Estimating latent heat flux from a vineyard using scintillometry

The combination of a near-infrared and a microwave scintillometer were used to estimate the line-averaged, latent heat flux density (lambda E-s) from a well-irrigated, vineyard valley during summer. The 2 km scintillometer be am passed over the valley floor at a height (z) of 30 m, Eddy covariance to wers instrumented at 3 m above the valley surface provided an independent c heck elf vineyard evaporation. A formula for free convective lambda E-s com pared favourably to the eddy covariance values, lambda E-e at low wind spee ds and under clear skies. As the convective boundary layer (CBL) developed and passed through the scintillometer beam it caused additional scintillati ons, in which case lambda E-s >> lambda E-e, During unstable conditions the comparisons were in; close agreement. However lambda E-s tended to overest imate lambda E-e as the wind speed increased. For near-neutral conditions t he scintillometer gave unrealistically large values of lambda E-s, The addi tional scintillations originated from the strong entrainment of advected dr y and warm air into the newly formed surface boundary layer. During calm overcast days, cold days and during the early morning periods w hen the surface fluxes were small, the signal strength of the infrared scin tillometer approached the system noise.