Exploring ABL Convective Patterns with Physically Sound Low-Order Models

The issue of convective 2D rolls vs 3D cells in the atmospheric boundary layer (ABL) resulting from the interplay of buoyancy and shear is explored using a class of low-order models called G-models (physically sound extensions of the celebrated Lorenz model). While it is known that some amount of vertical wind shear is necessary for the formation of rolls in the ABL, there have also been studies that found buoyancy to be the dominating mechanism for determining flow pattern, and still others where both have been found to be important. We study these complex dynamics of the ABL via developing G-models of 3D Rayleigh-Bénard convection with shear. Simulations were conducted using various values for buoyancy and shear to see which combinations result in rolls or in cells. The results proved comparable with observations, indicating the validity of G-models as a way of exploring this issue. For moderate values of buoyancy, the shear alone is capable of controlling the occurrence of rolls or cells, though the whole picture depends on both buoyancy and shear.