"that measures wind speed in knots and wind direction in degrees relative to the heading of the boat. Modern instrumentation can calculate the true wind velocity when the apparent wind and boat speed and direction are input. In sailboat racing, and especially in speed sailing, apparent wind is a vital factor, when determining the points of sail a sailboat can effectively travel in. A vessel traveling at increasing speed relative to the ""prevailing wind"" will encounter the wind driving the sail at a decreasing angle and increasing velocity. Eventually, the increased drag and diminished degree of efficiency of a sail"
"Wind gradient In common usage, wind gradient, more specifically wind speed gradient or wind velocity gradient, or alternatively shear wind, is the vertical gradient of the mean horizontal wind speed in the lower atmosphere. It is the rate of increase of wind strength with unit increase in height above ground level. In metric units, it is often measured in units of meters per second of speed, per kilometer of height (m/s/km), which reduces to the standard unit of shear rate, inverse seconds (s). Surface friction forces the surface wind to slow and turn near the surface of the Earth, blowing"
"3 May 1999 is often quoted as the highest-recorded surface wind speed, although another figure of has also been quoted for the same tornado. Yet another number used by the Center for Severe Weather Research for that measurement is . However, speeds measured by Doppler radar are not considered official records. An anemometer is one of the tools used to measure wind speed. A device consisting of a vertical pillar and three or four concave cups, the anemometer captures the horizontal movement of air particles (wind speed). Another tool used to measure wind velocity includes a GPS combined with pitot"
"used by the National Oceanic and Atmospheric Administration and other agencies to express the activity of individual tropical cyclones that are above tropical storm strength and entire tropical cyclone seasons. It is calculated by taking the squares of the estimated maximum sustained velocity of every active tropical storm (wind speed 35 knots or higher) at six-hour intervals. The numbers are usually divided by 10,000 to make them more manageable. The unit of ACE is 10 kn, and for use as an index the unit is assumed. As well as being squared for ACE, wind speed can also be cubed, which"
"Wind speed Wind speed, or wind flow velocity, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Note that wind direction is usually almost parallel to isobars (and not perpendicular, as one might expect), due to Earth's rotation. Wind speed affects weather forecasting, aviation and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications. Wind speed is now commonly measured with an anemometer, but can also be classified using the older Beaufort scale, which is based on personal observation of specifically defined"
"Wind gust A gust or wind gust is a brief increase in the speed of the wind, usually less than 20 seconds. It is of a more transient character than a squall, which last minutes, and is followed by a lull or slackening in the wind speed. Generally, winds are least gusty over large water surfaces and most gusty over rough land and near high buildings. The wind is measured using an anemometer or estimated with a windsock. The average value of the latter is generally measured over a period of 2 minutes before the meteorological observation according to the"
"measured by the propagation speed of ultrasound signals or by the effect of ventilation on the resistance of a heated wire. Another type of anemometer uses pitot tubes that take advantage of the pressure differential between an inner tube and an outer tube that is exposed to the wind to determine the dynamic pressure, which is then used to compute the wind speed. Sustained wind speeds are reported globally at a height and are averaged over a 10‑minute time frame. The United States reports winds over a 1‑minute average for tropical cyclones, and a 2‑minute average within weather observations. India"
"wind. The fastest wind speed not related to tornadoes ever recorded was during the passage of Tropical Cyclone Olivia on 10 April 1996: an automatic weather station on Barrow Island, Australia, registered a maximum wind gust of 408 km/h (220 kn; 253 mph; 113 m/s). The wind gust was evaluated by the WMO Evaluation Panel who found that the anemometer was mechanically sound and the gust was within statistical probability and ratified the measurement in 2010. The anemometer was mounted 10 m above ground level (and thus 64 m above sea level). During the cyclone, several extreme gusts of greater"
"Normally the wind speed increases with increasing height. In flat terrain the wind speed increases logarithmically with height. In complex terrain the wind profile is not a simple increase and additionally a separation of the flow might occur, leading to heavily increased turbulence. The extreme wind speeds are based on the 3 second average wind speed. Turbulence is measured at 15 m/s wind speed. This is the definition in IEC 61400-1 edition 2. For U.S. waters however, several hurricanes have already exceeded wind class Ia with speeds above the 70 m/s (156 mph), and efforts are being made to provide"
"directions are measured in units from 0° to 360°, but can alternatively be expressed from -180° to 180°. Winds are named for the direction from which they come, followed by the suffix ""-erly"". For example, winds from the north are called ""northerly winds"" (""north"" + ""-erly""). A variety of instruments can be used to measure wind direction, such as the windsock and wind vane. Both of these instruments work by moving to minimize air resistance. The way a weather vane is pointed by prevailing winds indicates the direction from which the wind is blowing. The larger opening of a windsock"
"typically reports winds over a 3‑minute average. Knowing the wind sampling average is important, as the value of a one-minute sustained wind is typically 14% greater than a ten-minute sustained wind. A short burst of high speed wind is termed a wind gust, one technical definition of a wind gust is: the maxima that exceed the lowest wind speed measured during a ten-minute time interval by for periods of seconds. A squall is an increase of the wind speed above a certain threshold, which lasts for a minute or more. To determine winds aloft, rawinsondes determine wind speed by GPS,"
"constant torque and responded more quickly to gusts than the four-cup anemometer. The three-cup anemometer was further modified by the Australian Dr. Derek Weston in 1991 to measure both wind direction and wind speed. Weston added a tag to one cup, which causes the cupwheel speed to increase and decrease as the tag moves alternately with and against the wind. Wind direction is calculated from these cyclical changes in cupwheel speed, while wind speed is determined from the average cupwheel speed. Three-cup anemometers are currently used as the industry standard for wind resource assessment studies & practice. One of the"
"at 0 °C and 1 atmosphere of absolute pressure ... and 1 lbmol of any ideal gas equals 379.482 scf of that gas at 60 °F and 1 atmosphere of absolute pressure. Notes: Meteorological data includes windspeeds which may be expressed as statute miles per hour, knots, or meters per second. Here are the conversion factors for those various expressions of windspeed: 1 m/s = 2.237 statute mile/h = 1.944 knots<br> 1 knot = 1.151 statute mile/h = 0.514 m/s<br> 1 statute mile/h = 0.869 knots = 0.447 m/s Note: Many environmental protection agencies have issued regulations that limit the"
"warning. These designations were standardized nationally in 2008, whereas ""light wind"" can refer to 0 to 12 or 0 to 15 knots and ""moderate wind"" 12 to 19 or 16 to 19 knots, depending on regional custom, definition or practice. Prior to 2008, a ""strong wind warning"" would have been referred to as a ""small craft warning"" by Environment Canada, similar to US terminology. (Canada and the USA have the Great Lakes in common.) Beaufort scale The Beaufort scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the"
"tube. A fluid flow velocity tool, the Pitot tube is primarily used to determine the air velocity of an aircraft. Wind speed is a common factor in the design of structures and buildings around the world. It is often the governing factor in the required lateral strength of a structure's design. 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). This design wind speed is accepted by"
"introduced in 1805, and in 1921 quantified. It expresses the wind speed (v) by the formula: Most UK tornadoes are T6 or below with the strongest known UK tornado being a T8. For comparison, the strongest detected winds in a United States tornado (during the 1999 Oklahoma tornado outbreak) would be T11 using the following formulae: where ""v"" is wind speed and ""T"" is TORRO intensity number. Wind speed is defined as a 3-second gust at 10 m AGL. Alternatively, the T-Scale formula may be expressed as: or TORRO claims it differs from the Fujita scale in that it is"
"is the wind speed specified in meters/second. The power coefficient, formula_7 is a quantity that expresses what fraction of the power in the wind is being extracted by the wind turbine. It is generally assumed to be a function of both tip-speed ratio and pitch angle. Below is a plot of the variation of the power coefficient with variations in the tip-speed ratio when the pitch is held constant: Originally, wind turbines were fixed speed. This has the benefit that the rotor speed in the generator is constant, thus the frequency of the AC Voltage is fixed. This allows the"
"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 t seconds, V, and mean wind speed over one hour V. Wind speed Wind speed, or wind flow velocity, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Note that wind direction is usually almost parallel to isobars (and not perpendicular, as one might expect), due to Earth's rotation. Wind speed affects weather forecasting, aviation and maritime"
"Knot (unit) The knot () is a unit of speed equal to one nautical mile per hour, exactly (approximately ). The ISO standard symbol for the knot is . The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE); is also common, especially in aviation where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one"
"United States, temperature and dewpoint are plotted in degrees Celsius. The wind barb points in the direction from which the wind is coming. Each full flag on the wind barb represents of wind, each half flag represents . When winds reach , a filled in triangle is used for each of wind. In the United States, rainfall plotted in the corner of the station model are in inches. The international standard rainfall measurement unit is the millimeter. Once a map has a field of station models plotted, the analyzing isobars (lines of equal pressure), isallobars (lines of equal pressure change),"
"is now handled with the use of computer numerical models such as ADCIRC and SLOSH. In 2012, the NHC expanded the windspeed range for Category 4 by 1 mph in both directions, to 130–156 mph, with corresponding changes in the other units (113–136 kn, 209–251 km/h), instead of 131–155 mph (114–135 kn, 210–249 km/h). The NHC and the Central Pacific Hurricane Center assign tropical cyclone intensities in 5 knot increments, and then convert to mph and km/h with a similar rounding for other reports. So an intensity of 115 kn is rated Category 4, but the conversion to miles per"
"wind speed, and the top wind speed for Category “""c""” (""c"" = 1 ... 4; there is no upper limit for category 5) can be expressed as 83×10 miles per hour rounded to the nearest multiple of 5 – except that after the change mentioned above, Category 4 is now widened by 1 mph in each direction and that the calculated value for Category 2 (""c"" = 2) is rounded down from 112.8 mph to 110 mph. The five categories are described in the following subsections, in order of increasing intensity. Very dangerous winds will produce some damage Category 1"
"11 o'clock are equated to half value, and winds at 12 and 6 o'clock are equated to no value. The minute of angle correction (full value) is then commonly estimated as ((Range [meters] / 100) × Wind [mph]) / ""C"", where ""C"" is a constant. The constant ""C"" equals 15 for ranges from 100 to 500 meters, 14 for 600 meters, 13 for 700–800 meters, 12 for 900 meters, and 11 for 1,000 meters. For full-value winds, this full windage correction is used. For half-value winds, the minute of correction in windage given by this formula is halved; for no-value"
"conditions. Knot (unit) The knot () is a unit of speed equal to one nautical mile per hour, exactly (approximately ). The ISO standard symbol for the knot is . The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE); is also common, especially in aviation where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in"
"weather stations are equipped with a mechanical wind vane and cup system to measure wind speed and direction. This system is simple in design: the wind spins three horizontally turned cups around the base of the wind vane, providing an estimation of the wind's speed, while the vane on top turns so that the face of the vane offers the least resistance to the wind, causing it to point in the direction the wind is coming from and thus providing the wind direction. The new generation of sensors use sound waves to measure wind speed and direction. The measurement is"
"knots are encoded by adding 50 to the direction and subtracting 100 from the speed. Thus, for example, the wind forecast for Abilene (ABI) at 30,000 feet, shown above as 7603, indicates a forecast wind of 260 degrees at 103 knots (so that the direction became 76 26+50, and speed became 03 103-100). This forecast is now made four times a day based on 0000Z, 0600Z, 1200Z, and 1800Z data (the Z stands for Zulu and indicates Coordinated Universal Time). The forecasts are valid 6 (FD1/8), 12 (FD2/9), and 24 (FD3/10) hours after the observation date/times of 0000Z and 1200Z"
"amount of deflection from vertical that is observed, while the wind direction is provided by which way this deflection occurs. A mirror, located under the telltale, and a calibration ""cross,"" above (as observed through the mirror) are employed to increase the accuracy of the measurement. Either the SSI or RAC cameras could make this measurement, though the former was typically used. Periodic observations both day and night aid in understanding the diurnal variability of wind at the ""Phoenix"" landing site. The wind speeds ranged from 11 km to 58 km per hour. The usual average speed was 36 km per"
"velocity. The corresponding basic SI derived unit is s or Hz. When measuring angular speed, the unit radians per second is used. Formally, hertz (Hz) and radian per second (rad/s) are two different names for the same SI unit, s. However, they are used for two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity). The conversion between a frequency (measured in hertz) and an angular velocity (measured in radians per second) are: Thus a disc rotating at 60 rpm is said to be rotating at either 2 rad/s or 1 Hz, where the"
"time, wind speed may vary over short periods of time as gusts. These considerations may be described empirically. Measurements show that wind speed, (""V"" (""h"" ) ) varies, according to a power law with height (""h"" ) above a non-zero measurement height datum (""h"" —e.g. at the height of the foot of a sail), using a reference wind speed measured at the datum height (""V"" (""h"" ) ), as follows: Where the power law exponent (""p"") has values that have been empirically determined to range from 0.11 over the ocean to 0.31 over the land. This means that a ""V"""
"heated anemometer. The anemometer, specifically designed for use on Mount Washington was later tested by the US National Weather Bureau and confirmed to be accurate. Wind speeds within certain atmospheric phenomena (such as tornadoes) may greatly exceed these values but have never been accurately measured. Directly measuring these tornadic winds is rarely done as the violent wind would destroy the instruments. A method of estimating speed is to use Doppler on Wheels to sense the wind speeds remotely, and, using this method, the figure of 486 km/h (302 mph; 135 m/s) during the 1999 Bridge Creek–Moore tornado in Oklahoma on"
"Metre per hour Metre per hour (American spelling: meter per hour) is a metric unit of both speed (scalar) and velocity (Vector (geometry)). Its symbol is m/h or m·h (not to be confused with the imperial unit symbol mph. By definition, an object travelling at a speed of 1 m/h for an hour would move 1 metre. The term is rarely used however as the units of metres per second and kilometres per hour are considered sufficient for the majority of circumstances. Metres per hour can however be convenient for documenting extremely slow moving objects. A Garden Snail for instance,"
"law relating wind velocity to Beaufort force. Wave heights in the scale are for conditions in the open ocean, not along the shore. The wind speeds in different units are not mathematically equivalent; e.g. 12–19 km/h is not equivalent to 8–12 mph, and both are not equivalent to 7–10 knots. The reason is that the Beaufort scale is not an exact nor an objective scale. It was based on visual and subjective observation of a ship and of the sea. The corresponding integral wind speeds were determined later, but the values in different units were never made equivalent. The scale"
"increase efficiency. Wind power measures how much energy is available in the wind, and it can be represented by the following equation formula_1 where r is air density, A is rotor area, and V is wind velocity. This means that the amount of energy available in the wind is directly proportional to the wind speed cubed. For example, assuming that all other variables are held constant, doubling the wind speed would increase the available energy in the wind by 8 times. A slight increase in wind speed results in dramatic increases in wind power. Unfortunately, this means that if the"