Effect of Secondary Circulations on the Surface–Atmosphere Exchange of Energy at an Isolated Semi-arid Forest

Kröniger, Konstantin; Roo, Frederik De; Brugger, Peter; Huq, S.; Banerjee, Tirtha; Zinsser, Judith P.; Rotenberg, Eyal; Yakir, Dan; Rohatyn, Shani; Mauder, Matthias

doi:10.1007/s10546-018-0370-6

Cited by 15 publications

(11 citation statements)

References 64 publications

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“…However, as we go up above roughly 100 m, this behavior flips. Lastly, Kröniger et al (2018) found in his simulations that large rotational systems developed at specific locations connected to surface features. Therefore, we conclude that the bulk transport in the convective mixed layer by a secondary circulation is from the forest to the desert, but it is advected with the mean wind and heavily influenced by surface features on a smaller scale than the forest itself.…”

Section: Discussionmentioning

confidence: 97%

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Turbulent transport of energy across a forest and a semiarid shrubland

et al. 2018

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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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Section: Discussionmentioning

confidence: 97%

“…Moreover, a different set of coordinate rotation is applied for the desert data after 23 August. In addition, two Doppler lidars were used at the two locations which measured vertical velocities Kröniger et al, 2018). The Doppler lidars used were StreamLine systems from HaloPhotonics.…”

Section: Research Sitementioning

confidence: 99%

Turbulent transport of energy across a forest and a semiarid shrubland

et al. 2018

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“…To compute the mechanical production term, we momentarily assume that the TKE budget is well balanced and Monin-Obukhov similarity theory (MOST) (Monin and Obukhov, 1954) is valid (Kaimal and Finnigan, 1994;Banerjee et al, 2016;Li et al, 2016). This allows us to write…”

Section: Theorymentioning

confidence: 99%

“…The buoyancy term can directly be computed from the EC measurements as well. To compute the dissipation term , we use the scaling relation of second-order structure function (Salesky et al, 2013;Banerjee et al, 2015Banerjee et al, , 2016Li et al, 2016)…”

Section: Theorymentioning

confidence: 99%

Response to comments by reviewer 1, Prof. Gil Bohrer.

Banerjee¹

2018

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“…Patton et al (2016Patton et al ( ) used (2048Patton et al ( , 2048Patton et al ( , 1024 grid points with a grid resolution of (2.5, 2.5, 2) m to study the influence of atmospheric stability on canopy turbulence. More recently, with the help of supercomputers, Kröniger et al (2018) used 13 • 10 9 grid points to simulate a domain of 30.72 km × 15.36 km × 2.56 km to study the influence of wind speeds on the surface-atmosphere exchange and the role of secondary circulations in the energy exchange. The atmospheric boundary-layer community has greatly benefited from the higher detail available in these LES to study turbulent processes that cannot be measured in the field in three-dimensional detail.…”

Section: Introductionmentioning

confidence: 99%

Vertically nested LES for high-resolution simulation of the surface layer in PALM (version 5.0)

Huq¹,

Roo²,

Raasch³

et al. 2018

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Abstract. Large-eddy simulation (LES) has become a well-established tool in the atmospheric boundary-layer research community to study turbulence. It allows three-dimensional realizations of the turbulent fields, which large-scale models and most experimental studies cannot yield. To resolve the largest eddies in the mixed layer, a moderate grid resolution in the range of 10 to 100 m is often sufficient, and these simulations can be run on a computing cluster with few hundred processors, or even on a workstation for simple configurations. The desired resolution is usually limited by the computational resources. However, to compare with tower measurements of turbulence and exchange fluxes in the surface layer a much higher resolution is required. In spite of the growth in computational power, a high-resolution simulation LES of the surface layer is often not feasible: to fully resolve the energy containing eddies near the surface a grid spacing of O(1 m) is required. One way to tackle this problem is to employ a vertical grid nesting technique, where the surface is simulated at the necessary fine grid resolution, and it is coupled with a standard, coarse, LES that resolves the turbulence in the whole boundary-layer. We modified the LES model PALM (Parallelized Large-eddy simulation Model) and implemented a two-way nesting technique, with coupling in both directions between the coarse and the fine grid. The coupling algorithm has to ensure correct boundary conditions for the fine grid. Our nesting algorithm is realized by modifying the standard third order Runge-Kutta time stepping to allow communication of data between the two grids. The two grids are concurrently advanced in time while ensuring that the sum of resolved and subgrid-scale kinetic energy is conserved. We design a validation test and show that the temporal averaged profiles from the fine grid agree well compared to the reference simulation with high-resolution in the entire domain. The overall performance and scalability of the nesting algorithm is found to be satisfactory. Our nesting results in more than 80 percent savings in computational power for 5 times higher resolution in each direction in the surface layer.

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Effect of Secondary Circulations on the Surface–Atmosphere Exchange of Energy at an Isolated Semi-arid Forest

Cited by 15 publications

References 64 publications

Turbulent transport of energy across a forest and a semiarid shrubland

Turbulent transport of energy across a forest and a semiarid shrubland

Response to comments by reviewer 1, Prof. Gil Bohrer.

Vertically nested LES for high-resolution simulation of the surface layer in PALM (version 5.0)

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