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

2018 ◽  
Vol 146 (11) ◽  
pp. 3901-3925 ◽  
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.

scholarly journals Impact of model improvements on 80-m wind speeds during the second Wind Forecast Improvement Project (WFIP2)

2019 ◽  
Author(s):  
Laura Bianco ◽  
Irina V. Djalalova ◽  
James M. Wilczak ◽  
Joseph B. Olson ◽  
Jaymes S. Kenyon ◽  
...  
Keyword(s):  
High Resolution ◽  
Wind Speed ◽  
Weather Prediction ◽  
Mean Bias Error ◽  
Grid Spacing ◽  
Improvement Project ◽  
Experimental Physics ◽  
Wind Speeds ◽  
The Impact ◽  
Horizontal Grid

Abstract. During the second Wind Forecast Improvement Project (WFIP2; Oct 2015–Mar 2017, Columbia River Gorge and Basin area) several improvements to the parameterizations applied in the High Resolution Rapid Refresh (HRRR – 3 km horizontal grid spacing) and the High Resolution Rapid Refresh Nest (HRRRNEST – 750 m horizontal grid spacing) Numerical Weather Prediction (NWP) models were tested during four 6-week reforecast periods (one for each season). For these tests the models were run in control (CNT) and experimental (EXP) configurations, with the EXP configuration including all the improved parameterizations. The impacts of the experimental parameterizations on the forecast of 80-m wind speeds (hub height) from the HRRR and HRRRNEST models are assessed, using observations collected by 19 sodars and 3 profiling lidars for verification. Improvements due to the experimental physics (EXP vs CNT runs) versus those due to finer horizontal grid spacing (HRRRNEST vs HRRR), and the combination of the two are compared, using standard bulk statistics such as Mean Absolute Error (MAE) and Mean Bias Error (bias). On average, the HRRR 80-m wind speed MAE is reduced by 3–4 % due to the experimental physics. The impact of the finer horizontal grid spacing in the CNT runs also shows a positive improvement of 5 % on MAE, which is particularly large at nighttime and during the morning transition. Lastly, the combined impact of the experimental physics and finer horizontal grid spacing produces larger improvements in the 80-m wind speed MAE, up to 7–8 %. The improvements are evaluated as a function of the model's initialization time, forecast horizon, time of the day, season of the year, site elevation, and meteorological phenomena, also looking for the causes of model weaknesses. Finally, bias correction methods are applied to the 80-m wind speed model outputs to measure their impact on the improvements due to the removal of the systematic component of the errors.

scholarly journals Impact of model improvements on 80 m wind speeds during the second Wind Forecast Improvement Project (WFIP2)

2019 ◽  
Vol 12 (11) ◽  
pp. 4803-4821 ◽  
Author(s):  
Laura Bianco ◽  
Irina V. Djalalova ◽  
James M. Wilczak ◽  
Joseph B. Olson ◽  
Jaymes S. Kenyon ◽  
...  
Keyword(s):  
High Resolution ◽  
Wind Speed ◽  
Weather Prediction ◽  
Mean Bias Error ◽  
Grid Spacing ◽  
Improvement Project ◽  
Experimental Physics ◽  
Wind Speeds ◽  
The Impact ◽  
Horizontal Grid

Abstract. During the second Wind Forecast Improvement Project (WFIP2; October 2015–March 2017, held in the Columbia River Gorge and Basin area of eastern Washington and Oregon states), several improvements to the parameterizations used in the High Resolution Rapid Refresh (HRRR – 3 km horizontal grid spacing) and the High Resolution Rapid Refresh Nest (HRRRNEST – 750 m horizontal grid spacing) numerical weather prediction (NWP) models were tested during four 6-week reforecast periods (one for each season). For these tests the models were run in control (CNT) and experimental (EXP) configurations, with the EXP configuration including all the improved parameterizations. The impacts of the experimental parameterizations on the forecast of 80 m wind speeds (wind turbine hub height) from the HRRR and HRRRNEST models are assessed, using observations collected by 19 sodars and three profiling lidars for comparison. Improvements due to the experimental physics (EXP vs. CNT runs) and those due to finer horizontal grid spacing (HRRRNEST vs. HRRR) and the combination of the two are compared, using standard bulk statistics such as mean absolute error (MAE) and mean bias error (bias). On average, the HRRR 80 m wind speed MAE is reduced by 3 %–4 % due to the experimental physics. The impact of the finer horizontal grid spacing in the CNT runs also shows a positive improvement of 5 % on MAE, which is particularly large at nighttime and during the morning transition. Lastly, the combined impact of the experimental physics and finer horizontal grid spacing produces larger improvements in the 80 m wind speed MAE, up to 7 %–8 %. The improvements are evaluated as a function of the model's initialization time, forecast horizon, time of the day, season of the year, site elevation, and meteorological phenomena. Causes of model weaknesses are identified. Finally, bias correction methods are applied to the 80 m wind speed model outputs to measure their impact on the improvements due to the removal of the systematic component of the errors.

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 EFFECTS OF MESH RESOLUTION ON THE SIMULATION OF SEVERE THUNDERSTORM: THE NEED OF PARALLEL COMPUTING AND DISTRIBUTED TECHNIQUES

2014 ◽  
Vol 44 (1) ◽  
pp. 31-40
Author(s):  
C. A. AGUIRRE ◽  
R. R. PAZ ◽  
A. B. BRIZUELA
Keyword(s):  
Grid Spacing ◽  
Electrical Transmission ◽  
Transmission Networks ◽  
Severe Thunderstorm ◽  
Wind Speeds ◽  
Eddy Simulation ◽  
Element Size ◽  
Large Eddy ◽  
Mesh Resolution ◽  
Geographical Grid

In the design of civil structures, it is necessary to consider the effect of the dynamic loads caused by changes in meteorological conditions such as wind speeds or ice deposits. In Argentina, the Standard of the Argentine Electrotechnical Association (AEA, 2006) is used to calculate structures of electrical transmission networks. This Standard specifies the value that must be assigned to the load by effect of the wind. This value is obtained from the meteorological records measured at conventional meteorological stations such as those of the National Meteorological Service. Nevertheless, to fit this parameter, it is also necessary to carry out local studies with updated information, considering the roughness and, in certain cases, the relief of the ground. Computational mechanics addresses this problem and is currently being used to estimate the values of maximum winds by simulations of severe meteorological events. However, it is also necessary to evaluate the results of this tool to know its accuracy in relation to the parameters of the numerical model. This work shows the use of the Large-eddy Simulation considering two options in the choice of element size used for a geographical grid domain in the thunderstorm occurred in Aranguren, Argentina, in 1998. In the first option, a processor is used to compute this event through a 406-meter grid-spacing in horizontal direction and in the second option a four-processor parallel method is used to obtain a more refined 200meter grid-spacing. The last option allows simulating severe events such as down-burst or vortex occurrence with more details.

scholarly journals Wind and Gravity in Shaping Picea Trunks

2020 ◽  
Author(s):  
Markku Larjavaara ◽  
Mikko Auvinen ◽  
Anu Kantola ◽  
Annikki Mäkelä
Keyword(s):  
Dense Layer ◽  
Bending Moments ◽  
Large Eddy Simulation Model ◽  
Wind Speeds ◽  
Eddy Simulation ◽  
Wind Gusts ◽  
Biomechanical Modelling ◽  
Large Eddy ◽  
Significant Step ◽  
Biomechanical Approach

Abstract Background:Understanding why trunks (tree stems) are the size that they are is important. However, this understanding is fragmented into isolated schools of thought and has been far from complete. Realistic calculations on minimum trunk diameters needed to resist bending moments caused by wind and gravity would be a significant step forward. However, advancements using this biomechanical approach have been delayed by difficulties in modelling wind gusts. We felled and measured five Norway spruces (Picea abies) in an unthinned monoculture in southeastern Finland planted 67 years earlier. We focused on forces working on storm-bent (maximally bent) trees caused by gravity and the strongest gust in a one-hour simulation with a large-eddy simulation model. Results:The three largest trees resisted mean above-canopy wind speeds ranging from 10.2 m s-1 to 12.7 m s-1 (3.3-fold in the gust), but the two smallest were well protected by a dense layer of leaves from the bending tops of larger trees, and could have resisted stronger winds. Gravity caused approximately one quarter of the critical bending moments. Conclusions:Our biomechanical modelling of trunk taper based on wind and gravity leads to diameters close to those measured, and we discuss the potential causes of the deviations. This approach could also be used to model tree biomasses and how those may change with changing climate.

scholarly journals Wind and Gravity in Shaping Picea Trunks

2021 ◽  
Author(s):  
Markku Larjavaara ◽  
Mikko Auvinen ◽  
Anu Kantola ◽  
Annikki Mäkelä
Keyword(s):  
Picea Abies ◽  
Dense Layer ◽  
Bending Moments ◽  
Large Eddy Simulation Model ◽  
Wind Speeds ◽  
Eddy Simulation ◽  
Wind Gusts ◽  
Large Eddy ◽  
Significant Step ◽  
Biomechanical Approach

Abstract Understanding why trunks (tree stems) are the size that they are is important. However, this understanding is fragmented into isolated schools of thought and has been far from complete. Realistic calculations on minimum trunk diameters needed to resist bending moments caused by wind and gravity would be a significant step forward. However, advancements using this biomechanical approach have been delayed by difficulties in modelling bending of trunks and wind gusts. We felled and measured five Norway spruces (Picea abies) in an unthinned monoculture in southeastern Finland planted 67 years earlier. We focused on forces working on storm-bent (maximally bent) trees caused by gravity and the strongest gust in a one-hour simulation with a large-eddy simulation model. The weakest points along the trunks of the three largest trees resisted mean above-canopy wind speeds ranging from 10.2 m s-1 to 12.7 m s-1 (3.3-fold in the strongest gust), but the two smallest were well protected by a dense layer of leaves from the bending tops of larger trees, and could have resisted stronger winds. Gravity caused approximately one quarter of the critical bending moments. The wind that breaks the trunks in their weakest points is close to breaking them in other points, supporting importance of bending moments caused by wind and gravity in evolution of trunk taper. This approach could also be used to model tree biomasses and how those may change with changing climate.

scholarly journals Large-eddy simulation of traffic-related air pollution at a very high-resolution in a mega-city: Evaluation against mobile sensors and insights for influencing factors

2020 ◽  
Author(s):  
Yanxu Zhang ◽  
Xingpei Ye ◽  
Shibao Wang ◽  
Xiaojing He ◽  
Lingyao Dong ◽  
...  
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
High Resolution ◽  
Large Eddy Simulation ◽  
Urban Air ◽  
Dispersion Pattern ◽  
Wind Speeds ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Very High

Abstract. Urban air pollution has tremendous spatial variability at scales ranged from kilometer to meters due to unevenly distributed emission sources, complex flow patterns, and photochemical reactions. However, high-resolution air quality information is not available through traditional approaches such as ground-based measurements and regional air quality models (with typical resolution >1 km). Here we develop a ten-meter resolution air quality model for traffic-related CO pollution based on the parallelized large-eddy simulation model (PALM). The model performance is evaluated with measurements obtained from sensors deployed on a taxi platform, which collects data with a comparable spatial resolution to our model. The very high resolution of the model reveals a detailed geographical dispersion pattern of air pollution in and out of the road network. The model results (0.92 ± 0.40 mg/m3) agree well with the measurements (0.90 ± 0.58 mg/m3, n = 114,502). The model has similar spatial patterns with that of the measurements, and the r2 value of a linear regression between model and measurement data is 0.50 ± 0.07 during non-rush hours with middle and low wind speeds. A non-linear relationship is found between average modeled concentrations and wind speed with higher concentrations under calm wind speeds. The modeled concentrations are also 20–30 % higher in streets that align with the wind direction within ~20°. We find that streets with higher buildings in the downwind have lower modeled concentrations at the pedestrian level, and similar effects are found for the variability in building heights (including gaps between buildings). The modeled concentrations also decay fast in the first ~50 m from the nearest highway and arterial road but change slower further away. This study demonstrates the potential of large eddy simulation in urban air quality modeling, which is a vigorous part of the smart city system and could inform urban planning and air quality management.

scholarly journals Evaluation of a forest parameterization to improve boundary layer flow simulations over complex terrain

2021 ◽  
Author(s):  
Julian Quimbayo-Duarte ◽  
Johannes Wagner ◽  
Norman Wildmann ◽  
Thomas Gerz ◽  
Juerg Schmidli
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Wind Speed ◽  
Complex Terrain ◽  
Grid Spacing ◽  
Short Term ◽  
Valley Wind ◽  
Layer Flow ◽  
Horizontal Grid

Abstract. We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather research and forecasting model using its large eddy simulation mode (WRF-LES). The short-term high resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 hours and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.

scholarly journals Observational and Modelling Study of a Major Downburst Event in Liguria: The 14 October 2016 Case

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 788 ◽  
Author(s):  
Antonio Parodi ◽  
Martina Lagasio ◽  
Maurizio Maugeri ◽  
Barbara Turato ◽  
William Gallus
Keyword(s):  
High Resolution ◽  
Mediterranean Region ◽  
The United States ◽  
Weather Research And Forecasting ◽  
Grid Spacing ◽  
Wind Gusts ◽  
Weather Events ◽  
Modelling Analysis ◽  
Arw Model ◽  
Horizontal Grid

Downbursts are very disruptive weather events that can produce large amounts of damage. The most studied downbursts are those occurring in the United States and continental Europe, but they can happen globally. This work is an observational and modelling analysis of a major downburst event that occurred on 14 October 2016 over eastern Liguria (Italy). This downburst affected an area 30 km long and 10 km wide, producing observed wind gusts of 40 m/s with major impacts to railways, trees, and houses, with more than 2.5 million euros of damage. First, the general environment influencing this downburst is identified and analyzed, then the event is reproduced with a small multi-physics high-resolution ensemble using the Weather Research and Forecasting (WRF)–advanced research WRF (ARW) model, with 1 km horizontal grid spacing. The event was poorly predicted beforehand, and the difficulty in forecasting this event is confirmed by the fact that so few ensemble members suggested the occurrence of damaging winds over eastern Liguria. However, one of the eight members performed well and its output helped to reveal the primary mechanisms for the downburst, suggesting that high-resolution ensembles using mixed physics may be a useful tool for improving the prediction of similar extreme events in the Mediterranean region in the future.

scholarly journals Large-eddy simulation of traffic-related air pollution at a very high resolution in a mega-city: evaluation against mobile sensors and insights for influencing factors

2021 ◽  
Vol 21 (4) ◽  
pp. 2917-2929
Author(s):  
Yanxu Zhang ◽  
Xingpei Ye ◽  
Shibao Wang ◽  
Xiaojing He ◽  
Lingyao Dong ◽  
...  
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
High Resolution ◽  
Large Eddy Simulation ◽  
Urban Air ◽  
Dispersion Pattern ◽  
Wind Speeds ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Very High

Abstract. Urban air pollution has tremendous spatial variability at scales ranging from kilometers to meters due to unevenly distributed emission sources, complex flow patterns, and photochemical reactions. However, high-resolution air quality information is not available through traditional approaches such as ground-based measurements and regional air quality models (with typical resolution > 1 km). Here we develop a 10 m resolution air quality model for traffic-related CO pollution based on the Parallelized Large-Eddy Simulation Model (PALM). The model performance is evaluated with measurements obtained from sensors deployed on a taxi platform, which collects data with a comparable spatial resolution to our model. The very high resolution of the model reveals a detailed geographical dispersion pattern of air pollution in and out of the road network. The model results (0.92 ± 0.40 mg m−3) agree well with the measurements (0.90 ± 0.58 mg m−3, n=114 502). The model has similar spatial patterns to those of the measurements, and the r2 value of a linear regression between model and measurement data is 0.50 ± 0.07 during non-rush hours with middle and low wind speeds. A non-linear relationship is found between average modeled concentrations and wind speed with higher concentrations under calm wind speeds. The modeled concentrations are also 20 %–30 % higher in streets that align with the wind direction within ∼ 20∘. We find that streets with higher buildings downwind have lower modeled concentrations at the pedestrian level, and similar effects are found for the variability in building heights (including gaps between buildings). The modeled concentrations also decay fast in the first ∼ 50 m from the nearest highway and arterial road but change slower further away. This study demonstrates the potential of large-eddy simulation in urban air quality modeling, which is a vigorous part of the smart city system and could inform urban planning and air quality management.

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