The radius of maximum wind (RMW) is the distance between the center of a

cyclone 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 (opposite to an ant ...

and its band of strongest

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

s. It is a parameter in atmospheric dynamics and tropical cyclone forecasting. The highest

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

fall rates occur near the RMW of

tropical cyclone A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...

s. The extent of a cyclone's

storm surge A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the ...

and its maximum potential intensity can be determined using the RMW. As

maximum sustained wind 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 ma ...

s increase, the RMW decreases. Recently, RMW has been used in descriptions of

tornado A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...

es. When designing

building A building or edifice is an enclosed Structure#Load-bearing, structure with a roof, walls and window, windows, usually standing permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, a ...

s to prevent against failure from atmospheric pressure change, RMW can be used in the calculations.

Determination

The RMW is traditionally measured by reconnaissance aircraft in the Atlantic basin. It can also be determined on weather maps as the distance between the cyclone center and the system's greatest pressure gradient. Using

weather satellite A weather satellite or meteorological satellite is a type of Earth observation satellite that is primarily used to monitor the weather and climate of the Earth. Satellites are mainly of two types: polar orbiting (covering the entire Earth asyn ...

data, the distance between the coldest cloud top temperature and the warmest temperature within the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

, in infrared satellite imagery, is one method of determining RMW. The reason why this method has merit is that the strongest winds within

s tend to be located under the deepest

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

, which is seen on satellite imagery as the coldest cloud tops. Use of velocity data from Doppler

weather radar A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation (meteorology), precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern w ...

can also be used to determine this quantity, both for tornadoes and tropical cyclones near the coast.

Tornadoes

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 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 and from the center (or eye) of the tornado. 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 .

Tropical cyclones

An average value for the RMW of was calculated as the mean (or average) of all hurricanes with a lowest central

atmospheric pressure Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1,013. ...

between a pressure of and . As tropical cyclones intensify, maximum sustained winds increase as the RMW decreases. However, values for RMW produced based on central pressure or maximum wind speed could be substantial scattering around the regression lines. The heaviest rainfall within intense tropical cyclones has been observed in the vicinity of the RMW. 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. 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. 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. Tropical cyclones mix the ocean water within a radius three times that of the RMW, which lowers

sea surface temperature Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

s due to

upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted sur ...

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

References

{{good article Tropical cyclone meteorology Tornado Weather hazards Wind Radii

Determination

Tornadoes

Tropical cyclones

See also

References