FY 1989

A study of the planetary boundary layer over the polynya downwind of St. Lawrence Island in the Bering Sea using aircraft data

Walter, B.A.

Bound.-Lay. Meteorol., 48(3), 255–282, doi: 10.1007/BF00158327 (1989)

Turbulence data collected with the gust probe system on the NOAA P-3 aircraft over the polynya downwind of St. Lawrence Island in the Bering Sea are used to study the fluxes of heat, momentum, and moisture from the polynya. The data also allow study of the effect of the topography of St. Lawrence Island on the atmospheric boundary-layer flow over the polynya and ultimately on ice production in the polynya. Two cases are studied: one (Feb. 15, 1982) where the topographic effects are minimal and the other (Feb. 18, 1983) where the topographic effects are dominant. Calculation of the surface drag coefficient, C_D, for the Feb. 15, 1982 case over young grey/white ice gave a value of 1.2 × 10⁻³, which is in close agreement with previous results. The value of the drag coefficient for the grey/white ice regime on Feb. 18, 1983, where the upstream topography on St. Lawrence Island had an important influence on the flow over the polynya, was 3.2 × 10⁻³. It was determined that this higher value was related to the more efficient mixing of momentum downward by turbulent eddies generated by flow over and around the topography. The area-averaged heat transfer coefficient, C_H, over the polynya was on the order of 1.1 × 10⁻³ for both days, but there were large variations in heat flux across the polynya due to variations in the flow caused by the topography. Conditional sampling techniques applied to the turbulence data showed that the fractional areas occupied by updrafts and downdrafts were 28% and 36%, respectively, and that these results were within the range of values found in previous studies for over-land and over-ocean conditions.