Sensible and latent-heat flux predictions using conditional sampling methods

The conditional sampling formulation typically used in eddy accumulation flux measurements was tested at two sites using velocity, temperature, and specific humidity time series measurements. The first site was at Owen's Lake in southern California, and the second site was an irrigated bare soil field at the Campbell Tract facility in Davis, California. The constant beta relating the turbulent flux to the accumulated concentration difference between updrafts and downdrafts was related to the statistics of the vertical velocity. It was found that this formulation for beta reproduces the extreme fluxes (both senible and latent heat) better than previous beta formulations. The overall comparison between eddy correlation measured fluxes and conditional sampling predicted fluxes for a wide range of atmospheric stability conditions was excellent (R2 = 0.97). On average, the mean beta obtained from our experiments for temperature and water vapor is in good agreement (+/-4%) with other reported beta values for carbon dioxide, water vapor, ozone, and temperature. These results suggest that the conditional sampling formulation used in eddy accumulation methods is useful for routine flux measurements of passive greenhouse gases.