author = "Zahn, Einara and Dias, Nelson L. and Araujo, Alessandro and 
                         S{\'a}, Leonardo Deane de Abreu and Soergel, Matthias and Trebs, 
                         Ivonne and Wolff, Stefan and Manzi, Antonio Ocimar",
          affiliation = "{Universidade Federal do Paran{\'a} (UFPR)} and {Universidade 
                         Federal do Paran{\'a} (UFPR)} and {Empresa Brasileira de Pesquisa 
                         Agropecu{\'a}ria (EMBRAPA)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)} and {Max Planck Institute for Chemistry} and 
                         {Environmental Research and Innovation (ERIN)} and {Max Planck 
                         Institute for Chemistry} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)}",
                title = "Scalar turbulent behavior in the roughness sublayer of an 
                         Amazonian forest",
              journal = "Atmospheric Chemistry and Physics",
                 year = "2016",
               volume = "16",
               number = "17",
                pages = "11349--11366",
                month = "Sept.",
             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 81.6m 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 degrees < vertical bar Z 
                         vertical bar < 20 degrees. 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 degrees < vertical bar Z vertical bar < 20 degrees, 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.",
                  doi = "10.5194/acp-16-11349-2016",
                  url = "http://dx.doi.org/10.5194/acp-16-11349-2016",
                 issn = "1680-7316 and 1680-7324",
             language = "en",
           targetfile = "zahna_scalar.pdf",
        urlaccessdate = "28 nov. 2020"