Grey zone simulations of the morning convective boundary layer development

Efstathiou, Georgios A.; Beare, Robert J.; Osborne, S.; Lock, A. P.

doi:10.1002/2016jd024860

Cited by 26 publications

(33 citation statements)

References 35 publications

(106 reference statements)

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“…Wyngaard (2004) has pointed out that moderately fine resolution may have difficulty dealing with planetary boundary layer (PBL) parameterizations: conventional PBL schemes do not assume that cases exist in which some turbulence eddies are resolved while many other smaller scale eddies have to be parameterized. Such a resolution range is referred to as a "gray zone" or "Terra Incognita" for which a suitable parameterization is still under discussion for PBL convection (e.g., Honnert et al 2011;Zhou et al 2014;Ito et al 2015;Shin and Hong 2015;Efstathiou et al 2016;Kitamura 2016). Another study suggested a horizontal grid spacing of ~100 m is required to faithfully reproduce cumulus clouds (Bryan et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Stalled Improvement in a Numerical Weather Prediction Model as Horizontal Resolution Increases to the Sub-Kilometer Scale

Ito¹,

Hayashi²,

Hashimoto³

et al. 2017

SOLA

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This study evaluated the performance of a regional weather prediction model. The horizontal resolution is increased to the sub-kilometer scale in a series of experiments over areas of Japan through the summer or winter seasons of 2015−2016. The performance improves less when increasing the horizontal resolution from 2 km to 1 km or 500 m than it does from 5 km to 2 km, especially when topography and ice microphysics are less relevant. Although the velocity and magnitude of updrafts, cloud size, and convection in the boundary layer indeed change with the horizontal resolution, these differences turn out to have little impact on the model performance.(Citation: Ito, J., S. Hayashi, A. Hashimoto, H. Ohtake, F. Uno, H. Yoshimura, T. Kato, and Y. Yamada, 2017: Stalled improvement in a numerical weather prediction model as horizontal resolution increases to the sub-kilometer scale. SOLA, 13, 151− 156,

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Section: Introductionmentioning

confidence: 99%

Stalled Improvement in a Numerical Weather Prediction Model as Horizontal Resolution Increases to the Sub-Kilometer Scale

Ito¹,

Hayashi²,

Hashimoto³

et al. 2017

SOLA

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“…There has also been similar work to investigate the behaviour of partially resolved turbulence in convective boundary layers -in particular the transition from high-resolution LES simulations to lower-resolution mesoscale simulations (Efstathiou and Beare, 2015). Efstathiou et al (2016) compared the representation of morning boundary-layer development in 50 m LES with two grey zone boundary-layer implementations at lower resolutions (down to 3,200 m). They evaluated the resulting deficiencies in either evolution of turbulent kinetic energy (TKE) or the amount of instability in the profiles and concluded that both formulations have strengths and weaknesses which highlights the inevitable issues with resolutions that are currently computationally feasible.…”

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confidence: 99%

The impact of spin‐up and resolution on the representation of a clear convective boundary layer over London in order 100 m grid‐length versions of the Met Office Unified Model

Lean

Barlow

Halios

2019

Quart J Royal Meteoro Soc

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With a number of operational centres looking forward to the possibilities of “city scale” NWP and climate modelling it is important to understand the behaviour of order 100 m models over cities. A key issue is how to handle the representation of partially resolved turbulence in these models. In this article we compare the representation of a clear convective boundary‐layer case in London in 100 and 50 m grid‐length versions of the Unified Model (MetUM) with observations. Comparison of Doppler lidar observations of the vertical velocity shows that convective overturning in the boundary layer is broadly well represented in terms of its depth and magnitude. The role of model resolution was investigated by comparing a 50 m grid‐length model with the 100 m one. It is found that, although going to 50 m grid length does not greatly change many of the bulk properties (mixing height, heat flux profiles, etc.) the spatial structure of the overturning is significantly different. This is confirmed with spectral analysis which shows that the 50 m model resolves significantly more of the energetic eddies, and a length‐scale analysis that shows the 50 and 100 m models produce convective structures 2–3 times larger than observed. We conclude that, for the MetUM, model grid‐lengths of order 100 m may well be sufficient for predicting many bulk and statistical properties of convective boundary layers; however, the details of the spatial structures around convective overturning in these situations are likely to be still under‐resolved. Spin‐up artefacts emanating from the inflow boundary of the model are investigated by comparing with a smaller 100 m grid‐length domain which is more dominated by such effects. These manifest themselves as along‐wind boundary‐layer rolls which produce a less realistic comparison with the lidar observations. A stability analysis is presented in order to better understand the formation of these rolls.

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“…The implementation of the PGB scheme as outlined here follows Efstathiou et al. () which may be consulted for full details. It is based on the approach of Boutle et al.…”

Section: Sub‐grid Schemesmentioning

confidence: 99%

“…Efstathiou et al. () tested a simple version of the PGB scheme in the Met Office large‐eddy model (LEM) and compared it with the bounding approach (Efstathiou and Beare, ) for idealized simulations of an evolving convective BL (CBL) in the grey zone. In the LEM framework, PGB was able to reproduce first‐ and second‐order quantities at both the LES and mesoscale limits.…”

Section: Introductionmentioning

confidence: 99%

“…LASD is blended with a non‐local 1D BL scheme in the LEM and tested for an evolving CBL similarly to Efstathiou et al. , (; ). In particular, the ability of the new blending scheme to provide a smooth transition of the first‐ and second‐order quantities across the grey zone is examined in comparison with the standard blending scheme and with coarse‐grained LES results.…”

Section: Introductionmentioning

confidence: 99%

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A dynamic extension of the pragmatic blending scheme for scale‐dependent sub‐grid mixing

Efstathiou

Plant

2019

Quart J Royal Meteoro Soc

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A recent pragmatic blending approach treats sub-grid turbulent mixing using a weighted average of a 1D mesoscale model and a 3D Smagorinsky formulation. Here the approach is modified and extended to incorporate a scale-dependent dynamic Smagorinsky scheme instead of a static Smagorinsky scheme. Results from simulating an evolving convective boundary layer show that the new scheme is able to improve the representation of turbulence statistics and potential temperature profiles at grey-zone resolutions during the transition from the shallow morning to the deep afternoon boundary layer. This is achieved mainly because the new scheme enables and controls an improved spin-up of resolved turbulence. The dynamic blending scheme is shown to be more adaptive to the evolving flow and somewhat less sensitive to the blending parameters. The new approach appears to offer a more robust and more flexible formulation of blending and the results strongly encourage further assessment and development. KEYWORDSboundary-layer scheme, dynamic turbulence model, grey zone, sub-grid parametrization 1 the resolved scales. This approach is common in performing large-eddy simulations (LESs), and such simulations have proved valuable for our understanding of boundary-layer (BL) turbulence and for developing BL parametrizations suitable for NWP. However, if the dominant turbulence length-scales are similar to the grid scale, then models will partially resolve the dominant modes of BL turbulence. These resolutions comprise the terra incognita or the grey zone of BL turbu-This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Grey zone simulations of the morning convective boundary layer development

Cited by 26 publications

References 35 publications

Stalled Improvement in a Numerical Weather Prediction Model as Horizontal Resolution Increases to the Sub-Kilometer Scale

Stalled Improvement in a Numerical Weather Prediction Model as Horizontal Resolution Increases to the Sub-Kilometer Scale

The impact of spin‐up and resolution on the representation of a clear convective boundary layer over London in order 100 m grid‐length versions of the Met Office Unified Model

A dynamic extension of the pragmatic blending scheme for scale‐dependent sub‐grid mixing

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