Turbulence and Climate Prediction
Environmental Engineering Seminar
NASA Jet Propulsion Laboratory
California Institute of Technology
Turbulence is often referred to as the greatest unsolved problem of classical physics. The atmosphere and the ocean are turbulent fluids. Turbulence and convection (small-scale mixing and transport processes in the atmosphere and ocean) are at the core of key climate prediction science problems. For example, 1) the cloud-climate feedback (how clouds will respond to climate change, and in turn will impact climate) is essentially a problem concerning the interactions between a highly turbulent flow with water phase transitions and radiation; 2) The extreme weather and climate change problem is essentially about how moist convection will respond to a warmer world. Most of these turbulent processes are not resolved explicitly in climate models: the grid-resolutions are too coarse. However, these small-scale sub-grid processes (turbulence, convection, clouds) play a key role in regulating the large-scale climate. This talk will focus on a key issue: how to represent in an integrated manner sub-grid scale turbulent and convective motions in climate models. Modern unified approaches to model turbulence and convection involving optimal combinations of eddy-diffusivity and mass-flux (EDMF) methods will be discussed in detail. We will also describe in detail a new Large-Eddy Simulation (LES) model developed at JPL/Caltech to help design these new unified methods. Finally, the impact of these new EDMF approaches when implemented in climate models will illustrate the key role that turbulence plays in the overall climate system.