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A large set of tower data was used to identify the gap that separates small-scale turbulence and mesoscale structures in the
cospectra of surface fluxes. The cospectra were obtained using a multi-resolution decomposition algorithm. The gap time scale
τ
g
was found by fitting a fifth-order polynomial to the cospectra and identifying special points occurring after the peak at
small scales. In unstable conditions (day) τ
g
was found to fall as the mean wind speed increased, while no such dependence was observed in stable conditions (night). The
gap scale was found to change very weakly with stability both in moderately stable and moderately unstable conditions, with
a sharp drop from about 1100 to 250 s occurring in near-neutral conditions. The vertical fluxes computed at different averaging
intervals were found to correlate exceptionally well with each other, the scatter being somewhat larger during the night.
Although considerable discrepancy may occur for individual records, when averaged over 10 months, the difference in the flux
estimated at 7 to 109 min intervals never exceeded 4%, which is comparable or less than the instrumental error. 相似文献
2.
The acoustical tomography scheme for inferring a three-dimensional sound-speed field within some area based on the measurements of horizontal refraction angles is reviewed. The numerical simulations made so far were based on the assumption of the adiabaticity of low-frequency mode propagation. In this paper, an inversion scheme is presented that accounts for the acoustic mode interaction. We found that, generally, the interaction weakly affects the horizontal refraction angle, and it can be accounted for by iterations. Numerical simulations for the case of an Atlantic “meddy” corresponding to a strong double channel stratification are presented. Only three iterations were required to retrieve the exact strong sound-speed-field inhomogeneity within an area of 500 km×500 km 相似文献
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