Articles | Volume 16, issue 17
Atmos. Chem. Phys., 16, 11349–11366, 2016

Special issue: Amazon Tall Tower Observatory (ATTO) Special Issue

Atmos. Chem. Phys., 16, 11349–11366, 2016

Research article 13 Sep 2016

Research article | 13 Sep 2016

Scalar turbulent behavior in the roughness sublayer of an Amazonian forest

Einara Zahn1, Nelson L. Dias2, Alessandro Araújo3, Leonardo D. A. Sá4, Matthias Sörgel5, Ivonne Trebs6, Stefan Wolff5, and Antônio Manzi7 Einara Zahn et al.
  • 1Graduate Program in Environmental Engineering (PPGEA), Federal University of Paraná, Curitiba, PR, 81531-980, Brazil
  • 2Department of Environmental Engineering, Federal University of Paraná, Curitiba, PR, 81531-980, Brazil
  • 3Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Trav. Dr. Enéas Pinheiro, Belém, PA, 66095-100, Brazil
  • 4Centro Regional da Amazônia, Instituto Nacional de Pesquisas Espaciais (INPE), Av. Perimetral 2651, Belém, PA, 66077-830, Brazil
  • 5Biogeochemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, 55020 Mainz, Germany
  • 6Luxembourg Institute of Science and Technology, Environmental Research and Innovation (ERIN) Department, 4422 Belvaux, Luxembourg
  • 7Centro de Previsão de Tempo e Estudos Climáticos (CPTEC), Instituto Nacional de Pesquisas Espaciais (INPE), Rodovia Dutra Km 39, Cachoeira Paulista, SP, 12630-000, Brazil

Abstract. An important current problem in micrometeorology is the characterization of turbulence in the roughness sublayer (RSL), where most of the measurements above tall forests are made. There, scalar turbulent fluctuations display significant departures from the predictions of Monin–Obukhov similarity theory (MOST). In this work, we analyze turbulence data of virtual temperature, carbon dioxide, and water vapor in the RSL above an Amazonian forest (with a canopy height of 40 m), measured at 39.4 and 81.6 m above the ground under unstable conditions. We found that dimensionless statistics related to the rate of dissipation of turbulence kinetic energy (TKE) and the scalar variance display significant departures from MOST as expected, whereas the vertical velocity variance follows MOST much more closely. Much better agreement between the dimensionless statistics with the Obukhov similarity variable, however, was found for the subset of measurements made at a low zenith angle Z, in the range 0°  <  |Z|  <  20°. We conjecture that this improvement is due to the relationship between sunlight incidence and the “activation–deactivation” of scalar sinks and sources vertically distributed in the forest. Finally, we evaluated the relaxation coefficient of relaxed eddy accumulation: it is also affected by zenith angle, with considerable improvement in the range 0°  <  |Z|  <  20°, and its values fall within the range reported in the literature for the unstable surface layer. In general, our results indicate the possibility of better stability-derived flux estimates for low zenith angle ranges.

Short summary
Preliminary data from the ATTO project were analyzed to characterize the exchange of heat, water vapor, and CO2 between the Amazon forest and the atmosphere. The forest roughness makes estimation of their fluxes difficult, and even measurements at 42 m above the canopy show a lot of scatter. Still, measurements made around noon showed much better conformity with standard theories for the exchange of these quantities, opening the possibility of good flux estimates when the sun is high.
Final-revised paper