Finescale structure and microphysics of coastal stratus

Observations were made of unbroken marine stratus off the coast of Oregon u sing the combined capabilities of in situ probes and a 95-GHz radar mounted on an aircraft. Reflectivity and Doppler velocity measurements were obtain ed in vertical and horizontal planes that extend from the flight lines. Dat a from three consecutive days were used to examine echo structure and micro physics characteristics. The clouds appeared horizontally homogeneous and l ight drizzle reached the surface in all three cases. Radar reflectivity is dominated by drizzle drops over the lower two-thirds to four-fifths of the clouds and by cloud droplets above that. Cells with a bove-average drizzle concentrations exist in all cases and exhibit a large range of sizes. The cells have irregular horizontal cross sections but occu r with a dominant spacing that is roughly 1.2-1.5 times the depth of the cl oud layer. Doppler velocities in the vertical are downward in all but a ver y small fraction of the cloud volumes. The cross correlation between reflec tivity and vertical Doppler velocity changes sign at or below the midpoint of the cloud, indicating that in the upper parts of the clouds above-averag e reflectivities are associated with smaller downward velocities. This corr elation and related observations are interpreted as the combined results of upward transport of drizzle drops and of downward motion of regions dilute d by entrainment. The in situ measurements support these conclusions.