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

The characteristics of roughness length for temperature, z(T), over melting snow and ice are examined on the base elf data gathered during one summer season on the Greenland ice sheet. Despite fixed surface temperature and ho mogeneous surface conditions, z(T) is highly variable, taking on values bet ween 10(-5) and 1 m. Mean value and median are computed as 2 x 10(-2) m and 1 x 10(-3) m. It thus turns out that z(T) is about 10 to 100 times larger than the aerodynamic roughness length, to. This disparity cannot be explain ed in terms of the roughness Reynolds number. Rather, the data show that ov er melting snow and ice, and for slightly stable conditions, z(T) is unique ly determined by the temperature defect.