Vertical cascade structure of the atmosphere and multifractal dropsonde outages

Abstract : We use 220 atmospheric profiles from state-of-the-art dropsondes to test the predictions of multiplicative cascade models of the atmosphere on the horizontal velocity, pressure, temperature, log potential temperature, log equivalent potential temperature, air density, humidity, and vertical sonde velocity. We found that the predictions were accurately verified (to within +/- 1 to +/- 2% over 10 m to 1 km for the statistical moments up to second order); the effective outer cascade scale L(eff) was in the range 1-30 km. In order to perform the analyses and to correctly interpret the results, we needed to overcome technical difficulties caused by the sonde's highly intermittent sampling. This intermittency is the result of both data outages and variable sonde fall speeds; we (surprisingly) found that the outages also had a cascade structure. The wide-range scaling of the sampling rate implies a variable sonde resolution, so that interpolation onto regular grids should generally be avoided (e.g., it would give rise to serious artifacts in estimating the corresponding spectra). In earlier studies, before the cascade nature of the outages was understood, interpolation was avoided by studying the fluctuations using all the pairs of measurement points; this was adequate for fluctuation scaling exponents in the range 0 <= H <= 1. However, determining the cascade structure involves systematically degrading the resolution of fluxes (not fluctuations) so that the variable resolution and their attendant biases could not be avoided. We therefore developed a new method of estimating the fluxes and theoretically determined the corrections necessary to estimate the unbiased exponents. The resulting sonde cascade picture was given further support by (much more straightforward) analysis of uniformly sampled vertical cross sections of the atmosphere obtained from airborne lidar. Using the turbulent fluxes obtained from these various sources, we determined the corresponding cascade regimes and the corresponding exponents as well as the small deviations from the theoretical behavior. In addition to the fluxes, we also studied the fluctuations. To do this we generalized the data point pair method (restricted to nonconservation parameters 0 <= H <= 1) to data triplets (extending the method to 0 <= H <= 2). The resulting fluctuations were analyzed using (generalized) structure functions. We found that while the scaling of the fluxes often broke down at scales greater than about 1 km, the scaling of the fluctuations extended over the entire range 10 m to 10 km.
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Article dans une revue
Journal of Geophysical Research: Atmospheres, American Geophysical Union, 2009, 114 (?), 〈10.1029/2008JD010651〉
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Soumis le : lundi 25 juin 2012 - 11:11:55
Dernière modification le : jeudi 22 mars 2018 - 22:34:51

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S. Lovejoy, A. F. Tuck, S. J. Hovde, D Schertzer. Vertical cascade structure of the atmosphere and multifractal dropsonde outages. Journal of Geophysical Research: Atmospheres, American Geophysical Union, 2009, 114 (?), 〈10.1029/2008JD010651〉. 〈hal-00711505〉



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