Mesoscale Cellular Convection: Fluid Dynamics Meets Cloud Physics and Radiation (The Bernhard Haurwitz Memorial Lecturer) (Invited Presentation)

Marine boundary layer clouds often show mesoscale cellular convection (MCC) -- patterning in the form of lines, polygons with clouds at their centers (closed cells) or edges (open cells), or less organized clumps of cumulus clouds. These features have a typical wavelength 30-50 times as large as the boundary-layer depth. Cloud physicists have developed several theories for types of MCC, but they all have shortcomings. Large-eddy simulations and remote sensing are now providing opportunities to better understand MCC. They suggest that MCC can be regarded as a form of spontaneous clumping of the boundary-layer humidity into moister and drier patches. This clumping is supported by cloud-radiation interaction (for closed cells in shallow layers) or latent heating (for open cells and disorganized clumps in deeper boundary layers). These processes amplify the cellular structure via fascinating interactions between turbulence, entrainment, and mesoscale circulations.