Dimensionless criteria for the production‐dissipation equilibrium of scalar fluctuations and their implications for scalar similarity

Abstract

.[1] In water resources it is common to consider that two scalars have a similar behavior in the atmospheric surface layer. This is a consequence of Monin-Obukhov similarity theory whose direct implication is that all similarity functions between two scalars are equal. However, many works show that scalar similarity does not always hold under unstable conditions, a fact for which it is often difficult to establish a physical cause. In this paper, using a data set measured during winter over a tropical lake in Brazil (Furnas Lake), we found a relation between temperature-water vapor similarity and the strength of the surface forcing; we also confirmed that the classical balance between gradient production and molecular dissipation of scalar variance and covariance is key to scalar similarity. This balance can be disrupted by large values of the third-order transport terms, and possibly by nonstationary terms as well. In connection with the scalar variance and covariance budgets, we propose a new set of dimensionless scalar flux numbers which are able to make a good diagnosis of the aforementioned balance (or the lack thereof) for each budget. The fact that different Monin-Obukhov functions are not equally capable of identifying scalar similarity is also demonstrated and a new bulk indicator of scalar flux similarity is proposed whose absolute value, unlike the relative transfer efficiency, is bounded above by 1; this new indicator holds also in the spectral domain. Finally, we verify that low-frequency dissimilarity has a larger impact over scalar similarity than over scalar flux similarity.

Scalar turbulent behavior in the roughness sublayer of an Amazonian forest

“…A sufficient condition for this to happen, and the simplest although by no means a necessary condition, is the validity of the wellknown hypothesis of perfect similarity between scalars (Hill, 1989;Dias and Brutsaert, 1996), which often fails under unstable conditions due to phenomena originating above the surface layer and to the transport of scalar variance from above (Cancelli et al, 2012(Cancelli et al, , 2014. Furthermore, the physics of the roughness sublayer proper may complicate this picture even more.…”

“…Different from the correlation coefficient between the two scalars, r ab , rte ab is a better descriptor of scalar flux similarity (Cancelli et al, 2012). ste ab , proposed by Cancelli et al (2012), has a similar interpretation but is explicitly designed so that, unlike rte ab , it is always bounded from above by 1. Both rte ab and ste ab were calculated for all pairs of scalars.…”

The Amazon Tall Tower Observatory (ATTO): overview of pilot measurements on ecosystem ecology, meteorology, trace gases, and aerosols

“…Finally, we tried to apply some concepts recently developed by Cancelli et al (2012) to relate the applicability of MOST to the strength of the surface forcing. Cancelli et al (2012) found that the applicability of MOST can be well predicted by their "surface flux number",…”

Estimativa De Fluxo De Calor Latente Em Reservatórios Através De Uma Rede Neural Artificial

“…O monitoramento micrometeorológico tem sido utilizado como uma importante ferramenta na análise dos dados ambientais, em especial a medição de fluxos superficiais através do método de covariâncias turbulentas ou eddy covariance (Dias et al, 2002;Aubinet et al, 2012;Scientifc, 1996;Lee et al, 2004 Após a aplicação de técnicas de correção e filtragem eliminando os dados fisicamente inconsistentes (outliers, Vissotto Jr. e Dias (2013)), os efeitos devido a sensibilidade dos sensores, pista de vento e advecção (Vissotto Jr et al, 2009;Cancelli et al, 2012) a série de dados fica com lacunas que precisam ser preenchidas.…”