Effects of Surface and Top Wind Shear on the Spatial Organization of Marine Stratocumulus‐Topped Boundary Layers

The convective nature of Stratocumulus topped boundary layers (STBL) involves the motion of updrafts and downdrafts, driven by surface fluxes and radiative cooling, respectively. The balance between shear and buoyant forcings at the surface can determine the organization of updrafts between cellular and roll structures. We investigate the effect of varying shear at the surface and top of the STBL using Large Eddy Simulations, taking DYCOMS II RF01 as a base case. We focus on spatial identification of the following features: coherent updrafts and downdrafts, and observe how they are affected by varying shear. Stronger surface shear organizes the updrafts in rolls, causes less well‐mixed thermodynamic profiles, and decreases cloud fraction and liquid water path (LWP). Stronger top shear also decreases cloud fraction and LWP more than surface shear, by thinning the cloud from the top. Features with stronger top than surface shear are associated with a net downward momentum transport and show early signs of decoupling. Classifying updrafts and downdrafts based on their vertical span and horizontal size confirms the dominance of tall objects spanning the whole STBL. Tall objects occupy 30% of the volume in the STBL, while short ones occupy less than 1%. For updraft and downdraft fluxes, these tall objects explain 65% of the vertical velocity variance and 83% of the buoyancy flux, on average. Stronger top shear also weakens the contribution of downdrafts to the turbulent fluxes and tilts the otherwise vertical development of updrafts. Plain Language Summary Stratocumulus clouds form in the atmospheric boundary layer, close to the Earth's surface. Turbulence in this boundary layer causes large circulation composed of strong motions going up and down called updrafts and downdrafts. At the surface and top of the boundary layer, wind speed can change abruptly, generating wind shear. We investigate the effect of changes in wind shear on the organization of the clouds, updrafts, and downdrafts. By simulating atmospheric flow, we observe that stronger surface wind reduces the amount of clouds, strong top shear modifies the shape of cloud tops, and only when shear is strong both at the surface and top, clouds are elongated in the wind direction. Of all the updrafts and downdrafts found, the tallest ones dominate in volume occupied and in the transport of momentum, heat, and moisture in the boundary layer. Key Points The spatial organization of Stratocumulus‐topped bound