scholarly journals Dependence of near-surface similarity scaling on the anisotropy of atmospheric turbulence

2018 ◽  
Vol 144 (712) ◽  
pp. 641-657 ◽  
Author(s):  
Ivana Stiperski ◽  
Marc Calaf
Keyword(s):  
Atmospheric Turbulence ◽  
Near Surface ◽  
Similarity Scaling ◽  
Surface Similarity

scholarly journals The effect of atmospheric turbulence and chamber deployment period on autochamber CO<sub>2</sub> and CH<sub>4</sub> flux measurements in an ombrotrophic peatland

2012 ◽  
Vol 9 (2) ◽  
pp. 1439-1482 ◽  
Author(s):  
D. Y. F. Lai ◽  
N. T. Roulet ◽  
E. R. Humphreys ◽  
T. R. Moore ◽  
M. Dalva
Keyword(s):  
Atmospheric Turbulence ◽  
Concentration Gradient ◽  
Co2 Concentration ◽  
Time Of Day ◽  
Reliable Estimate ◽  
Organic Soils ◽  
Atmospheric Conditions ◽  
Near Surface ◽  
Ch4 Flux ◽  
Flux Measurements

Abstract. Accurate quantification of soil-atmosphere gas exchange is essential for understanding the magnitude and controls of greenhouse gas emissions. We used an automatic closed dynamic chamber system to measure the fluxes of CO2 and CH4 for several years at the ombrotrophic Mer Bleue peatland near Ottawa, Canada and found that atmospheric turbulence and chamber deployment period had a considerable influence on the observed flux rates. With a short deployment period of 2.5 min, CH4 flux exhibited strong diel patterns and both CH4 and nighttime CO2 effluxes were highly and negatively correlated with friction velocity as were the CO2 concentration gradients in the top 20 cm of peat. This suggests winds were flushing the very porous and relatively dry near surface peat layers, altering the concentration gradient and resulting in a 9 to 57% underestimate of CH4 flux at any time of day and a 13 to 21% underestimate of nighttime CO2 fluxes in highly turbulent conditions. Conversely, there was evidence of an overestimation of ~100% of CH4 and nighttime CO2 effluxes in calm atmospheric conditions possibly due to enhanced near-surface gas concentration gradient by mixing of chamber headspace air by fans. These problems were resolved by extending the deployment period to 30 min. After 13 min of chamber closure, the flux rate of CH4 and nighttime CO2 became constant and were not affected by turbulence thereafter, yielding a reliable estimate of the net biological fluxes. The measurement biases we observed likely exist to some extent in all chamber flux measurements made on porous and aerated substrate, such as peatlands, organic soils in tundra and forests, and snow-covered surfaces, but would be difficult to detect unless high frequency, semi-continuous observations are made.

scholarly journals Climatic Variability of Near-Surface Turbulent Kinetic Energy over the United States: Implications for Fire-Weather Predictions

2013 ◽  
Vol 52 (4) ◽  
pp. 753-772 ◽  
Author(s):  
Warren E. Heilman ◽  
Xindi Bian
Keyword(s):  
United States ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Atmospheric Turbulence ◽  
Climatic Variability ◽  
Fire Behavior ◽  
The United States ◽  
Spatial And Temporal Variability ◽  
Fire Weather ◽  
Near Surface

AbstractRecent research suggests that high levels of ambient near-surface atmospheric turbulence are often associated with rapid and sometimes erratic wildland fire spread that may eventually lead to large burn areas. Previous research has also examined the feasibility of using near-surface atmospheric turbulent kinetic energy (TKEs) alone or in combination with the Haines index (HI) as an additional indicator of anomalous atmospheric conditions conducive to erratic or extreme fire behavior. However, the application of TKEs-based indices for operational fire-weather predictions in the United States on a regional or national basis first requires a climatic assessment of the spatial and temporal patterns of the indices that can then be used for testing their operational effectiveness. This study provides an initial examination of some of the spatial and temporal variability patterns across the United States of TKEs and the product of HI and TKEs (HITKEs) using data from the North American Regional Reanalysis dataset covering the 1979–2008 period. The analyses suggest that there are regional differences in the behavior of these indices and that regionally dependent threshold values for TKEs and HITKEs may be needed for their potential use as operational indicators of anomalous atmospheric turbulence conditions conducive to erratic fire behavior. The analyses also indicate that broad areas within the northeastern, southeastern, and southwestern regions of the United States have experienced statistically significant positive trends in TKEs and HITKEs values over the 1979–2008 period, with the most substantial increases in values occurring over the 1994–2008 period.

scholarly journals Scaling, Anisotropy, and Complexity in Near-Surface Atmospheric Turbulence

2019 ◽  
Vol 124 (3) ◽  
pp. 1428-1448 ◽  
Author(s):  
Ivana Stiperski ◽  
Marc Calaf ◽  
Mathias W. Rotach
Keyword(s):  
Atmospheric Turbulence ◽  
Near Surface

scholarly journals Anisotropy of Unstably Stratified Near-Surface Turbulence

2021 ◽  
Author(s):  
Ivana Stiperski ◽  
Marcelo Chamecki ◽  
Marc Calaf
Keyword(s):  
Scaling Relations ◽  
Convective Conditions ◽  
Complex Flow ◽  
Near Surface ◽  
Dimensional Group ◽  
Surface Turbulence ◽  
Turbulence Kinetic Energy Budget ◽  
Similarity Scaling ◽  
Shear Production

AbstractClassic Monin–Obukov similarity scaling states that in a stationary, horizontally homogeneous flow, in the absence of subsidence, turbulence is dictated by the balance between shear production and buoyancy production/destruction, whose ratio is characterized by a single universal scaling parameter. An evident breakdown in scaling is observed though, through large scatter in traditional scaling relations for the horizontal velocity variances under unstable stratification, or more generally in complex flow conditions. This breakdown suggests the existence of processes other than local shear and buoyancy that modulate near-surface turbulence. Recent studies on the role of anisotropy in similarity scaling have shown that anisotropy, even if calculated locally, may encode the information about these missing processes. We therefore examine the possible processes that govern the degree of anisotropy in convective conditions. We first use the reduced turbulence-kinetic-energy budget to show that anisotropy in convective conditions cannot be uniquely described by a balance of buoyancy and shear production and dissipation, but that other terms in the budget play an important role. Subsequently, we identify a ratio of local time scales that acts as a proxy for the anisotropic state of convective turbulence. This ratio can be used to formulate a new non-dimensional group. Results show that building on this approach the role of anisotropy in scaling relations over complex terrain can be placed into a more generalized framework.

scholarly journals Probing near-surface atmospheric turbulence with lidar measurements and high-resolution hydrodynamic models

2001 ◽  
Author(s):  
Chih-Yue J. Kao ◽  
D. I. Cooper ◽  
J. M. Reisner ◽  
William E. Eichinger ◽  
Michael Ghil
Keyword(s):  
High Resolution ◽  
Atmospheric Turbulence ◽  
Hydrodynamic Models ◽  
Near Surface ◽  
Lidar Measurements

scholarly journals The effect of atmospheric turbulence and chamber deployment period on autochamber CO<sub>2</sub> and CH<sub>4</sub> flux measurements in an ombrotrophic peatland

2012 ◽  
Vol 9 (8) ◽  
pp. 3305-3322 ◽  
Author(s):  
D. Y. F. Lai ◽  
N. T. Roulet ◽  
E. R. Humphreys ◽  
T. R. Moore ◽  
M. Dalva
Keyword(s):  
Atmospheric Turbulence ◽  
Concentration Gradient ◽  
Time Of Day ◽  
Reliable Estimate ◽  
Organic Soils ◽  
Atmospheric Conditions ◽  
Near Surface ◽  
Ch4 Flux ◽  
Gas Concentration ◽  
Flux Measurements

Abstract. Accurate quantification of soil-atmosphere gas exchange is essential for understanding the magnitude and controls of greenhouse gas emissions. We used an automatic, closed, dynamic chamber system to measure the fluxes of CO2 and CH4 for several years at the ombrotrophic Mer Bleue peatland near Ottawa, Canada and found that atmospheric turbulence and chamber deployment period had a considerable influence on the observed flux rates. With a short deployment period of 2.5 min, CH4 flux exhibited strong diel patterns and both CH4 and nighttime CO2 effluxes were highly and negatively correlated with ambient friction velocity as were the CO2 concentration gradients in the top 20 cm of peat. This suggests winds were flushing the very porous and relatively dry near-surface peat layers and reducing the belowground gas concentration gradient, which then led to flux underestimations owing to a decrease in turbulence inside the headspace during chamber deployment compared to the ambient windy conditions. We found a 9 to 57% underestimate of the net biological CH4 flux at any time of day and a 13 to 21% underestimate of nighttime CO2 effluxes in highly turbulent conditions. Conversely, there was evidence of an overestimation of ~ 100% of net biological CH4 and nighttime CO2 fluxes in calm atmospheric conditions possibly due to enhanced near-surface gas concentration gradient by mixing of chamber headspace air by fans. These problems were resolved by extending the deployment period to 30 min. After 13 min of chamber closure, the flux rate of CH4 and nighttime CO2 became constant and were not affected by turbulence thereafter, yielding a reliable estimate of the net biological fluxes. The measurement biases we observed likely exist to some extent in all chamber flux measurements made on porous and aerated substrate, such as peatlands, organic soils in tundra and forests, and snow-covered surfaces, but would be difficult to detect unless high frequency, semi-continuous observations were made.

scholarly journals Probing near-surface atmospheric turbulence with high-resolution lidar measurements and models

2002 ◽  
Vol 107 (D10) ◽  
pp. ACL 7-1-ACL 7-9 ◽  
Author(s):  
C.-Y. J. Kao ◽  
D. I. Cooper ◽  
J. M. Reisner ◽  
W. E. Eichinger ◽  
M. Ghil
Keyword(s):  
High Resolution ◽  
Atmospheric Turbulence ◽  
Near Surface ◽  
Lidar Measurements
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