High-Resolution Large-Eddy Simulations of Flow in the Complex Terrain of the Canadian Rockies

Canada First Research Excellence Fund's Global Water Futures Programme, the Natural Sciences and Engineering Research Council of Canada, Alberta Innovates, the Canada Foundation for Innovation, and the NSERC CREATE program in Water SecurityPeer ReviewedImproving the calculation of land-atmosphere fluxes of heat and water vapor in mountain terrain requires better resolution of thermally driven diurnal winds (i.e., valley, slope winds) due to differential heating by terrain and radiative fluxes. In this study, the Weather Research and Forecasting model is used to simulate flow in large-eddy simulation (LES) mode over the complex terrain of the Fortress Mountain and Marmot Creek research basins, Kananaskis Valley, Canadian Rockies, Alberta in mid-summer. The model was used to examine the temporal and spatial evolution of local winds and near-surface boundary layer processes with variability in topography and elevation. Numerically resolving complex terrain wind flow effects require smaller grid cell size. However, the use of terrain-following coordinates in most numerical weather prediction models results in large numerical errors when flow over steep terrain is simulated. These errors propagate through the domain and can result in numerical instability. To avoid this issue when simulating flow over steep terrain a local smoothing approach was used, where smoothing is applied only where slope exceeds some predetermined threshold. LES results from local smoothing were compared with a mesoscale model and LES with global smoothing. Simulations are evaluated using sounding data and meteorological stations. The differences in flow patterns and reversals in two mountain basins suggest that valley geometry and volume is relevant to the break up of inversion layers, removal of cold-air pools, and strength of thermally driven winds

Coupled mesoscale-LES modeling of a diurnal cycle during the CWEX-13 field campaign: From weather to boundary-layer eddies

Multiscale modeling of a diurnal cycle of real‐world conditions is presented for the first time, validated using data from the CWEX‐13 field experiment. Dynamical downscaling from synoptic‐scale down to resolved three‐dimensional eddies in the atmospheric boundary layer (ABL) was performed, spanning 4 orders of magnitude in horizontal grid resolution: from 111 km down to 8.2 m (30 m) in stable (convective) conditions. Computationally efficient mesoscale‐to‐microscale transition was made possible by the generalized cell perturbation method with time‐varying parameters derived from mesoscale forcing conditions, which substantially reduced the fetch to achieve fully developed turbulence. In addition, careful design of the simulations was made to inhibit the presence of under‐resolved convection at convection‐resolving mesoscale resolution and to ensure proper turbulence representation in stably‐stratified conditions. Comparison to in situ wind‐profiling lidar and near‐surface sonic anemometer measurements demonstrated the ability to reproduce the ABL structure throughout the entire diurnal cycle with a high degree of fidelity. The multiscale simulations exhibit realistic atmospheric features such as convective rolls and global intermittency. Also, the diurnal evolution of turbulence was accurately simulated, with probability density functions of resolved turbulent velocity fluctuations nearly identical to the lidar measurements. Explicit representation of turbulence in the stably‐stratified ABL was found to provide the right balance with larger scales, resulting in the development of intra‐hour variability as observed by the wind lidar; this variability was not captured by the mesoscale model. Moreover, multiscale simulations improved mean ABL characteristics such as horizontal velocity, vertical wind shear, and turbulence. Multiscale modeling of a real‐world diurnal cycle is presented for the first time, enabled by the generalized cell perturbation method The multiscale simulations exhibited realistic atmospheric features not captured by the mesoscale model such as convective rolls, global intermittency, and intra‐hour variability Diurnal evolution of turbulence was accurately simulated, with probability density functions of resolved turbulent velocity fluctuations nearly identical to CWEX‐13 lidar measurement

Prevalence of post-intensive care syndrome in mechanically ventilated patients with COVID-19

Coronavirus disease 19 (COVID-19) patients usually require long periods of mechanical ventilation and sedation, which added to steroid therapy, favours a predisposition to the development of delirium and subsequent mental health disorders, as well as physical and respiratory sequelae. The aim of this study was to determine the prevalence of post-intensive care syndrome (PICS) at 3 months after hospital discharge, in a cohort of mechanically ventilated patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). An ambispective, observational study was conducted in three hospitals with intensive care unit (ICU) follow-up clinics. We studied adults who survived a critical illness due to SARS-CoV-2 infection requiring invasive mechanical ventilation. A physical (muscle strength and pulmonary function), functional [12-Item Short Form Health Survey (SF-12), and Barthel score], psychological [hospital anxiety and depression (HADS) and posttraumatic stress disorder symptom severity scales], and cognitive [Montreal cognitive assessment (MoCA) test] assessment were performed. A total of 186 patients were evaluated at 88 days (IQR 68–121) after hospital discharge. Mean age was 59 ± 12 years old, 126 (68%) patients were men, and median length of mechanical ventilation was 14 days (IQR 8–31). About 3 out of 4 patients (n = 139, 75%) met PICS criteria. Symptoms of cognitive and psychiatric disorders were found in 59 (32%) and 58 (31%) patients, respectively. Ninety-one (49%) patients had muscle weakness. Pulmonary function tests in patients with no respiratory comorbidities showed a normal pattern in 93 (50%) patients, and a restrictive disorder in 62 (33%) patients. Also, 69 patients (37%) were on sick leave, while 32 (17%) had resumed work at the time of assessment. In conclusion, survivors of critical illness due to SARS-CoV-2 infection requiring mechanical ventilation have a high prevalence of PICS. Physical domain is the most frequently damaged, followed by cognitive and psychiatric disorders. ICU follow-up clinics enable the assistance of this vulnerable populationThis study did not receive any funding or fnancial support. JMA and JV are funded by Grants from the Instituto de Salud Carlos III, Spain (CB06/06/1088, PI19/00141)

Simulating Real Atmospheric Boundary Layers at Gray-Zone Resolutions: How Do Currently Available Turbulence Parameterizations Perform?

Recent computational and modeling advances have led a diverse modeling community to experiment with atmospheric boundary layer (ABL) simulations at subkilometer horizontal scales. Accurately parameterizing turbulence at these scales is a complex problem. The modeling solutions proposed to date are still in the development phase and remain largely unvalidated. This work assesses the performance of methods currently available in the Weather Research and Forecasting (WRF) model to represent ABL turbulence at a gray-zone grid spacing of 333 m. We consider three one-dimensional boundary layer parameterizations (MYNN, YSU and Shin-Hong) and coarse large-eddy simulations (LES). The reference dataset consists of five real-case simulations performed with WRF-LES nested down to 25 m. Results reveal that users should refrain from coarse LES and favor the scale-aware, Shin-Hong parameterization over traditional one-dimensional schemes. Overall, the spread in model performance is large for the cellular convection regime corresponding to the majority of our cases, with coarse LES overestimating turbulent energy across scales and YSU underestimating it and failing to reproduce its horizontal structure. Despite yielding the best results, the Shin-Hong scheme overestimates the effect of grid dependence on turbulent transport, highlighting the outstanding need for improved solutions to seamlessly parameterize turbulence across scales

A High Resolution Coupled Fire–Atmosphere Forecasting System to Minimize the Impacts of Wildland Fires: Applications to the Chimney Tops II Wildland Event

Wildland fires are responsible for large socio-economic impacts. Fires affect the environment, damage structures, threaten lives, cause health issues, and involve large suppression costs. These impacts can be mitigated via accurate fire spread forecast to inform the incident management team. We show that a fire forecast system based on a numerical weather prediction (NWP) model coupled with a wildland fire behavior model can provide this forecast. This was illustrated with the Chimney Tops II wildland fire responsible for large socio-economic impacts. The system was run at high horizontal resolution (111 m) over the region affected by the fire to provide a fine representation of the terrain and fuel heterogeneities and explicitly resolve atmospheric turbulence. Our findings suggest that one can use the high spatial resolution winds, fire spread and smoke forecast to minimize the adverse impacts of wildland fires

Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

Large eddy simulations (LESs) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind and Raman lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to “gray zone modeling” when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the downwind vertical wind structure. Additionally, the model results accurately reproduce the development of the daytime convective boundary layer measured by the Raman lidar

Nested mesoscale‐to‐LES modeling of the atmospheric boundary layer in the presence of under‐resolved convective structures

Multiscale atmospheric simulations can be computationally prohibitive, as they require large domains and fine spatiotemporal resolutions. Grid‐nesting can alleviate this by bridging mesoscales and microscales, but one turbulence scheme must run at resolutions within a range of scales known as the terra incognita (TI). TI grid‐cell sizes can violate both mesoscale and microscale subgrid‐scale parametrization assumptions, resulting in unrealistic flow structures. Herein we assess the impact of unrealistic lateral boundary conditions from parent mesoscale simulations at TI resolutions on nested large eddy simulations (LES), to determine whether parent domains bias the nested LES. We present a series of idealized nested mesoscale‐to‐LES runs of a dry convective boundary layer (CBL) with different parent resolutions in the TI. We compare the nested LES with a stand‐alone LES with periodic boundary conditions. The nested LES domains develop ∼20% smaller convective structures, while potential temperature profiles are nearly identical for both the mesoscales and LES simulations. The horizontal wind speed and surface wind shear in the nested simulations closely resemble the reference LES. Heat fluxes are overestimated by up to ∼0.01 K m s −1 in the top half of the PBL for all nested simulations. Overestimates of turbulent kinetic energy (TKE) and Reynolds stress in the nested domains are proportional to the parent domain's grid‐cell size, and are almost eliminated for the simulation with the finest parent grid‐cell size. Based on these results, we recommend that LES of the CBL be forced by mesoscale simulations with the finest practical resolution. Grid‐nesting enables coupling between mesoscale and LES models LES nested within unrealistic mesoscale models of the CBL require a long fetch (∼30–40 km) to reach stable turbulent statistics LES nest performance improves with increasing mesoscale parent resolutio

Gray Zone Partitioning Functions and Parameterization of Turbulence Fluxes in the Convective Atmospheric Boundary Layer

Here, we present the first attempt to fully represent three-dimensional turbulence fluxes in the “Terra Incognita” or the gray zone in other words. In order to derive partitioning functions, representing the partitioning between subgrid and total fluxes, we make use of high-resolution large-eddy simulations (LES), which are performed with the Weather Research and Forecasting (WRF) model. LES computations are performed for various levels of convective instability, ranging from pure buoyant to strongly sheared convection. Then, the resulting reference-LES fields are successively coarse grained from its original microscale grid spacing ((Formula presented.) m) up to typical mesoscale grid spacings ((Formula presented.) km). The given process is applied by means of an advanced filter, that is, the Butterworth filter. It enables a clear scale-specific filtering that results in a more controlled energy transition from lower to higher wavenumbers, unlike the drawbacks of current filters in use. Finally, we parameterize the subgrid scale (SGS) partitioning functions of 10 SGS turbulence quantities: momentum fluxes (τij, six terms), heat fluxes (qj, three terms), and turbulence kinetic energy (k). Turbulence partitioning relations are parameterized in a scale-aware, stability-dependent, and height-dependent form, using the sigmoidal Gompertz function. Thus, the new gray zone model provides a framework that bridges the mesoscale and microscale limits and that is suitable for the development of next generation three-dimensional, multiscale turbulence parameterization methods or planetary boundary layer schemes.SCOPUS: ar.jinfo:eu-repo/semantics/publishe