Local scaling characteristics of Antarctic surface layer turbulence

Basu, Sukanta; Ruiz-Columbie, Arquimedes; Phillipson, J. A.; Harshan, S.

doi:10.5194/tc-4-325-2010

Cited by 3 publications

(1 citation statement)

References 26 publications

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“…4b, R wT and R wq denote vertical transport efficiencies of sensible heat and latent heat, respectively (R ws = ±1 defines optimally efficient transport). R wT hardly sees significant changes, with an overall average of −0.33 ± 0.05, a value close to those previously reported, such as −0.35 over a melting valley glacier (Weber 2007) and −0.38 in the interior of the Antarctic plateau (Basu et al 2010). In general, R wq (absolute values) has a clear evolution that suggests that the latent heat is more efficiently transported to the air through sublimation/evaporation (β < 0; P1 and P3) than to the surface through deposition/condensation (β > 0; P2).…”

Section: Temporal Evolution and Diurnal Behaviour Of The Roughness Lesupporting

confidence: 66%

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Guo

Yang

Zhao

et al. 2011

Boundary-Layer Meteorol

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We present a field investigation over a melting valley glacier on the Tibetan Plateau. In the ablation zone, aerodynamic roughness lengths (z 0M ) vary on the order of 10 −4 -10 −2 m, whose evolution corresponds to three melt phases with distinct surface cover and moisture exchange: snow (sublimation/evaporation), bare ice (deposition/condensation), and ice hummocks (sublimation/evaporation). Bowen-ratio similarity is validated in the stably stratified katabatic winds, which suggests a useful means for data quality check. A roughness sublayer is regarded as irrelevant to the present ablation season, because selected characteristics of scalar turbulence over smooth snow are quite similar to those over hummocky ice. We evaluate three parametrizations of the scalar roughness lengths (z 0T for temperature and z 0q for humidity), viz. key factors for the accurate estimation of sensible heat and latent heat fluxes using the bulk aerodynamic method. The first approach is based on surface-renewal models and has been widely applied in glaciated areas; the second has never received application over an ice/snow surface, despite its validity in (semi-)arid regions; the third, a derivative of the first, is proposed for use specifically over rough ice defined as z 0M > 10 −3 m or so. This empirical z 0M threshold value is deemed of general relevance to glaciated areas (e.g. ice sheet/cap and valley/outlet glaciers), above which the first approach gives notably underestimated z 0T,q . The first and the third approaches tend to underestimate and overestimate turbulent heat/moisture exchange, respectively, frequently leading to relative errors higher than 30%. Comparatively, the second approach produces fairly low errors in energy flux estimates both in individual melt phases and over the whole ablation season; it thus emerges as a practically useful choice to parametrize z 0T,q in glaciated areas. Moreover, we find all 123 308 X. Guo et al. three candidate parametrizations unable to predict diurnal variations in the excess resistances to humidity transfer, thus encouraging more efforts for improvement.

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Section: Temporal Evolution and Diurnal Behaviour Of The Roughness Lesupporting

confidence: 66%

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Guo

Yang

Zhao

et al. 2011

Boundary-Layer Meteorol

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A Spectral Budget Model for the Longitudinal Turbulent Velocity in the Stable Atmospheric Surface Layer

Banerjee

Juang

et al. 2015

Journal of the Atmospheric Sciences

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A spectral budget model is developed to describe the scaling behavior of the longitudinal turbulent velocity variance with the stability parameter and the normalized height in an idealized stably stratified atmospheric surface layer (ASL), where z is the height from the surface, L is the Obukhov length, and δ is the boundary layer height. The proposed framework employs Kolmogorov’s hypothesis for describing the shape of the longitudinal velocity spectra in the inertial subrange, Heisenberg’s eddy viscosity as a closure for the pressure redistribution and turbulent transfer terms, and the Monin–Obukhov similarity theory (MOST) scaling for linking the mean longitudinal velocity and temperature profiles to ζ. At a given friction velocity , reduces with increasing ζ as expected. The model is consistent with the disputed z-less stratification when the stability correction function for momentum increases with increasing ζ linearly or as a power law with the exponent exceeding unity. For the Businger–Dyer stability correction function for momentum, which varies linearly with ζ, the limit of the z-less onset is . The proposed framework explains why does not follow MOST scaling even when the mean velocity and temperature profiles may follow MOST in the ASL. It also explains how δ ceases to be a scaling variable in more strongly stable (although well-developed turbulent) ranges.

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Closure Schemes for Stably Stratified Atmospheric Flows without Turbulence Cutoff

Katul

Zilitinkevich

2016

Journal of the Atmospheric Sciences

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Two recently proposed turbulence closure schemes are compared against the conventional Mellor–Yamada (MY) model for stably stratified atmospheric flows. The Energy- and Flux-Budget (EFB) approach solves the budgets of turbulent momentum and heat fluxes and turbulent kinetic and potential energies. The Cospectral Budget (CSB) approach is formulated in wavenumber space and integrated across all turbulent scales to obtain flow variables in physical space. Unlike the MY model, which is subject to a “critical gradient Richardson number,” both EFB and CSB models allow turbulence to exist at any gradient Richardson number and predict a saturation of flux Richardson number () at sufficiently large . The CSB approach further predicts the value of and reveals a unique expression linking the Rotta and von Kármán constants. Hence, all constants in the CSB model are nontunable and stability independent. All models agree that the dimensionless sensible heat flux decays with increasing . However, the decay rate and subsequent cutoff in the MY model appear abrupt. The MY model further exhibits an abrupt cutoff in the turbulent stress normalized by vertical velocity variance, while the CSB and EFB models display increasing trends. The EFB model produces a rapid increase in the ratio of turbulent potential energy and vertical velocity variance as is approached, suggesting a strong self-preservation mechanism. Vertical anisotropy in the turbulent kinetic energy is parameterized in different ways in MY and EFB, but this consideration is not required in CSB. Differences between EFB and CSB model predictions originate from how the vertical anisotropy is specified in the EFB model.

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Local scaling characteristics of Antarctic surface layer turbulence

Cited by 3 publications

References 26 publications

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

A Spectral Budget Model for the Longitudinal Turbulent Velocity in the Stable Atmospheric Surface Layer

Closure Schemes for Stably Stratified Atmospheric Flows without Turbulence Cutoff

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