Wind Speed 55 Mph

[Grethe Presnar]

Inmeteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer.

Wind speed affects weather forecasting, aviation and maritime operations, construction projects, growth and metabolism rates of many plant species, and countless other implications.[2] Wind direction is usually almost parallel to isobars (and not perpendicular, as one might expect), due to Earth's rotation.

The meter per second (m/s) is the SI unit for velocity and the unit recommended by the World Meteorological Organization for reporting wind speeds, and used amongst others in weather forecasts in the Nordic countries.[3] Since 2010 the International Civil Aviation Organization (ICAO) also recommends meters per second for reporting wind speed when approaching runways, replacing their former recommendation of using kilometers per hour (km/h).[4]

For historical reasons, other units such as miles per hour (mph), knots (kn),[5] and feet per second (ft/s) are also sometimes used to measure wind speeds. Historically, wind speeds have also been classified using the Beaufort scale, which is based on visual observations of specifically defined wind effects at sea or on land.

Wind speed is affected by a number of factors and situations, operating on varying scales (from micro to macro scales). These include the pressure gradient, Rossby waves, jet streams, and local weather conditions. There are also links to be found between wind speed and wind direction, notably with the pressure gradient and terrain conditions.

The Pressure gradient describes the difference in air pressure between two points in the atmosphere or on the surface of the Earth. It is vital to wind speed, because the greater the difference in pressure, the faster the wind flows (from the high to low pressure) to balance out the variation. The pressure gradient, when combined with the Coriolis effect and friction, also influences wind direction.

Rossby waves are strong winds in the upper troposphere. These operate on a global scale and move from west to east (hence being known as westerlies). The Rossby waves are themselves a different wind speed from that experienced in the lower troposphere.

Local weather conditions play a key role in influencing wind speed, as the formation of hurricanes, monsoons, and cyclones as freak weather conditions can drastically affect the flow velocity of the wind.[citation needed]

Wind speeds can be much higher on exoplanets. Scientists at the University of Warwick in 2015 determined that HD 189733b has winds of 2,400 m/s (8,600 km/h; 4,700 kn). In a press release, the University announced that the methods used from measuring HD 189733b's wind speeds could be used to measure wind speeds on Earth-like exoplanets.[14]

An anemometer is one of the tools used to measure wind speed.[15] A device consisting of a vertical pillar and three or four concave cups, the anemometer captures the horizontal movement of air particles (wind speed).

Unlike traditional cup-and-vane anemometers, ultrasonic wind sensors have no moving parts and are therefore used to measure wind speed in applications that require maintenance-free performance, such as atop wind turbines. As the name suggests, ultrasonic wind sensors measure the wind speed using high-frequency sound. An ultrasonic anemometer has two or three pairs of sound transmitters and receivers. Each transmitter constantly beams high-frequency sound to its receiver. Electronic circuits inside measure the time it takes for the sound to make its journey from each transmitter to the corresponding receiver. Depending on how the wind blows, some of the sound beams will be affected more than the others, slowing it down or speeding it up very slightly. The circuits measure the difference in speeds of the beams and use that to calculate how fast the wind is blowing.[16]

Acoustic resonance wind sensors are a variant of the ultrasonic sensor. Instead of using time of flight measurement, acoustic resonance sensors use resonating acoustic waves within a small purpose-built cavity. Built into the cavity is an array of ultrasonic transducers, which are used to create the separate standing-wave patterns at ultrasonic frequencies. As wind passes through the cavity, a change in the wave's property occurs (phase shift). By measuring the amount of phase shift in the received signals by each transducer, and then by mathematically processing the data, the sensor is able to provide an accurate horizontal measurement of wind speed and direction.[17]

Another tool used to measure wind velocity includes a GPS combined with pitot tube.[citation needed] A fluid flow velocity tool, the Pitot tube is primarily used to determine the air velocity of an aircraft.

In the United States, the wind speed used in design is often referred to as a "3-second gust", which is the highest sustained gust over a 3-second period having a probability of being exceeded per year of 1 in 50 (ASCE 7-05, updated to ASCE 7-16).[18] This design wind speed is accepted by most building codes in the United States and often governs the lateral design of buildings and structures.

In Canada, reference wind pressures are used in design and are based on the "mean hourly" wind speed having a probability of being exceeded per year of 1 in 50. The reference wind pressure q is calculated using the equation q = ρv2 / 2, where ρ is the air density and v is the wind speed.[19]

Historically, wind speeds have been reported with a variety of averaging times (such as fastest mile, 3-second gust, 1-minute, and mean hourly) which designers may have to take into account. To convert wind speeds from one averaging time to another, the Durst Curve was developed, which defines the relation between probable maximum wind speed averaged over some number of seconds to the mean wind speed over one hour.[20]

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based only on a hurricane's maximum sustained wind speed. This scale does not take into account other potentially deadly hazards such as storm surge, rainfall flooding, and tornadoes.

The Saffir-Simpson Hurricane Wind Scale estimates potential property damage. While all hurricanes produce life-threatening winds, hurricanes rated Category 3 and higher are known as major hurricanes*. Major hurricanes can cause devastating to catastrophic wind damage and significant loss of life simply due to the strength of their winds. Hurricanes of all categories can produce deadly storm surge, rain-induced floods, and tornadoes. These hazards require people to take protective action, including evacuating from areas vulnerable to storm surge.

*In the western North Pacific, the term "super typhoon" is used for tropical cyclones with sustained winds exceeding 150 mph.

Includes Onset's research-grade plug-and-play Wind Speed Smart Sensor and the Wind Direction Smart Sensor. This combination provides average wind speed, highest 3-second wind gust, and average wind direction for the measurement interval. These durable sensors will provide many years of accurate and reliable performance.

NOTE: Mount these on the M-CAA Full Cross Arm for proper sensor spacing for accurate wind measurement in all wind directions. The cross arm must be mounted on a stable mast, using guy wires as needed to prevent the sensors from vibrating in high winds.

The reoccupation of the summit began on October 14, 1932. Foremost among the work of the Observatory staff was regular weather observations. The crew members were also involved in testing radio equipment. Observers also performed balloon soundings, to learn more about the air circulation patterns that were found in mountain regions. The Observatory crew worked with the AMC to better inform mountain visitors about the harsh and dangerous weather so often found on Mount Washington.

While the original concept was to operate the weather station for only one year, the success of the work there led Dodge, Brooks, and others to continue operations for another year. That year was a momentous one, as April 12, 1934 saw a truly remarkable event, the clocking of a world record wind of 231 miles per hour. The noteworthy weather, and the capable recording of such a weather extreme, helped secure a long-term place on the mountain for the Observatory.

In 1993, the Observatory expanded its educational offerings to include EduTrips, winter overnight visits to the summit providing instruction in topics pertinent to the mountain environment. While Observatory staff have, for many decades, provided in-person presentations to educational and civic groups about the Observatory and Mount Washington, those activities have been enhanced in recent years with more virtual programs, plus a renewed attention to programs for schools, science centers, libraries, and other such venues.

Now approaching one hundred years of service to the scientific community and to the public, the Mount Washington Observatory continues its work in the three main areas of activity for which it was founded: to maintain a rigorous program of weather observations and related environmental monitoring, to perform and to collaborate with others in performing basic and applied scientific research, and to participate in public education about weather, climate, and the mountain environment.

Analytical expressions which specify non-dimensionalized wind speed and potential temperature gradients as functions of stability are integrated. The integrated equations are tested against Swinhank's wind and temperature profiles measured at Kerang, Australia. It is found that a representation suggested independently by Businger and by Dyer gives the best fit to temperature profiles and describes the wind profiles equally as well as a relation suggested by Panofsky et al.

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