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

2018 ◽  
Author(s):  
Paula Doubrawa ◽  
Alex Montornès ◽  
Rebecca J. Barthelmie ◽  
Sara C. Pryor ◽  
Pau Casso
Keyword(s):  
Kinetic Energy ◽  
Spectral Range ◽  
Vertical Wind Shear ◽  
Flow Fields ◽  
Real Case ◽  
Gray Zone ◽  
Model Errors ◽  
Adequate Treatment ◽  
Micro Scale ◽  
Atmospheric Simulations

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 multi-day, 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 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, 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 simulated spectra follow the expected f−5/3 slope and produce good agreement with measurements.

Composited structure of shallow cumulus clouds

2021 ◽  
Author(s):  
Chris Holloway ◽  
Jian-Feng Gu ◽  
Bob Plant ◽  
Todd Jones
Keyword(s):  
Kinetic Energy ◽  
Vertical Velocity ◽  
Inversion Layer ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Theoretical Models ◽  
Turbulence Kinetic Energy ◽  
Cloud Base ◽  
Asymmetric Structures ◽  
Negatively Buoyant

<div> <div> <div> <div> <p>The normalized distributions of thermodynamic and dynamical variables both within and outside shallow clouds are investigated through a composite algorithm using large eddy simulation of the BOMEX case. The normalized magnitude is maximum near cloud center and decreases outwards. While relative humidity (RH) and cloud liquid water (<em>q<sub>l </sub></em>) decrease smoothly to match the environment, the vertical velocity, virtual potential temperature (<em>θ<sub>v </sub></em>) and potential temperature (<em>θ</em>) perturbations have more complicated behaviour towards the cloud boundary. Below the inversion layer, <em>θ<sub>v</sub></em> becomes <span>negative before the vertical velocity has turned from updraft to subsiding shell outside the cloud, indicating the presence of a transition zone where the updraft is negatively buoyant. Due to the downdraft outside the cloud and the enhanced horizontal turbulent mixing across the edge, the normalized turbulence kinetic energy (TKE) and horizontal turbulence kinetic energy (HTKE) decrease more slowly from the cloud center outwards than the thermodynamic variables. The distributions all present asymmetric structures in response to the vertical wind shear, with more negatively buoyant air, stronger downdrafts and larger TKE on the downshear side. We discuss several implications of the distributions for theoretical models and parameterizations. Positive buoyancy near cloud base is mostly due to </span><span>the virtual effect of water vapor, emphasising the role of moisture in triggering. The mean vertical velocity is found </span><span>to be approximately half the maximum vertical velocity within each cloud, providing a constraint on some models. Finally, products of normalized distributions for different variables are shown to be able to well represent the vertical heat and moisture fluxes, but they underestimate fluxes in the inversion layer because they do not capture cloud top downdrafts.</span></p> </div> </div> </div> </div>

scholarly journals Turbulence Adjustment and Scaling in an Offshore Convective Internal Boundary Layer: A CASPER Case Study

2020 ◽  
Vol 77 (5) ◽  
pp. 1661-1681
Author(s):  
Qingfang Jiang ◽  
Qing Wang ◽  
Shouping Wang ◽  
Saša Gaberšek
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Kinetic Energy ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Internal Boundary Layer ◽  
Turbulence Kinetic Energy ◽  
Internal Boundary ◽  
Field Observations ◽  
The Mean

Abstract The characteristics of a convective internal boundary layer (CIBL) documented offshore during the East Coast phase of the Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER-EAST) field campaign has been examined using field observations, a coupled mesoscale model (i.e., Navy’s COAMPS) simulation, and a couple of surface-layer-resolving large-eddy simulations (LESs). The Lagrangian modeling approach has been adopted with the LES domain being advected from a cool and rough land surface to a warmer and smoother sea surface by the mean offshore winds in the CIBL. The surface fluxes from the LES control run are in reasonable agreement with field observations, and the general CIBL characteristics are consistent with previous studies. According to the LESs, in the nearshore adjustment zone (i.e., fetch < 8 km), the low-level winds and surface friction velocity increase rapidly, and the mean wind profile and vertical velocity skewness in the surface layer deviate substantially from the Monin–Obukhov similarity theory (MOST) scaling. Farther offshore, the nondimensional vertical wind shear and scalar gradients and higher-order moments are consistent with the MOST scaling. An elevated turbulent layer is present immediately below the CIBL top, associated with the vertical wind shear across the CIBL top inversion. Episodic shear instability events occur with a time scale between 10 and 30 min, leading to the formation of elevated maxima in turbulence kinetic energy and momentum fluxes. During these events, the turbulence kinetic energy production exceeds the dissipation, suggesting that the CIBL remains in nonequilibrium.

scholarly journals SIMULASI NUMERIK MEKANISME TURBULENSI DEKAT AWAN KONVEKTIF

2021 ◽  
Vol 22 (1) ◽  
pp. 25-33
Author(s):  
Ni Putu Tiana Verayanti ◽  
I Kadek Nova Arta Kusuma
Keyword(s):  
Kinetic Energy ◽  
Satellite Imagery ◽  
Wind Shear ◽  
Richardson Number ◽  
Vertical Wind Shear ◽  
Commercial Aircraft ◽  
Convective Clouds ◽  
Air Turbulence ◽  
North Sumatra ◽  
Cumulonimbus Cloud

Intisari Turbulensi yang dialami oleh pesawat komersial rute Jakarta-Medan telah dilaporkan mengalami Clear Air Turbulence (CAT) di atas Sumatera Utara pada tanggal 24 Oktober 2017. Namun berdasarkan data citra satelit Himawari dari Badan Meteorologi, Klimatologi, dan Geofisika (BMKG) Indonesia menyebutkan bahwa di sekitar lokasi turbulensi terdapat awan kumulonimbus. Penelitian ini memanfaatkan model WRF-ARW dengan resolusi spasial dan temporal tinggi untuk mengetahui secara detail proses yang terjadi pada awan konvektif penyebab Near Cloud Turbulence (NCT). Turbulensi tersebut disebabkan oleh bilangan Richardson rendah yang terbentuk di wilayah udara jernih (clear air) yang berjarak 300-700 m di atas puncak awan dan diperkuat dengan adanya Turbulensi Energi Kinetik (TKE) mencapai 4,4 m2 / s2 dan geser angin vertikal (VWS) oleh arus keluar awan konvektif.  Abstract Turbulence encountered by commercial aircraft Jakarta-Medan routes has been reported that experienced Clear Air Turbulence (CAT) over North Sumatra on October 24th, 2017. However, based on Himawari satellite imagery data produced by Agency for Meteorology, Climatology, and Geophysics (BMKG), Indonesia stated that there was a cumulonimbus cloud around the turbulence location. This study utilizes WRF-ARW models with a high spatial and temporal resolution to find out in detail the processes that occur in convective clouds causing Near Cloud Turbulence (NCT). The turbulence was caused by a low Richardson number formed in the clear-air area, which has a distance of 300 - 700 m above the cloud top and reinforced by the existence of Turbulence Kinetic Energy (TKE) reaching 4,4 m2/s2 and vertical wind shear (VWS) by deep convection’s outflow.

scholarly journals A Physical Basis for the Probabilistic Prediction of the Accumulated Tropical Cyclone Kinetic Energy in the Western North Pacific

2013 ◽  
Vol 26 (20) ◽  
pp. 7981-7991 ◽  
Author(s):  
Hye-Mi Kim ◽  
Myong-In Lee ◽  
Peter J. Webster ◽  
Dongmin Kim ◽  
Jin Ho Yoo
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
El Niño ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
El Nino ◽  
Vertical Wind Shear ◽  
Tropical Storm ◽  
Probabilistic Prediction

Abstract The relationship between El Niño–Southern Oscillation (ENSO) and tropical storm (TS) activity over the western North Pacific Ocean is examined for the period from 1981 to 2010. In El Niño years, TS genesis locations are generally shifted to the southeast relative to normal years and the passages of TSs tend to recurve to the northeast. TSs of greater duration and more intensity during an El Niño summer induce an increase of the accumulated tropical cyclone kinetic energy (ACE). Based on the strong relationship between the TS properties and ENSO, a probabilistic prediction for seasonal ACE is investigated using a hybrid dynamical–statistical model. A statistical relationship is developed between the observed ACE and large-scale variables taken from the ECMWF seasonal forecast system 4 hindcasts. The ACE correlates positively with the SST anomaly over the central to eastern Pacific and negatively with the vertical wind shear near the date line. The vertical wind shear anomalies over the central and western Pacific are selected as predictors based on sensitivity tests of ACE predictive skill. The hybrid model performs quite well in forecasting seasonal ACE with a correlation coefficient between the observed and predicted ACE at 0.80 over the 30-yr period. A relative operating characteristic analysis also indicates that the ensembles have significant probabilistic skill for both the above-normal and below-normal categories. By comparing the ACE prediction over the period from 2003 to 2011, the hybrid model appears more skillful than the forecast from the Tropical Storm Risk consortium.

scholarly journals Migration by soaring or flapping: numerical atmospheric simulations reveal that turbulence kinetic energy dictates bee-eater flight mode

2011 ◽  
Vol 278 (1723) ◽  
pp. 3380-3386 ◽  
Author(s):  
Nir Sapir ◽  
Nir Horvitz ◽  
Martin Wikelski ◽  
Roni Avissar ◽  
Yitzhak Mahrer ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Radio Telemetry ◽  
Atmospheric Modeling ◽  
Turbulence Kinetic Energy ◽  
Flight Behaviour ◽  
Bird Flight ◽  
Flight Mode ◽  
Migrating Birds ◽  
Abundance And Distribution ◽  
Atmospheric Simulations

Aerial migrants commonly face atmospheric dynamics that may affect their movement and behaviour. Specifically, bird flight mode has been suggested to depend on convective updraught availability and tailwind assistance. However, this has not been tested thus far since both bird tracks and meteorological conditions are difficult to measure in detail throughout extended migratory flyways. Here, we applied, to our knowledge, the first comprehensive numerical atmospheric simulations by mean of the Regional Atmospheric Modeling System (RAMS) to study how meteorological processes affect the flight behaviour of migrating birds. We followed European bee-eaters ( Merops apiaster ) over southern Israel using radio telemetry and contrasted bird flight mode (flapping, soaring–gliding or mixed flight) against explanatory meteorological variables estimated by RAMS simulations at a spatial grid resolution of 250 × 250 m 2 . We found that temperature and especially turbulence kinetic energy (TKE) determine bee-eater flight mode, whereas, unexpectedly, no effect of tailwind assistance was found. TKE during soaring–gliding was significantly higher and distinct from TKE during flapping. We propose that applying detailed atmospheric simulations over extended migratory flyways can elucidate the highly dynamic behaviour of air-borne organisms, help predict the abundance and distribution of migrating birds, and aid in mitigating hazardous implications of bird migration.

scholarly journals A Three-Dimensional Scale-Adaptive Turbulent Kinetic Energy Scheme in the WRF-ARW Model

2018 ◽  
Vol 146 (7) ◽  
pp. 2023-2045 ◽  
Author(s):  
Xu Zhang ◽  
Jian-Wen Bao ◽  
Baode Chen ◽  
Evelyn D. Grell
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulent Mixing ◽  
Conventional Treatment ◽  
Three Dimensional ◽  
Wrf Model ◽  
Zone Model ◽  
Gray Zone ◽  
Size Change ◽  
Convective Boundary

A new three-dimensional (3D) turbulent kinetic energy (TKE) subgrid mixing scheme is developed using the Advanced Research version of the Weather Research and Forecasting (WRF) Model (WRF-ARW) to address the gray-zone problem in the parameterization of subgrid turbulent mixing. The new scheme combines the horizontal and vertical subgrid turbulent mixing into a single energetically consistent framework, in contrast to the conventionally separate treatment of the vertical and horizontal mixing. The new scheme is self-adaptive to the grid-size change between the large-eddy simulation (LES) and mesoscale limits. A series of dry convective boundary layer (CBL) idealized simulations are carried out to compare the performance of the new scheme and the conventional treatment of subgrid mixing to the WRF-ARW LES dataset. The importance of including the nonlocal component in the vertical buoyancy specification in the newly developed general TKE-based scheme is illustrated in the comparison. The improvements of the new scheme with the conventional treatment of subgrid mixing across the gray-zone model resolutions are demonstrated through the partitioning of the total vertical flux profiles. Results from real-case simulations show the feasibility of using the new scheme in the WRF Model in lieu of the conventional treatment of subgrid mixing.

scholarly journals The Representation of Cumulus Convection in High-Resolution Simulations of the 2013 Colorado Front Range Flood

2016 ◽  
Vol 144 (11) ◽  
pp. 4265-4278 ◽  
Author(s):  
Kelly M. Mahoney
Keyword(s):  
Extreme Rainfall ◽  
Heavy Rain ◽  
Moisture Flux ◽  
Heavy Precipitation ◽  
Colorado Front Range ◽  
Convective Precipitation ◽  
Gray Zone ◽  
Front Range ◽  
Model Errors ◽  
The Impact

Abstract Model simulations of the 2013 Colorado Front Range floods are performed using 4-km horizontal grid spacing to evaluate the impact of using explicit convection (EC) versus parameterized convection (CP) in the model convective physics “gray zone.” Significant differences in heavy precipitation forecasts are found across multiple regions in which heavy rain and high-impact flooding occurred. The relative contribution of CP-generated precipitation to total precipitation suggests that greater CP scheme activity in areas upstream of the Front Range flooding may have led to significant downstream model error. Heavy convective precipitation simulated by the Kain–Fritsch CP scheme in particular led to an alteration of the low-level moisture flux and moisture transport fields that ultimately prevented the generation of heavy precipitation in downstream areas as observed. An updated, scale-aware version of the Kain–Fritsch scheme is also tested, and decreased model errors both up- and downstream suggest that scale-aware updates yield improvements in the simulation of this event. Comparisons among multiple CP schemes demonstrate that there are model convective physics gray zone considerations that significantly impact the simulation of extreme rainfall in this event.

scholarly journals Accuracy of Rotational and Divergent Kinetic Energy Spectra Diagnosed from Flight-Track Winds

2016 ◽  
Vol 73 (8) ◽  
pp. 3273-3286 ◽  
Author(s):  
Lotte Bierdel ◽  
Chris Snyder ◽  
Sang-Hun Park ◽  
William C. Skamarock
Keyword(s):  
Water Vapor ◽  
Kinetic Energy ◽  
Energy Spectra ◽  
Commercial Aircraft ◽  
Rotational Mode ◽  
One Dimensional ◽  
Significant Dependence ◽  
Rotational Components ◽  
Atmospheric Simulations

Abstract Under assumptions of horizontal homogeneity and isotropy, one may derive relations between rotational or divergent kinetic energy spectra and velocities along one-dimensional tracks, such as might be measured by aircraft. Two recent studies, differing in details of their implementation, have applied these relations to the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) dataset and reached different conclusions with regard to the mesoscale ratio of divergent to rotational kinetic energy. In this study the accuracy of the method is assessed using global atmospheric simulations performed with the Model for Prediction Across Scales, where the exact decomposition of the horizontal winds into divergent and rotational components may be easily computed. For data from the global simulations, the two approaches yield similar and very accurate results. Errors are largest for the divergent component on synoptic scales, which is shown to be related to a very dominant rotational mode. The errors are, in particular, sufficiently small so that the mesoscale ratio of divergent to rotational kinetic energy can be derived correctly. The proposed technique thus provides a strong observational check of model results with existing large commercial aircraft datasets. The results do, however, show a significant dependence on the height and latitude ranges considered, and the disparate conclusions drawn from previous applications to MOZAIC data may result from the use of different subsets of the data.

Model Error in Filtering Random Compressible Flows Utilizing Noisy Lagrangian Tracers

2016 ◽  
Vol 144 (11) ◽  
pp. 4037-4061 ◽  
Author(s):  
Nan Chen ◽  
Andrew J. Majda
Keyword(s):  
Compressible Flows ◽  
Forecast Model ◽  
Flow Fields ◽  
Model Error ◽  
Primary Concern ◽  
Model Errors ◽  
Computationally Efficient ◽  
Forecast Models ◽  
Lagrangian Tracers ◽  
Rotating Shallow Water

Abstract Lagrangian tracers are drifters and floaters that collect real-time information of fluid flows. This paper studies the model error in filtering multiscale random rotating compressible flow fields utilizing noisy Lagrangian tracers. The random flow fields are defined through random amplitudes of Fourier eigenmodes of the rotating shallow-water equations that contain both incompressible geostrophically balanced (GB) flows and rotating compressible gravity waves, where filtering the slow-varying GB flows is of primary concern. Despite the inherent nonlinearity in the observations with mixed GB and gravity modes, there are closed analytical formulas for filtering the underlying flows. Besides the full optimal filter, two practical imperfect filters are proposed. An information-theoretic framework is developed for assessing the model error in the imperfect filters, which can apply to a single realization of the observations. All the filters are comparably skillful in a fast rotation regime (Rossby number ). In a moderate rotation regime (), significant model errors are found in the reduced filter containing only GB forecast model, while the computationally efficient 3D-Var filter with a diagonal covariance matrix remains skillful. First linear then nonlinear coupling of GB and gravity modes is introduced in the random Fourier amplitudes, while linear forecast models are retained to ensure the filter estimates have closed analytical expressions. All the filters remain skillful in the regime. In the regime, the full filter with a linear forecast model has an acceptable filtering skill, while large model errors are shown in the other two imperfect filters.

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