LINEAL EDDY FEATURES UNDER STRONG SHEAR CONDITIONS

Large eddy simulation of a marine boundary layer (BL) with strong wind shear and weak buoyancy flux, over a relatively large horizontal doma in (25 x 18 km) and long time period (16 h), produces lineal eddy stru ctures with along-axis variations. These ''rolls'' are transient, thei r lifetime being roughly 8 h and their horizontal-to-vertical aspect r atio increases with time. At all heights above the surface layer, even above the BL, temporally coherent features propagate with a speed sli ghtly slower than the vertically averaged BL velocity. The length scal e of along-roll variation is about four and one-half times the corresp onding cross-roll length scale. To examine the importance of the roll circulations, fluxes of momentum, heat, and water vapor are partitione d into roll and non-roll contributions, and additionally separated int o contributions from the ascending and descending roll regions, to rev eal differences in advective roll transport and in roll modulation of smaller-scale transfer. The roll influence is largest at mid-BL for mo mentum and moisture fluxes but largest near the BL top for heat flux. The implied K-theory mixing coefficients are quite different for each variable, even if the influence of the roll circulations is removed. H orizontal variations of surface flux are opposite in sign to flux vari ations within the BL bulk.