Resumo

RODRIGUES, Abel Martins  e  PITA, Gabriel Paulo Alcântara. Caracterização do Escoamento e Fluxo Atmosférico de Calor Latente em Montado de Sobro. Silva Lus. [online]. 2003, vol.11, n.2, pp.165-184. ISSN 0870-6352.

At an observation tower in a cork oak stand, experimental measurements were made of the usual micrometeorological variables and of the turbulent fluctuations of wind velocity components and air temperature, in order to characterize their influence on the evapotranspiration regime and, by inspection of the Penman-Monteith equation, as well as time and frequency domain analysis of turbulent flow. The total mean daily ratio between the latent heat flux and equilibrium evapotranspiration was 0.44, typical of a dry canopy. The mean daily value of the coupling coefficient was 0.18, representative of an imposed evaporation, with a strong dependence on atmospheric humidity and canopy resistance. Canopy resistance increased during the afternoon, with an increasung atmospheric vapor pressure deficit, indicating a partial stomatal closure. The spectra of air temperature and velocity components fitted well with the usual empirical functions. The slopes of spectral curves followed the -2/3 power law in the inertial subrange. The calculated mean integral eulerian length scales, relating to tree heigths, calculated from autocorrelation functions, for the horizontal and vertical velocity components of wind velocity, were 8.65 and 0.69. Their corresponding time scales were 12 and 0.96 s. An application of the quadrant method confirmed the importance of intermittent sweeps and ejections, in the descendent transport of horizontal momentum.

Palavras-chave : cork oak stand; power spectra; coupling; time and length scales.

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