A Global Climatology of Tropical Cyclone Eyes

2018 ◽  
Vol 146 (7) ◽  
pp. 2089-2101 ◽  
Author(s):  
Kenneth R. Knapp ◽  
Christopher S. Velden ◽  
Anthony J. Wimmers
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Objective Measure ◽  
Infrared Images ◽  
Area At Risk ◽  
Wind Speeds ◽  
Time Period ◽  
Agency Practices ◽  
Eye Location ◽  
The Western Pacific

Abstract Intense tropical cyclones (TCs) generally produce a cloud-free center with calm winds, called the eye. The Automated Rotational Center Hurricane Eye Retrieval (ARCHER) algorithm is used to analyze Hurricane Satellite (HURSAT) B1 infrared satellite imagery data for storms occurring globally from 1982 to 2015. HURSAT B1 data provide 3-hourly observations of TCs. The result is a 34-yr climatology of eye location and size. During that time period, eyes are identified in about 13% of all infrared images and slightly more than half of all storms produced an eye. Those that produce an eye have (on average) 30 h of eye scenes. Hurricane Ioke (1992) had the most eye images (98, which is 12 complete days with an eye). The median wind speed of a system with an eye is 97 kt (50 m s−1) [cf. 35 kt (18 m s−1) for those without an eye]. Eyes are much more frequent in the Northern Hemisphere (particularly in the western Pacific) but eyes are larger in the Southern Hemisphere. The regions where eyes occur are expanding poleward, thus expanding the area at risk of TC-related damage. Also, eye scene occurrence can provide an objective measure of TC activity in place of those based on maximum wind speeds, which can be affected by available observations and forecast agency practices.

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 Calculating Dropwindsonde Location and Time from TEMP-DROP Messages for Accurate Assimilation and Analysis

2017 ◽  
Vol 34 (8) ◽  
pp. 1673-1678 ◽  
Author(s):  
Sim D. Aberson ◽  
Kathryn J. Sellwood ◽  
Paul A. Leighton
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Current Practice ◽  
Wind Speeds ◽  
The Mean ◽  
Fall Speed ◽  
Mean Differences ◽  
Release Location

AbstractCurrent practice is to transmit dropwindsonde data from aircraft using the TEMP-DROP format, which provides only the release location and time with 0.1° latitude × 0.1° longitude (about 11 km) and 1-h resolutions, respectively. The current dropwindsonde has a fall speed of approximately 15 m s−1, so the instrument will be advected faster horizontally than it will descend if the wind speed exceeds this value. Where wind speeds are greatest, such as in tropical cyclones, this will introduce large errors in the location of the observations, especially near the surface. A technique to calculate the correct time and location of each observation in the TEMP-DROP message is introduced. The mean differences between the calculated and reported locations are about 0.5 km for distance and 15 s for time, or <1% of the error size for distance and <10% for time.

A Comparison of ASOS Near-Surface Winds and WSR-88D-Derived Wind Speed Profiles Measured in Landfalling Tropical Cyclones

2016 ◽  
Vol 31 (4) ◽  
pp. 1343-1361 ◽  
Author(s):  
Richard J. Krupar ◽  
John L. Schroeder ◽  
Douglas A. Smith ◽  
Song-Lak Kang ◽  
Sylvie Lorsolo
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Linear Regression ◽  
Tropical Cyclones ◽  
Estimation Methods ◽  
Speed Ratio ◽  
Near Surface ◽  
Site Specific ◽  
Wind Speeds ◽  
Landfalling Tropical Cyclones

Abstract A set of velocity–azimuth display (VAD) wind speed profiles derived from coastal Weather Surveillance Radar-1988 Doppler (WSR-88D) systems was paired with Automated Surface Observing System (ASOS) 10-m standardized mean and nonstandardized gust wind speeds measured within 10 km of nearby WSR-88Ds. The goal was to formulate an appropriate methodology and empirical relationships to estimate overland near-surface wind conditions in landfalling tropical cyclones (TCs) using VAD tropical cyclone boundary layer (TCBL) lower-tropospheric wind measurements. A total of 17 TCs and seven ASOS/WSR-88D sites were used to construct a unique comparative dataset. Four estimation methods including the log and power laws, mean and gust wind speed ratio (WSR) methods, and curve fitting with linear regression and polynomial fits were evaluated. Results from the evaluation show that WSR-88D site-specific linear regression equations using a VAD 0–200-m layer average wind speed and nonzero intercepts provided the most accurate predictions of the ASOS 10-m standardized mean wind speed. Results also show that a non-site-specific linear regression model using a VAD 0–500-m mean boundary layer (MBL) wind speed and nonzero intercept is 1.07% more accurate than using a single-gust WSR to predict ASOS 10-m nonstandardized gust wind speeds. Only 2.15% of the ASOS 10-m nonstandardized maximum 3-s gust wind speeds were found to exceed the VAD 0–500-m MBL wind speed, indicating that the VAD 0–500-m MBL wind speed represents a viable source of momentum available for transport to the surface in the form of a gust.

Estimation of Surface Wind Speeds in Tropical Cyclones

1960 ◽  
Vol 41 (1) ◽  
pp. 9-13
Author(s):  
C. L. Jordan ◽  
Limon E. Fortner
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Wind Speeds

The surface wind-speed reports in tropical cyclones given by aircraft-reconnaissance observers are based almost exclusively on state-of-sea observations. The reliability of wind estimates prepared in this manner is considered along with some of the practical difficulties involved in making observations from reconnaissance aircraft.

scholarly journals A Model for Air–Sea Interaction Bulk Coefficient over a Warm Mature Sea under Strong Wind

2008 ◽  
Vol 38 (6) ◽  
pp. 1313-1326 ◽  
Author(s):  
Naoto Kihara ◽  
Hiromaru Hirakuchi
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Present Model ◽  
Heat Fluxes ◽  
Strong Wind ◽  
Exchange Coefficient ◽  
Total Enthalpy ◽  
Wind Speeds ◽  
A Value ◽  
Strong Winds

Abstract A boundary layer model for evaluating sensible and latent heat fluxes over a mature sea accounting for sea spray effects at wind speeds of up to 28 m s−1 is presented. Heat exchange across the ocean surface controls the development of tropical cyclones, and Emanuel’s theory suggests that the ratio of the exchange coefficient of total enthalpy to the drag coefficient should be greater than 0.75 to maintain the intensity of tropical cyclones. However, traditional bulk algorithms predict a monotonic decrease in this ratio with increasing wind speed, giving a value of less than 0.5 under tropical cyclone conditions. The present model describes a decrease in the ratio with increasing wind speed under weak to moderate winds (&lt;20 m s−1), and a plateau at approximately 0.7 under strong winds (&gt;20 m s−1).

scholarly journals The Sound of Tropical Cyclones

2014 ◽  
Vol 44 (10) ◽  
pp. 2763-2778 ◽  
Author(s):  
Zhongxiang Zhao ◽  
Eric A. D’Asaro ◽  
Jeffrey A. Nystuen
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Wind Waves ◽  
Sound Field ◽  
Sound Level ◽  
Sound Attenuation ◽  
Low Frequencies ◽  
Wind Speeds ◽  
Sound Levels ◽  
Breaking Wind Waves

Abstract Underwater ambient sound levels beneath tropical cyclones were measured using hydrophones onboard Lagrangian floats, which were air deployed in the paths of Hurricane Gustav (2008) and Typhoons Megi (2010) and Fanapi (2010). The sound levels at 40 Hz–50 kHz from 1- to 50-m depth were measured at wind speeds up to 45 m s−1. The measurements reveal a complex dependence of the sound level on wind speed due to the competing effects of sound generation by breaking wind waves and sound attenuation by quiescent bubbles. Sound level increases monotonically with increasing wind speed only for low frequencies (&lt;200 Hz). At higher frequencies (&gt;200 Hz), sound level first increases and then decreases with increasing wind speed. There is a wind speed that produces a maximum sound level for each frequency; the wind speed of the maximum sound level decreases with frequency. Sound level at &gt;20 kHz mostly decreases with wind speed over the wind range 15–45 m s−1. The sound field is nearly uniform with depth in the upper 50 m with nearly all sound attenuation limited to the upper 2 m at all measured frequencies. A simple model of bubble trajectories based on the measured float trajectories finds that resonant bubbles at the high-frequency end of the observations (25 kHz) could easily be advected deeper than 2 m during tropical cyclones. Thus, bubble rise velocity alone cannot explain the lack of sound attenuation at these depths.

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.

SHAPING OF AN AUTONOMOUS POWER SYSTEM FOR GUARANTEED POWER SUPPLY WITH THE PREDOMINANCE WIND ENERGY

2018 ◽  
pp. 28-50
Author(s):  
S. G. Ignatiev ◽  
S. V. Kiseleva
Keyword(s):  
Energy Storage ◽  
Wind Speed ◽  
Wind Energy ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Energy Demand ◽  
Diesel Generator ◽  
Average Wind Speed ◽  
Wind Speeds ◽  
Average Wind

Optimization of the autonomous wind-diesel plants composition and of their power for guaranteed energy supply, despite the long history of research, the diversity of approaches and methods, is an urgent problem. In this paper, a detailed analysis of the wind energy characteristics is proposed to shape an autonomous power system for a guaranteed power supply with predominance wind energy. The analysis was carried out on the basis of wind speed measurements in the south of the European part of Russia during 8 months at different heights with a discreteness of 10 minutes. As a result, we have obtained a sequence of average daily wind speeds and the sequences constructed by arbitrary variations in the distribution of average daily wind speeds in this interval. These sequences have been used to calculate energy balances in systems (wind turbines + diesel generator + consumer with constant and limited daily energy demand) and (wind turbines + diesel generator + consumer with constant and limited daily energy demand + energy storage). In order to maximize the use of wind energy, the wind turbine integrally for the period in question is assumed to produce the required amount of energy. For the generality of consideration, we have introduced the relative values of the required energy, relative energy produced by the wind turbine and the diesel generator and relative storage capacity by normalizing them to the swept area of the wind wheel. The paper shows the effect of the average wind speed over the period on the energy characteristics of the system (wind turbine + diesel generator + consumer). It was found that the wind turbine energy produced, wind turbine energy used by the consumer, fuel consumption, and fuel economy depend (close to cubic dependence) upon the specified average wind speed. It was found that, for the same system with a limited amount of required energy and high average wind speed over the period, the wind turbines with lower generator power and smaller wind wheel radius use wind energy more efficiently than the wind turbines with higher generator power and larger wind wheel radius at less average wind speed. For the system (wind turbine + diesel generator + energy storage + consumer) with increasing average speed for a given amount of energy required, which in general is covered by the energy production of wind turbines for the period, the maximum size capacity of the storage device decreases. With decreasing the energy storage capacity, the influence of the random nature of the change in wind speed decreases, and at some values of the relative capacity, it can be neglected.

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