Analysis of Different Gray Zone Treatments in WRF-LES Real Case Simulations

Abstract

Abstract. When conducting meso-micro scale coupled atmospheric simulations, it is crucial to ensure an adequate treatment of gray zone or terra incognita resolutions in which a large portion of the kinetic energy is naturally produced by the momentum balance equations in the model, while the remaining part still needs to be parameterized. In this work, we conduct three multiday, real case, full-physics atmospheric simulations that are fully coupled from the meso to the micro scale and in which the only difference is the treatment of boundary layer physics at the gray zone domain. One simulation uses a well-established 5 parameterization, another uses its scale-aware version previously modified to accommodate gray zone resolutions, and a final one uses no parameterization at all and assumes that the gray zone domain can be run in large-eddy simulation (LES) mode.The simulated fields are cross-compared, and further compared to measurements collected during the Prince Edward Island Wind Energy Experiment. Use of LES in the gray zone domain influences the flow fields in a manner that is robust to temporal averaging. The best predictions of vertical wind shear were found for the simulations in which the gray zone is parameterized, 10 and the inclusion of a micro scale nest run in LES mode within the gray zone domains increased the model errors by producing overly homogeneous flow fields. The parameterized simulations also produced better agreement in terms of kinetic energy spectra at the two innermost simulation domains. In the gray zone domain, the energy decays as f −3 throughout most of the spectral range considered. In the micro scale domain, the same is only seen in the low-frequency end of the gray zone spectral range. In the high-frequency end, the energy decay follows a f −1 slope. Outside the gray zone spectral range, the micro scale 15 simulated spectra follow the expected f −5/3 slope and produce good agreement with measurements.

Transition Zone Radiative Effects in Shortwave Radiation Parameterizations: Case of Weather Research and Forecasting Model

“…The Advanced Research WRF (WRF-ARW) is a state-of-the-art open source mesoscale atmospheric model, developed by National Center for Atmospheric Research (NCAR) for both research and numerical weather prediction purposes (Powers et al, 2017). This model, which is probably the most popular meteorological (it also has a climatic version) model worldwide, has the capability to be used for a wide range of applications, such as real-time numerical weather prediction, data assimilation, parameterized-physics research, regional climate simulations, air quality modeling, atmosphere-ocean coupling, and idealized simulations (Blossey et al, 2013;Doubrawa et al, 2018;Jimenez et al, 2016;Lin et al, 2015;Moeng et al, 2007;Montornès et al, 2016;Wang et al, 2009;Yamaguchi & Feingold, 2012;Zhong et al, 2016). In addition, it can be ran at different domains and offers various options for parameterization of convective processes, turbulent transports, evolution of surface temperature and soil moisture, and soil-air interactions (Ruiz-Arias et al, 2013;Skamarock et al, 2008).…”

Effect of Scale-Aware Nonlocal Planetary Boundary Layer Scheme on Lake-Effect Precipitation at Gray-Zone Resolutions

“…They found that vertical motions and convective rolls are intensified in the subkilometer simulations with the scale-aware PBL parameterization. Since then, several studies have further investigated the effects of the SH parameterization and found that it performs better at gray-zone resolutions than its conventional parameterization of Hong et al (2006), which scheme has been developed at Yonsei University and thus is named YSU hereinafter (e.g., Doubrawa et al 2018;Xu et al 2018). However, all of these studies consider dry CBLs; the scale-aware PBL parameterization has not been tested for moist CBLs, where PBL parameterizations interact strongly with microphysical processes within convection.…”

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

“…The further 1 h outputs with 5 s interval (approximately the advection timescale of the smallest resolved eddies, which is equivalently twice the grid resolution of 20 m) were used for the analysis. We take advantage of the homogeneous turbulence in the spanwise direction (Ghannam et al, 2015) and calculate all resolved-scale turbulent quantities by averaging in the spanwise direction (the y direction) and in time t over the last 1 h period. This averaging is referred to as "the y − t averaging" hereafter and is denoted by ϕ , for example, for the y − t-averaged ϕ.…”