1,721,020 research outputs found
Laboratory measurements in the convective boundary layer by means of a PTV system
No full textThe aim of this study is to better characterize the Convective Boundary Layer of the atmosphere (CBL). The investigation has been performed in a water tank model by means of a PTV system, which allowed measuring the velocity field during the evolution of the phenomenon.
Experimental data show a good agreement with other laboratory measures and field measurements, supporting the validity of the performed simulation and of the achieved results. The analysis has been focused on the spatial features of the CBL, which have seldom been studied due to the difficulties in measuring the whole velocity field in controlled and repeatable conditions. Spatial characterization reflects fundamental features of CBL, such as heterogeneity and anisotropies. The computation of spatial autocorrelations and the subsequent estimates of the integral scales have provided important information on the convective structures responsible for the mixing processes within the atmospheric boundary layer. Actually, spatial CBL characterization has also important implications in the development of appropriate Sub Grid Scale (SGS) parameterizations reproducing small scale physics in Large Eddy Simulation (LES) models. Indeed, most recent SGS schemes are based on directly computing the stress tensors, needed by LESs, from the small scales velocity field reproduced by means of scale invariant tools, which use, as input, the resolved velocity field. Therefore, studying the spatial scale invariant properties of CBL velocity fields has a meaningful practical significance. Specifically, different scaling regimes have been investigated on the velocity field at different non dimensional elevations. Experimental data display Generalized Extended Self Similarity (GESS) scaling for both horizontal and vertical velocity components. Moreover, GESS scaling exponents computed on vertical velocities are higher than horizontal ones and exhibit a distinct trend with the non dimensional elevation
Identification of coherent structures in the Convective Boundary Layer
No full textAccording to several results presented in literature, Finite-Time Lyapunov Exponents (FTLE) methodology represents a powerful tool for the analysis and characterization of unsteady
phenomena. Using a laboratory model, we investigated the
adoption of the FTLE for the identification and characterization
of coherent structures in the Convective Boundary Layer (CBL).
The investigation was carried out in a convective tank, using
distilled water as the working fluid. The simulated phenomenon was then analyzed by means of image analysis techniques on an illuminated vertical plane. Specifically, the 2D velocity fields were retrieved by means of RIV (Robust Image Velocimetry). Comparison with numerical and in situ measurements reported in literature confirmed the soundness of the obtained velocity fields.
The inspection of FTLE spatial fields obtained by the
time-resolved RIV measurements allowed the identification
of CBL coherent structures. This result is not trivial due
to the unsteady and fully turbulent nature of the analyzed
phenomenon. Moreover, FTLE statistics were analyzed both
for the whole CBL and as a function of the non-dimensional
elevation. Results revealed important phenomenological
features of coherent structures linked to the mixing processes
in the CBL
Performances of a Log-Poisson multifractal model in space-time rainfall downscaling (solicited)
No full textOrographic influences in rainfall downscaling
Full text linkThe problem of rainfall downscaling in a mountainous region is discussed, and a simple methodology aimed at introducing spatial heterogeneity induced by orography in downscaling models is proposed. This procedure was calibrated and applied to rainfall data retrieved by the high temporal resolution rain gage network of the Sardinian Hydrological Survey
Space-time Multifractality of Remotely Sensed Rainfall Fields
No full textA methodology aimed at characterizing the scaling properties of precipitation fields in space and time is revised and applied to remotely sensed rainfall data retrieved during two oceanic campaigns (GATE and TOGA-COARE), and a land campaign (TRMM-LBA). The presence of spatial heterogeneity induced by orography is investigated on data retrieved over land (TRMM-LBA): the performed analyses show that the orographic induced heterogeneity seems to be negligible for the examined data. Moreover, the scaling properties observed on rainfall over land are compared with those detected on ocean rainfall for several space-time events. Results of a multifractal analysis enable a common calibration of the STRAIN space-time rainfall downscaling cascade model for the three datasets. Generated synthetic fields preserve the observed rainfall space-time variability
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