Fine-Scale Structures in the Mid-Level Eyewall of Super Typhoon Rammasun (2014) Simulated With the WRF-LES Framework

It has been numerically demonstrated that the turbulence above the boundary is important to tropical cyclone intensification and rapid intensification, but the three-dimensional structures of the sub-grid-scale (SGS) eddy have not been revealed due to the lack of observational data. In this study, two numerical simulations of Super Typhoon Rammasun (2014) were conducted with the Advanced Weather Research and Forecast (WRF) model by incorporating the large-eddy simulation (LES) technique, in which the enhanced eyewall convection and the process of rapid intensification are captured. Consistent with previous observational studies, the strong turbulent kinetic energy (TKE) is found throughout the whole eyewall inside of the radius of maximum wind in both experiments. The simulations indicate that the strong TKE is associated with horizontal rolls with the horizontal extent of 2–4 km, which are aligned azimuthally in the intense eyewall convection. It is indicated that the three-dimensional structures of the SGS eddy can be simulated with the vertical grid spacing of ∼100 m when the horizontal grid spacing is 74 m. It is suggested that there is considerable turbulence associated with azimuthally-aligned horizontal rolls in the mid-level eyewall of tropical cyclone.

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Prevalence of tornado-scale vortices in the tropical cyclone eyewall

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1807217115 ◽

2018 ◽

Vol 115 (33) ◽

pp. 8307-8310 ◽

Cited By ~ 8

Author(s):

Liguang Wu ◽

Qingyuan Liu ◽

Yubin Li

Keyword(s):

Boundary Layer ◽

Tropical Cyclone ◽

Turbulent Boundary Layer ◽

Numerical Experiment ◽

Wrf Model ◽

Convective Clouds ◽

Eddy Simulation ◽

Large Eddy ◽

Fast Movement ◽

Horizontal Grid

Analyses of datasets from manned research flights that penetrated hurricane eyes and tropical cyclone (TC) damage surveys strongly suggest the existence of tornado-scale vortices in the turbulent boundary layer of the TC eyewall. However, their small horizontal scale, their fast movement, and the associated severe turbulence make the tornado-scale vortex very difficult to observe directly. To understand tornado-scale vortices in the TC eyewall and their influence on the TC vortex, mesoscale rainbands, and convective clouds, a numerical experiment including seven nested domains with the smallest horizontal grid interval of 37 m is conducted to perform a large eddy simulation (LES) with the Advanced Weather Research and Forecast (WRF) model. We show that most of the observed features associated with tornado-scale vortices can be realistically simulated in the WRF-LES framework. The numerical simulation confirms the existence of simulated tornado-scale vortices in the turbulent boundary layer of the TC eyewall. Our numerical experiment suggests that tornado-scale vortices are prevalent at the inner edge of the intense eyewall convection.

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Evaluation of the Impact of Horizontal Grid Spacing in Terra Incognita on Coupled Mesoscale–Microscale Simulations Using the WRF Framework

Monthly Weather Review ◽

10.1175/mwr-d-18-0282.1 ◽

2019 ◽

Vol 147 (3) ◽

pp. 1007-1027 ◽

Cited By ~ 10

Author(s):

Raj K. Rai ◽

Larry K. Berg ◽

Branko Kosović ◽

Sue Ellen Haupt ◽

Jeffrey D. Mirocha ◽

...

Keyword(s):

Spatial Scales ◽

Wrf Model ◽

Spectral Energy ◽

Grid Spacing ◽

Terra Incognita ◽

Wide Range ◽

Large Eddy ◽

Microscale Simulations ◽

The Impact ◽

Horizontal Grid

Abstract Coupled mesoscale–microscale simulations are required to provide time-varying weather-dependent inflow and forcing for large-eddy simulations under general flow conditions. Such coupling necessarily spans a wide range of spatial scales (i.e., ~10 m to ~10 km). Herein, we use simulations that involve multiple nested domains with horizontal grid spacings in the terra incognita (i.e., km) that may affect simulated conditions in both the outer and inner domains. We examine the impact on simulated wind speed and turbulence associated with forcing provided by a terrain with grid spacing in the terra incognita. We perform a suite of simulations that use combinations of varying horizontal grid spacings and turbulence parameterization/modeling using the Weather Research and Forecasting (WRF) Model using a combination of planetary boundary layer (PBL) and large-eddy simulation subgrid-scale (LES-SGS) models. The results are analyzed in terms of spectral energy, turbulence kinetic energy, and proper orthogonal decomposition (POD) energy. The results show that the output from the microscale domain depends on the type of turbulence model (e.g., PBL or LES-SGS model) used for a given horizontal grid spacing but is independent of the horizontal grid spacing and turbulence modeling of the parent domain. Simulation using a single domain produced less POD energy in the first few modes compared to a coupled simulation (one-way nesting) for similar horizontal grid spacing, which highlights that coupled simulations are required to accurately pass the mesoscale features into the microscale domain.

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The Dispersion of Silver Iodide Particles from Ground-Based Generators over Complex Terrain. Part II: WRF Large-Eddy Simulations versus Observations

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-13-0241.1 ◽

2014 ◽

Vol 53 (6) ◽

pp. 1342-1361 ◽

Cited By ~ 27

Author(s):

Lulin Xue ◽

Xia Chu ◽

Roy Rasmussen ◽

Daniel Breed ◽

Bruce Boe ◽

...

Keyword(s):

Complex Terrain ◽

Silver Iodide ◽

Wrf Model ◽

Static Stability ◽

Particle Dispersion ◽

Grid Spacing ◽

Medicine Bow Mountains ◽

Eddy Simulation ◽

Large Eddy ◽

Orographic Clouds

AbstractA numerical modeling study has been conducted to explore the ability of the Weather Research and Forecasting (WRF) model-based large-eddy simulation (LES) with 100-m grid spacing to reproduce silver iodide (AgI) particle dispersion by comparing the model results with measurements made on 16 February 2011 over the Medicine Bow Mountains in Wyoming. Xue et al.'s recently developed AgI cloud-seeding parameterization was applied in this study to simulate AgI release from ground-based generators. Qualitative and quantitative comparisons between the LES results and observed AgI concentrations were conducted. Analyses of turbulent kinetic energy (TKE) features within the planetary boundary layer (PBL) and comparisons between the 100-m LES and simulations with 500-m grid spacing were performed as well. The results showed the following: 1) Despite the moist bias close to the ground and above 4 km AGL, the LES with 100-m grid spacing captured the essential environmental conditions except for a slightly more stable PBL relative to the observed soundings. 2) Wind shear is the dominant TKE production mechanism in wintertime PBL over complex terrain and generates a PBL of about 1000-m depth. The terrain-induced turbulent eddies are primarily responsible for the vertical dispersion of AgI particles. 3) The LES-simulated AgI plumes were shallow and narrow, in agreement with observations. The LES overestimated AgI concentrations close to the ground, which is consistent with the higher static stability in the model than is observed. 4) Non-LES simulations using PBL schemes had difficulty in capturing the shear-dominant turbulent PBL structure over complex terrain in wintertime. Therefore, LES of wintertime orographic clouds with grid spacing close to 500 m or finer are recommended.

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Where is the Interface of the Stratocumulus-Topped PBL?

Journal of the Atmospheric Sciences ◽

10.1175/jas3470.1 ◽

2005 ◽

Vol 62 (7) ◽

pp. 2626-2631 ◽

Cited By ~ 34

Author(s):

C-H. Moeng ◽

B. Stevens ◽

P. P. Sullivan

Keyword(s):

Turbulent Mixing ◽

Grid Spacing ◽

Free Atmosphere ◽

Maximum Gradient ◽

Eddy Simulation ◽

Large Eddy ◽

Vertical Grid ◽

Fine Resolution ◽

Local Cloud ◽

Simulated Flow

Abstract Various locally defined (not horizontal mean) interfaces between the stratocumulus-topped PBL and the free atmosphere are investigated using a fine-resolution large-eddy simulation with a vertical grid spacing of about 4 m. The local cloud-top height is found to be always below the height where the maximum gradient of the local sounding occurs, and the maximum-gradient height is always below the interface where PBL air can reach via turbulent motions. The distances between these local interfaces are of significant amount, a few tens of meters on average. Air between the cloud-top and maximum-gradient interfaces is fully turbulent, unsaturated, but rather moist. Air between the maximum-gradient and turbulent-mixing interfaces consists of turbulent motions that are intermittent in space and time. The simulated flow shows no clearly defined interface that separates cloudy, turbulent air mass from clear, nonturbulent air above, even locally.

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Sensitivity of Simulated Tropical Cyclone Structure and Intensity to Horizontal Resolution

Monthly Weather Review ◽

10.1175/2009mwr2976.1 ◽

2010 ◽

Vol 138 (3) ◽

pp. 688-704 ◽

Cited By ~ 132

Author(s):

Megan S. Gentry ◽

Gary M. Lackmann

Keyword(s):

Tropical Cyclone ◽

Wrf Model ◽

Domain Size ◽

Horizontal Resolution ◽

Weather Research And Forecasting ◽

Grid Spacing ◽

Physical Processes ◽

Hurricane Ivan ◽

Horizontal Grid ◽

Grid Length

Abstract The Weather Research and Forecasting (WRF) model is used to test the sensitivity of simulations of Hurricane Ivan (2004) to changes in horizontal grid spacing for grid lengths from 8 to 1 km. As resolution is increased, minimum central pressure decreases significantly (by 30 hPa from 8- to 1-km grid spacing), although this increase in intensity is not uniform across similar reductions in grid spacing, even when pressure fields are interpolated to a common grid. This implies that the additional strengthening of the simulated tropical cyclone (TC) at higher resolution is not attributable to sampling, but is due to changes in the representation of physical processes important to TC intensity. The most apparent changes in simulated TC structure with resolution occur near a grid length of 4 km. At 4-km grid spacing and below, polygonal eyewall segments appear, suggestive of breaking vortex Rossby waves. With sub-4-km grid lengths, localized, intense updraft cores within the eyewall are numerous and both polygonal and circular eyewall shapes appear regularly. Higher-resolution simulations produce a greater variety of shapes, transitioning more frequently between polygonal and circular eyewalls relative to lower-resolution simulations. It is hypothesized that this is because of the ability to resolve a greater range of wavenumbers in high-resolution simulations. Also, as resolution is increased, a broader range of updraft and downdraft velocities is present in the eyewall. These results suggest that grid spacing of 2 km or less is needed for representation of important physical processes in the TC eyewall. Grid-length and domain size suggestions for operational prediction are provided; for operational prediction, a grid length of 3 km or less is recommended.

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Using Simulated Dropsondes to Understand Extreme Updrafts and Wind Speeds in Tropical Cyclones

Monthly Weather Review ◽

10.1175/mwr-d-18-0041.1 ◽

2018 ◽

Vol 146 (11) ◽

pp. 3901-3925 ◽

Cited By ~ 6

Author(s):

Daniel P. Stern ◽

George H. Bryan

Keyword(s):

High Resolution ◽

Wind Speed ◽

Tropical Cyclones ◽

Grid Spacing ◽

Wind Speeds ◽

Eddy Simulation ◽

Wind Gusts ◽

Large Eddy ◽

Horizontal Grid ◽

Insight Into

Abstract Extreme updrafts (≥10 m s−1) and wind gusts (≥90 m s−1) are ubiquitous within the low-level eyewall of intense tropical cyclones (TCs). Previous studies suggest that both of these features are associated with coherent subkilometer-scale vortices. Here, over 100 000 “virtual” dropsonde trajectories are examined within a large-eddy simulation (31.25-m horizontal grid spacing) of a category 5 hurricane in order to gain insight into the nature of these features and to better understand and interpret dropsonde observations. At such a high resolution, profiles of wind speed and vertical velocity from the virtual sondes are difficult to distinguish from those of real dropsondes. PDFs of the strength of updrafts and wind gusts compare well between the simulated and observed dropsondes, as do the respective range of heights over which these features are found. Individual simulated updrafts can be tracked for periods of up to several minutes, revealing structures that are both coherent and rapidly evolving. It appears that the updrafts are closely associated with vortices and wind speed maxima, consistent with previous studies. The peak instantaneous wind gusts in the simulations (up to 150 m s−1) are substantially stronger than have ever been observed. Using the virtual sondes, it is demonstrated that the probability of sampling such extremes is vanishingly small, and it is argued that actual intense TCs might also be characterized by gusts of these magnitudes.

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Correction: Wall-Modeled Large Eddy Simulation of a Three-Dimensional Shock-Boundary Layer Interaction

2018 AIAA Aerospace Sciences Meeting ◽

10.2514/6.2018-1298.c1 ◽

2018 ◽

Author(s):

Nicholas Marco ◽

Jeffrey R. Komives

Keyword(s):

Boundary Layer ◽

Large Eddy Simulation ◽

Three Dimensional ◽

Layer Interaction ◽

Eddy Simulation ◽

Shock Boundary Layer Interaction ◽

Large Eddy ◽

Boundary Layer Interaction

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Large Eddy Simulation of Three-Dimensional High Speed Aerodynamics Flows

10.21236/ada386842 ◽

2000 ◽

Author(s):

Doyle Knight ◽

Hong Yan

Keyword(s):

Large Eddy Simulation ◽

High Speed ◽

Three Dimensional ◽

Eddy Simulation ◽

Large Eddy

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A THREE DIMENSIONAL MODEL OF THE GULF OF ALASKA

Coastal Engineering Proceedings ◽

10.9753/icce.v20.193 ◽

1986 ◽

Vol 1 (20) ◽

pp. 193 ◽

Cited By ~ 2

Author(s):

Shiao-Kung Liu ◽

Jan J. Leendertse

Keyword(s):

Three Dimensional ◽

Gulf Of Alaska ◽

Vertical Shear ◽

Dimensional Model ◽

Three Dimensional Model ◽

Weather Model ◽

Closure Scheme ◽

Vertical Grid ◽

Northern Pacific ◽

Horizontal Grid

This paper presents the development of a three dimensional model of the Gulf of Alaska. The model extends between the Vancouver Island and the Aleutian Islands covering approximatedly 1.5 million square kilometers over the northern Pacific Ocean. Formulated on an ellipsoidal horizontal grid and variable vertical grid, the model is schematized over a 81 x 53 x 10 grid structure. The solution scheme is implicit over the vertical and is programmed using one-dimensional dynamic array for the efficient use of machine storage. The turbulence closure scheme for the non-homogeneous vertical shear is formulated so that the potential and kinetic energetics are monitored and transferred in a closed form. The hydrodynamic model is coupled to a two-dimensional stochastic weather model and an oil-spill trajectory/weathering model. The former also simulates stochastically the cyclogenetic/cyclolytic processes within the modeled area. The paper also compares the computed results with the available field data. Good agreements are found in tidal amplitude and phases as well as currents.

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