scholarly journals An Examination of Tropical and Extratropical Gust Factors and the Associated Wind Speed Histograms

2005 ◽  
Vol 44 (2) ◽  
pp. 270-280 ◽  
Author(s):  
B. M. Paulsen ◽  
J. L. Schroeder
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Deep Convection ◽  
Transitional Flow ◽  
Wind Gust ◽  
Measuring Device ◽  
Gust Factor ◽  
Mean Wind Speed ◽  
Landfalling Tropical Cyclones ◽  
Gust Factors

Abstract A gust factor, defined as the ratio between a peak wind gust and mean wind speed over a period of time, can be used along with other statistics to examine the structure of the wind. Gust factors are heavily dependent on upstream terrain conditions (roughness), but are also affected by transitional flow regimes (specifically, changes in terrain and the distance from the upstream terrain change to the measuring device), anemometer height, stability of the boundary layer, and, potentially, the presence of deep convection. Previous studies have yielded conflicting results regarding differences in gust factors that might exist between winds generated by tropical cyclones and those generated by extratropical systems. Using high-resolution wind speed data collected from both landfalling tropical cyclones and extratropical systems, two databases of wind characteristics were developed. Gust factors from tropical cyclone and extratropical winds were examined, summarized, and compared. Further analysis was conducted to examine and compare the characteristics of the associated tropical and extratropical wind speed histograms. As expected, the mean gust factor was found to increase with increasing upstream surface roughness. Some differences were observed between data from the tropical environment and the extratropical environment. Mean gust factors from the tropical regime were found to be higher than mean gust factors from the extratropical environment within each roughness regime and the wind speed histograms generated from data from the two environments indicated some differences.

scholarly journals Drifting-snow studies over an instrumented mountainous site: II. Measurements and numerical model at small scale

2001 ◽  
Vol 32 ◽  
pp. 175-181 ◽  
Author(s):  
Jean-Luc Michaux ◽  
Florence Naaim-Bouvet ◽  
Mohamed Naaim
Keyword(s):  
Wind Speed ◽  
Numerical Model ◽  
Small Scale ◽  
Wind Gust ◽  
Strong Wind ◽  
Experimental Site ◽  
In Situ Data ◽  
Drifting Snow ◽  
Mean Wind Speed ◽  
Gust Factors

AbstractThe Érosion torrentielle, neige et avalanche (Etna) unit of CEMAGREF and the Centre d’Etudes de la Neige of Météo-France have been working on snowdrift for 10 years. A numerical model was developed at CEMAGREF to simulate snowdrift (Naaim and others, 1998). To validate this model on in situ data, a high-altitude experimental site was developed, located at 2700 m a.s.l. at the Lac Blanc Pass near the Alpe d’Huez ski resort. It is a nearly flat area and faces winds primarily from north and south. After describing the experimental site, we present the processed data of winter 1998/99. First, we analyze the data from CEMAGREF’s acoustic snowdrift sensor. It is sensitive to snow depth and snow-particle type, so additional calibration is necessary. Nevertheless, it allowed us to study non- stationary aspects of drifting snow. An analysis of gust factors for wind and drifting snow indicates that strong wind-gust factors exist in the mountains, and that drifting snow is more important during a regular and strong wind episode than during high wind-gust periods. Therefore, the numerical model presented here uses only the recorded mean wind speed. The model, which attempts to reproduce several days of storm, takes into account the modification of input parameters (e.g wind speed) as a function of time. The comparison between numerical results and measurements for a given meteorological event shows good agreement.

scholarly journals Meteorologically Stratified Gust Factors for Forecasting Peak Wind Gusts Across the United States

2021 ◽  
pp. 1-17
Author(s):  
Jonathan D. W. Kahl ◽  
Brandon R. Selbig ◽  
Austin R. Harris
Keyword(s):  
United States ◽  
Wind Speed ◽  
Power Distribution ◽  
The United States ◽  
Wind Gust ◽  
Average Wind Speed ◽  
Gust Factor ◽  
Wind Gusts ◽  
Wide Range ◽  
Gust Factors

AbstractWind gusts are common to everyday life and affect a wide range of interests including wind energy, structural design, forestry, and fire danger. Strong gusts are a common environmental hazard that can damage buildings, bridges, aircraft, and trains, and interrupt electric power distribution, air traffic, waterways transport, and port operations. Despite representing the component of wind most likely to be associated with serious and costly hazards, reliable forecasts of peak wind gusts have remained elusive. A project at the University of Wisconsin-Milwaukee is addressing the need for improved peak gust forecasts with the development of the meteorologically stratified gust factor (MSGF) model. The MSGF model combines gust factors (the ratio of peak wind gust to average wind speed) with wind speed and direction forecasts to predict hourly peak wind gusts. The MSGF method thus represents a simple, viable option for the operational prediction of peak wind gusts. Here we describe the results of a project designed to provide the site-specific gust factors necessary for operational use of the MSGF model at a large number of locations across the United States. Gust web diagrams depicting the wind speed- and wind direction-stratified gust factors, as well as peak gust climatologies, are presented for all sites analyzed.

scholarly journals Gust Factors: Meteorologically Stratified Climatology, Data Artifacts, and Utility in Forecasting Peak Gusts

2017 ◽  
Vol 56 (12) ◽  
pp. 3151-3166 ◽  
Author(s):  
Austin R. Harris ◽  
Jonathan D. W. Kahl
Keyword(s):  
Wind Speed ◽  
Meteorological Factors ◽  
Factor Models ◽  
Wind Gust ◽  
Gust Factor ◽  
Wind Measurements ◽  
The Mean ◽  
Substantial Bias ◽  
Wind Speed Forecast ◽  
Gust Factors

AbstractGust factors in Milwaukee, Wisconsin, are investigated using Automated Surface Observing System (ASOS) wind measurements from 2007 to 2014. Wind and gust observations reported in the standard hourly ASOS dataset are shown to contain substantial bias caused by sampling and reporting protocols that restrict the reporting of gusts to arbitrarily defined “gusty” periods occurring during small subsets of each hour. The hourly ASOS gust reports are found to be inadequate for describing the gust characteristics of the site and ill suited for the study of gust factors. A gust-factor climatology was established for Milwaukee using the higher-resolution, 1-min version of the ASOS dataset. The mean gust factor is 1.74. Stratified climatologies demonstrate that Milwaukee gust factors vary substantially with meteorological factors, with wind speed and wind direction exerting the strongest controls. A variety of modified gust-factor models were evaluated in which the peak wind gust is estimated by multiplying a gust factor by the observed, rather than forecast, wind speed. Errors thus obtained are entirely attributable to utility of the gust factor in forecasting peak gusts, having eliminated any error associated with the wind speed forecast. Results show that gust-factor models demonstrate skill in estimating peak gusts and improve with the use of meteorologically stratified gust factors.

Spatial variations of North Atlantic landfalling tropical cyclone wind speed decay over the continental United States

2021 ◽  
Author(s):  
Yi-Jie Zhu ◽  
Jennifer M. Collins ◽  
Philip J. Klotzbach
Keyword(s):  
United States ◽  
Wind Speed ◽  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
East Coast ◽  
Gulf Coast ◽  
Spatial Variations ◽  
Decay Model ◽  
Weak Intensity ◽  
Landfalling Tropical Cyclones

AbstractUnderstanding tropical cyclone wind speed decay during the post-landfall stage is critical for inland hazard preparation. This paper examines the spatial variation of wind speed decay of tropical cyclones over the continental United States. We find that tropical cyclones making landfall over the Gulf Coast decay faster within the first 24 hours after landfall than those making landfall over the Atlantic East Coast. The variation of the decay rate over the Gulf Coast remains larger than that over the Atlantic East Coast for tropical cyclones that had made landfall more than 24 hours prior. Besides an average weaker tropical cyclone landfall intensity, the near-parallel trajectory and the proximity of storms to the coastline also help to explain the slower post-landfall wind speed decay for Atlantic East Coast landfalling tropical cyclones. Tropical cyclones crossing the Florida peninsula only slowly weaken after landfall, with an average of less than 20% post-landfall wind speed drop while transiting the state. The existence of these spatial variations also brings into question the utility of a uniform wind decay model. While weak intensity decay over the Florida peninsula is well estimated by the uniform wind decay model, the error from the uniform wind decay model increases with tropical cyclones making direct landfall more parallel to the Atlantic East Coast. The underestimation of inland wind speed by the uniform wind decay model found over the western Gulf Coast brings attention to the role of land-air interactions in the decay of inland tropical cyclones.

scholarly journals An Examination of Wind Decay, Sustained Wind Speed Forecasts, and Gust Factors for Recent Tropical Cyclones in the Mid-Atlantic Region of the United States

2015 ◽  
Vol 30 (1) ◽  
pp. 153-176 ◽  
Author(s):  
Bryce Tyner ◽  
Anantha Aiyyer ◽  
Jonathan Blaes ◽  
Donald Reid Hawkins
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Tropical Cyclones ◽  
Surface Wind ◽  
Software Tool ◽  
Weather Forecast ◽  
The United States ◽  
Atlantic Region ◽  
Wind Speeds ◽  
Gust Factors

Abstract In this study, several analyses were conducted that were aimed at improving sustained wind speed and gust forecasts for tropical cyclones (TCs) affecting coastal regions. An objective wind speed forecast analysis of recent TCs affecting the mid-Atlantic region was first conducted to set a benchmark for improvement. Forecasts from the National Digital Forecast Database were compared to observations and surface wind analyses in the region. The analysis suggests a general overprediction of sustained wind speeds, especially for areas affected by the strongest winds. Currently, National Weather Service Weather Forecast Offices use a software tool known as the Tropical Cyclone Forecast/Advisory (TCM) wind tool (TCMWindTool) to develop their wind forecast grids. The tool assumes linear decay in the sustained wind speeds when interpolating the National Hurricane Center 12–24-hourly TCM product to hourly grids. An analysis of postlandfall wind decay for recent TCs was conducted to evaluate this assumption. Results indicate that large errors in the forecasted wind speeds can emerge, especially for stronger storms. Finally, an analysis of gust factors for recent TCs affecting the region was conducted. Gust factors associated with weak sustained wind speeds are shown to be highly variable but average around 1.5. The gust factors decrease to values around 1.2 for wind speeds above 40 knots (kt; 1 kt = 0.51 m s−1) and are in general insensitive to the wind direction, suggesting local rather than upstream surface roughness largely dictates the gust factor at a given location. Forecasters are encouraged to increase land reduction factors used in the TCMWindTool and to modify gust factors to account for factors including the sustained wind speed and local surface roughness.

scholarly journals Secondary Eyewall Formation in Tropical Cyclones by Outflow–Jet Interaction

2017 ◽  
Vol 74 (6) ◽  
pp. 1941-1958 ◽  
Author(s):  
Yi Dai ◽  
Sharanya J. Majumdar ◽  
David S. Nolan
Keyword(s):  
Wind Speed ◽  
Numerical Simulations ◽  
Tropical Cyclones ◽  
Deep Convection ◽  
Stratiform Cloud ◽  
Jet Interaction ◽  
Secondary Eyewall Formation ◽  
Stratiform Region ◽  
Upper Level ◽  
Convective Cells

Abstract This study uses idealized numerical simulations to show that the interaction between tropical cyclones and a midlatitude jet can result in secondary eyewall formation. It is argued that the eddy activity by the outflow–jet interaction can enhance the upper-level outflow, thereby creating an asymmetric stratiform region outside of the primary eyewall. Numerous long-lasting deep convective cells are able to form in the stratiform cloud, creating forcing necessary for the secondary eyewall. The low-level inflow and the TC’s primary circulation advect the deep convective cells inward and cyclonically. The secondary eyewall forms after the deep convection has surrounded the TC. In contrast, numerical simulations without the jet do not show secondary eyewall formation. For moderately strong jets of wind speed 15–30 m s−1, there is little sensitivity to the jet strength. There is sensitivity to the distance between the jet and the TC, with secondary eyewall formation evident when their separation is 15° latitude but not when the separation exceeds 20°.

scholarly journals Effects of Sensor Response and Gust Duration on Maximum Wind Gust Measurements and Data Homogenisation

2020 ◽  
Author(s):  
Amir Ali Safaei Pirooz ◽  
Richard G.J. Flay ◽  
Lorenzo Minola ◽  
Cesar Azorin-Molina ◽  
Deliang Chen
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Turbulence Intensity ◽  
Moving Average ◽  
Wind Gust ◽  
Gust Factor ◽  
Wind Speeds ◽  
Research Areas ◽  
Factor Ratios ◽  
Cup Anemometer

<p>Wind speed data recorded using different signal-processing procedures can introduce errors in the wind speed measurements. This study aims to assess the effects of a set of various moving average filter durations and turbulence intensities on the recorded maximum gust wind speeds. For this purpose, a series of wind-tunnel experiments was carried out at the University of Auckland, New Zealand, on the widely-used Vaisala WAA151 cup anemometer. The variations of gust and peak factors, and turbulence intensities measured by the cup anemometer as a function of the averaging duration and turbulence intensity are presented. The wind-tunnel results are compared with values computed from a theoretical approach, namely random process and linear system theory, and the results were also validated against values reported in the literature where possible.</p><p>To summarise, the major findings of this experimental study are:</p><ol><li>The results show that increasing the effective gust duration reduces both the gust and peak factors, resulting in an underestimation of maximum gust wind speeds and an overestimation of minimum gust wind speeds.</li> <li>The maximum difference between gust factors obtained for high (e.g. 3-s to 5-s) and low (raw, unfiltered measurements) gust durations reached values of 25% – 30% for the high turbulence conditions, and up to 5% – 10% for low turbulence intensities.</li> <li>Gust factor ratios, an important parameter that allow the measurements from a specific gust duration to be converted to other gust durations of interest, are reported for various gust durations as a function of turbulence intensity.</li> <li>The differences and gust factor ratios computed in this study can be applied directly to full-scale measurements, and can be used in several research areas, including analysing and homogenisation of historical wind speed time series, comparing gust climatologies of countries where different gust durations have been adopted, and so on. These factors clearly play an essential role in meteorological, climatological and wind engineering studies.</li> </ol>

scholarly journals Characteristics of Typhoon “Fung-Wong” Near Earth Pulsation

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xiujun Li ◽  
Yongguang Li ◽  
Jianting Zhou ◽  
Qian Wang ◽  
Xu Wang
Keyword(s):  
Wind Speed ◽  
Turbulence Intensity ◽  
Wind Field ◽  
Coherence Function ◽  
Intensity Attenuation ◽  
Gust Factor ◽  
Peak Factor ◽  
Mean Wind Speed ◽  
Wind Characteristic ◽  
Empirical Curve

To study the wind field characteristics near the ground pulsation in typhoon conditions, wind field conditions in the area affected by Typhoon “Fung-Wong” were monitored using wind field instruments installed in the construction building of Wenzhou University, China. Real-time wind field data were collected during typhoons. Wind characteristic parameters such as mean wind speed, wind direction angle, turbulence intensity, gust factor, peak factor, coherence function, and autocorrelation were analyzed, and the wind field characteristics during the typhoon were summarized. The results indicated that the longitudinal and lateral turbulence intensities decreased with an increase in the mean wind speed, and there was an obvious linear relationship between them. The vertical and horizontal gust factor and peak factor decreased with an increase in mean wind speed, and the trend was more obvious in the horizontal direction. There was a significant correlation between the gust factor and the peak factor. The turbulence intensity and gust factor decreased with time, and the turbulence intensity attenuation speed increased with time. The empirical curve presented by Davenport (1961) can simulate the correlation characteristics of the fluctuating wind speed components of Typhoon Fung-Wong at some measuring points. With an increase in the time difference, the dependence of the instantaneous values at the two time points gradually decreased.

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