Carbon dioxide exchange and nocturnal processes over a mixed deciduous forest

Lee, Xuhui; Black, T. Andrew; Hartog, G. Den; Neumann, H. H.; Nesic, Zoran; Olejnik, Janusz

doi:10.1016/0168-1923(95)02310-0

Cited by 45 publications

(29 citation statements)

References 24 publications

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“…It is known that the submeso energy is generally greater in complex terrain (Nappo 1991;Vickers and Mahrt 2006). It is also possible that, in a fashion similar to semi-open forest canopies, the irregular roughness elements in the vicinity of the Lucas Heights tower can occasionally induce gravity waves in very stable conditions near the surface that have phase angles significantly different from ±90 • and can therefore contribute to fluxes of momentum and heat (Lee et al 1996(Lee et al , 1997. In complex topography, Acevedo and Fitzjarrald (2003) found that temperature recoupling between regional stations at different altitudes occurred more frequently as wind speeds or cloud fractions increased.…”

Section: Discussionmentioning

confidence: 99%

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Williams

Chambers

Griffiths

2013

Boundary-Layer Meteorol

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Vertical mixing of the nocturnal stable boundary layer (SBL) over a complex land surface is investigated for a range of stabilities, using a decoupling index (0 < D rb < 1) based on the 2-50 m bulk gradient of the ubiquitous natural trace gas radon-222. The relationship between D rb and the bulk Richardson number (R ib ) exhibits three broad regions: (1) a well-mixed region (D rb ≈ 0.05) in weakly stable conditions (R ib < 0.03); (2) a steeply increasing region (0.05 < D rb < 0.9) for "transitional" stabilities (0.03 < R ib < 1); and (3) a decoupled region (D rb ≈ 0.9-1.0) in very stable conditions (R ib > 1). D rb exhibits a large variability within individual R ib bins, however, due to a range of competing processes influencing bulk mixing under different conditions. To explore these processes in R ib -D rb space, we perform a bivariate analysis of the bulk thermodynamic gradients, various indicators of external influences, and key turbulence quantities at 10 and 50 m. Strong and consistent patterns are found, and five distinct regions in R ib -D rb space are identified and associated with archetypal stable boundary-layer regimes. Results demonstrate that the introduction of a scalar decoupling index yields valuable information about turbulent mixing in the SBL that cannot be gained directly from a single bulk thermodynamic stability parameter. A significant part of the high variability observed in turbulence statistics during very stable conditions is attributable to changes in the degree of decoupling of the SBL from the residual layer above. When examined in R ib -D rb space, it is seen that very different turbulence regimes can occur for the same value of R ib , depending on the particular combination of values for the bulk temperature gradient and wind shear, together with external factors. Extremely low turbulent variances and fluxes are found at 50 m height when R ib > 1 and D rb ≈ 1 (fully decoupled). These "quiescent" cases tend to occur when geostrophic forcing is very weak and subsidence is present, but are not associated with the largest bulk temperature gradients. Humidity and net radiation data indicate the presence of low cloud, patchy fog or dew, any of which may aid decoupling in these cases by preventing temperature gradients from increasing sufficiently to favour gravity wave activity. The largest temperature gradients in our dataset are actually associated with smaller values of the decoupling index (D rb < 0.7), indicating the presence of mixing. Strong evidence is seen from enhanced turbulence levels, fluxes and submeso activity at 50 m, as well as high temperature variances and heat flux intermittencies at 10 m, suggesting this region of the R ib -D rb distribution can be identified as a top-down mixing regime. This may indicate an important role for gravity waves and other wave-like phenomena in providing the energy required for sporadic mixing at this complex terrain site.

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Section: Discussionmentioning

confidence: 99%

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Williams

Chambers

Griffiths

2013

Boundary-Layer Meteorol

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“…0148-0227/99/1999JD900227509.00 eral major field campaigns, including canopy turbulence [Shaw et al, 1988], ozone and volatile organic compound exchanges [Fuentes et al, 1992;Fuentes and Wang, 1999], and nocturnal atmospheric processes [Lee et al, 1996]. There are several important features about this forest that we wish to emphasize here.…”

Section: Paper Number 1999jd900227mentioning

confidence: 99%

Long‐term observation of the atmospheric exchange of CO₂ with a temperate deciduous forest in southern Ontario, Canada

et al. 1999

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“…However, disagreement between calculations and measurements may not be a result of invalid respiration calculations by the model. It is widely suspected that nocturnal measurements of CO2 Huxes are error-prone under stable conditions and low wind speeds (Lee et al 1996;Moncrieff. Mahli & Leuning 1996) despite the attempt to tneasure the storage of CO2 in the canopy air space.…”

Section: Laodel Calculationsmentioning

confidence: 99%

Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought

Baldocchi¹

1997

Plant Cell & Environment

288

234

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Forests in the south-eastern United States experienced a prolonged dry spell and above-normal temperatures during the 1995 growing season. During this episode, nearly continuous, eddy covariance measurements of carbon dioxide and water vapour fluxes were acquired over a temperate, hardwood forest. These data are used to examine how environmental factors and accumulating soil moisture deficits affected the diurnal pattern and magnitude of canopy-scale carbon dioxide and water vapour fluxes. The field data are also used to test an integrative leaf-to-canopy scaling model (CANOAK), which uses micrometeorological and physiological theory, to calculate mass and energy fluxes. When soil moisture was ample in the spring, peak rates of net ecosystem CO2 exchange (A'pj occurred around midday and exceeded 20 ;Umol m~^ s"'. Rates of A',; were near optimal when air temperature ranged between 22 and 25°C. The accumulation of soil moisture deficits and a co-occurrence of high temperatures caused peak rates of daytime carbon dioxide uptake to occur earlier in the morning. High air temperatures and soil moisture deficits were also correlated with a dramatic reduction in the magnitude of N^. On average, the magnitude of N,i decreased from 20 to 7 ^umol m"^ s"' as air temperature increased from 24 to 30°C and the soil dried. The CANAOK model yielded accurate estimates of canopyscale carbon dioxide and water vapour fluxes when the forest had an ample supply of soil moisture. During the drought and heat spell, a cumulative drought index was needed to adjust the proportionality constant of the stomata] conductance model to yield accurate estimates of canopy CO2 exchange. The adoption of the drought index also enabled the CANOAK model to give improved estimates of evaporation until midday. On the other hand, the scheme failed to yield accurate estimates of evaporation during the afternoon.

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Carbon dioxide exchange and nocturnal processes over a mixed deciduous forest

Cited by 45 publications

References 24 publications

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Long‐term observation of the atmospheric exchange of CO₂ with a temperate deciduous forest in southern Ontario, Canada

Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought

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Carbon dioxide exchange and nocturnal processes over a mixed deciduous forest

Cited by 45 publications

References 24 publications

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Long‐term observation of the atmospheric exchange of CO2 with a temperate deciduous forest in southern Ontario, Canada

Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought

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Long‐term observation of the atmospheric exchange of CO₂ with a temperate deciduous forest in southern Ontario, Canada