Turbulent transport of energy across a forest and a semiarid shrubland

Abstract. The role of secondary circulations has recently been studied in the context of well-defined surface heterogeneity in a semiarid ecosystem where it was found that energy balance closure over a desert–forest system and the structure of the boundary layer was impacted by advection and flux divergence. As a part of the CliFF (“Climate feedbacks and benefits of semi-arid forests”, a collaboration between KIT, Germany, and the Weizmann Institute, Israel) campaign, we studied the boundary layer dynamics and turbulent transport of energy corresponding to this effect in Yatir Forest situated in the Negev Desert in Israel. The forest surrounded by small shrubs presents a distinct feature of surface heterogeneity, allowing us to study the differences between their interactions with the atmosphere above by conducting measurements with two eddy covariance (EC) stations and two Doppler lidars. As expected, the turbulence intensity and vertical fluxes of momentum and sensible heat are found to be higher above the forest compared to the shrubland. Turbulent statistics indicative of nonlocal motions are also found to differ over the forest and shrubland and also display a strong diurnal cycle. The production of turbulent kinetic energy (TKE) over the forest is strongly mechanical, while buoyancy effects generate most of the TKE over the shrubland. Overall TKE production is much higher above the forest compared to the shrubland. The forest is also found to be more efficient in dissipating TKE. The TKE budget appears to be balanced on average both for the forest and shrubland, although the imbalance of the TKE budget, which includes the role of TKE transport, is found to be quite different in terms of diurnal cycles for the forest and shrubland. The difference in turbulent quantities and the relationships between the components of TKE budget are used to infer the characteristics of the turbulent transport of energy between the desert and the forest.

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Turbulent transport of energy across a forest and a semi-arid shrubland

10.5194/acp-2017-159 ◽

2017 ◽

Cited By ~ 2

Author(s):

Tirtha Banerjee ◽

Peter Brugger ◽

Frederik De Roo ◽

Konstantin Kröniger ◽

Dan Yakir ◽

...

Keyword(s):

Boundary Layer ◽

Turbulent Transport ◽

Longitudinal Velocity ◽

Atmospheric Stability ◽

Surface Heterogeneity ◽

Flux Divergence ◽

Diurnal Cycles ◽

Turbulent Statistics ◽

Semi Arid

Abstract. The role of secondary circulations has recently been studied in the context of well defined surface heterogeneity in a semi-arid ecosystem where it was found that energy balance closure over a desert-forest system and the structure of the boundary layer was impacted by advection and flux divergence. As a part of the CliFF (Climate Feedbacks and benefits of semi-arid forests, a collaboration between KIT, Germany and the Weizmann Institute, Israel) campaign, we studied the boundary layer dynamics and turbulent transport of energy corresponding to this effect in the Yatir forest situated in the Negev desert in Israel. The forest surrounded by small shrubs presents a distinct feature of surface heterogeneity, allowing us to study the differences between their interactions with the atmosphere above by conducting measurements with two EC stations and two Doppler LiDARs. As expected, the turbulence intensity and vertical fluxes of momentum and sensible heat are found to be higher above the forest compared to the shrubland. Turbulent statistics indicative of nonlocal motions are also found to differ over the forest and shrubland and also display a strong diurnal cycle. The production of turbulent kinetic energy (TKE) over the forest is strongly mechanical, while buoyancy effects generate most of the TKE over the shrubland. Overall TKE production is much higher above the forest compared to the shrubland. The forest is also found to be more efficient in dissipating TKE. The TKE budget appears to be balanced on average both for the forest and shrubland, although the imbalance of the TKE budget, which contains the role of TKE transport, is found to be quite different in terms of their variation with atmospheric stability and diurnal cycles for the forest and shrubland. The effect of very large mesoscale motions is also directly quantified following a recent formulation by Banerjee and Katul, 2013, using the measured longitudinal velocity variances and boundary layer heights. The difference of turbulent quantities and the relationships between the components of TKE budget are used to infer the characteristics of turbulent transport of energy between the desert and the forest.

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Comparison of aerosol properties from the Indian Himalayas and the Indo-Gangetic plains

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-11417-2011 ◽

2011 ◽

Vol 11 (4) ◽

pp. 11417-11453 ◽

Cited By ~ 10

Author(s):

T. Raatikainen ◽

A.-P. Hyvärinen ◽

J. Hatakka ◽

T. S. Panwar ◽

R. K. Hooda ◽

...

Keyword(s):

Boundary Layer ◽

Monsoon Season ◽

Data Sets ◽

New Delhi ◽

Gangetic Plains ◽

Diurnal Cycles ◽

Measurement Site ◽

Background Measurement ◽

The Difference ◽

Boundary Layer Dynamics

Abstract. Gual Pahari is a polluted semi-urban background measurement site at the Indo-Gangetic plains close to New Delhi and Mukteshwar is a relatively clean background measurement site at the foothills of the Himalayas about 270 km NE from Gual Pahari and about 2 km above the nearby plains. Two years long data sets including aerosol and meteorological parameters as well as modeled backward trajectories and boundary layer heights were compared. The purpose was to see how aerosol concentrations vary between clean and polluted sites not very far from each other. Specifically, we were exploring the effect of boundary layer evolution on aerosol concentrations. The measurements showed that especially during the coldest winter months, aerosol concentrations are significantly lower in Mukteshwar. On the other hand, the difference is smaller and also the concentration trends are quite similar from April to October. With the exception of the monsoon season, when rains are affecting on aerosol concentrations, clear but practically opposite diurnal cycles are observed. When the lowest daily aerosol concentrations are seen during afternoon hours in Gual Pahari, there is a peak in Mukteshwar aerosol concentrations. In addition to local sources and long-range transport of dust, boundary layer dynamics can explain the observed differences and similarities. When mixing of air masses is limited during the relatively cool winter months, aerosol pollutions are accumulated to the plains, but Mukteshwar is above the pollution layer. When mixing increases in the spring, aerosol concentrations are increased in Mukteshwar and decreased in Gual Pahari. The effect of mixing is also clear in the diurnal concentration cycles. When daytime mixing decreases aerosol concentrations in Gual Pahari, those are increased in Mukteshwar.

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Surface heterogeneity impacts on boundary layer dynamics via energy balance partitioning

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-17815-2010 ◽

2010 ◽

Vol 10 (7) ◽

pp. 17815-17851 ◽

Cited By ~ 1

Author(s):

N. A. Brunsell ◽

D. B. Mechem ◽

M. C. Anderson

Keyword(s):

Boundary Layer ◽

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Surface Heterogeneity ◽

Length Scales ◽

Surface Conditions ◽

Boundary Layer Dynamics

Abstract. The role of land-atmosphere interactions under heterogeneous surface conditions is investigated in order to identify mechanisms responsible for altering surface heat and moisture fluxes. Twelve coupled land surface – large eddy simulation scenarios with four different length scales of surface variability under three different horizontal wind speeds are used in the analysis. The base case uses Landsat ETM imagery over the Cloud Land Surface Interaction Campaign (CLASIC) field site for 3 June 2007. Using wavelets, the surface fields are band-pass filtered in order to maintain the spatial mean and variances to length scales of 200 m, 1600 m, and 12.8 km as lower boundary conditions to the model. The simulations exhibit little variation in net radiation. Rather, a change in the partitioning of the surface energy between sensible and latent heat flux is responsible for differences in boundary layer dynamics. The sensible heat flux is dominant for intermediate surface length scales. For smaller and larger scales of surface heterogeneity, which can be viewed as being more homogeneous, the latent heat flux becomes increasingly important. The results reflect a general decrease of the Bowen ratio as the surface conditions transition from heterogeneous to homogeneous. Air temperature is less sensitive to surface heterogeneity than water vapor, which implies that the role of surface heterogeneity in modifying the local temperature gradients in order to maximize convective heat fluxes. More homogeneous surface conditions, on the other hand, tend to maximize latent heat flux. Scalar vertical profiles respond predictably to the partitioning of surface energy. Fourier spectra of the vertical wind speed, air temperature and specific humidity (w, T and q) and associated cospectra (w'T', w'q' and T'q'), however, are insensitive to the length scale of surface heterogeneity, but the near surface spectra are sensitive to the mean wind speed.

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Response of a tropical cyclone to a subsurface ocean eddy and the role of boundary layer dynamics

Quarterly Journal of the Royal Meteorological Society ◽

10.1002/qj.4210 ◽

2021 ◽

Author(s):

Arjun U. Kumar ◽

Nils Brüggemann ◽

Roger K. Smith ◽

Jochem Marotzke

Keyword(s):

Boundary Layer ◽

Tropical Cyclone ◽

Subsurface Ocean ◽

Boundary Layer Dynamics

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Surface Temperature Variations in East Africa and Possible Causes

Journal of Climate ◽

10.1175/2008jcli2726.1 ◽

2009 ◽

Vol 22 (12) ◽

pp. 3342-3356 ◽

Cited By ~ 73

Author(s):

John R. Christy ◽

William B. Norris ◽

Richard T. McNider

Keyword(s):

Boundary Layer ◽

Time Series ◽

East Africa ◽

Mount Kilimanjaro ◽

Uncertainty Estimates ◽

Break Points ◽

The Difference ◽

Boundary Layer Dynamics ◽

Climate Analysis

Abstract Surface temperatures have been observed in East Africa for more than 100 yr, but heretofore have not been subject to a rigorous climate analysis. To pursue this goal monthly averages of maximum (TMax), minimum (TMin), and mean (TMean) temperatures were obtained for Kenya and Tanzania from several sources. After the data were organized into time series for specific sites (60 in Kenya and 58 in Tanzania), the series were adjusted for break points and merged into individual gridcell squares of 1.25°, 2.5°, and 5.0°. Results for the most data-rich 5° cell, which includes Nairobi, Mount Kilimanjaro, and Mount Kenya, indicate that since 1905, and even recently, the trend of TMax is not significantly different from zero. However, TMin results suggest an accelerating temperature rise. Uncertainty estimates indicate that the trend of the difference time series (TMax − TMin) is significantly less than zero for 1946–2004, the period with the highest density of observations. This trend difference continues in the most recent period (1979–2004), in contrast with findings in recent periods for global datasets, which generally have sparse coverage of East Africa. The differences between TMax and TMin trends, especially recently, may reflect a response to complex changes in the boundary layer dynamics; TMax represents the significantly greater daytime vertical connection to the deep atmosphere, whereas TMin often represents only a shallow layer whose temperature is more dependent on the turbulent state than on the temperature aloft. Because the turbulent state in the stable boundary layer is highly dependent on local land use and perhaps locally produced aerosols, the significant human development of the surface may be responsible for the rising TMin while having little impact on TMax in East Africa. This indicates that time series of TMax and TMin should become separate variables in the study of long-term changes.

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EFFECT OF REYNOLDS NUMBER ON THE SUCTION INFLUENCE ON THE TURBULENT BOUNDARY LAYER STRUCTURES

Revista de Engenharia Térmica ◽

10.5380/reterm.v6i2.61692 ◽

2007 ◽

Vol 6 (2) ◽

pp. 62

Author(s):

M. O. Oyewola

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Turbulent Boundary Layer ◽

Large Scale ◽

Turbulent Transport ◽

Turbulence Statistics ◽

Third Order ◽

Actual Mechanism ◽

Layer Structures ◽

Turbulent Statistics

The effect of Reynolds number on the influence of suction on the turbulentboundary layer structures has been quantified through the measurements ofthird- and fourth-order turbulence statistics for several suction rates and streamwise locations downstream of the suction strip. Third- and fourthorderturbulence statistics are more sensitive to a change in boundary condition than second-order moments. The data of the third-order turbulent statistics reveal an alteration in the turbulent transport as a result of the manipulation of the organised motion by suction. The alteration is increased as the suction rate is increased but reduces as the Reynolds number is increased. The results support that, relative to no suction case, Reynolds number modulates the behaviour of higher-order turbulent statistics without changing the actual mechanism of suction on the boundary layer. In general, it is proposed that Reynolds number effect on suction influence in a turbulent boundary layer is universal for the large-scale quantities. This argument is supported by the behaviour of root mean square fluctuating spanwise vorticity.

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Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-19247-2014 ◽

2014 ◽

Vol 14 (13) ◽

pp. 19247-19291 ◽

Cited By ~ 9

Author(s):

H. Pietersen ◽

J. Vilà-Guerau de Arellano ◽

P. Augustin ◽

O. de Coster ◽

H. Delbarre ◽

...

Keyword(s):

Boundary Layer ◽

Large Scale ◽

Surface Heterogeneity ◽

Small Scale ◽

Mountain Range ◽

Convective Boundary ◽

Good Correspondence ◽

Data Set ◽

Boundary Layer Height ◽

Boundary Layer Dynamics

Abstract. We study the disturbances of CBL dynamics due to large-scale atmospheric contributions for a representative day observed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) campaign. We first reproduce the observed boundary-layer dynamics by combining the Dutch Atmospheric Large-Eddy Simulation (DALES) model with a mixed-layer theory based model. We find that by only taking surface and entrainment fluxes into account, the boundary-layer height is overestimated by 70%. If we constrain our numerical experiments with the BLLAST comprehensive data set, we are able to quantify the contributions of advection of heat and moisture, and subsidence. We find that subsidence has a clear diurnal pattern. Supported by the presence of a nearby mountain range, this pattern suggests that not only synoptic scales exert their influence on the boundary layer, but also mesoscale circulations. Finally, we study whether the vertical and temporal evolution of turbulent variables are influenced by these large-scale forcings. Our model results show good correspondence of the vertical structure of turbulent variables with observations. Our findings further indicate that when large-scale advection and subsidence are applied, the values for turbulent kinetic are lower than without these large-scale forcings. We conclude that the prototypical CBL can still be used as a valid representation of the boundary-layer dynamics near regions characterized by complex topography and small-scale surface heterogeneity, provided that surface- and large-scale forcings are well characterized.

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