Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions

Zhong, Jian; Cai, Xiaoming; Xie, Zheng-Tong

doi:https://doi.org/10.5194/gmd-14-323-2021

Articles | Volume 14, issue 1

https://doi.org/10.5194/gmd-14-323-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-14-323-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 1

Development and technical paper

|

22 Jan 2021

Development and technical paper |

| 22 Jan 2021

Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions

Jian Zhong, Xiaoming Cai, and Zheng-Tong Xie

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Final revised paper (published on 22 Jan 2021)
Preprint (discussion started on 22 Jul 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Synthetic inflow turbulence generation for large-eddy simulations', Anonymous Referee #1, 27 Sep 2019
- AC1: 'Responses to comments from Referee #1', Jian Zhong, 15 Feb 2020
RC2: 'Comments on “Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions”', Anonymous Referee #2, 23 Nov 2019
- AC2: 'Responses to comments from Referee #2', Jian Zhong, 15 Feb 2020
RC3: 'Review of the manuscript GMD-2019-165: “Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions”', Anonymous Referee #3, 16 Dec 2019
- AC3: 'Responses to comments from Referee #3', Jian Zhong, 15 Feb 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Jian Zhong on behalf of the Authors (15 Feb 2020) Author's response Manuscript

ED: Reject (05 Mar 2020) by James Maddison

ED: Referee Nomination & Report Request started (27 Sep 2020) by James Maddison

RR by Anonymous Referee #3 (06 Oct 2020)

Suggestions for revision or reasons for rejection

Review of the revised manuscript GMD-2019-165: “Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions” by Jian Zhong, Xiaoming Cai1 and Zheng-Tong Xie submitted for publication in the journal Geoscientific Model Development.

In the revised manuscript “Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions” the authors have made relatively minor changes to the exposition of the methodology for generation of inflow turbulence for large-eddy simulations based on synthetic turbulence generation approach developed by Xie and Castro (2008) implemented in the Weather Research and Forecasting model. In addition, the results presented in the revised manuscript are improved in comparison to the original manuscript.

General Remarks

While, the revised manuscript includes improved results, the main deficiency of the manuscript remains – the synthetic inflow turbulence generation methodology developed by Xie and Castro (2008) was previously implemented in the Weather Research and Forecasting model by Muñoz-Esparza et al. (2015) and extensively tested. It is therefore not clear what new research is presented in this manuscript. One element that is explored in greater detail is integral length scale, however, the authors do not clearly articulate any potential differences in implementation or results of simulations. Furthermore, the authors claim that the simulations presented in the manuscript are of neutral atmospheric conditions, however, Coriolis force was not used in the simulations and therefore important characteristic of a real atmospheric boundary layer, namely wind veering, could not be reproduced. Finally, although minor changes to the background material and exposition were introduced, some of these include misrepresentation of previous work. Examples are given below under Specific Remarks.
Taking all the above into account I do not recommend the manuscript for publication in the journal Goescientific Model Development.

Specific Remarks

Page 2, line 13 – It is stated that: “Therefore such periodic WRF-LES simulations are restricted to studies of the atmospheric boundary layer flow with a single domain (e.g. Zhu et al., 2016; Kirkil et al., 2012; Kang and Lenschow, 2014; Ma and Liu, 2017) or the outmost domain for the nested 15 cases (e.g. Moeng et al., 2007; Khani and Porte-Agel, 2017; Nunalee et al., 2014).” However, the simulation listed here are quite different. While Moeng et al. (2007) present simulations included two-way nested domains where periodicity on the outer domain impacts the flow on the inner domain, Nunalee et al. (2014) present a one-way nested simulations where inner domain is not impacted by periodicity on the outer domain, so that such setup can be used for simulation of heterogeneous boundary layers.

Page 3, line 21 – It is stated that: “Generally speaking, these methods impose “white-noise” perturbations, thus having a flat spectrum, to a variable (e.g. temperature) at the inlet, and the model dynamics will “process” the signals once these signals are advected into the domain, e.g. to dissipate high-wavenumber signals quickly and to adjust low-wavenumber signals gradually.” This statement misrepresents the temperature perturbation methodology. Temperature perturbations are introduced at a specific length and time scale related to the highest well resolved wave number in LES and therefore they cannot be considered “white noise.” White noise can be defined as “random signal having equal intensity at different frequencies, giving it a constant power spectral density.”

Page 3, line 25 – It is stated: “It is thus not surprising that a large distance of about 20-40 boundary-layer depths 25 (Munoz-Esparza et al., 2015; Mazzaro et al., 2019) is normally required to allow a transition to fully-developed turbulence.” However, Munoz-Esparza et al. (2015) demonstrated that “From those results, it is evident that the performance of the cell perturbation method is not affected by these factors, rather induces turbulent structures that become fully developed at x/zi0 ≈ 15.” See also Figure 18 in Munoz-Esparza et al. 2015.

Furthermore, the difference between the application of synthetic inflow turbulence generator presented in the manuscript and the temperature perturbation methodology presented in Munoz-Esparza et al. (2015) is not recognized by the authors. Temperature perturbation is introduced for mesoscale to microscale coupling approach where smooth mesoscale flow (no resolved turbulence) is forcing microscale flow and for that purpose one-way nesting approach is used in WRF. The nesting approach necessarily represents a different challenge for transition to fully-developed turbulence due to nesting compared to just specifying inflow turbulence, e.g., there is significant difference in inflow turbulence levels between the results presented in the manuscript and those in Munoz-Esparza et al. (2015).

Page 10, line 6 – It is stated: “The spectrum in Munoz-Esparza et al. (2015) drops steeper at high wave numbers, mainly due to a coarser resolution…” The drop in the spectra is related to the implicit filter associated with the numerical discretization and drops at lower wave numbers due to coarser resolution, but it does not drop steeper. Steepness of the drop is related to the implicit filter. It has been determined that the effective resolution of WRF is ~7 dx (Skamarock 2004).

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RR by Anonymous Referee #1 (13 Oct 2020)

ED: Publish subject to minor revisions (review by editor) (27 Oct 2020) by James Maddison

AR by Jian Zhong on behalf of the Authors (05 Nov 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (20 Nov 2020) by James Maddison

AR by Jian Zhong on behalf of the Authors (20 Nov 2020) Author's response Manuscript

ED: Publish as is (27 Nov 2020) by James Maddison

Short summary

A synthetic inflow turbulence generator was implemented in the idealised Weather Research and Forecasting large eddy simulation. The inflow case yielded a mean velocity profile and second-moment profiles that agreed well with those generated using periodic boundary conditions, after a short adjustment distance. This implementation can be extended to a multi-scale seamless nesting simulation from a meso-scale domain with a kilometre-scale resolution to LES domains with metre-scale resolutions.