Near-surface streaks: comparison of LES with theory

The dynamics of near-surface streaks in the neutrally stratified, rotating planetary boundary layer (PBL) are investigated using large eddy simulation (LES). Streaks are regions of alternating high and low speed fluid organized into nearly linear bands oriented up to ~30 deg relative to the surface isobars which evolve through a continuous cycle of generation, growth, decay and reformation. The primary horizontal wavelength of the streaks is on the order of several hundred meters and they extend from the surface layer into the lower portion of the outer PBL. We compare the LES results to the theoretical prediction of Foster (1997) who proposed that streaks are associated with non-normal mode 'optimal' perturbations. We find that the early stages of streak formation and growth are consistent with the linear theory of Foster (1997). We also report evidence of important nonlinear dynamics during the later stages of the streak lifecycle.