The contribution of upwind sources to measurements of vertical scalar flux density as a function of fetch ('footprint') is predicted using a Markovian simulation of fluid particle trajectories. Results suggest that both footprint peak position and magnitude change dramatically with surface roughness, thermal stability and observation levels. Results also indicate that the much used 100 to 1 fetch-to-height ratio grossly underestimates fetch requirements when observations are made above smooth surfaces, in stable conditions or at high observation levels.

Abstract. Modifications of the design and calibration procedure of a diffusion porometer permit determinations of stomatal resistance which agree well with results obtained bv leaf energy balance. The energy balance and the diffusion porometer measurements indicate that the boundary layer resistances of leaves in the field are substantially less than those predicted from hcat transport formulas based on wind flow and leaf size.

Evaporation, drainage, and changes in storage for a bare Plainfield sand were measured with a lysimeter during June, July, and August 1967, under natural rainfall conditions. Cumulative evaporation at any stage was proportional to the square root of time following each heavy rainfall. The drainage rate was found to be an exponential function of water storage. Both relations can be predicted from flow theory with knowledge of soil capillary conductivity, diffusivity, and moisture retention characteristics. Using these two relations and daily rainfall data, the water storage in the top 150 cm was predicted over the season to within 0.3 cm.

No abstract

Two three-dimensional split-film anemometers were used to measure turbulence statistics within and above a corn canopy. Normalised profiles of mean windspeed, root-mean-square velocity, momentum flux, and heat flux were constructed from half-hourly averages by dividing within-canopy measurements by the simultaneous canopy-top measurement. With the exception of the heat flux, these profiles showed consistent shape from day to day. Time series of the three velocity components were recorded on magnetic tape and subsequently analysed to obtain Eulerian time and length scales and the power spectrum of each component at several heights. The timescale was found to have a local minimum value at the top of the canopy. However the length scale L, formed from the timescale and the root-mean-square vertical velocity varied with height as L, = 0.1 z. The power-spectra were non-dimensionalised to facilitate comparison of spectra at different heights and times. All spectra had -5/3 regions spanning at least two decades in frequency.