Air‐ice drag coefficients for first‐year sea ice derived from aircraft measurements

Turbulent flux measurements were made at four levels (42, 90, 195, and 340 m) by the NOAA P‐3 aircraft over first‐year sea ice in the northern Bering Sea during February 1982. Three profiles of momentum flux and mean wind were used to calculate an air‐ice drag coefficient C D of 3.0 ± .6 × 10 −3 referenced to a 10‐m anemometer height. The boundary layer was slightly unstable ( z i / L = −1.2, where z i , was the inversion height of 660 m and L the Monin‐Obukhov length). The mean wind speed at the 42‐m height was 17 m/s, and the air temperature was −20°C. From turbulent heat flux measurements the value of the bulk heat transfer coefficient C H was 0.73 ± 1.6 × 10 −3 , giving a C H / C D of 0.24. The Bowen ratio was greater than 2.8. Comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement, which increases confidence in the calculations. The geostrophic drag coefficient | u * |/| G |, where u * is the friction velocity and G is the geostrophic wind, was 0.047. The turning angle of the surface wind (measured by an anemometer at a height of 3 m on the ice) was 32°, and the ratio of surface wind speed to the geostrophic wind speed was 0.76.