ARCTIC BOUNDARY-LAYER IN THE FALL SEASON OVER OPEN AND FROZEN SEA

This study is based on aircraft data collected on research flights in the Beaufort Arctic Storms Experiment (BASE). The experiment was condu cted during the fall, when the frozen parts of the sea surface and the lower troposphere are subject to strong radiative cooling, while the temperature of the open water stays near -1 or -2 degrees C, leading t o the formation of two different types of boundary layers. Data from a boundary layer over open water and a boundary layer over frozen sea s urface with open leads are examined in detail. The boundary layer over open water was capped by a stratus layer in which large temperature f luxes were observed. Recent advection of air from the colder coastal r egions over warm water was probably responsible for the large temperat ure differences at the sea-air interface. The boundary layer over ice was clear and very stably stratified, with a low-level potential tempe rature lapse rate in the 20 -57 K km(-1) range. Turbulent fluxes were very weak or nonexistent, except at the lowest observation level, 40 m above surface, in an area over many open leads. In this boundary laye r, wave-like features were common. Some were identified as gravity wav es, but others with shorter wavelengths could have been due to horizon tal roll vortices generated by convection from the leads.