The air-ice drag coefficient measured for a year over Arctic sea ice

During SHEBA, the experiment to study the Surface Heat Budget of the Arctic Ocean, we measured the air-ice drag coefficient by both eddy-correlation and profile analysis on a 20-m tower in the main camp and by eddy-correlation at four remote sites within 1-10 km of the main camp. From the eddy-correlation measurements in the main camp alone, we have over 4000 hourly averaged estimates of the neutral-stability drag coefficient for a reference height of 10 meters, C_DN10. Monthly averages of these C_DN10 values show a gradual increase from 1.1x10^-3 in November 1997 to 1.5x10^-3 in May 1998, probably as a consequence of ridge building. C_DN10 increases more steeply in June, July, and August to its August 1998 annual peak of 1.9x10^-3 as melt ponds formed and grew in spatial extent. In September 1998, C_DN10 began decreasing as snow filled in the now-frozen melt ponds and, thus, smoothed the ice surface. We will look for corroboration of this trend in C_DN10 values from the four remote sites but will also use these data, collected over various ice types, to try to understand the distribution of C_DN10 values that went into constituting the monthly averages. In other words, we will explore ways to predict and parameterize the individual C_DN10 values.