HR: 17:20h
AN: NG54A-05    [Abstracts]
TI: Isotropic turbulence, stable layers: facts or fictions?
AU: * Lovejoy, S
EM: lovejoy@physics.mcgill.ca
AF: Physics, Mcgill University, 3600 University st., Montreal, Qc H3A 2T8, Canada
AU: Tuck, A
EM: Adrian.F.Tuck@noaa.gov
AF: NOAA, 325 Broadway, Boulder, Co 80305-3337, United States
AU: Hovde, S
EM: Susan.J.Hovde@noaa.gov
AF: NOAA, 325 Broadway, Boulder, Co 80305-3337, United States
AU: Schertzer, D
EM: Daniel.Schertzer@cereve.enpc.fr
AF: CERERVE, ENPC, 6-8 Ave. Blaise Pascale, Marne-La-Vallée, 77455, France
AB: Using state of the art drop sonde data (from 237 sondes over the Pacific) we examine two classical and fundamental idealizations of atmospheric science showing that they are untenable in the light of the vertical structure. The first is the notion of stable atmospheric layers. This is used for understanding atmospheric dynamics and thermodynamics, including the most advanced dynamical meteorological notions such as potential vorticity. Using the drop sonde data, we show that each apparently stable layer is actually composed of a hierarchy of unstable layers themselves with embedded stable sublayers, each with unstable sub-sub layers etc. i.e. in a Russian doll-like fractal hierarchy whose dimension we estimate. We therefore argue that the notion is untenable and must be replaced by modern scaling notions. The second idealization we examine is the turbulence assumption of isotropy. If we include intermittency, Kolmorogov's landmark proposal that fully developed turbulence has an "inertial subrange" with isotropic energy spectrum E(k)=k**-beta with beta=5/3 has apparently been spectacularly confirmed in both the horizontal direction and in the time domain (k is a wavenumber). For gradients over a horizontal distance deltax this implies deltav=deltaz**Hh (Hh=1/3 corresponds to beta=5/3). Remarkably, Hv for gradients over vertical distances deltaz (deltav=deltaz**Hv) has not been seriously investigated. Using drop sonde data of horizontal wind, we find that from scales of 5 m to 10 km from the surface layer through to the top of the troposphere, Hv is close to (or larger) than the Bolgiano-Obukhov value 3/5. Hv greater than Hh implies that a) the atmosphere becomes progressively less stratified at smaller scales although in a scaling way; b) that at most a single (roughly) isotropic "sphero- scale" exists (often in the range 1-100 cm).
DE: 0350 Pressure, density, and temperature
DE: 4415 Cascades
DE: 4440 Fractals and multifractals
SC: Nonlinear Geophysics [NG]
MN: 2007 Joint Assembly