The Influence of Submeso Processes on Stable Boundary Layer Similarity Relationships

Abstract

Previous observational studies in the stable boundary layer diverge appreciably on the values of dimensionless ratios between turbulence-related quantities and on their stability dependence. In the present study, the hypothesis that such variability is caused by the influence of locally dependent nonturbulent processes, referred to as submeso, is tested and confirmed. This is done using six datasets collected at sites with different surface coverage. The time-scale dependence of wind components and temperature fluctuations is presented using the multiresolution decomposition, which allows the identification of the turbulence and submeso contributions to spectra and cospectra. In the submeso range, the spectra of turbulence kinetic energy range increases exponentially with time scale. The exponent decreases with the magnitude of the turbulent fluctuations at a similar manner at all sites. This fact is used to determine the smaller time scale with relevant influence of submeso processes and a ratio that quantifies the relative importance of such nonturbulent processes with respect to turbulence. Based on that, values for the local stability parameter that are unaffected by nonturbulent processes are found. It is shown that the dimensionless ratios do not usually converge to a given value as the time scale increases and that it is as a consequence of the locally dependent submeso influence. The ratios and their stability dependence are determined at the time scales with least influence of nonturbulent processes, but significant site-to-site variability persists. Combining all datasets, expressions for the dependence of the dimensionless ratios on the local stability parameter that minimize the role of the submeso contribution are proposed.

Dependence of Turbulent Velocities on Wind Speed and Stratification

“…Because the relationship between the turbulence and the weak stratified flow depends on the site-dependent submeso motions, this turbulence relationship is site dependent (Acevedo et al 2014) and the above results cannot be interpreted as universal. The turbulence behaviour needs further examination in terms of variations within the network and should also be extended to other field sites.…”

“…Such nonstationarity can be internally forced through interactions of the turbulence with the mean flow (van de Wiel et al 2012a) or forced by submeso motions (Mahrt 2010b). Acevedo et al (2014) find that the submeso motions introduce a site dependency for the relationship between the turbulence and the mean flow for stable conditions. In addition, non-turbulent large coherent structures may also be generated within a stratified boundary layer due to intrinsic development (Ansorge and Mellado 2014) without propagating modes or surface heterogeneity.…”

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

“…Although the horizontal velocities in Fig. 12 are highly in phase between 42 and 80 m, it is clear from this plot that the wind speed is generally higher at 80 m, while there are more turbulent fluctuations at 42 m. When these signals are decomposed in terms of their time scale to provide a turbulent kinetic energy (TKE) spectrum (Acevedo et al, 2014), the more intense turbulence at 42 m appears as a peak at time scales just greater than 10 s (Fig. 13).…”

Um Estudo Do Efeito De Obstruções No Escoamento De Submeso Na Camada Limite Convectiva

“…A ECT média horizontal para movimentos no alcance do submeso seguiu uma lei de escala para ambas as estações (Figura 2), aumentando exponencialmente para escalas de tempo de menor frequência, o que está de acordo semelhantemente com resultados encontrados por Mahrt (2009) e Acevedo et al (2014). A ressalva está na divisão da escala entre subesmo e a turbulência encontrada por esses autores, em torno de um a dois minutos e a encontrada neste trabalho, de cerca de 40 minutos.…”