A note on the roughness length for temperature over melting snow and ice

The characteristics of roughness length for temperature, zT , over melting snow and ice are examined on the base of data gathered during one summer season on the Greenland ice sheet. Despite fixed surface temperature and homogeneous surface conditions, zT is highly variable, taking on values between 10 −5 and 1 m. Mean value and median are computed as 2 × 10 −2 m and 1 × 10 −3 m. It thus turns out that zT is about 10 to 100 times larger than the aerodynamic roughness length, z 0. This disparity cannot be explained in terms of the roughness Reynolds number. Rather, the data show that over melting snow and ice, and for slightly stable conditions, zT is uniquely determined by the temperature defect.