TY - JOUR
T1 - An analysis of intermittency, scaling, and surface renewal in atmospheric surface layer turbulence
AU - Katul, Gabriel
AU - Porporato, Amilcare
AU - Cava, Daniela
AU - Siqueira, Mario
N1 - Funding Information:
The authors acknowledge support from the National Science Foundation (NSF-EAR-99-03471 and -DMS-00-72585), the Biological and Environmental Research (BER) Program, the US Department of Energy, through the southeast Regional Center (SERC) of the National Institute for Global Environmental Change (NIGEC) and through the Terrestrial Carbon Processes Program (TCP) and the FACE project, the Italian MURST Project ‘Sviluppo di tecnologie innovative e di processi biotecnologici in condizioni controllate nel settore delle colture vegetali: Diagnosi e Prognosi di situazioni di stress idrico per la vegetazione’, and ‘Conselho Nacional de Desenvolvimento Científico e Tecnológico’ (CNPq) of Brazil.
PY - 2006/3/15
Y1 - 2006/3/15
N2 - Turbulent velocity and scalar concentration time series were collected in the atmosphere above an ice sheet, a mesic grassland, and a temperate pine forest, thereby encompassing a wide range of roughness conditions encountered in nature. Intermittency and scaling properties of such series were then analyzed using Tsallis's non-extensive thermostatistics. While theoretical links between the Tsallis's non-extensive thermostatistics and Navier-Stokes turbulence remain questionable, the Tsallis distribution (a special interpretation of Student's t-distribution) provides a unifying framework to investigate two inter-connected problems: similarity between scalars and velocity statistics within the inertial subrange and "contamination" of internal intermittency by "external" factors. In particular, we show that "internal" intermittency models, including the She-Leveque, Lognormal, and Log-stable, reproduce the observed Tsallis parameters well for velocities within the inertial subrange, despite the differences in surface roughness conditions, but fail to describe the fluctuations for the scalars (e.g., air temperature CO2 and water vapor). Such scalars appear more intermittent than velocity when the underlying surface is a large source or sink. The dissimilarity in statistics between velocity and scalars within the inertial subrange is shown to be strongly dependent on "external" intermittency. The genesis of "external" intermittency for scalars is linked to the classical Higbie surface renewal process and scalar source strength. Surface renewal leads to a ramp-like pattern in the scalar concentration (or temperature) time series with a gradual increase (rise-phase) associated with sweeping motion from the atmosphere onto the surface or into the canopy and a sharp drop associated with an ejection phase from the surface (or the canopy) back into the atmosphere. The duration of the rise-phase is on the order of the integral time scale, while the duration of the ejection phase is much shorter and is shown to impact the distributional tails at the small scales. Implications for "scalar turbulence" models are also discussed in the context of biosphere-atmosphere CO2 exchange.
AB - Turbulent velocity and scalar concentration time series were collected in the atmosphere above an ice sheet, a mesic grassland, and a temperate pine forest, thereby encompassing a wide range of roughness conditions encountered in nature. Intermittency and scaling properties of such series were then analyzed using Tsallis's non-extensive thermostatistics. While theoretical links between the Tsallis's non-extensive thermostatistics and Navier-Stokes turbulence remain questionable, the Tsallis distribution (a special interpretation of Student's t-distribution) provides a unifying framework to investigate two inter-connected problems: similarity between scalars and velocity statistics within the inertial subrange and "contamination" of internal intermittency by "external" factors. In particular, we show that "internal" intermittency models, including the She-Leveque, Lognormal, and Log-stable, reproduce the observed Tsallis parameters well for velocities within the inertial subrange, despite the differences in surface roughness conditions, but fail to describe the fluctuations for the scalars (e.g., air temperature CO2 and water vapor). Such scalars appear more intermittent than velocity when the underlying surface is a large source or sink. The dissimilarity in statistics between velocity and scalars within the inertial subrange is shown to be strongly dependent on "external" intermittency. The genesis of "external" intermittency for scalars is linked to the classical Higbie surface renewal process and scalar source strength. Surface renewal leads to a ramp-like pattern in the scalar concentration (or temperature) time series with a gradual increase (rise-phase) associated with sweeping motion from the atmosphere onto the surface or into the canopy and a sharp drop associated with an ejection phase from the surface (or the canopy) back into the atmosphere. The duration of the rise-phase is on the order of the integral time scale, while the duration of the ejection phase is much shorter and is shown to impact the distributional tails at the small scales. Implications for "scalar turbulence" models are also discussed in the context of biosphere-atmosphere CO2 exchange.
KW - Antartica
KW - Atmosphere turbulence
KW - Grassland
KW - Intermittency
KW - Pine forest
KW - Scalar transfer
KW - Surface renewal
KW - Tsallis statistics
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UR - http://www.scopus.com/inward/citedby.url?scp=33645763276&partnerID=8YFLogxK
U2 - 10.1016/j.physd.2006.02.004
DO - 10.1016/j.physd.2006.02.004
M3 - Article
AN - SCOPUS:33645763276
SN - 0167-2789
VL - 215
SP - 117
EP - 126
JO - Physica D: Nonlinear Phenomena
JF - Physica D: Nonlinear Phenomena
IS - 2
ER -