Abstract
Fast measurements of ozone and dimethylsulfide (DMS) from Lagrangian, nocturnal flights over the northeastern subtropical Pacific during DYCOMS-II (the second Dynamics and Chemistry of Marine Stratocumulus experiment) are used as the basis for an empirical study of scalar diffusion in the stratocumulus topped boundary layer (STBL). In general, DMS is continually emitted from the ocean surface whereas ozone is entrained from the free troposphere and gradually deposited at the surface; thus, the tracers provide complementary views of the turbulent processes in the STBL. Aside from independent measurements of the entrainment velocity, based on the ratios of their fluxes to their concentration difference across the top of the inversion, these data are used to investigate the nature of top-down/bottom-up diffusion, ozone deposition to the surface, and ozone uptake by cloud droplets. The analysis is facilitated both by the diametrically separated source regions of ozone and DMS (and thus their countercurrent flux profiles), and by the predominantly nocturnal environment of the experiment, which removes complicating source/sink terms in the scalar budgets of both of these species due to the absence of photochemical activity. In addition, considerable attention is devoted to evaluating how mesoscale variability, a substantial complication on several flights, might affect the analysis.
