Radius of maximum wind

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The radius of maximum wind of a tropical cyclone lies just within the eyewall of an intense tropical cyclone, such as Hurricane Isabel from 2003 Hurricane Isabel from ISS.jpg
The radius of maximum wind of a tropical cyclone lies just within the eyewall of an intense tropical cyclone, such as Hurricane Isabel from 2003

The radius of maximum wind (RMW) is the distance between the center of a cyclone and its band of strongest winds. It is a parameter in atmospheric dynamics and tropical cyclone forecasting. [1] The highest rainfall rates occur near the RMW of tropical cyclones. The extent of a cyclone's storm surge and its maximum potential intensity can be determined using the RMW. As maximum sustained winds increase, the RMW decreases. Recently, RMW has been used in descriptions of tornadoes. When designing buildings to prevent against failure from atmospheric pressure change, RMW can be used in the calculations. [2]

Contents

Determination

The RMW is traditionally measured by reconnaissance aircraft in the Atlantic basin. [1] It can also be determined on weather maps as the distance between the cyclone center and the system's greatest pressure gradient. [3] Using weather satellite data, the distance between the coldest cloud top temperature and the warmest temperature within the eye, in infrared satellite imagery, is one method of determining RMW. The reason why this method has merit is that the strongest winds within tropical cyclones tend to be located under the deepest convection, which is seen on satellite imagery as the coldest cloud tops. [1] Use of velocity data from Doppler weather radar can also be used to determine this quantity, both for tornadoes and tropical cyclones near the coast.

Tornadoes

Radar imagery of a tornado and associated mesocyclone in Wyoming on 5 June 2009. Reflectivity data on the left show the rain-free interior of the tornado. Velocity data on the right show where the strongest winds are located. 05june-rapiddow-wide.gif
Radar imagery of a tornado and associated mesocyclone in Wyoming on 5 June 2009. Reflectivity data on the left show the rain-free interior of the tornado. Velocity data on the right show where the strongest winds are located.

In the case of tornadoes, knowledge of the RMW is important as atmospheric pressure change (APC) within sealed buildings can cause failure of the structure. Most buildings have openings totaling one square foot per 1,000-cubic-foot (28 m3) volume to help equalize air pressure between the inside and outside of the structures. The APC is around one-half of its maximum value at the RMW, which normally ranges between 150 feet (46 m) and 500 feet (150 m) from the center (or eye) of the tornado. [4] The widest tornado as measured by actual radar wind measurements was the Mulhall tornado in northern Oklahoma, part of the 1999 Oklahoma tornado outbreak, which had a radius of maximum wind of over 800 meters (2,600 ft). [5]

Tropical cyclones

An average value for the RMW of 47 kilometers (29 mi) was calculated as the mean (or average) of all hurricanes with a lowest central atmospheric pressure between a pressure of 909 hectopascals (26.8 inHg) and 993 hectopascals (29.3 inHg). [6] As tropical cyclones intensify, maximum sustained winds increase as the RMW decreases. [7] However, values for RMW produced based on central pressure or maximum wind speed could be substantial scattering around the regression lines. [8] The heaviest rainfall within intense tropical cyclones has been observed in the vicinity of the RMW. [9]

The radius of maximum wind helps determine the direct strikes of tropical cyclones. Tropical cyclones are considered to have made a direct strike to a landmass when a tropical cyclone passes close enough to a landmass that areas inside the radius of maximum wind are experienced on land. [10] The radius of maximum wind is used within the maximum potential intensity equation. The Emanuel equation for Maximum Intensity Potential relies upon the winds near the RMW of a tropical cyclone to determine its ultimate potential. [11]

The highest storm surge is normally coincident with the radius of maximum wind. Because the strongest winds within a tropical cyclone lie at the RMW, this is the region of a tropical cyclone which generates the dominant waves near the storm, and ultimately ocean swell away from the cyclone. [12] Tropical cyclones mix the ocean water within a radius three times that of the RMW, which lowers sea surface temperatures due to upwelling. [7]

Much is still unknown about the radius of maximum wind in tropical cyclones, including whether or not it can be predictable. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Cyclone</span> Large scale rotating air mass

In meteorology, a cyclone is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above. Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within the smaller mesoscale.

<span class="mw-page-title-main">Dropsonde</span> Meteorological instrument

A dropsonde is an expendable weather reconnaissance device created by the National Center for Atmospheric Research (NCAR), designed to be dropped from an aircraft at altitude over water to measure storm conditions as the device falls to the surface. The sonde contains a GPS receiver, along with pressure, temperature, and humidity (PTH) sensors to capture atmospheric profiles and thermodynamic data. It typically relays this data to a computer in the aircraft by radio transmission.

<span class="mw-page-title-main">1957 Atlantic hurricane season</span>

The 1957 Atlantic hurricane season featured one of the longest-travelling tropical cyclones in the Atlantic basin, Hurricane Carrie. Nevertheless, the season was generally inactive, with eight tropical storms – two of which went unnamed – and three hurricanes, two of which intensified further to attain major hurricane intensity. The season officially began on June 15 and ended on November 15, though the year's first tropical cyclone developed prior to the start of the season on June 8. The final storm dissipated on October 27, well before the official end of the season. The strongest hurricane of the year was Carrie, which reached the equivalent of a Category 4 hurricane on the Saffir–Simpson hurricane scale on two separate occasions in the open Atlantic; Carrie later caused the sinking of the German ship Pamir southwest of the Azores, resulting in 80 deaths.

<span class="mw-page-title-main">1940 Atlantic hurricane season</span>

The 1940 Atlantic hurricane season was a generally average period of tropical cyclogenesis in 1940. Though the season had no official bounds, most tropical cyclone activity occurred during August and September. Throughout the year, fourteen tropical cyclones formed, of which nine reached tropical storm intensity; six were hurricanes. None of the hurricanes reached major hurricane intensity. Tropical cyclones that did not approach populated areas or shipping lanes, especially if they were relatively weak and of short duration, may have remained undetected. Because technologies such as satellite monitoring were not available until the 1960s, historical data on tropical cyclones from this period are often not reliable. As a result of a reanalysis project which analyzed the season in 2012, an additional hurricane was added to HURDAT. The year's first tropical storm formed on May 19 off the northern coast of Hispaniola. At the time, this was a rare occurrence, as only four other tropical disturbances were known to have formed prior during this period; since then, reanalysis of previous seasons has concluded that there were more than four tropical cyclones in May before 1940. The season's final system was a tropical disturbance situated in the Greater Antilles, which dissipated on November 8.

This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.

<span class="mw-page-title-main">Rainband</span> Cloud and precipitation structure

A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands in tropical cyclones can be either stratiform or convective and are curved in shape. They consist of showers and thunderstorms, and along with the eyewall and the eye, they make up a tropical cyclone. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.

<span class="mw-page-title-main">Eye (cyclone)</span> Central area of calm weather in a tropical cyclone

The eye is a region of mostly calm weather at the center of a tropical cyclone. The eye of a storm is a roughly circular area, typically 30–65 kilometers in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds of the cyclone occur. The cyclone's lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm.

<span class="mw-page-title-main">Dvorak technique</span> Subjective technique to estimate tropical cyclone intensity

The Dvorak technique is a widely used system to estimate tropical cyclone intensity based solely on visible and infrared satellite images. Within the Dvorak satellite strength estimate for tropical cyclones, there are several visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity. The primary patterns used are curved band pattern (T1.0-T4.5), shear pattern (T1.5–T3.5), central dense overcast (CDO) pattern (T2.5–T5.0), central cold cover (CCC) pattern, banding eye pattern (T4.0–T4.5), and eye pattern (T4.5–T8.0).

<span class="mw-page-title-main">Central dense overcast</span> Large central area of thunderstorms surrounding its circulation center

The central dense overcast, or CDO, of a tropical cyclone or strong subtropical cyclone is the large central area of thunderstorms surrounding its circulation center, caused by the formation of its eyewall. It can be round, angular, oval, or irregular in shape. This feature shows up in tropical cyclones of tropical storm or hurricane strength. How far the center is embedded within the CDO, and the temperature difference between the cloud tops within the CDO and the cyclone's eye, can help determine a tropical cyclone's intensity with the Dvorak technique. Locating the center within the CDO can be a problem with strong tropical storms and minimal hurricanes as its location can be obscured by the CDO's high cloud canopy. This center location problem can be resolved through the use of microwave satellite imagery.

<span class="mw-page-title-main">Tropical cyclogenesis</span> Development and strengthening of a tropical cyclone in the atmosphere

Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occur are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.

<span class="mw-page-title-main">Extratropical cyclone</span> Type of cyclone

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to severe hail, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.

<span class="mw-page-title-main">Tropical cyclone</span> Type of rapidly rotating storm system

A tropical cyclone is a rapidly rotating storm system with a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn or more.

<span class="mw-page-title-main">Tropical cyclone forecasting</span> Science of forecasting how a tropical cyclone moves and its effects

Tropical cyclone forecasting is the science of forecasting where a tropical cyclone's center, and its effects, are expected to be at some point in the future. There are several elements to tropical cyclone forecasting: track forecasting, intensity forecasting, rainfall forecasting, storm surge, tornado, and seasonal forecasting. While skill is increasing in regard to track forecasting, intensity forecasting skill remains unchanged over the past several years. Seasonal forecasting began in the 1980s in the Atlantic basin and has spread into other basins in the years since.

<span class="mw-page-title-main">Tropical cyclone track forecasting</span> Predicting where a tropical cyclone is going to track over the next five days, every 6 to 12 hours

Tropical cyclone track forecasting involves predicting where a tropical cyclone is going to track over the next five days, every 6 to 12 hours. The history of tropical cyclone track forecasting has evolved from a single-station approach to a comprehensive approach which uses a variety of meteorological tools and methods to make predictions. The weather of a particular location can show signs of the approaching tropical cyclone, such as increasing swell, increasing cloudiness, falling barometric pressure, increasing tides, squalls and heavy rainfall.

The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a certain distance from the center, known as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Wind measuring has been standardized globally to reflect the winds at 10 metres (33 ft) above mean sea level, and the maximum sustained wind represents the highest average wind over either a one-minute (US) or ten-minute time span, anywhere within the tropical cyclone. Surface winds are highly variable due to friction between the atmosphere and the Earth's surface, as well as near hills and mountains over land.

<span class="mw-page-title-main">Glossary of tropical cyclone terms</span>

The following is a glossary of tropical cyclone terms.

The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.

References

  1. 1 2 3 S. A. Hsu and Adele Babin. "Estimating the Radius of Maximum Winds Via Satellite During Hurricane Lili (2002) Over the Gulf of Mexico" (PDF). Archived from the original (PDF) on 6 February 2012. Retrieved 18 March 2007.
  2. ↑ Donald W. Burgess and Michael A. Magsig. Understanding WSR-88D Signatures for the 3 May 1999 Oklahoma City Tornado. Archived 21 March 2013 at the Wayback Machine Retrieved on 2007-03-18.
  3. ↑ Brian W. Blanchard and S. A. Hsu (8 June 2006). "On the Radial Variation of the Tangential Wind Speed Outside the Radius of Maximum Wind During Hurricane Wilma (2005)" (PDF). Louisiana State University. Archived from the original (PDF) on 28 July 2010. Retrieved 20 November 2009.
  4. ↑ United States Department of Energy. "Natural Phenomena Hazards Design and Evaluation Criteria for Department of Energy: E.2.2 Additional Adverse Effects of Tornadoes". p. E7. Retrieved 20 November 2009.
  5. ↑ Wurman, Joshua; C. Alexander; P. Robinson; Y. Richardson (January 2007). "Low-Level Winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas". Bulletin of the American Meteorological Society . 88 (1). American Meteorological Society: 31–46. Bibcode:2007BAMS...88...31W. doi: 10.1175/BAMS-88-1-31 (inactive 29 November 2024).{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
  6. ↑ S. A. Hsu and Zhongde Yana (Spring 1998). "A Note on the Radius of Maximum Winds for Hurricanes". Journal of Coastal Research. 12 (2). Coastal Education & Research Foundation, Inc.: 667–668. JSTOR   4298820.
  7. 1 2 Hugh Willoughby (6 October 2006). "Sixth International Workshop on Tropical Cyclones Topic 1 : Tropical Cyclone Structure and Structure Change" (PDF). Severe Weather Information Centre. Archived from the original (PDF) on 19 February 2012. Retrieved 20 November 2009.
  8. ↑ "Maximum wind radius estimated by the 50 kt radius: improvement of storm surge forecasting over the western North Pacific" (PDF). 11 March 2016. Retrieved 10 November 2016.
  9. ↑ Teruo Muramatsu (1985). "The Study on the Changes of the Three-dimensional Structure and the Movement Speed of the Typhoon through its Life Time" (PDF). Tech. Rep. Meteorol. Res. Inst. Number 14: 3. Retrieved 20 November 2009.
  10. ↑ National Weather Service (25 June 2009). "Glossary: D". National Oceanic and Atmospheric Administration . Retrieved 20 November 2009.
  11. ↑ Kerry A. Emanuel. Maximum Intensity Estimation. Retrieved on 2007-03-18.
  12. ↑ Edward J. Walsh and C. Wayne Wright. Hurricane Wave Topography and Directional Wave Spectra in Near Real-Time. Archived 29 November 2007 at the Wayback Machine Retrieved on 2007-03-18.
  13. ↑ Agnieszka A. S. Mrowiec, S. T. Garner and O. Pauluis (25 April 2006). "What Sets a Hurricane's Radius of Maximum Wind?". 27th Conference on Hurricanes and Tropical Meteorology. American Meteorological Society . Retrieved 20 November 2009.

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