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Radius of maximum wind

Radius of maximum wind is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Radius of maximum wind rather than just read about it. In short: 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.

Radius of maximum wind — main illustration
Radius of maximum wind — illustration

Key takeaways

  • Radius of maximum wind belongs to earth science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Radius of maximum wind to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Radius of maximum wind from memory before moving on to harder problems.

Reference excerpt

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. 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.

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 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. 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

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. 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).

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

See also Radius of outermost closed isobar

References

Illustrations

Radius of maximum wind: 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 of a tropical cyclone lies just within the eyewall of an intense tropical cyclone, such as Hurricane Isabel from 2003
Radius of maximum wind: 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.
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.

Worked examples

Example 1 — a first encounter with Radius of maximum wind

Start with the simplest possible case. Write down what Radius of maximum wind claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Radius of maximum wind before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Radius of maximum wind ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Radius of maximum wind

In research
Radius of maximum wind appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Radius of maximum wind in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Radius of maximum wind is common in secondary-school and first-year university syllabi. It links to neighbouring topics Radii, Tornado, Tropical cyclone meteorology, so understanding it makes those chapters shorter.
In everyday life
Look for Radius of maximum wind outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Radius of maximum wind in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Radius of maximum wind means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Radius of maximum wind out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Radius of maximum wind in simple terms?

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.

Why does Radius of maximum wind matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Radius of maximum wind?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Radius of maximum wind.

Tags

  • Radii
  • Tornado
  • Tropical cyclone meteorology
  • Weather hazards
  • Wind

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