Dificuldades de estimativa dos parâmetros de rugosidade aerodinâmica pelo perfil logarítmico do vento sobre vegetação esparsa em região semi-árida

Abstract

ABSTRACT. The zero-plane displacement (d) and the roughness length (z 0 ) of sparse shrubs in semi-arid region were determined by the conventional (statistical) method during the HAPEX-Sahel experiment. Measurements of the wind profile at four levels above of surface (3.0, 4.1, 5.3 and 8.5 m) and eddy correlation turbulent fluxes determined at 9 m were used. The method was applied in neutral atmospheric conditions, with stability parameter ζ < |0.0325|, wind speed > 1 m s −1 in the lower level and the friction velocity > 0.1 m s −1 determined by eddy correlations. Approximately 4.3% of the observation satisfied these restrictions, but only 1% had adequate fetch conditions. The value of d was equal to 1.09 ± 0.14 m and it represented about 53% of the height of the vegetation (h) and z 0 = 0.184 ± 0.017 m = 0.089h. The data selection criteria used was satisfactory, but the applicability of the method is restricted by the difficulties in observing adiabatic conditions and adequate fetch. Alternative estimates with a single height of measurement above the inertial sublayer gave physically inconsistent estimates of d and z 0 .Keywords: zero-plane displacement, roughness length, roughness sublayer, fetch, HAPEX-Sahel. Palavras-chave: deslocamento do plano zero, comprimento de rugosidade, subcamada rugosa, bordadura, HAPEX-Sahel. RESUMO. O deslocamento do plano zero

Fator de desacoplamento em um canavial irrigado no submédio do Vale do São Francisco

“…3 (Monteith & Unsworth, 1990): O deslocamento do plano zero (d) foi estimado pelo método estatístico a partir dos valores médios de velocidade do vento para períodos de 30 min, utilizando-se os dados obtidos em condições próximas às da neutralidade (Arya, 2001). Em suma, o método estatístico consiste em utilizar um algoritmo iterativo para maximizar o coeficiente de determinação entre ln(z-d) e "u" (Steduto & Hsiao, 1998;Lyra & Pereira, 2007). Devido à inércia dos anemômetros de concha, foram desconsiderados os perfis em que a velocidade do vento foi inferior a 1,0 m s -1 (Lyra & Pereira, 2007).…”

“…Em suma, o método estatístico consiste em utilizar um algoritmo iterativo para maximizar o coeficiente de determinação entre ln(z-d) e "u" (Steduto & Hsiao, 1998;Lyra & Pereira, 2007). Devido à inércia dos anemômetros de concha, foram desconsiderados os perfis em que a velocidade do vento foi inferior a 1,0 m s -1 (Lyra & Pereira, 2007). O número de Richardson (Ri) foi utilizado para caracterizar as condições de estabilidade atmosférica e, posteriormente, identificar os perfis próximos à neutralidade (-0,01 < Ri < 0,01) (Arya, 2001).…”

Wind Intensity and Power Density in the Brazilian Dry Tropical Forests (Caatinga)

“…At levels closer to the earth's surface, the interval of greatest magnitude of the wind occurs during the day, from dawn to late afternoon, and the strong thermal gradient generated by surface heating is the main mechanism for this condition. However, with the increase in height, there is a variation in this cycle, and the wind at night starts to gain speed over a certain period (Arya, 2001;Lyra and Pereira, 2007).…”

Patterns and Controls of the Latent and Sensible Heat Fluxes in the Brazilian Pampa Biome

“…where g (m s −2 ) is the gravity acceleration, Temp ( • C) is the air temperature, and others as described above. Stable atmosphere corresponds to positive values of ζ, unstable to negative values of ζ, and atmospheric neutrality to values within the interval 0 < ζ<|0.0325| [60].…”