scholarly journals An improved non-iterative surface layer flux scheme for atmospheric stable stratification condition

2013 ◽  
Vol 6 (4) ◽  
pp. 6459-6492
Author(s):  
Y. Li ◽  
Z. Gao ◽  
D. Li ◽  
L. Wang ◽  
H. Wang
Keyword(s):  
Full Range ◽  
Stable Stratification ◽  
Iteration Scheme ◽  
Surface Fluxes ◽  
Turbulent Transfer ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Iterative Computation ◽  
Stable Conditions ◽  
Relative Errors

Abstract. Parameterization of turbulent fluxes under stably stratified conditions has always been a challenge. Current surface fluxes calculation schemes either need iterations or suffer low accuracy. In this paper, a non-iteration scheme is proposed to approach the classic iterative computation results using multiple regressions. It can be applied to the full range of roughness status 10 ≤ z/z0 ≤ 105 and −0.5 ≤ log(z0/z0h) ≤ 30 under stable conditions 0< RiB ≤ 2.5. The maximum (average) relative errors for the turbulent transfer coefficients for momentum and sensible heat are 12% (1%) and 9% (1%), respectively.

scholarly journals An improved non-iterative surface layer flux scheme for atmospheric stable stratification conditions

2014 ◽  
Vol 7 (2) ◽  
pp. 515-529 ◽  
Author(s):  
Y. Li ◽  
Z. Gao ◽  
D. Li ◽  
L. Wang ◽  
H. Wang
Keyword(s):  
Iterative Scheme ◽  
Full Range ◽  
Stable Stratification ◽  
Surface Fluxes ◽  
Turbulent Transfer ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Iterative Computation ◽  
Stable Conditions ◽  
Relative Errors

Abstract. Parameterization of turbulent fluxes under stably stratified conditions has always been a challenge. Current surface fluxes calculation schemes either need iterations or suffer low accuracy. In this paper, a non-iterative scheme is proposed to approach the classic iterative computation results using multiple regressions. It can be applied to the full range of roughness status 10 ≤ z/z0 ≤ 105 and −0.5 ≤ log (z0/z0h) ≤ 30 under stable conditions 0 < RiB ≤ 2.5. The maximum (average) relative errors for the turbulent transfer coefficients for momentum and sensible heat are 12% (1%) and 9% (1%), respectively.

Sensitivity studies with different formulations for similarity functions used in surface layer scheme, over the tropical region, in a climate model

2020 ◽  
Author(s):  
Prabhakar Namdev ◽  
Maithili Sharan ◽  
Saroj Kanta Mishra
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Climate Model ◽  
Stable Stratification ◽  
Turbulent Fluxes ◽  
Surface Fluxes ◽  
Tropical Region ◽  
Similarity Functions ◽  
Unstable Stratification ◽  
Stable Conditions

&lt;p&gt;The lowest portion of the planetary boundary layer (PBL), where the turbulent fluxes are assumed to be constant, is known as the atmospheric surface layer (ASL). Within the surface layer, the surface exchange processes play an important role in land-atmosphere interaction. Thus, a precise formulation of the surface fluxes is crucial to ensure an adequate atmospheric evolution by numerical models. The Monin&amp;#8211;Obukhov Similarity Theory (MOST) is a widely used framework to estimate the surface turbulent fluxes within the surface layer. MOST uses similarity functions of momentum (&amp;#966;&lt;sub&gt;m&lt;/sub&gt;) and heat (&amp;#966;&lt;sub&gt;h&lt;/sub&gt;) for non-dimensional wind and temperature profiles. Over the years, various formulations for these similarity functions have been proposed by the researchers ranging from linear to non-linear forms. These formulations have limitations in the weak wind, stable, and unstable atmospheric conditions. In the surface layer scheme currently available in the Community Atmosphere Model version 5 (CAM5.0), the stable and unstable regimes are divided into four parts, and the corresponding similarity functions are the functions proposed by Kader and Yaglom (1990) for strong unstable stratification, by Businger et al. (1971) for weak unstable stratification, functions by Dyer (1974) for weak stable stratification, and for moderate to strongly stable stratification, the functions from Holtslag et al. (1990) have been utilized. The criteria used for this classification are somewhat ad-hoc, and there is an abrupt transition between different regimes encountered. &amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160; &amp;#160; &amp;#160; &amp;#160;In the present study, an effort has been made to implement the similarity functions proposed by Grachev et al. (2007) for stable conditions and Fairall et al. (1996) for unstable conditions in the surface layer scheme of Community Land Model (CLM) for CAM5.0. In the modified version, the similarity functions for unstable conditions are a combination of commonly used Paulson type expressions for near-neutral stratification and an expression proposed by Carl et al. (1973) that takes in to account highly convective conditions. Similarly, the formulation proposed by Grachev et al., for stable conditions, can cover a wider range of stable stratifications. The simulations with CAM5 model using the existing and modified version of surface layer scheme have been performed with 1&amp;#176; resolution for ten years, and the impact of modified functions on the simulation of various important near-surface variables over the tropical region is analyzed. It is found that the scheme with modified functions improving the simulation of surface variables as compared with the existing scheme over the tropical region. In addition, the limitations arbitrarily imposed on particular variables in the existing surface layer scheme can be eliminated or suppressed by using these modified functions. &amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Fairall CW, Bradley EF, Rogers DP, Edson JB, Young GS (1996) Bulk parameterization of air-sea fluxes for tropical ocean global atmosphere coupled-ocean atmosphere response experiment. J Geophys Res 101(C2):3747&amp;#8211;3764&lt;/p&gt;&lt;p&gt;Grachev, A.A., Andreas, E.L., Fairall, C.W., Guest, P.S. and Persson, P.O.G. (2007a) SHEBA: flux&amp;#8211;profile relationships in stable atmospheric boundary layer. Boundary-Layer Meteorology,124, 315&amp;#8211;333.&lt;/p&gt;&lt;p&gt;Keywords:&lt;/p&gt;&lt;p&gt;Boundary layer, Turbulence, Climate Model, Surface Fluxes&lt;/p&gt;

scholarly journals An Approach for Calculation of Turbulent Transfer Coefficient for Momentum inside Vegetation Canopies

2006 ◽  
Vol 45 (2) ◽  
pp. 348-356 ◽  
Author(s):  
D. T. Mihailovic ◽  
B. Lalic ◽  
J. Eitzinger ◽  
S. Malinovic ◽  
I. Arsenic
Keyword(s):  
Transfer Coefficient ◽  
Land Surface ◽  
Attenuation Factor ◽  
Surface Fluxes ◽  
Turbulent Transfer ◽  
Vegetation Canopy ◽  
Transfer Coefficients ◽  
Vegetation Canopies ◽  
Turbulent Transfer Coefficient ◽  
Wind Profiles

Abstract A method for calculating the profile of turbulent transfer coefficient for momentum inside a vegetation canopy for use in land surface schemes is presented. It is done through the following steps. First, an equation for the turbulent transfer coefficient for momentum inside a vegetation canopy using the “sandwich” approach for its representation is derived. Second, it is examined analytically to determine whether its solution is always positive. Third, the equation for the turbulent transfer coefficient is solved numerically, using an iterative procedure for calculating the attenuation factor in the expression for the wind speed inside a vegetation canopy that is assumed to be a linear combination of an exponential function and a logarithmic function. The proposed method is tested using 1) the observations for the wind profiles in a Japanese larch plantation and a pine forest and 2) the outputs for surface fluxes and total soil water content obtained by the Land–Air Parameterization Scheme (LAPS) with the forcing data and observations in a soybean field at the Caumont site in France during the 1986 growing season. Also, a test is performed that compares the proposed method with the method for calculating the turbulent transfer coefficients for momentum inside a vegetation canopy commonly used in land surface schemes.

Two Experiments on Using a Scintillometer to Infer the Surface Fluxes of Momentum and Sensible Heat

2012 ◽  
Vol 51 (9) ◽  
pp. 1685-1701 ◽  
Author(s):  
Edgar L Andreas
Keyword(s):  
Eddy Covariance ◽  
Correlation Coefficients ◽  
Arctic Sea Ice ◽  
Surface Fluxes ◽  
Index Structure ◽  
Quality Data ◽  
Sensible Heat ◽  
Traditional Use ◽  
Similarity Functions ◽  
Essential Question

AbstractA traditional use of scintillometry is to infer path-averaged values of the turbulent surface fluxes of sensible heat Hs and momentum τ (, where ρ is air density and u* is the friction velocity). Many scintillometer setups, however, measure only the path-averaged refractive-index structure parameter ; the wind information necessary for inferring u* and Hs comes from point measurements or is absent. The Scintec AG SLS20 surface-layer scintillometer system, however, measures both and the inner scale of turbulence ℓ0, where ℓ0 is related to the dissipation rate of turbulent kinetic energy ɛ. The SLS20 is thus presumed to provide path-averaged estimates of both u* and Hs. This paper describes comparisons between SLS20-derived estimates of u* and Hs and simultaneous eddy-covariance measurements of these quantities during two experiments: one, over Arctic sea ice; and a second, over a midlatitude land site during spring. For both experiments, the correlation between scintillometer and eddy-covariance fluxes is reasonable: correlation coefficients are typically above 0.7 for the better-quality data. For both experiments, though, the scintillometer usually underestimates u* and underestimates the magnitude of Hs when compared with the corresponding eddy-covariance values. The data also tend to be more scattered when < 10−14 m−2/3: the signal-to-noise ratio for scintillometer-derived fluxes decreases as decreases. An essential question that arises during these comparisons is what similarity functions to use for inferring fluxes from the scintillometer and ℓ0 measurements. The paper thus closes by evaluating whether any of four candidate sets of similarity functions is consistent with the scintillometer data.

Diffusion Layer Theory for Turbulent Vapor Condensation With Noncondensable Gases

1993 ◽  
Vol 115 (4) ◽  
pp. 998-1003 ◽  
Author(s):  
P. F. Peterson ◽  
V. E. Schrock ◽  
T. Kageyama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mass Transfer ◽  
Vapor Condensation ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gas ◽  
Noncondensable Gases ◽  
Vertical Tubes

In turbulent condensation with noncondensable gas, a thin noncondensable layer accumulates and generates a diffusional resistance to condensation and sensible heat transfer. By expressing the driving potential for mass transfer as a difference in saturation temperatures and using appropriate thermodynamic relationships, here an effective “condensation” thermal conductivity is derived. With this formulation, experimental results for vertical tubes and plates demonstrate that condensation obeys the heat and mass transfer analogy, when condensation and sensible heat transfer are considered simultaneously. The sum of the condensation and sensible heat transfer coefficients becomes infinite at small gas concentrations, and approaches the sensible heat transfer coefficient at large concentrations. The “condensation” thermal conductivity is easily applied to engineering analysis, and the theory further demonstrates that condensation on large vertical surfaces is independent of the surface height.

The Turbulent Transfer Model Applied to Geodolite Measurements

1984 ◽  
Vol 38 (2) ◽  
pp. 79-90
Author(s):  
C. S. Fraser
Keyword(s):  
Long Range ◽  
Meteorological Parameters ◽  
Sensible Heat Flux ◽  
Reduction Technique ◽  
Transfer Model ◽  
Turbulent Transfer ◽  
Sensible Heat ◽  
Vertical Temperature Gradient ◽  
Vertical Temperature ◽  
Wave Path

This paper reports on an application of the Turbulent Transfer Model (TTM) for the atmospheric reduction of long-range geodolite EDM measurements. To apply the TTM, additional meteorological parameters must be determined. For this application, the sensible heat flux, which is central to the modeling of the vertical temperature gradient, has been empirically modeled. The atmospheric reduction obtained with the TTM is compared to both the distance corrected for refraction by the standard reduction technique, and the “true” distance which has been determined using temperatures measured along the wave path by an aircraft. The results indicate that the TTM can yield a significant improvement in accuracy over the standard reduction for long-range electrooptical EDM. To attain this improvement only a few additional, and mainly qualitative field observations need to be recorded.

scholarly journals A New Value of the von Kármán Constant: Implications and Implementation

2009 ◽  
Vol 48 (5) ◽  
pp. 923-944 ◽  
Author(s):  
Edgar L. Andreas
Keyword(s):  
Boundary Layer ◽  
Similarity Theory ◽  
Stable Stratification ◽  
Transfer Coefficients ◽  
Obukhov Length ◽  
Von Karman ◽  
Roughness Lengths ◽  
Experimental Values ◽  
Definition Of ◽  
Von Kármán

Abstract The von Kármán constant k occurs throughout the mathematics that describe the atmospheric boundary layer. In particular, because k was originally included in the definition of the Obukhov length, its value has both explicit and implicit effects on the functions of Monin–Obukhov similarity theory. Although credible experimental evidence has appeared sporadically that the von Kármán constant is different than the canonical value of 0.40, the mathematics of boundary layer meteorology still retain k = 0.40—probably because the task of revising all of this math to implement a new value of k is so daunting. This study therefore outlines how to make these revisions in the nondimensional flux–gradient relations; in variance, covariance, and dissipation functions; and in structure parameters of Monin–Obukhov similarity theory. It also demonstrates how measured values of the drag coefficient (CD), the transfer coefficients for sensible (CH) and latent (CE) heat, and the roughness lengths for wind speed (z0), temperature (zT), and humidity (zQ) must be modified for a new value of the von Kármán constant. For the range of credible experimental values for k, 0.35–0.436, revised values of CD, CH, CE, z0, zT, and zQ could be quite different from values obtained assuming k = 0.40, especially if the original measurements were made in stable stratification. However, for the value of k recommended here, 0.39, no revisions to the transfer coefficients and roughness lengths should be necessary. Henceforth, use the original measured values of transfer coefficients and roughness lengths but do use similarity functions modified to reflect k = 0.39.

scholarly journals A Clustering Method to Characterize Intermittent Bursts of Turbulence and Interaction with Submesomotions in the Stable Boundary Layer

2015 ◽  
Vol 72 (4) ◽  
pp. 1504-1517 ◽  
Author(s):  
Nikki Vercauteren ◽  
Rupert Klein
Keyword(s):  
Thermal Stratification ◽  
Factor Model ◽  
Similarity Theory ◽  
Stable Stratification ◽  
Small Scale ◽  
Clustering Method ◽  
Atmospheric Boundary Layers ◽  
Optimal Sequence ◽  
Stable Conditions ◽  
Turbulence Data

Abstract Atmospheric boundary layers with stable stratification include a variety of small-scale nonturbulent motions such as waves, microfronts, and other complex structures. When the thermal stratification becomes strong, the presence of such motions could affect the turbulent mixing to a large extent, and common similarity theory that is used to describe weakly stable conditions may become unreliable. The authors apply a statistical clustering methodology based on a bounded variation, finite-element method (FEM-BV) to characterize the interaction between small-scale nonturbulent motions and turbulence. The clustering methodology achieves a multiscale representation of nonstationary turbulence data by approximating them through an optimal sequence of locally stationary multivariate autoregressive factor model (VARX) processes and some slow hidden process switching between them. The clustering method is used to separate periods with different influence of the nonturbulent motions on the vertical velocity fluctuations. The methodology can be used in a later stage to derive a stochastic parameterization for the interactions between nonturbulent and turbulent motions.

Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

2013 ◽  
Vol 17 (14) ◽  
pp. 1-22 ◽  
Author(s):  
Allison L. Steiner ◽  
Dori Mermelstein ◽  
Susan J. Cheng ◽  
Tracy E. Twine ◽  
Andrew Oliphant
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Latent Heat ◽  
Atmospheric Aerosols ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Environmental Drivers ◽  
Sensible Heat

Abstract Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

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