HR: 0830h
AN: NG51A-0836    [PDF]
TI: Lidar Investigation of Atmospheric Stratification: $D_el=2$, $7/3$, $23/9$ or $3$?
AU: Lilley, M
EM: lilleym@physics.mcgill.ca
AF: Dept. of Physics, McGill University, 3600 University St., Montreal, QC H3A-2T8 Canada
AU: Strawbridge, K
EM: kevin.strawbridge@ec.gc.ca
AF: Center for Atmospheric Research Experiments, Air Quality Research Processes Division, Environment Canada, R.R. #1, Egbert, ON L0L-1N0 Canada
AU: * Lovejoy, S
EM: lovejoy@physics.mcgill.ca
AF: Dept. of Physics, McGill University, 3600 University St., Montreal, QC H3A-2T8 Canada
AU: Schertzer, D
EM: daniel.schertzer@cereve.enpc.fr
AF: CEREVE, Ecole Nationale des Ponts et Chaussees, 6-8 avenue Blaise Pascal, Marnes-La-Vallee, 77455 France
AB: Practically all theories of turbulence assume isotropy or at least local isotropy. In buoyancy driven flows the justification is not obvious because gravity breaks the isotropy and acts at all scales. The classical assumption is that gravity leads to a basic stably stratified state while simultaneously postulating that the perturbations are nevertheless statistically isotropic. In the atmosphere, the scale height (about 10km) presents a further challenge: isotropic three dimensional turbulence cannot extend to very large scales. The standard model postulates an intermediate "meso-scale gap" followed at larger scales by two dimensional horizontally isotropic turbulence. Today, although we still lack a consensus about the full horizontal atmospheric statistics, the meso-scale gap separating these D=3, D=2 regimes has not been observed and there is wide consensus that the horizontal wind is scaling in the horizontal with spectral exponent $\beta_h =5/3$ out to at least several hundred km. In the vertical direction, the spectral exponent $\beta_v > \beta_h$ implying scaling stratification with the volume of structures growing at a rate $D_el=2+ (\beta_h-1)/(\beta_v-1)$. The two main contending proposals being $\beta_v =11/5$ (buoyancy driven, Bolgiano-Obhukov) and $\beta_v=3$ (gravity waves, Lumley-Shur) implying $D_el=7/3$, $23/9$ respectively. In this talk we describe some recent results using state-of-the-art lidar data of passive scalars, over the range 3 m to 4.5 km in the vertical and 100 m to 120 km in the horizontal, we directly estimate $D_el=2.56\pm0.05$ supporting the 23/9 dimensional "unified scaling" model . We discuss this in relation to other measurement campaigns, and also the implications for modelling the atmosphere. Finally, we show how to make multifractal models of vertical cross-sections which are very close to the data.
DE: 3360 Remote sensing
DE: 3367 Theoretical modeling
DE: 3379 Turbulence
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting