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A review is given of relevant work on the internal boundary layer (IBL) associated with: (i) Small-scale flow in neutral conditions across an abrupt change in surface roughness.(ii) Small-scale flow in non-neutral conditions across an abrupt change in surface roughness, temperature or heat/moisture flux. (iii) Mesoscale flow, with emphasis on flow across the coastline for both convective and stably stratified conditions. The major theme in all cases is on the downstream, modified profile form (wind and temperature), and on the growth relations for IBL depth.

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W m Ϫ2 in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (Ϯ10 W m Ϫ2). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models' neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of

SUMMARYRecent atmospheric and wind tunnel data on the heat, mass and momentum transfer above natural and artificial surfaces indicate a general increase in the quantity kB-' (= ln(z,/z,), where z p is the roughness length appropriate to the quantity p) between aerodynamically smooth and fully rough flow. Below a roughness Reynolds number, utzo/u, of about 100, kB-l appears to be a single valued function of utz0/u, closely approximated by the assumption of a molecular sub-layer for heat and water vapour fluxes. Beyond u,zo/u = 100, there is no unique value of kB-', but rather the observations suggest that the behaviour falls into either of two categories. For surfaces comprised of arrays of widely spaced solid roughness elements, kB -' continues to increase (with some evidence for a plateau being reached by about utzo/u = 1,000, when kB-' 2: lo), whilst for surfaces comprised of randomly distributed fibrous roughness elements, kB gradually decreases with increasing roughness Reynolds number beyond about 100.