Characteristics of the marine boundary layers during two Lagrangian measurement periods 2. Turbulence structure

Characteristics of turbulence mixing in remote marine boundary layers are a nalyzed using aircraft measurements from six flights during the two intensi ve Lagrangian measurement periods of ACE1 (the southern hemisphere Aerosol Characterization Experiment). The six cases studied here represent a variet y of boundary layer conditions in the region south of Tasmania, Australia. Our study indicated that (1) Lagrangian A (LA) had stronger turbulence mixi ng and entrainment compared to Lagrangian B (LB) due to greater shear gener ation of turbulence kinetic energy (TKE), (2) strong mesoscale variation in boundary layer turbulence and thus turbulence mixing existed in the ACE1 r egion during LB due to variations in sea surface temperature (SST), (3) sta ble thermal stratification in the boundary layer was found during the last flight of each Lagrangian, consequently, TKE decreased rapidly with height resulting in small or near-zero entrainment rate in spite of strong shear f orcing at the surface and in the boundary layer; and (4) the buffer layer, which lies above the boundary layer and below the main inversion, had weak and intermittent turbulence mostly associated with cloud bands and cumulus. Evidence of entrainment was found in the buffer layer. However, it is diff icult to quantify by flux measurements due to the weak and intermittent nat ure of the turbulence field.