particle-based Lagrangian approach that gains popularity in cloud modeling. Application of such an approach to the problem of droplet spectral broadening in warm shallow clouds will illustrate key advantages of the method. Prospects of applying Lagrangian methodology to more complex simulations involving clouds will be discussed.