Analysis of oscillations in the stable atmospheric boundary layer using wavelet methods

Abstract

A wavelet method is used to estimate kinetic energy and fluxes from data collected under stable conditions during the CASES-99 field campaign. Results in the high frequency range are compared with those obtained by the traditional method used to estimate turbulent moments, which is based on the Reynolds decomposition of variables into a mean and a turbulent part. The fact that the wavelet transform performs much better as a filter than the averaging process accounts for most of the disagreements between results. Since the wavelet method can be applied at very different spectral ranges, it is also used to analyse two different coherent structures: a density current and a train of internal gravity waves. The strong burst of turbulence related to the density current reflects the complexity of the first event. The wavelet method discriminates the different scales of motion, which are present in the perturbation, and is therefore an ideal tool for assessing the interactions between them. A method based on the phase difference between wavelet-transformed time series is then applied to the analysis of the horizontal and vertical structure of the gravity waves, and a three-dimensional image of the oscillations is provided.

Analysis of turbulence in fog episodes

“…As widely explained in Terradellas et al (2005), time series of observational data of the wind components can be used to estimate either the turbulence kinetic energy or the contribution to the total kinetic energy produced by oscillations within any range of scales.…”

“…Whereas several authors, such as Roach et al (1976) state that turbulence is a factor that inhibits the onset of radiation fog, others (e.g. Welch and Welicki, 1986) support the theory that turbulence constitutes a contributing factor. A combination of both theories leads to the conclusion that there is a threshold relationship between turbulence and fog formation (Zhou and Ferrier, 2008).…”

“…A combination of both theories leads to the conclusion that there is a threshold relationship between turbulence and fog formation (Zhou and Ferrier, 2008). Terradellas et al (2005) present a wavelet method to estimate turbulent parameters from the analysis of time series of observational data and outline its advantages over the traditional method based on the Reynolds decomposition. The wavelet technique is especially useful in the stable boundary layer, the natural framework for fog formation, where…”

Intermittent turbulence contributes to vertical diffusion of PM<sub>2.5</sub> in the North China Plain

“…Some potential causes include gravity waves (Sorbjan and Czerwinska, 2013;Strang and Fernado, 2001), solitary waves (Terradellas et al, 2005), horizontal meandering of the mean wind field (Anfossi et al, 2005), and low-level jets (LLJs, Marht, 2014).…”

“…Moreover, the turbulence in the ABL is inherently nonlinear (Holtslag, 2015) and has complex interaction with other motions, such as low-level jets, gravity waves, solitary waves and other non-turbulence motions (Banta et al, 2006;Sun et al, 2015;Terradellas et al, 2005). To date, different methods have 20 been applied to describe the levels of intermittency, such as the flatness (Frisch, 1995), FI index (Mahrt, 1998), wavelet analysis (Salmond, 2005) and so on.…”