scholarly journals Sensitivity of Simulated Tropical Cyclone Structure and Intensity to Horizontal Resolution

2010 ◽  
Vol 138 (3) ◽  
pp. 688-704 ◽  
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.

Analysis of Idealized Tropical Cyclone Simulations Using the Weather Research and Forecasting Model: Sensitivity to Turbulence Parameterization and Grid Spacing

2009 ◽  
Vol 137 (2) ◽  
pp. 745-765 ◽  
Author(s):  
Kevin A. Hill ◽  
Gary M. Lackmann
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Maximum Intensity ◽  
Weather Research And Forecasting ◽  
Grid Spacing ◽  
Exchange Coefficient ◽  
Model Sensitivity ◽  
Wind Speeds ◽  
Horizontal Grid ◽  
Weather Research

Abstract The Weather Research and Forecasting Advanced Research Model (WRF-ARW) was used to perform idealized tropical cyclone (TC) simulations, with domains of 36-, 12-, and 4-km horizontal grid spacing. Tests were conducted to determine the sensitivity of TC intensity to the available surface layer (SL) and planetary boundary layer (PBL) parameterizations, including the Yonsei University (YSU) and Mellor–Yamada–Janjic (MYJ) schemes, and to horizontal grid spacing. Simulations were run until a quasi-steady TC intensity was attained. Differences in minimum central pressure (Pmin) of up to 35 hPa and maximum 10-m wind (V10max) differences of up to 30 m s−1 were present between a convection-resolving nested domain with 4-km grid spacing and a parent domain with cumulus parameterization and 36-km grid spacing. Simulations using 4-km grid spacing are the most intense, with the maximum intensity falling close to empirical estimates of maximum TC intensity. Sensitivity to SL and PBL parameterization also exists, most notably in simulations with 4-km grid spacing, where the maximum intensity varied by up to ∼10 m s−1 (V10max) or ∼13 hPa (Pmin). Values of surface latent heat flux (LHFLX) are larger in MYJ than in YSU at the same wind speeds, and the differences increase with wind speed, approaching 1000 W m−2 at wind speeds in excess of 55 m s−1. This difference was traced to a larger exchange coefficient for moisture, CQ, in the MYJ scheme. The exchange coefficients for sensible heat (Cθ) and momentum (CD) varied by <7% between the SL schemes at the same wind speeds. The ratio Cθ/CD varied by <5% between the schemes, whereas CQ/CD was up to 100% larger in MYJ, and the latter is theorized to contribute to the differences in simulated maximum intensity. Differences in PBL scheme mixing also likely played a role in the model sensitivity. Observations of the exchange coefficients, published elsewhere and limited to wind speeds <30 m s−1, suggest that CQ is too large in the MYJ SL scheme, whereas YSU incorporates values more consistent with observations. The exchange coefficient for momentum increases linearly with wind speed in both schemes, whereas observations suggest that the value of CD becomes quasi-steady beyond some critical wind speed (∼30 m s−1).

scholarly journals Simulation of the Summer Monsoon Rainfall over East Asia Using the NCEP GFS Cumulus Parameterization at Different Horizontal Resolutions

2014 ◽  
Vol 29 (5) ◽  
pp. 1143-1154 ◽  
Author(s):  
Kyo-Sun Sunny Lim ◽  
Song-You Hong ◽  
Jin-Ho Yoon ◽  
Jongil Han
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Wrf Model ◽  
Horizontal Resolution ◽  
Cumulus Parameterization ◽  
Grid Spacing ◽  
Simulated Precipitation ◽  
Horizontal Grid

Abstract The most recent version of the simplified Arakawa–Schubert (SAS) cumulus scheme in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) (GFS SAS) is implemented in the Weather Research and Forecasting (WRF) Model with a modification of the triggering condition and the convective mass flux in order to make it dependent on the model’s horizontal grid spacing. The East Asian summer monsoon season of 2006 is selected in order to evaluate the performance of the modified GFS SAS scheme. In comparison to the original GFS SAS scheme, the modified GFS SAS scheme shows overall better agreement with the observations in terms of the simulated monsoon rainfall. The simulated precipitation from the original GFS SAS scheme is insensitive to the model’s horizontal grid spacing, which is counterintuitive because the portion of the resolved clouds in a grid box should increase as the model grid spacing decreases. This behavior of the original GFS SAS scheme is alleviated by the modified GFS SAS scheme. In addition, three different cumulus schemes (Grell and Freitas, Kain and Fritsch, and Betts–Miller–Janjić) are chosen to investigate the role of a horizontal resolution on the simulated monsoon rainfall. Although the forecast skill of the surface rainfall does not always improve as the spatial resolution increases, the improvement of the probability density function of the rain rate with the smaller grid spacing is robust regardless of the cumulus parameterization scheme.

scholarly journals Sensitivity of Fine-Scale Structure in Tropical Cyclone Boundary Layer to Model Horizontal Resolution at Sub-Kilometer Grid Spacing

2021 ◽  
Vol 9 ◽  
Author(s):  
Hongxiong Xu ◽  
Yuqing Wang
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Mesoscale Model ◽  
Horizontal Resolution ◽  
Scale Structure ◽  
Fine Scale ◽  
Grid Spacing ◽  
Large Eddies ◽  
Horizontal Grid

In view of the increasing interest in the explicit simulation of fine-scale features in the tropical cyclone (TC) boundary layer (TCBL), the effects of horizontal grid spacing on a 7–10 h simulation of an idealized TC are examined using the Weather Research and Forecast (ARW-WRF) mesoscale model with one-way moving nests and the nonlinear backscatter with anisotropy (NBA) sub-grid-scale (SGS) scheme. In general, reducing the horizontal grid spacing from 2 km to 500 m tends to produce a stronger TC with lower minimum sea level pressure (MSLP), stronger surface winds, and smaller TC inner core size. However, large eddies cannot be resolved at these grid spacings. In contrast, reducing the horizontal grid spacing from 500 to 166 m and further to 55 m leads to a decrease in TC intensity and an increase in the inner-core TC size. Moreover, although the 166-m grid spacing starts to resolve large eddies in terms of TCBL horizontal rolls and tornado-scale vortex, the use of the finest grid spacing of 55 m tends to produce shorter wavelengths in the turbulent motion and stronger multi-scale turbulence interaction. It is concluded that a grid spacing of sub-100-meters is desirable to produce more detailed and fine-scale structure of TCBL horizontal rolls and tornado-scale vortices, while the relatively coarse sub-kilometer grid spacing (e.g., 500 m) is more cost-effective and feasible for research that is not interested in the turbulence processes and for real-time operational TC forecasting in the near future.

scholarly journals Mesoscale Horizontal Kinetic Energy Spectra of a Tropical Cyclone

2018 ◽  
Vol 75 (10) ◽  
pp. 3579-3596 ◽  
Author(s):  
Yuan Wang ◽  
Lifeng Zhang ◽  
Jun Peng ◽  
Saisai Liu
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Physical Processes ◽  
Upper Troposphere ◽  
Mature Period ◽  
Vertically Propagating

A high-resolution cloud-permitting simulation with the Weather Research and Forecasting (WRF) Model is performed to investigate the mesoscale horizontal kinetic energy (HKE) spectra of a tropical cyclone (TC). The spectrum displays an arc-like shape in the troposphere and a quasi-linear shape in the lower stratosphere for wavelengths below 500 km during the mature period of the TC, while they both develop a quasi −5/3 slope. The total HKE spectrum is dominated by its rotational component in the troposphere but by its divergent component in the lower stratosphere. Further spectral HKE budget diagnosis reveals a generally downscale cascade of HKE, although a local upscale cascade gradually forms in the lower stratosphere. However, the mesoscale energy spectrum is not only governed by the energy cascade, but is evidently influenced also by other physical processes, among which the buoyancy effect converts available potential energy (APE) to HKE in the mid- and upper troposphere and converts HKE to APE in the lower stratosphere, the vertically propagating inertia–gravity waves transport the HKE from the upper troposphere to lower and higher layers, and the vertical transportation of convection always transports HKE upward.

Characterizing and Optimizing Precipitation Forecasts from a Convection-Permitting Ensemble Initialized by a Mesoscale Ensemble Kalman Filter

2014 ◽  
Vol 29 (6) ◽  
pp. 1295-1318 ◽  
Author(s):  
Craig S. Schwartz ◽  
Glen S. Romine ◽  
Kathryn R. Smith ◽  
Morris L. Weisman
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Initial Conditions ◽  
Characteristic Curve ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Relative Operating Characteristic ◽  
Horizontal Grid ◽  
Grid Length ◽  
Heavy Rainfall Events

Abstract Convection-permitting Weather Research and Forecasting (WRF) Model forecasts with 3-km horizontal grid spacing were produced for a 50-member ensemble over a domain spanning three-quarters of the contiguous United States between 25 May and 25 June 2012. Initial conditions for the 3-km forecasts were provided by a continuously cycling ensemble Kalman filter (EnKF) analysis–forecast system with 15-km horizontal grid length. The 3-km forecasts were evaluated using both probabilistic and deterministic techniques with a focus on hourly precipitation. All 3-km ensemble members overpredicted rainfall and there was insufficient forecast precipitation spread. However, the ensemble demonstrated skill at discriminating between both light and heavy rainfall events, as measured by the area under the relative operating characteristic curve. Subensembles composed of 20–30 members usually demonstrated comparable resolution, reliability, and skill as the full 50-member ensemble. On average, deterministic forecasts initialized from mean EnKF analyses were at least as or more skillful than forecasts initialized from individual ensemble members “closest” to the mean EnKF analyses, and “patched together” forecasts composed of members closest to the ensemble mean during each forecast interval were skillful but came with caveats. The collective results underscore the need to improve convection-permitting ensemble spread and have important implications for optimizing EnKF-initialized forecasts.

scholarly journals Evaluating Weather Research and Forecasting (WRF) Model Predictions of Turbulent Flow Parameters in a Dry Convective Boundary Layer

2011 ◽  
Vol 50 (12) ◽  
pp. 2429-2444 ◽  
Author(s):  
Jeremy A. Gibbs ◽  
Evgeni Fedorovich ◽  
Alexander M. J. van Eijk
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Grid Spacing ◽  
Convective Boundary ◽  
Parameterization Schemes ◽  
Model Predictions ◽  
Horizontal Grid ◽  
Weather Research

AbstractWeather Research and Forecasting (WRF) model predictions using different boundary layer schemes and horizontal grid spacings were compared with observational and numerical large-eddy simulation data for conditions corresponding to a dry atmospheric convective boundary layer (CBL) over the southern Great Plains (SGP). The first studied case exhibited a dryline passage during the simulation window, and the second studied case was used to examine the CBL in a post-cold-frontal environment. The model runs were conducted with three boundary layer parameterization schemes (Yonsei University, Mellor–Yamada–Janjić, and asymmetrical convective) commonly employed within the WRF model environment to represent effects of small-scale turbulent transport. A study domain was centered over the Atmospheric Radiation Measurement Program SGP site in Lamont, Oklahoma. Results show that near-surface flow and turbulence parameters are predicted reasonably well with all tested horizontal grid spacings (1, 2, and 4 km) and that value added through refining grid spacing was minimal at best for conditions considered in this study. In accord with this result, it was suggested that the 16-fold increase in computing overhead associated with changing from 4- to 1-km grid spacing was not justified. Therefore, only differences among schemes at 4-km spacing were presented in detail. WRF model predictions generally overestimated the contribution to turbulence generation by mechanical forcing over buoyancy forcing in both studied CBL cases. Nonlocal parameterization schemes were found to match observational data more closely than did the local scheme, although differences among the predictions with all three schemes were relatively small.

Simulation of the Downshear Reformation of a Tropical Cyclone

2015 ◽  
Vol 72 (12) ◽  
pp. 4529-4551 ◽  
Author(s):  
Leon T. Nguyen ◽  
John Molinari
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Diabatic Heating ◽  
Wrf Model ◽  
Relative Vorticity ◽  
Horizontal Resolution ◽  
Cyclonic Circulation ◽  
Tropical Storm ◽  
Weather Research And Forecasting ◽  
Cyclonic Vorticity

Abstract The downshear reformation of Tropical Storm Gabrielle (2001) was simulated at 1-km horizontal resolution using the Weather Research and Forecasting (WRF) Model. The environmental shear tilted the initial parent vortex downshear left and forced azimuthal wavenumber-1 kinematic, thermodynamic, and convective asymmetries. The combination of surface enthalpy fluxes and a lack of penetrative downdrafts right of shear allowed boundary layer moist entropy to increase to a maximum downshear right. This contributed to convective instability that fueled the downshear convection. Within this convection, an intense mesovortex rapidly developed, with maximum boundary layer relative vorticity reaching 2.2 × 10−2 s−1. Extreme vortex stretching played a key role in the boundary layer spinup of the mesovortex. Cyclonic vorticity remained maximized in the boundary layer and intensified upward with the growth of the convective plume. The circulation associated with the mesovortex and adjacent localized cyclonic vorticity anomalies comprised a developing “inner vortex” on the downshear-left (downtilt) periphery of the parent cyclonic circulation. The inner vortex was nearly upright within a parent vortex that was tilted significantly with height. This inner vortex became the dominant vortex of the system, advecting and absorbing the broad, tilted parent vortex. The reduction of tropical cyclone (TC) vortex tilt from 65 to 20 km in 3 h reflected the emerging dominance of this upright inner vortex. The authors hypothesize that downshear reformation, resulting from diabatic heating associated with asymmetric convection, can aid the TC’s resistance to shear by reducing vortex tilt and by enabling more diabatic heating to occur near the center, a region known to favor TC intensification.

scholarly journals Impacts of Topsoil and Surface Water Salinity on Agriculture: A Study at Paikgachha, Khulna

2021 ◽  
Vol 8 (2) ◽  
pp. 25-32
Author(s):  
Md Ferdous ur Rahman Bhuiya ◽  
Md Humayun Kabir ◽  
Muhammad Ferdaus
Keyword(s):  
Tropical Cyclone ◽  
West Bengal ◽  
Small Deviation ◽  
Wrf Model ◽  
India Meteorological Department ◽  
Horizontal Resolution ◽  
Weather Research And Forecasting ◽  
Sea Level Pressure ◽  
Surface Water Salinity ◽  
Maximum Sustained Wind Speed

Studying the structure, intensity and track of tropical cyclone is very important in effective tropical cyclone warning. In this study, an attempt has been made to simulate the Super Cyclone Amphan to reproduce the structure, intensity and track of the storm that occurred over the Bay of Bengal and made landfall over the coastal zone of Sundarban between Western Bangladesh and Eastern West Bengal of India on 20 May 2020. The Weather Research and Forecasting (WRF) Model was run 120 hours from 0000 UTC of 16 May to 0000 UTC of 21 May 2021 with 9 km horizontal resolution to simulate the selected storm. The model simulated intensity and track of the storm were compared with that of best track data of India Meteorological Department (IMD). The results obtained from the WRF model indicated that the intensity of the selected cyclone in terms of Mean Sea Level Pressure (MSLP) and Maximum Sustained Wind speed (MSW) were 905 hPa and 243 kph whereas the observed MSLP and MSW were close to 920 hPa and 241 kph respectively. It was also indicated that the model predicted the track of the cyclone reasonably well and it was quite close to the best track data throughout its path till landfall with very small deviation and the cyclone made landfall at 7-8 hours before the actual landfall with 167.4 km position error. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 8(2), 2019, P 25-32

Numerical Study of the 6 May 2012 Tsukuba Supercell Tornado: Vorticity Sources Responsible for Tornadogenesis

2020 ◽  
Vol 148 (3) ◽  
pp. 1205-1228 ◽  
Author(s):  
Tao Tao ◽  
Tetsuro Tamura
Keyword(s):  
Numerical Study ◽  
Wrf Model ◽  
Surface Friction ◽  
Weather Research And Forecasting ◽  
Streamwise Vorticity ◽  
Grid Spacing ◽  
Low Level ◽  
Vorticity Source ◽  
Horizontal Grid ◽  
Remarkable Progress

Abstract Remarkable progress has been achieved in understanding the vorticity source responsible for tornadogenesis. Nevertheless, the answer to this question remains elusive, particularly after introducing surface friction in realistic tornado simulations. In this study, a simulation using the Weather Research and Forecasting (WRF) Model is conducted based on the F3 supercell tornado that hit Tsukuba City, Japan, on 6 May 2012. The simulation uses triply nested domains, and the tornado is successfully reproduced in the innermost domain with 50-m horizontal grid spacing. The circulation analyses reveal that the frictional term is the dominant vorticity source responsible for the vortices at both the pretornadic and tornadogenesis times. The detailed vorticity source analyses of the air parcels show that the vorticity of the tornado at the genesis time mainly originates from the frictionally generated crosswise vorticity near the ground. The crosswise vorticity is directly tilted (or first exchanged into streamwise vorticity and then tilted) into vertical vorticity when the air parcels enter the tornado. A rear-flank downdraft (RFD) surge from the south and west sides of a primary low-level mesocyclone (LMC) may trigger tornadogenesis by increasing the convergence near the ground. The RFD surge is not necessarily associated with the baroclinically generated vorticity. In this study, the baroclinity is weak across the hook echo, which may cause a lack of baroclinically generated vorticity in the RFD surge.

Next-Day Convection-Allowing WRF Model Guidance: A Second Look at 2-km versus 4-km Grid Spacing

2009 ◽  
Vol 137 (10) ◽  
pp. 3351-3372 ◽  
Author(s):  
Craig S. Schwartz ◽  
John S. Kain ◽  
Steven J. Weiss ◽  
Ming Xue ◽  
David R. Bright ◽  
...  
Keyword(s):  
Wrf Model ◽  
Heavy Rain ◽  
The United States ◽  
Skill Score ◽  
Horizontal Resolution ◽  
Substantial Improvement ◽  
Added Value ◽  
Grid Spacing ◽  
Similar Work ◽  
Horizontal Grid

Abstract During the 2007 NOAA Hazardous Weather Testbed (HWT) Spring Experiment, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma produced convection-allowing forecasts from a single deterministic 2-km model and a 10-member 4-km-resolution ensemble. In this study, the 2-km deterministic output was compared with forecasts from the 4-km ensemble control member. Other than the difference in horizontal resolution, the two sets of forecasts featured identical Advanced Research Weather Research and Forecasting model (ARW-WRF) configurations, including vertical resolution, forecast domain, initial and lateral boundary conditions, and physical parameterizations. Therefore, forecast disparities were attributed solely to differences in horizontal grid spacing. This study is a follow-up to similar work that was based on results from the 2005 Spring Experiment. Unlike the 2005 experiment, however, model configurations were more rigorously controlled in the present study, providing a more robust dataset and a cleaner isolation of the dependence on horizontal resolution. Additionally, in this study, the 2- and 4-km outputs were compared with 12-km forecasts from the North American Mesoscale (NAM) model. Model forecasts were analyzed using objective verification of mean hourly precipitation and visual comparison of individual events, primarily during the 21- to 33-h forecast period to examine the utility of the models as next-day guidance. On average, both the 2- and 4-km model forecasts showed substantial improvement over the 12-km NAM. However, although the 2-km forecasts produced more-detailed structures on the smallest resolvable scales, the patterns of convective initiation, evolution, and organization were remarkably similar to the 4-km output. Moreover, on average, metrics such as equitable threat score, frequency bias, and fractions skill score revealed no statistical improvement of the 2-km forecasts compared to the 4-km forecasts. These results, based on the 2007 dataset, corroborate previous findings, suggesting that decreasing horizontal grid spacing from 4 to 2 km provides little added value as next-day guidance for severe convective storm and heavy rain forecasters in the United States.

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