Scintillometry has proven to be a suitable method to obtain surface fluxes over heterogeneous areas over spatial scales of up to 10 km. We will present two of many field-studies conducted by the Meteorology and Air Quality Group of Wageningen University to illustrate this point. Different scintillometer types have been tested. Optical scintillometers yield the structure parameter of temperature, CT2, for long-path Large Aperture Scintillometers (LAS) and both CT2 and the dissipation rate of turbulent kinetic energy, e, for short-path laser scintillometers. CT2 and e are related to the surface fluxes of heat, H, and momentum, t, by virtue of Monin-Obukhov similarity theory. For the LAS - that provides CT2 only - t is obtained from additional wind speed measurements and an estimate of the roughness length. An optical scintillometer in combination with a millimeter-wave scintillometer (MWS) yields both CT2 and Cq2, the structure parameter of humidity, from which the sensible and the latent heat flux can be determined. The following two scintillometer field experiments will be discussed: EVAGRIPS, Lindenberg, Germany 2003. This study deals with a LAS and a MWS (94 GHz) installed over path length of 5 km at 45 m height over a heterogeneous flat agricultural terrain consisting of a mix of lakes, forest and agriculture fields over undulating terrain. The concept of an effective scintillometer height will be introduced, which needs to be applied when the scintillometer height is not constant over the path. RAPID, Idaho, USA, 1999. This study deals with the estimation of evapotranspiration using a LAS and laser scintillometer installed at field scale (~500m) over irrigated alfalfa in an area affected by advection of warm and dry desert air. In these conditions the sensible heat becomes negative and the water vapor deficit is increased, both enhancing evapotranspiration. References: De Bruin, H.A.R.: 2002, 'Introduction, renaissance of scintillometry', Boundary-Layer Meteorol. 105, 1-4. De Bruin, H.A.R., Hartogensis, O.K., Allen, R.G., and Kramer, J.W.J.L., 2004: 'Note on the Regional Advection Perturbations in an Irrigated Desert (RAPID) Experiment', Theor. Appl. Climatol. 80, 143-152. Hartogensis, O.K., De Bruin, H.A.R., Van De Wiel, B.J.H.: 2002, 'Displaced-Beam Small Aperture Scintillometer Test. Part II: Cases-99 Stable Boundary-Layer Experiment', Boundary-Layer Meteorol. 105, 149-176. Meijninger, W.M.L.; Beyrich, F.; Lüdi, A.; Kohsiek, W.; De Bruin, H.A.R.: 2005, 'Scintillometer-Based Turbulent Fluxes of Sensible and Latent Heat Over a Heterogeneous Land Surface : a Contribution to Litfass-2003 Boundary-Layer Meteorol. 121, 89-110.
|Number of pages||1|
|Publication status||Published - 2007|