BOUNDARY-LAYER BUDGETS FOR REGIONAL ESTIMATES OF SCALAR FLUXES

The paper considers the theory and application of budget techniques fo r regional scalar awe estimation using the daytime convective boundary layer (CBL) and the nocturnal boundary layer (NBL). CBL techniques tr eat the well mixed layer of air between heights of, say, 100 m and 100 0 m as an integrator of surface fluxes along the path of a column of a ir moving over the landscape. They calculate the average surface flux from the scalar concentration in and above the mixed layer, and the CB L height. The flux estimates are averaged over regions of 10-10(4) km( 2) extending 10 to 100 km upwind. An integral form of the CBL budget i s used to estimate daily regional rates of CO2 uptake and evaporation from three data sets. There was plausible agreement between the estima tes and locally measured fluxes. CBL budgets have great potential for estimating regional scalar fluxes, but there is an urgent need for val idation through direct measurements of fluxes and budget parameters. N BL budgets are useful when low-level, radiative inversions inhibit ver tical mixing. Surface scalar fluxes can then be estimated from the rat e of concentration change below the inversion. An example application for estimating the nocturnal CO2 flux is given. While simple in concep t. NBL budgets are more difficult to apply in practice because of the unpredictability of the depth of the layer and sometimes, its absence altogether. On the other hand, the depth of the atmospheric mixing cha mber is better defined, few assumptions are required and the concentra tion changes usually will be larger and hence more easily detectable t han in CBI, budgetting.