Comparison of areally averaged turbulent fluxes over non-homogeneous terrain: Results from the EFEDA-field experiment

In June 1991 the EFEDA-field experiment (ECHIVAL Field Experiment in a Desertification-Threatened Area) was carried out in the Spanish province Castilla-La Mancha, to improve the understanding of the interactions between the soil, the vegetation and the atmosphere.Here results of energy balance studies at the Barrax site are given, one of the three intensively studied experimental sites within Castilla-La Mancha. This area is characterized by a large fraction of irrigated fields (40%) while the remaining 60% was fallow land at the end of June 1991. The energy balances over these two characteristic land-use classes totally differ. While for the irrigated fields the evapotranspiration is dominant, for the non-irrigated fields the sensible and the soil heat fluxes dominate and the latent heat flux is nearly negligible.In order to achieve areally averaged turbulent fluxes, surface, SODAR and aircraft data have been used. Comparing the surface fluxes from all three facilities, it can be found that:The sensible heat flux estimation from SODAR (Σw-method) gives reliable results when a calibration of Σw is done with another independent system (e.g. aircraft).Aircraft measurements in conjunction with energy budget methods yield surface fluxes of sensible heat, which are about 20% lower than the areally averaged values calculated by the surface measurements. The areally averaged latent heat fluxes from aircraft and surface measurements agree better than the sensible heat fluxes.

[1]  J. Kaimal,et al.  Turbulence Structure in the Convective Boundary Layer , 1976 .

[2]  Estimates of surface heat flux from sodar and laser scintillation measurements in the unstable boundary layer , 1980 .

[3]  Sodar estimates of surface heat flux and mixed layer depth compared with direct measurements , 1990 .

[4]  William H. Press,et al.  The Art of Scientific Computing Second Edition , 1998 .

[5]  R. Haverkamp,et al.  Bare-ground surface heat and water exchanges under dry conditions: Observations and parameterization , 1993 .

[6]  R. Stull.  An Introduction to Boundary Layer Meteorology , 1988 .

[7]  H. DeBruin,et al.  EFEDA - European field experiment in a desertification-threatened area , 1993 .

[8]  S. Caughey,et al.  Some aspects of turbulence structure through the depth of the convective boundary layer , 1979 .

[9]  W. Elliott,et al.  The growth of the atmospheric internal boundary layer , 1958 .

[10]  B. Strauss,et al.  Measuring Heat Flux and Structure Functions of Temperature Fluctuations with an Acoustic Doppler Sodar , 1980 .

[11]  E. Youngs,et al.  Fundamentals of Soil Physics. , 1982 .

[12]  S. Caughey,et al.  Measurements of boundary layer structure and development over SE England using aircraft and tethered balloon instrumentation , 1979 .

[13]  J. I. MacPherson,et al.  Boundary-layer heat and moisture budgets from fife , 1990 .

[14]  R. Coulter,et al.  Acoustic Remote Sensing , 1986 .

[15]  Donald H. Lenschow,et al.  Length Scales in the Convective Boundary Layer , 1986 .

[16]  P. Sellers,et al.  The First ISLSCP Field Experiment (FIFE) , 1988 .

[17]  E. K. Webb,et al.  Correction of flux measurements for density effects due to heat and water vapour transfer , 1980 .

[18]  J. I. MacPherson,et al.  An evaluation of aircraft flux measurements of CO2, water vapor and sensible heat , 1989 .

[19]  Donald H. Lenschow,et al.  Airplane Measurements of Planetary Boundary Layer Structure , 1970 .

[20]  Landoberflächenprozesse über ebenem landwirtschaftlich genutztem Gelände: ein Vergleich von Messung und Rechnung unter Verwendung von LOTREX-10E/HIBE88-Daten , 1993 .

[21]  J. Andre,et al.  Regional estimates of heat and evaporation fluxes over non-homogeneous terrain. Examples from the HAPEX-MOBILHY programme , 1990 .

[22]  J. Lagouarde,et al.  Daily sensible heat flux estimation from a single measurement of surface temperature and maximum air temperature , 1992 .

[23]  F. Fiedler,et al.  Modification of turbulent fluxes and temperature fields in the atmospheric surface layer over two adjacent agricultural areas : a case study , 1991 .

[24]  F. Fiedler,et al.  1Simulation of unstationary wind and temperature fields over complex terrain and comparison with observations , 1991 .