Lineal Eddy Features under Strong Shear Conditions

Abstract

Abstract Large eddy simulation of a marine boundary layer (BL) with strong wind shear and weak buoyancy flux, over a relatively large horizontal domain (25×18 km) and long time period (16 h), produces lineal eddy structures with along-axis variations. These “rolls” are transient, their lifetime being roughly 8 h and their horizontal-to-vertical aspect ratio increases with time. At all heights above the surface layer, even above the BL, temporally coherent features propogate with a speed slightly slower than the vertically averaged BL velocity. The length scale of along-roll variation is about four and one-half times the corresponding cross-roll length scale. To examine the importance of the roll circulations, fluxes of momentum, heat, and water vapor are partitioned into roll and non-roll contributions, and additionally separated into contributions from the ascending and descending roll regions, to reveal differences in advective roll transport and in roll modulation of smaller-scale transfer. The roll in...