Turbulence observations above a smooth melting surface on the Greenland ice sheet

Measurements of profiles and turbulent fluxes have been made over a smooth, melting surface on the southwestern part of the Greenland ice sheet in July 1991. For a reference height of 0.8 m, and flux measurements at 4 m and 13 m, the best values for the roughness lengths are 3 x 10(-4) m for wind speed, 2 x 10(-6) m for temperature, and 5 x 10(-4) m for moisture. The uncertainty in the corresponding exchange coefficients is about 10%. The roughness length for temperature (z(T)) is much smaller than expected from theory, as was also found in a number of earlier investigations. The possibility is considered that absorption of shortwave radiation by aerosol particles accumulating near the surface lowers the z(T) values. Consequently, z(T) using lower measurement heights should probably be close to z(0). However, evidence for this remains rather indirect. Further, it is shown that reliable results for the sensible heat flux can be obtained using the product of the observed standard deviation for temperature fluctuations and wind speed.