Spectral Analysis of Turbulent Aerosol Fluxes by Fourier Transform, Wavelet Analysis, and Multiresolution Decomposition

Aerosol number fluxes are spectrally analyzed using fast Fourier transform analysis, wavelet analysis and multiresolution decomposition. All three methods yield similar spectral features in general, although a detailed evaluation of the cospectra shows some differences, e.g. due to different resolutions in the time and frequency domains. Wavelet analysis yields aerosol flux estimates with a high time resolution that can be used to assess the flux variability. Multiresolution decomposition has been applied successfully to evaluate cospectra of the aerosol number flux, the buoyancy flux and the momentum flux of three 1-day datasets from diverse environments. For all scalars and all environments, the dimensionless frequency ( f ) of the cospectral peak was found between f = 0.1 and 0.2. In addition, the cospectral gap time scale of the aerosol number flux was found between 100 and 1,000 s. Thus, in this study several spectral features such as the dominant time scale and the cospectral gap time scale of aerosol number fluxes are similar to buoyancy fluxes. However, the shape of aerosol number flux cospectra often deviates from buoyancy and momentum flux cospectra, especially at very small and at very large time scales.