Roughness lengths for temperature and momentum over heterogeneous terrain

Measurements are presented describing the behaviour of roughness lengths for momentum and temperature for heterogeneous terrain of low fractional rough cover. The momentum roughness lengths were found to be up to several orders of magnitude larger than that for temperature, behaviour which is characteristic of a bluff-rough type of surface and which is consistent with previous experimental and theoretical studies. This contrasts with observations over uniform, vegetated surfaces, which show only an order-of-magnitude increase of momentum roughness length over that for temperature.