Observations of Ship Tracks from Ship-Based Platforms

Abstract

Ship-based measurements in June 1994 provided information about ship-track clouds and associated atmospheric environment observed from below cloud levels that provide a perspective different from satellite and aircraft measurements. Surface measurements of latent and sensible heat fluxes, sea surface temperatures, and meteorological profiles with free and tethered balloons provided necessary input conditions for models of ship-track formation and maintenance. Remote sensing measurements showed a coupling of ship plume dynamics and entrainment into overlaying clouds. Morphological and dynamic effects were observed on clouds unique to the ship tracks. These morphological changes included lower cloud bases early in the ship-track formation, evidence of raised cloud bases in more mature tracks, sometimes higher cloud tops, thin cloud-free regions paralleling the tracks, and often stronger radar returns. The ship-based lidar aerosol measurements revealed that ship plumes often interacted with the overlying clouds in an intermittent rather than continuous manner. These observations imply that more must be learned about ship-track dynamics before simple relations between cloud condensation nuclei and cloud brightness can be developed.