View source for Radius of maximum wind

{{Short description|Meteorological concept}}
{{Use dmy dates|date=November 2022}}
[[File:Hurricane Isabel from ISS.jpg|right|300px|thumb|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 [[wind]]s.  It is a parameter in atmospheric dynamics and [[tropical cyclone forecasting]].<ref name="HSU">{{cite web|author=S. A. Hsu and Adele Babin|url=http://www.nwas.org/ej/hsu/hsu_babin_2005.pdf|title=Estimating the Radius of Maximum Winds Via Satellite During Hurricane Lili (2002) Over the Gulf of Mexico|access-date=2007-03-18|url-status=dead|archive-url=https://web.archive.org/web/20120206133851/http://www.nwas.org/ej/hsu/hsu_babin_2005.pdf|archive-date=6 February 2012}}</ref> The highest [[rain]]fall rates occur near the RMW of [[tropical cyclone]]s.  The extent of a cyclone's [[storm surge]] and its maximum potential intensity can be determined using the RMW.  As [[maximum sustained wind]]s increase, the RMW decreases.  Recently, RMW has been used in descriptions of [[tornado]]es. When designing [[building]]s to prevent against failure from atmospheric pressure change, RMW can be used in the calculations.<ref>Donald W. Burgess and Michael A. Magsig. [http://www.wdtb.noaa.gov/modules/sls00/M3RADAR.pdf Understanding WSR-88D Signatures for the 3 May 1999 Oklahoma City Tornado.] {{Webarchive|url=https://web.archive.org/web/20130321215633/http://www.wdtb.noaa.gov/modules/sls00/M3RADAR.pdf |date=21 March 2013 }} Retrieved on 2007-03-18.</ref>

==Determination==
The RMW is traditionally measured by reconnaissance aircraft in the Atlantic basin.<ref name="HSU"/> It can also be determined on [[surface weather analysis|weather maps]] as the distance between the cyclone center and the system's greatest pressure gradient.<ref>{{cite web|url=http://www.esl.lsu.edu/quicklinks/publications/pdfs/Blanchard.et.al.NWAEJOperationalMeteorology.2006.pdf|author=Brian W. Blanchard and S. A. Hsu|title=On the Radial Variation of the Tangential Wind Speed Outside the Radius of Maximum Wind During Hurricane Wilma (2005)|access-date=2009-11-20|date=2006-06-08|publisher=[[Louisiana State University]]|url-status=dead|archive-url=https://web.archive.org/web/20100728000814/http://www.esl.lsu.edu/quicklinks/publications/pdfs/Blanchard.et.al.NWAEJOperationalMeteorology.2006.pdf|archive-date=28 July 2010}}</ref> Using [[weather satellite]] data, the distance between the coldest cloud top temperature and the warmest temperature within the [[eye (cyclone)|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 cyclone]]s tend to be located under the deepest [[convection]], which is seen on satellite imagery as the coldest cloud tops.<ref name="HSU"/> 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==
[[File:05june-rapiddow-wide.gif|thumb|300px|right|Radar imagery of a tornado and associated mesocyclone in [[Tornadoes of 2009#June 5|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.]]
{{See also|Tornado}}
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 {{convert|1000|cuft|m3|adj=on}} 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 {{convert|150|ft|m}} and {{convert|500|ft|m}} from the center (or eye) of the tornado.<ref>{{cite web|url=http://www.tpub.com/content/doe2/STD-10202002/STD-102020020175.htm|title=Natural Phenomena Hazards Design and Evaluation Criteria for Department of Energy: E.2.2 Additional Adverse Effects of Tornadoes|author=United States Department of Energy|author-link=United States Department of Energy|access-date=2009-11-20|page=E7}}</ref> The widest tornado as measured by actual radar wind measurements was the [[Mulhall, Oklahoma|Mulhall]] tornado in northern Oklahoma, part of the [[1999 Oklahoma tornado outbreak]], which had a radius of maximum wind of over {{convert|800|m|ft|abbr=|sp=us}}.<ref name="Mulhall">{{cite journal |last=Wurman |first=Joshua |author2=C. Alexander |author3=P. Robinson |author4=Y. Richardson  |title=Low-Level Winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas |journal=[[Bulletin of the American Meteorological Society]] |volume=88 |issue=1 |pages=31–46 |publisher=[[American Meteorological Society]] |date=January 2007 |doi=10.1175/BAMS-88-1-31 |bibcode = 2007BAMS...88...31W |doi-access=free }}</ref>

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==Tropical cyclones==
{{See also|Tropical cyclone|Storm surge|Ocean swell}}
An average value for the RMW of {{convert|47|km|mi|abbr=|sp=us}} was calculated as the mean (or average) of all hurricanes with a lowest central [[atmospheric pressure]] between a pressure of {{convert|909|hPa|inHg}} and {{convert|993|hPa|inHg}}.<ref>{{cite journal|author=S. A. Hsu and Zhongde Yana|journal=Journal of Coastal Research|jstor=4298820|title=A Note on the Radius of Maximum Winds for Hurricanes|volume=12|number=2|date=Spring 1998|pages=667–668|publisher=Coastal Education & Research Foundation, Inc.}}</ref> As tropical cyclones intensify, maximum sustained winds increase as the RMW decreases.<ref name="Wil">{{cite web|url=http://severe.worldweather.org/iwtc/document/Topic_1_Hugh_Willoughby.pdf|author=Hugh Willoughby|title=Sixth International Workshop on Tropical Cyclones Topic 1 : Tropical Cyclone Structure and Structure Change|publisher=Severe Weather Information Centre|date=2006-10-06|access-date=2009-11-20|archive-date=19 February 2012|archive-url=https://web.archive.org/web/20120219052749/http://severe.worldweather.org/iwtc/document/Topic_1_Hugh_Willoughby.pdf|url-status=dead}}</ref> However, values for RMW produced based on central pressure or maximum wind speed could be substantial scattering around the regression
lines.<ref name="Tak">{{cite web|url=http://www.nat-hazards-earth-syst-sci.net/16/705/2016/nhess-16-705-2016.pdf|title=Maximum wind radius estimated by the 50 kt radius: improvement of storm surge forecasting over the western North Pacific|date=2016-03-11|access-date=2016-11-10}}</ref> The heaviest rainfall within intense tropical cyclones has been observed in the vicinity of the RMW.<ref>{{cite journal|url=http://www.mri-jma.go.jp/Publish/Technical/DATA/VOL_14/14_abs.pdf|title=The Study on the Changes of the Three-dimensional Structure and the Movement Speed of the Typhoon through its Life Time|author=Teruo Muramatsu|journal=Tech. Rep. Meteorol. Res. Inst. Number 14|year=1985|page=3|access-date=2009-11-20}}</ref>

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.<ref>{{cite web|author=National Weather Service|publisher=[[National Oceanic and Atmospheric Administration]]|date=2009-06-25|url=http://www.weather.gov/glossary/index.php?letter=d|title=Glossary: D|access-date=2009-11-20}}</ref> 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.<ref>Kerry A. Emanuel. [http://wind.mit.edu/~emanuel/pcmin/pclat/pclat.html Maximum Intensity Estimation.] Retrieved on 2007-03-18.</ref>

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.<ref>Edward J. Walsh and C. Wayne Wright. [http://www.onr.navy.mil/sci_tech/32/reports/docs/05/mmwalsh5.pdf Hurricane Wave Topography and Directional Wave Spectra in Near Real-Time.] {{webarchive|url=https://web.archive.org/web/20071129132811/http://www.onr.navy.mil/sci_tech/32/reports/docs/05/mmwalsh5.pdf |date=29 November 2007 }} Retrieved on 2007-03-18.</ref> Tropical cyclones mix the ocean water within a radius three times that of the RMW, which lowers [[sea surface temperature]]s due to [[upwelling]].<ref name="Wil"
/>

Much is still unknown about the radius of maximum wind in tropical cyclones, including whether or not it can be predictable.<ref>{{cite journal|url=http://ams.confex.com/ams/27Hurricanes/techprogram/paper_108632.htm|title=What Sets a Hurricane's Radius of Maximum Wind?|author=Agnieszka A. S. Mrowiec, S. T. Garner and O. Pauluis|journal=27th Conference on Hurricanes and Tropical Meteorology|publisher=[[American Meteorological Society]]|date=2006-04-25|access-date=2009-11-20}}</ref>

==See also==
* [[Radius of outermost closed isobar]]

==References==
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[[Category:Tropical cyclone meteorology]]
[[Category:Tornado]]
[[Category:Weather hazards]]
[[Category:Wind]]
[[Category:Radii]]