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Abstract:The wavelet spectral method was applied to aircraft-based measurements of atmospheric turbulence obtained during joint Russian-Japanese research on the atmospheric boundary layer near Yakutsk (eastern Siberia) in April-June 2000. Practical ways to apply Fourier and wavelet methods for aircraft-based turbulence data are described. Comparisons between Fourier and wavelet transform results are shown and they demonstrate, in conjunction with theoretical and experimental restrictions, that the Fourier transform method is not useful for studying non-homogeneous turbulence. The wavelet method is free from many disadvantages of Fourier analysis and can yield more informative results. Comparison of Fourier and Morlet wavelet spectra showed good agreement at high frequencies (small scales). The quality of the wavelet transform and corresponding software was estimated by comparing the original data with restored data constructed with an inverse wavelet transform. A Haar wavelet basis was inappropriate for the turbulence data; the 'mother' wavelet function recommended in this study is the Morlet wavelet. Good agreement was also shown between variances and covariances estimated with different mathematical techniques, i.e. through non-orthogonal wavelet spectra and through eddy correlation methods.

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Abstract:This paper outlines specifications and gives preliminary results of aircraft observations made during the Intensive Observation Period in 2000 (IOP2000) over the Yakutsk area of eastern Siberia. The observations were part of the GAME-Siberia project. Spatial and seasonal variation in the fluxes of sensible heat, latent heat, and carbon dioxide were determined using a Russian aircraft equipped with turbulence sensors. Two flight paths covered 12 ð 32 km 2 grids over heterogeneous forest and grass surfaces on the left-and right-hand banks of the Lena River. The spatial flux distributions were consistent with the underlying vegetation cover. A video camera recorded aerial images of the land, while a spectrometer observed the spectral reflectance of the land surface. These data helped describe the relationship between the atmosphere and the land surface. The vertical structure of the atmospheric boundary layer (ABL) was also observed on long flight paths between the left and right banks of the Lena River. Thermally induced internal boundary layers (TIBLs) developed in the ABL under different thermal and dynamic conditions near the Lena River. The horizontal and vertical distributions of sensible and latent heats in the ABL were consistent with the generation of cumulus, which appeared over the forested area, but not over the Lena River lowland.

Spectral analysis was performed on aircraft observations of a convective boundary layer (CBL) that developed over a thermally inhomogeneous, well-marked mesoscale land surface. The observations, part of the GAME-Siberia experiment, were recorded between April and June 2000 over the Lena River near Yakutsk City. A special integral parameter termed the 'reduced depth of the CBL' was used to scale the height of the mixed layer with variable depth. Analysis of wavelet cospectra and spectra facilitated the separation of fluxes and other variables into small-scale turbulent fluctuations (with scales less than the reduced depth of the CBL, approximately 2 km) and mesoscale fluctuations (up to 20 km). This separation approach allows for independent exploration of the scales. Analyses showed that vertical distributions obeyed different laws for small-scale fluxes and mesoscale fluxes (of sensible heat, water vapour, momentum and carbon dioxide) and for other variables (wind speed and air temperature fluctuations, coherence and degree of anisotropy). Vertical profiles of small-scale turbulent fluxes showed a strong decay that differed from generally accepted similarity models for the CBL. Vertical profiles of mesoscale fluxes and other variables clearly showed sharp inflections at the same relative (with respect to the reduced depth of the CBL) height of approximately 0.55 in the CBL. Conventional similarity models for sensible heat fluxes describe both small-scale turbulent and mesoscale flows. The present results suggest that mesoscale motions that reach up to the relative level of 0.55 could be initiated by thermal surface heterogeneity. Entrainment between the upper part of the CBL and the free atmosphere may cause mesoscale motions in that region of the CBL.