WRF-LES

Major problem

Major problem is that turbulence parameterizations in the commonly used one-dimensional (1D) planetary boundary layer (PBL) schemes only consider vertical exchange.

• The document gives a brief description of LES in WRF, which may also be helpful.

km_opt(max_dom)  = 1,	! eddy coefficient option
                    1 = constant (use khdif kvdif)
                    2 = 1.5 order TKE closure (3D)
                    3 = Smagorinsky first order closure (3D)
                        Note: option 2 and 3 are not recommended for DX > 2 km
                    4 = horizontal Smagorinsky first order closure
                        (recommended for real-data cases)
                    5 = SMS-3DTKE scale-adaptive LES/PBL scheme. It must be
                        used with diff_opt = 2. PBL schemes must be turned off
                        (bl_pbl_physics=0). It can work with sf_sfclay_physics = 1, 5, 91.

• Yamaguchi, Takanobu, and Graham Feingold. "Large‐eddy simulation of cloudy boundary layer with the Advanced Research WRF model." Journal of Advances in Modeling Earth Systems 4.3 (2012).
• Liu, Y., Y. Liu, D. Muñoz-Esparza, F. Hu, C. Yan, and S. Miao, 2020: Simulation of Flow Fields in Complex Terrain with WRF-LES: Sensitivity Assessment of Different PBL Treatments. J. Appl. Meteor. Climatol., 59, 1481–1501, https://doi.org/10.1175/JAMC-D-19-0304.1.
  • Employing the Shuttle Radar Topography Mission 1 arc s dataset (SRTM1; ~30 m) high-resolution topographic dataset instead of the traditional USGS_30s (~900 m) dataset effectively improves the model capability for reproducing fluctuations and turbulent features of surface winds.
  • Numerical artifacts might be produced in areas of complex terrain, where the assumption of horizontal homogeneity is violated (Goger et al. 2018, 2019) while horizontal exchanges and three-dimensional (3D) effects such as horizontal shear production are entirely neglected. 3D PBL schemes (Jiménez and Kosović 2016) should be able to alleviate the effect of complex terrain, yet there exist no robust approaches that have been validated in a wide range of atmospheric conditions.
  • In addition, mesoscale NWP models with relatively coarse resolution cannot capture microscale variabilities driven by atmospheric dynamics (turbulence effects are fully parameterized). Large-eddy simulation (LES) that can explicitly resolve the most energetic turbulent eddies could be an alternative to PBL schemes (Cuxart 2015).
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References

1. Goger, B., M. W. Rotach, A. Gohm, O. Fuhrer, I. Stiperski, and A. A. M. Holtslag, 2018: The impact of three-dimensional effects on the simulation of turbulence kinetic energy in a major alpine valley. Bound.-Layer Meteor., 168, 1–27.
2. Goger, B., M. W. Rotach, A. Gohm, I. Stiperski, O. Fuhrer, and G. de Morsier, 2019: A new horizontal length scale for a three-dimensional turbulence parameterization in mesoscale atmospheric modeling over highly complex terrain. J. Appl. Meteor. Climatol., 58, 2087–2102.
3. Jiménez, P. A., and B. Kosović, 2016: Implementation and evaluation of a three dimensional PBL parameterization for simulations of the flow over complex terrain. 17th Annual WRF Users’ Workshop, Boulder, CO, National Center for Atmospheric Research, 6.4.,.
4. Cuxart, J., 2015: When can a high-resolution simulation over complex terrain be called LES? Front. Earth Sci., 3, 87, https://doi.org/10.3389/feart.2015.00087.