Transport and mixing processes in the lower troposphere over the ocean

Aircraft observations in the lower troposphere over the eastern Pacific Ocean in summer are examined. The free troposphere was found to have a distinctly nonuniform, layered structure. In maritime air the layers consist of partially mixed air from several sources: moist ozone-depleted boundary layer air; very dry air with high ozone content that probably originated in the middle or upper troposphere; and air with relatively low ozone and moderate, varying moisture content that probably represents residues of convective clouds that had formed over the ocean upstream of the research area. The subtropical high results in stably stratified, subsiding air, where discrete horizontal layers with differing flow velocities transport air over long distances with little vertical mixing.