A multifractal analysis of lidar measured water vapour |
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| Authors: | J. E. Pinzón C. E. Puente M. B. Parlange W. Eichinger |
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| Affiliation: | (1) Hydrologic Science, University of California, 95616 Davis, CA, USA;(2) Present address: Institute of Theoretical Dynamics, University of California, 95616 Davis, CA, USA;(3) Present address: Department of Biological and Agricultural Engineering, University of California, 95616 Davis, CA, USA;(4) Present address: Los Almos National Laboratory, 87545 Los Alamos, NM, USA |
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| Abstract: | Accurate and fast-response measurements of space-time observations of specific humidity were made above a drying land surface at the University of California at Davis, using the Los Alamos water Raman-lidar. In an attempt to quantify the space-time intermittency features of turbulent flows in the lower atmosphere, a multifractal analysis of these water vapour measurements was performed. The structure of the specific humidity,  (x, t), was analyzed quantifying a scalar gradient measure![$$( sim [{text{grad }}theta {text{]}}^{text{2}} )$$](/content/k305122r4u147471/10546_2004_Article_BF00709237_TeX2GIFIE1.gif) both in time and space, for all possible one-dimensional cuts, i.e.![$$chi _t (x,t) = [partial theta (x,t)/partial t]^2$$](/content/k305122r4u147471/10546_2004_Article_BF00709237_TeX2GIFIE2.gif) and![$$chi _x (x,t) = [partial theta (x,t)/partial x]^2$$](/content/k305122r4u147471/10546_2004_Article_BF00709237_TeX2GIFIE3.gif) . The results confirm the multifractal nature of this scalar gradient measure (a type of scalar dissipation rate) and show that humidity measurements at fixed times ( x) are more intermittent (e.g. have less entropy dimension) than those at fixed locations in space (t). Similar multifractal behaviour of the spatial data, with and without a transformation from the observed wind velocities, supports the validity of Taylor's hypothesis for the studied fields. |
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