Determination of the type of atmospheric turbulence from meteorological measurements in operational mode
V.V. Nosov, V.P. Lukin, E.V. Nosov, A.V. Torgaev
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: Kolmogorov turbulence, atmospheric non-Kolmogorov turbulence, coherent turbulence, turbulence region, meteorological measurements
Abstract
To determinate the type of atmospheric turbulence (Kolmogorov, coherent, etc.) in operational mode, a new technique has been developed based on algorithm for spectral analysis of sequential overlapping samples from a continuously replenished population of meteorological measurement data. The samples are formed by the sliding time window. Criterion for turbulence type is the slope of inertial interval of the temperature fluctuation spectrum near the maximum, which is equal to “-5/3" under Kolmogorov turbulence and “-8/3" under coherent turbulence. The slope is calculated from the linear regression equation at the initial part of the spectrum, the length of which is set by the level of decrease by one order of magnitude from the maximum. It is shown that such slopes of the spectra for the recorded meteosituations under urban conditions are distributed lognormally. It is found that the proportion of non-Kolmogorov turbulence in more than 5 million calculated spectra is much larger than expected and amounts to 75-97% depending on the estimation rigor. It is shown that sequences of spectra with the same slope correspond to regions of turbulence of the same type. Boundaries of the regions are defined with accuracy of the sliding window shift step. The size of the regions is estimated based on information about wind speed and registration duration. It is shown that under comparable conditions the extent of the regions can significantly exceed the one for an ordinary single sample. To accelerate the post processing of large datasets, the algorithm uses the Message Passing Interface (MPI) for a computing cluster with an arbitrary number of nodes. The field of application of the technique in astronomical practice is the evaluation and registration of the sizes of spatial regions of “strong" and “weak" turbulence along optical path, in which the intensity of turbulence is in fixed intervals, as well as the sizes of regions with fixed temperature stratification.
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