Search

Measurements of three flux towers operated during the land atmosphere feedback experiment (LAFE) are used to investigate relationships between surface fluxes and variables of the land–atmosphere system. We study these relations by means of two machine learning (ML) techniques: multilayer perceptrons (MLP) and extreme gradient boosting (XGB). We compare their flux derivation performance with Monin–Obukhov similarity theory (MOST) and a similarity relationship using the bulk Richardson number (BRN). The ML approaches outperform MOST and BRN. Best agreement with the observations is achieved for the friction velocity. For the sensible heat flux and even more so for the latent heat flux, MOST and BRN deviate from the observations while MLP and XGB yield more accurate predictions. Using MOST and BRN for latent heat flux, the root mean square errors (RMSE) are 107 Wm - 2 and 121 Wm - 2 , respectively, as well as the intercepts of the regression lines are ≈ 110 Wm - 2 . For the ML methods, the RMSEs reduce to 31 Wm - 2 for MLP and 33 Wm - 2 for XGB as well as the intercepts to just 4 Wm - 2 for MLP and - 1 Wm - 2 for XGB with slopes of the regression lines close to 1, respectively. These results indicate significant deficiencies of MOST and BRN, particularly for the derivation of the latent heat flux. In fact, in contrast to the established theories, feature importance weighting demonstrates that the ML methods base their improved derivations on net radiation, the incoming and outgoing shortwave radiations, the air temperature gradient, and the available water contents, but not on the water vapor gradient. The results imply that further studies of surface fluxes and other turbulent variables with ML techniques provide great promise for deriving advanced flux parameterizations and their implementation in land–atmosphere system models. [ABSTRACT FROM AUTHOR]

Entrainment of density flows is a key parameter in constructing predictive models of global climate, ocean flows, and turbidity currents. Our numerical experiment, which included 10 subaqueous dilute density flows with a steady sustained inflow (SSI) on a 2D channel bed slope varying from 0.1° to 90°, showed that in the slope range of 0.1–20°, there is a linear relationship between the ambient fluid entrainment and channel bed slope. We also found a power law relation between the bulk Richardson number and bed slope. On a larger slope bed, these relations broke down due to the strong head drag, which suggests that there exists a regime change from bed-supported to plunging flows at around 20° for SSI density flows on a slope bed. These findings may provide a way to quickly evaluate or parameterize subaqueous SSI density flows in the suggested slope range. [ABSTRACT FROM AUTHOR]

The distribution of hurricane boundary layer heights (HBLHs) relative to the hurricane center is investigated in a composite framework, using total 2674 dropsondes collected within four times the radius of maximum wind speed (RMW) of 61 hurricanes during 2002–2020. The HBLH is computed by the bulk Richardson number (Ri b) method, which is sensitive to the critical Ri b choice and more reasonable when the surface friction effect is considered. The sea surface friction velocity is derived from the 10-m wind speed through an air-sea drag relation. The results show that the HBLH is significantly low in the eye zone (0–0.5 RMW), out of which the HBLH is highest in the gale region (0.5–1.5 RMW) and decreases with the radius to the hurricane center. Similar to the hurricane wind field asymmetry, the HBLH is generally higher in the right than in the left in relation to the hurricane motion direction. ERA5 generally overestimates the HBLH, but substantially underestimates the higher HBLHs around the RMW, showing different variation of HBLHs along with the radius compared to dropsonde observations. According to linear regression analyses, the HBLH at least determined by the Ri b method is importantly affected by the hurricane boundary layer dynamic factor, while has no significant correlation with the thermal factor. • The HBLH by the Ri b method is sensitive to considering surface friction effect or not. • The HBLH distribution is asymmetric relative to the hurricane motion direction. • The HBLH is highly correlated with the hurricane boundary layer dynamic factor. [ABSTRACT FROM AUTHOR]

A non-iterative analytical scheme is developed for unstable stratification that parametrizes the Monin-Obukhov stability parameter $$\zeta $$ ( $${=}z{/}L$$ , where z is the height above the ground and L is the Obukhov length) in terms of bulk Richardson number ( $$Ri_B$$ ) within the framework of Businger-Dyer type similarity functions. The proposed scheme is valid for a wide range of roughness lengths of heat and momentum. The absolute relative error in the transfer coefficients of heat and momentum is found to be less than 1.5% as compared to those obtained from an iterative scheme for Businger-Dyer type similarity functions. An attempt has been made to extend this scheme to incorporate the similarity functions having a theoretically consistent free convection limit. Further, the performance of the scheme is evaluated using observational data from two different sites. The proposed scheme is simple, non-iterative and relatively more accurate compared to the schemes reported in the literature and can be used as a potential alternative to iterative schemes used in numerical models of the atmosphere. [ABSTRACT FROM AUTHOR]

Wave and current supported gravity flows (WCSGFs) carry substantial fine-grained sediment across gently sloping seabeds of coastal and shelf waters, representing a primary mechanism of sediment transport. An existing buoyancy-friction model, which considers the important parameters of drag coefficient (C D) and bulk Richardson number (Ri b), has been widely used to analyze WCSGF dynamics. However, an improved validation of the two parameters on the basis of in situ measurements is still outstanding. Here, we analyze 23 short-lived WCSGF events that were recorded at the shallow sea floor of a muddy open coast to quantify the parameters. The C D values, as defined in the buoyancy-friction model, were found to be around 0.02 and 0.01 for early flood and ebb phases of the tide, respectively, which are significantly larger than the range of 0.001–0.006 reported elsewhere from in situ observations, numerical simulations and laboratory experiments. The calculations of Ri b from our WCSGF observations were all close to the critical value of 0.25, which supports the use of such a value in WCSGF models. Large C D values of our observed WCSGFs imply that strong currents can dilute the high-concentration layer and slow down the movement of WCSGFs, which reveals a remarkable difference between WCSGFs and gravity flows supported by waves alone. • An existing buoyancy-friction model is used to determine the drag coefficient (C D). • Strong currents dilute the high-concentration layer to enhance the C D. • The critical bulk Richardson number is close to 0.25. [ABSTRACT FROM AUTHOR]

A turbulence parametrization for wind speed in the stable boundary layer consisting of a single empirical parameter is proposed without the use of the eddy viscosity concept or turbulent kinetic energy equation. Instead, a drag-coefficient-type formulation as a function of the bulk Richardson number has been found to be able to reproduce observed stable boundary-layer wind speeds as effectively as a model based on the eddy viscosity approach. The advantage of this simpler approach is that the model can, in theory, be modified more easily for certain applications, such as the effects of large-scale wind parks on mesoscale meteorology. [ABSTRACT FROM AUTHOR]

A semi-analytical scheme is proposed to parametrize the Obukhov stability parameter $$\zeta $$ (= $$z/L$$ ; $$z$$ is the height above the ground and $$L$$ is the Obukhov length) in terms of the bulk Richardson number ( $$R_{iB}$$ ) in unstable conditions within the framework of Monin-Obukhov similarity (MOS) theory. The scheme involves, (i) a solution of a cubic equation in $$\zeta $$ whose coefficients depend on the gradient Richardson number ( $$R_{i}$$ ), and (ii) a relationship between $$R_{i}$$ and $$R_{iB}$$ . The proposed scheme is applicable for a wide range (i) $$-5\le R_{iB}\le 0$$ , (ii) $$0\le \hbox {ln}(z_{0}/z_{h})\le 29.0$$ , and (iii) $$10\le z/z_{0}\le 10^{5}$$ and performs relatively better than all other schemes in terms of accuracy in computation of surface-layer transfer coefficients. The absolute errors in computing the transfer coefficients do not exceed 7 %. The analysis presented here is found to be valid for different $$\gamma _{m}$$ and $$\gamma _{h}$$ appearing in the expressions of the similarity functions $$\varphi _{m}$$ and $$\varphi _{h}$$ (representing non-dimensional wind and temperature profiles), so long as the ratio of $$\gamma _{m}$$ to $$\gamma _{h} \ge 1$$ . The improved scheme can be easily employed in atmospheric modelling for a comprehensive range of $$R_{iB}$$ and a variety of surfaces. [ABSTRACT FROM AUTHOR]

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 ( $$0 < D_{rb} < 1$$ 0 < D r b < 1 ) based on the 2–50 m bulk gradient of the ubiquitous natural trace gas radon-222. The relationship between $$D_{rb}$$ D r b and the bulk Richardson number ( $$R_{ib}$$ R i b ) exhibits three broad regions: (1) a well-mixed region ( $$D_{rb} \approx 0.05$$ D r b ≈ 0.05 ) in weakly stable conditions ( $$R_{ib} < 0.03$$ R i b < 0.03 ); (2) a steeply increasing region ( $$0.05 < D_{rb} < 0.9$$ 0.05 < D r b < 0.9 ) for “transitional” stabilities ( $$0.03 < R_{ib} < 1$$ 0.03 < R i b < 1 ); and (3) a decoupled region ( $$D_{rb} \approx 0.9$$ D r b ≈ 0.9 –1.0) in very stable conditions ( $$R_{ib} > 1$$ R i b > 1 ). $$D_{rb}$$ D r b exhibits a large variability within individual $$R_{ib}$$ R i b bins, however, due to a range of competing processes influencing bulk mixing under different conditions. To explore these processes in $$R_{ib}$$ R i b – $$D_{rb}$$ D r b 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 $$R_{ib}$$ R i b – $$D_{rb}$$ D r b 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 $$R_{ib}$$ R i b – $$D_{rb}$$ D r b space, it is seen that very different turbulence regimes can occur for the same value of $$R_{ib}$$ R i b , 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 $$R_{ib} > 1$$ R i b > 1 and $$D_{rb} \approx 1$$ D r b ≈ 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 ( $$D_{rb} < 0.7$$ D r b < 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 $$R_{ib}$$ R i b – $$D_{rb}$$ D r b 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. [ABSTRACT FROM AUTHOR]

Abstract: Spatial and temporal variabilities in the vertical structure of Marine Atmospheric Boundary Layer (MABL) over the Bay of Bengal (BoB) are investigated through a ship-borne field experiment measurements pertaining to three different classes, namely: night, morning and afternoon conditions. High-resolution vertical profiles of meteorological parameters obtained through balloon-borne GPS Sondes during the Winter phase of Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) formed the primary database for the present investigation. The study advocates usage of wind shear profiles in association with virtual potential temperature (θ v ) and specific humidity (q) profiles for determination of the mixed layer heights (MLH). The mean values of turbulent flow thickness (TFT) obtained from the vertical profiles of Bulk Richardson Number (Ri B ) and MLH magnitudes for the entire cruise did not show any appreciable variations for three classes. During the entire cruise period, the MLH varied in a range from 450m to 1500m with a mean of about 900m, whereas the TFT variations were confined between 125m and 1475m with a mean of about 581m. The statistical means of TFT and MLH were similar for nighttime profiles, whereas they showed significant differences in the morning and afternoon conditions. Spatio-temporal variability in the MLH showed good correlation with the surface-layer sensible heat flux which is one of the driving mechanisms in mixing processes. [Copyright &y& Elsevier]

model was developed to predict the modification with fetch in offshore flow of mixing ratio, air-water exchange flux, and near-surface vertical gradients in mixing ratio of a scalar due to air-water exchange. The model was developed for planning and interpretation of air-water exchange flux measurements in the coastal zone. The Lagrangian model applies a mass balance over the internal boundary layer (IBL) using the integral depth scale approach, previously applied to development of the nocturnal boundary layer overland. Surface fluxes and vertical profiles in the surface layer were calculated using the NOAA COARE bulk algorithm and gas transfer model (e.g., Blomquist et al. , Geophys Res Lett 33:1-4). IBL height was assumed proportional to the square root of fetch, and estimates of the IBL growth rate coefficient, α, were obtained by three methods: (1) calibration of the model to a large dataset of air temperature and humidity modification over Lake Ontario in 1973, (2) atmospheric soundings from the 2004 New England Air Quality Study and (3) solution of a simplified diffusion equation and an estimate of eddy diffusivity from Monin-Obukhov similarity theory (MOST). Reasonable agreement was obtained between the calibrated and MOST values of α for stable, neutral, and unstable conditions, and estimates of α agreed with previously published parametrizations that were valid for the stable IBL only. The parametrization of α provides estimates of IBL height, and the model estimates modification of scalar mixing ratio, fluxes, and near-surface gradients, under conditions of coastal offshore flow (0-50 km) over a wide range in stability. [ABSTRACT FROM AUTHOR]

Utilizing the data of the intensive observation period (May-June 2000) of the Dunhuang land-surface process field experiment supported by the 'Atmosphere-land Interactive Field Experiment over Arid Regions of Northwest China(NWC-ALIEX)', the bulk momentum transfer coefficient ( C) and the bulk sensible heat transfer coefficient ( C) between the surface and the atmosphere over the arid Gobi Desert region are determined using three different methods. The results indicate that these coefficients, especially the means, are the same order of magnitude. The influence of the building near the observational station on the results is significant. When the building effect exists, the diurnal variation of the atmospheric bulk transfer coefficients and the bulk Richardson number are irregular. After the building effect is eliminated through analysing the wind direction, the bulk Richardson number and the range of the typical values of the bulk transfer coefficients over the Gobi are obtained. The diurnal variations of the bulk transfer coefficients are smoother than that without the building affect. The bulk transfer coefficients are larger in the daytime than in the nighttime. It is also worth noting that the variations of the bulk transfer coefficients and the bulk Richardson number are just opposite in phase, and that the bulk transfer coefficient for sensible heat flux is more related to the bulk Richardson number than that for momentum flux. The results are more reasonable than that after removing the building effect. The relation between the bulk transfer coefficients is also discussed. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The computation of surface fluxes by Monin-Obukhov similarity theory with different linear/non-linear similarity functions for non-dimensional wind and temperature profiles becomes limited to specific ranges of ζ =z/L (where z is the height above ground and L is the Obukhov length) and bulk Richardson number (RiB) under very stable conditions. A systematic mathematical analysis is carried out to estimate the upper bounds of z and RiB for the extent of applicability of different non-linear similarity functions in the surface layer under these conditions. A generalized methodology is proposed on the basis of momentum drag coefficient (CD) and heat exchange coefficient (CH) and applied to various non-linear similarity functions available in the literature. A theoretically derived criterion for the applicability of each of the non-linear similarity function is evaluated with observations from Cooperative Atmosphere-Surface Exchange Study-99 and UK Meteorological Office's Cardington datasets. The evaluation with both datasets for each non-linear similarity function confirms the validity of proposed theoretical results under very stable conditions. [ABSTRACT FROM AUTHOR]

Abstract: The linear functional forms of universal similarity functions (Φ m and Φ h) are commonly used to compute the surface layer fluxes. The applicability of these forms is limited [Sharan, M., Rama Krishna, T.V.B.P.S. and Aditi: 2003a, ‘On the bulk Richardson number and flux-profile relations in an atmospheric surface layer under weak wind stable conditions’, Atmos. Environ. 37, 3681–3691.] to R iB < Pr t γ / β 2 where R iB is bulk Richardson number, Pr t is turbulent Prandtl number and β and γ are constants appearing in the linear forms of Φ m and Φ h. Values of R iB larger than Pr t γ / β 2 are often observed in the observational studies especially in weak wind stable conditions. Thus, a mathematical analysis is carried out to estimate the upper bound of R iB and stability parameter z / L (where z is the height above the ground and L is Obukhov length) for the applicability of a non-linear functional form of the similarity function proposed by Webb [Webb, E.K.: 1970, ‘Profile relationships: the log-linear range, and extension to strong stability’, Quart. J. Roy. Meteorol. Soc. 96, 67–90.] in stable conditions. The upper bounds are estimated by analyzing the behaviour of momentum drag coefficient in weak wind stable conditions. It is shown that Webb''s formulation is applicable in the surface layer as long as z / L ≤ z / z 0 and (where z 0 is roughness length). [Copyright &y& Elsevier]

Abstract: A nomogram was prepared by [Golder, 1972. Boundary Layer Meteorology 3, 47–58] to compute the surface layer parameters in stable conditions. This note revisits the Golder''s curves and examines the methodology underlying their derivation in stable conditions. The inherent limitation in the methodology used for construction of Golder''s curves was also noticed by Trombetti et al. (1986). Surface layer fluxes computed using the parameters derived from modified curves are found to be closer to the turbulence measurements from CASES-99 experiment for stable conditions than those calculated from the [Golder, 1972. Boundary Layer Meteorology 3, 47–58] curves. [Copyright &y& Elsevier]

Wind speed profiles above a forest canopy relate to scalar exchange between the forest canopy and the atmosphere. Many studies have reported that vertical wind speed profiles above a relatively flat forest can be classified by a stability index developed assuming wind flow above a flat plane. However, can such a stability index be used to classify vertical wind speed profiles observed above a sloping forest at nighttime, where drainage flow often occurs? This paper examines the use of the bulk Richardson number to classify wind speed profiles observed above a sloping forest at nighttime. Wind speed profiles above a sloping forest were classified by the bulk Richardson numberRi B. Use ofRi B distinguished between drainage flow, shear flow, and transitional flow from drainage flow to shear flow. These results suggest thatRi B is useful to interpret nighttime CO2 and energy fluxes above a sloping forest. Through clear observational evidence, we also show that the reference height should be high enough to avoid drainage-flow effects when calculatingRi B. [ABSTRACT FROM AUTHOR]

For describing the surface fluxes in the atmospheric dispersion models, the commonly used linear universal similarity functions φm and φh for nondimensional wind and temperature profiles (J. Atmos. Sci. 28 (1971) 181; Boundary-Layer Meteorol. 7 (1974) 363) are analyzed under weak wind stable conditions. The stability parameter z/L (z is the height above the ground and L is the Obukhov length) is not known a priori. On the other hand, the bulk Richardson number (RiB) is readily available from profile measurements. Thus, a systematic mathematical analysis is carried out to analyze the applicability of the linear functions in terms of RiB. These linear functions are found to be valid as long as RiB is smaller than Prt γ/β2 where Prt is the turbulent Prandtl number and β and γ are constants appearing in the linear functions of φm and φh. The linear functional forms for φm and φh underestimate the Obukhov length resulting in the large value of the stability parameter when RiB&ges;Prt γ/β2 occurring in weak wind stable conditions.Using the data from plume validation field experiment conducted by Electric Power Research Institute at Kincaid, it is found that in 70% of the weak wind cases, the RiB is larger than Prt γ/β2. The similarity functions proposed by Beljaars and Holtslag (J. Appl. Meteorol. 30 (1991) 327) are shown to perform well in weak wind stable conditions for all the values of RiB. The computed surface fluxes are also compared with those based on turbulence measurements taken in Cooperative Atmospheric Surface Exchange Study. [Copyright &y& Elsevier]

An extensive meteorological dataset obtained from the plume validation experiment conducted by the Electric Power Research Institute (EPRI) at Kincaid during 1980–1981 is analysed for studying the characteristic differences in the surface-layer parameters in strong and weak wind stable conditions. The surface-layer parameters are computed using the similarity functions φm and φh proposed by Beljaars and Holtslag. The weak winds are characterized using the geostrophic wind speed as well as the wind speed at the 10-m level. The surface fluxes are found to be finite in weak wind conditions. Empirical formulations for the eddy diffusivities of momentum (KM) and heat (KH), and drag (CD) and heat exchange (CH) coefficients, as power law functions of the bulk Richardson number (RiB), are proposed under both strong and weak wind conditions. Results are close to those based on observations taken from the Indian Institute of Technology low wind diffusion experiment, the Land surface processes experiment, the Hanford diffusion experiment, the Cabauw field experiment and the Cooperative Atmospheric Surface Exchange Study 1999 (CASES-99) experiment. In addition, the fluxes obtained from the proposed empirical relations are in good agreement with those based on similarity theory as well as the turbulence measurements taken from the CASES-99 experiment. [ABSTRACT FROM AUTHOR]

Currently used and newly proposed calculation techniques for the height of the stable boundary layer (SBL), including the bulk-Richardson-number method, diagnostic equations for the equilibrium SBL height, and a relaxation-type prognostic equation, are discussed from the point of view of their physical basis and relevance to experimental data. Among diagnostic equations, the best fit to data exhibits an advanced Ekman-layer height model derived recently with due regard to the role of the free-flow stability. Its extension to non-steady regimes provides a prognostic equation recommended for use in practical applications. [ABSTRACT FROM AUTHOR]

A long-term record (1964–1995) of radiosonde data observed at the Bet-Dagan aerological station of the Israel Meteorological Service was analyzed to detect possible temporal trends in moisture content and instability of the atmospheric boundary layer. Bet-Dagan is situated in the central part of the south-east Mediterranean coastal plain. During this period surface characteristics in this region have changed drastically due to changes in land use, i.e., urbanization, development of irrigated agriculture and afforestation. The analysis of the radiosonde data reveals a clearly defined, statistically significant, increasing trend in the moisture content, mainly during summer. The stability of the surface layer, characterized by the bulk Richardson Number, shows a decreasing trend since the early 1960s. Relationships between these trends, land-use modifications and possible influence of large-scale influence are discussed. [ABSTRACT FROM AUTHOR]

An approximate method for calculating the relationship between z/L (z = reference height, L = Obukhov length) and the bulk Richardson number is presented. If this relationship is known, the momentum and heat fluxes can be computed easily without any iteration. The avoidance of iteration can speed up computations in large-scale models considerably (up to 10 times) and cases which do not converge or converge very slowly cannot occur. The proposed formulae take into account the difference between momentum (z0M) and heat roughness lengths (z0H). Because the roughness lengths are not neglected at any step of the derivation, the resulting analytical formulae can be used not only between the surface and the reference height but also between two finite levels z1 and z2 (by replacing z0M and z0H by z1 and z by z2). The equations remain correct even in the limit z1→ z2.The formulae are based upon the (partially modified) Businger–Dyer flux–profile relationships and, consequently, they are restricted to predominantly homogeneous terrain. These new approximations are an improvement over the existing solutions because they are simpler than most of the formulae in the literature and are able to match the numerical exact solution for different parameter sets (Businger, Dyer, Högström) with an maximum error of about 2% for a wide range of z/L, z/z0M and z0M/z0H. Furthermore, in stable conditions, schemes with and without a finite critical bulk Richardson number can be approximated. The possible ambiguity of the exact solution ζ=f(RIB) in (moderately) stable conditions is discussed briefly. The performance of the new formulae is compared to the exact numerical solution and to different formulae proposed in the literature. [ABSTRACT FROM AUTHOR]

Simple analytic approximate solutions are presented for the set of equations that follows from the Monin–Obukhov flux-profile relationships using the stability functions of Dyer (unstable case) and Beljaars–Holtslag (stable case). Several publications are devoted to the same subject, however the current approach contains some new features, namely: (a) it appears to be more accurate for unstable situations and (b) it applies also to the general case where wind speed (u) and potential temperature (θ) are given at different levels. In order to illustrate the accuracy of the approach a comparison with the actual solutions is presented for some selected combinations of θ and u levels typical for various practical applications. [ABSTRACT FROM AUTHOR]

• Estimated wind, temperature and soil heat flux profiles are almost accurate without considering detail radiative forcing. • ABL height estimated by turbulence closure model and BRN approach are found statistically similar through copula analysis. • Sensitivity analysis reveals that surface condition are more critical against atmospheric condition for ABL height. In this paper, a numerical study has been carried out to assess changes in Atmospheric Boundary Layer (ABL) height under changing hydro-climatic conditions. ABL height is estimated by using the data from experiments conducted at three different sites- LAnd Surface Process EXperiment (LASPEX-97) in Sabarmati river basin, Gujarat, India, during 1997; Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) in Lannemezan, France, during 2011 and Integrated Global Radiosonde Archive (IGRA) in Tucson at Arizona, USA, during 2011. Here ABL height is estimated, during Intensive Observation Period (IOP), using 1-D turbulence closure model at all three site locations as well as following the Bulk Richardson Number (BRN) Approach. For LASPEX-97 only, the 1-D model with module for sub-surface processes coupled with upper-surface model is used for the estimation and compared with the only upper-surface model. ABL height, estimated by the coupled model, is found to be slightly higher than that by the un-coupled model. A copula-based analysis indicates that ABL height estimated by the 1-D model and same by BRN-based approach are statistically similar within 90% confidence interval (CI) under similar stratification condition. Thus, it validates the 1-D turbulence closure model for ABL height estimation. The sensitivity analysis of height of ABL, derived by 1-D model, against critical parameters reveals that surface condition (soil temperature) is more critical than atmospheric condition (net radiation) in forcing change on height of ABL in summer. [ABSTRACT FROM AUTHOR]